chapter 7 · 181 assessment and harvest of largemouth bass–bluegill ponds harold l. schramm,...

181

Assessment and Harvest of Largemouth Bass–Bluegill Ponds

Harold l. ScHramm, Jr. and david W. WilliS

7.1 INTRODUCTION

A pond can provide a variety of fishing benefits, so it is important that the pond own-er determine the specific benefit or management goal for the pond. Angler preferences for recreational fisheries and suitability of fish species for ponds differ along with the variety of climatic conditions found throughout North America. These differences have prompted investigations of the suitability of different fishes, alone or in combination, for producing satisfying and sustainable recreational fishing opportunities in ponds. The combination of largemouth bass and bluegill (or bluegill and redear sunfish1) has been found suitable for producing sustainable fishing opportunities in ponds throughout most of temperate and sub-tropical North America. Other predator–prey combinations for ponds have been considered, but have either proven ineffective (northern pike–yellow perch), or are not sufficiently stud-ied (e.g., smallmouth bass-redear sunfish) to predict responses to population alteration or other management strategies. Nonreproducing (e.g., rainbow trout) or purposely nonrecruit-ing (e.g., channel catfish in ponds with no structures to provide cavities for nesting) fisher-ies are successfully used in some ponds, particularly smaller ponds. Management of these fisheries is frequently accomplished by initial and replacement stockings, with supplemental feeding often used to increase fish growth and production. Pond management is ripe for new ideas, especially for producing unique or exceptional fishing opportunities. One such example is the experimental use of all female largemouth bass to produce trophy bass op-portunities as recently implemented by private pond managers in the southern USA (Willis et al. 2010). Although seemingly a typical predator–prey system, the bass do not reproduce, and the prey base, which often includes threadfin shad as well as bluegill, may not be self-sustaining in the long term due to shad vulnerability to winter temperatures. The ponds thus are managed by stocking.

While excellent fishing can be produced by repeated stockings, the focus of this chapter is harvest, specifically how to use harvest to establish and sustain quality fishing in recreational fishing ponds. As such, this chapter describes the assessment and management of largemouth bass–bluegill ponds because these systems have received sufficient study to understand the

Chapter 7

1Many ponds contain bluegill as the only sunfish species, but mixed populations of bluegill and redear sunfish have been found to provide fishing opportunities and prey availability similar to ponds containing only bluegill. Bluegill should be interpreted as bluegill or bluegill and redear sunfish throughout this chapter.

182 Chapter 7

predator–prey dynamics and make reliable predictions about the effects of, or the need for, population manipulations that can be accomplished by angler harvest. Understanding the dy-namics of the largemouth bass-bluegill combination will provide insights to allow assessment of other species combinations as well.

Although the specific fishing objectives may differ among ponds, all largemouth bass–bluegill ponds must maintain some balance between the predators—largemouth bass—and the prey—bluegill—to remain productive and provide enjoyable fishing. The concept of “bal-ance” was described in Swingle’s seminal work on pond management (Swingle 1950; Chapter 1). Implied in the concept of balance is that a balanced fish community is a dynamic system characterized by continual reproduction of predator and prey species, diverse size composi-tion of prey species so that food is available for all sizes of predators, fast growth rates of predators and prey, and an annual yield of harvestable-size fish in proportion to basic fertility. In other words, a balanced community will have a sustained production of harvestable-size predators, prey, or both, depending on the management objective. After a pond is correctly built and correctly stocked, balance and the benefits it conveys is maintained by angler har-vest. Although angler harvest of the largest bluegill can affect the size structure of the bluegill population, the largemouth bass population is the principal agent for managing the bluegill population, and the bluegill population influences bass growth. Simply stated, most ponds are managed by judicious harvest of largemouth bass.

Some biologists, including some private-sector pond management specialists in the southern USA, believe that maintaining or achieving balance (sensu Swingle) should be dis-continued as a management goal and strategy. Because their management strategies often are designed to develop high-quality largemouth bass fisheries, they actually would consider a balanced bass–bluegill community to be unsuccessful (Willis et al. 2010). Moderate numbers and sizes of predator and prey species, thus, may not be considered a successful strategy. However, the concept of balance is still valid for teaching the variety of management options for ponds. Likewise, the vast majority of the 4.5 million ponds in the USA are not intensively managed for trophy bass, and the concept of balance remains a valid management paradigm for these systems.

7.2 ASSESSMENT AND HARVEST

The proper harvest of largemouth bass is guided by effective assessment of the pond and its fish community. Fishery assessment of any pond should be driven by representative samples of the fish populations and modulated by habitat conditions, available equipment, and personnel resources. Most productive ponds containing both self-sustaining predator and prey fishes have the characteristics of a balanced fish community. Although some of Swingle’s metrics for assessing pond balance may be outmoded or replaced with more eas-ily obtained metrics (Chapter 1), the concept still provides clear guidance for assessment: determine recruitment of predator and prey species; quantify or infer the length distributions, relative abundance (catch rate), and body condition (plumpness) of predator and prey popu-lations; and then use these data to make predictions about growth rates of predators and prey. In fact, estimating growth rate may be part of a pond assessment in unique circumstances where the cost of this additional workload and the necessary euthanizing of fish can be jus-tified. These important variables can be determined or inferred from samples collected by

183Assessment and Harvest of Largemouth Bass–Bluegill Ponds

various methods, usually electrofishing, but sometimes requiring other gears (e.g., seining) as well. Finally, angler-catch data have been used to assess the status of predator and prey populations in ponds; however, analyses have been limited, and further assessments would be beneficial.

7.2.1 Qualitative Assessment of Spawning and Recruitment

Swingle (1956) developed a key to help pond managers diagnose the state of predator and prey populations in largemouth bass–sunfish ponds. The assessment relies on the rela-tive abundances of young largemouth bass and bluegill that are effectively and economi-cally sampled by seining. Shoreline or quadrant seine hauls conducted with a 6-mm square (i.e., bar measure) mesh seine in summer to early fall, depending on geographic region, will collect young bass and sunfish if they are present. These seine samples provide direct evidence about the reproduction and recruitment of both predators and prey and allow infer-ences about the abundance and size distributions of predator and prey populations. Although Swingle’s key relies only on fish collected in seine samples, the inferences are supported by comprehensive assessments of numerous private and research ponds and a fundamental un-derstanding of predator–prey dynamics acquired from his work with these ponds. Swingle’s method is presented here in some detail because the original publications are not readily available, and the inferences about predator and prey populations are essential to effective pond management regardless of how the fish populations are sampled or what population variables are measured.

In his original work, Swingle used seine catches not only to infer predator and prey population demographics but also to question habitat suitability. In this discussion, water quality, including water temperature, and habitat conditions are assumed to be suitable for self-sustaining largemouth bass and bluegill populations and a balanced fish community. Further, it is assumed that the fish assemblage consists only of largemouth bass and blue-gill. For this assessment protocol, young largemouth bass are fish less than 150 mm total length, young bluegill are fish less than 40 mm, and intermediate bluegill are fish 40–100 mm. Readers should recognize that most of the following text is from Swingle (1956), but several modifications were made (noted below) when both authors agreed that the change was needed.

No young largemouth bass and:

A. Many recently hatched bluegill, no or very few intermediate bluegill

Probable situation: The presence of young bluegill indicates that bluegill spawned. The absence of young largemouth bass could be due to inadequate spawning conditions for large-mouth bass, but because bluegill spawned, it is highly likely that environmental conditions were suitable for bass to spawn. The scarcity of intermediate bluegill and young largemouth bass probably results from heavy bass predation.

Diagnosis: bass overcrowded; in rare instances, habitat may not be suitable for large-mouth bass reproduction.

184 Chapter 7

B. No (or few)2 recent hatch of bluegill, many intermediate bluegill

Probable situation: The presence of intermediate bluegill indicates that bluegill have suc-cessfully spawned in the previous year, but the absence (or scarcity) of age-0 bluegill indicates spawning did not occur this year or spawning occurred but few or no young bluegill survived.

Diagnosis: overcrowded bluegill population that interferes with bass and bluegill repro-duction or postreproduction survival. Largemouth bass, if present, are large, in good condi-tion, and have high growth rate as a result of the abundant prey supply.

C. No recent hatch of bluegill, few intermediate bluegill

Probable situation: This condition could result from unsuitable habitat conditions for bluegill reproduction, water quality conditions that would hinder survival of young bluegill (e.g., low alkalinity or nutrients), or other fish that would interfere with bluegill reproduction, but it could also indicate few adult bluegill and intense bass predation.

Diagnosis: determine the status of adult bluegill and the abundance of largemouth bass 150–300 mm.

Young largemouth bass present and:

A. Many recently hatched bluegill, few intermediate bluegill

Probable situation: Bass and bluegill are reproducing; bass are effectively reducing the number of bluegill.

Diagnosis: balanced fish community.

B. Many recently hatched bluegill, very few or no intermediate bluegill

Probable situation: Bass and bluegill are reproducing. The scarcity of intermediate blue-gill probably results from excessive predation by largemouth bass.

Diagnosis: bass are overcrowded and the population needs to be reduced.

C. No (or few) recent hatch of bluegill, many intermediate bluegill

Probable situation: Abundance of bluegill may be great enough to interfere with bluegill reproduction but not bass reproduction.

Diagnosis: Overabundant bluegill.

Authors’ note: in our experience, a dense bluegill population that interferes with bluegill reproduction but not bass reproduction would be unlikely.2Inserted by the authors. Dense bluegill populations, often dominated by intermediate bluegill, can interfere with largemouth bass reproduction, but we have not observed an absence of bluegill reproduction and recruitment when environmental conditions are suitable for bluegill reproduction.


7.2.2 Quantitative Assessment of Population Size Structure, Relative Abundance, and Condition

The common arsenal of population metrics used by most fisheries biologists, whether managing ponds or other waters, includes size structure (length frequency); fish abundance, either from population estimates or more often catch rates (i.e., catch per unit effort) that are used as a measure of relative abundance; and fish body condition. Fish growth analysis, while valuable for assessment, typically requires more effort and often requires euthanizing fish. Thus, fishery biologists often face the challenge of population and community assessment from indices of size structure, condition, and relative abundance. While each of these mea-sures has its own set of potential biases, the combination of information usually will provide sufficient information for a knowledgeable fishery biologist to determine the status of pond fish populations and the predator–prey community.

Estimating size structure, relative abundance, and condition requires representative sam-ples of the full size spectrum of juvenile and adult bluegill and largemouth bass, and these samples are most effectively obtained by boat electrofishing. Pope et al. (2009) recommended that electrofishing small, warmwater ponds with 60 Hz pulsed DC electrofishing along the shoreline at night and during spring (water temperatures 15–23°C) generally produced the greatest catch rates. Dipnets should be constructed with 6-mm square mesh to ensure com-plete sampling of stock-length bluegill (i.e., ≥80 mm). The electrofishing sample should be representative of the available habitats in the pond where electrofishing is effective. Elec-trofishing effort targeting specific habitats to increase the catch rate of largemouth bass can produce biased size structure estimates (Hubbard and Miranda 1988).

7.2.2.1 Size Structure Analysis

Assessing and manipulating the size structures (length frequency distributions) of large-mouth bass and sunfish populations are the key to bass-sunfish ponds that provide reward-ing fishing experiences. The concept of proportional stock density (PSD, subsequently re-named proportional size distribution; Guy et al. 2007) was proposed as a method to quantify a length-frequency distribution for a population (Anderson and Neumann 1996) and has since seen wide application and further development (e.g., Gabelhouse 1984a; Box 7.1). In a syn-thesis of data collected by the Central States Pond Management Work Group (see Chapter 1), Reynolds and Babb (1978) found that largemouth bass PSD could provide reliable indica-tions of bass population biomass, growth rate, mortality rate, maximum age, and consistency of recruitment in small impoundments in the Midwestern USA. Other studies (reviewed in Willis et al. 1993) indicated negative correlations for largemouth bass PSD with bass relative abundance and mortality and significant positive correlation with bass growth rate. Bluegill PSD was negatively related to bluegill recruitment and positively related to bluegill growth rate. In other words, PSD could be used as a surrogate of other important population variables (e.g., growth rate, abundance) that are, in addition to size structure, indicative of population dynamics in predator–prey systems.

As with any index based on sampling data, care must be taken to understand potential weaknesses and biases of PSD estimates. Highly variable recruitment can influence PSD val-ues (Carline et al. 1984), so the utility of PSD may be limited in ponds where erratic recruit-

186 Chapter 7

BOX 7.1. PROPORTIONAL SIZE DISTRIBUTION

Population size structure (length-frequency distributions) provides useful information about the demographics of a population and is especially useful for assessing predator-prey relations. Anderson (1976) developed the proportional stock density (PSD) index to repre-sent population size structures with a single value. Proportional stock density was subse-quently renamed to proportional size distribution (Guy et al. 2007), but neither the concept nor the acronym changed. PSD is simply the number of fish ≥ quality-length divided by the number of fish ≥ stock-length:

PSD = (number of fish ≥ quality length) / (number of fish ≥ stock length) ×100.

Lengths are measured as total length. Note that even though PSD is a percentage, it is unitless; and, by convention, no percentage symbol should be used. Stock length has been variously described (Gabelhouse 1984a), but the definition of greatest value for pond as-sessment is the minimum length effectively captured by fishery gears traditionally used to sample that species. Quality length was defined by Anderson (1976) as the minimum length of fish most anglers like to catch. Note that stock-length fish include all fish longer than stock length, so quality-length fish are also included as stock-length fish. Stock and quality lengths have been established for numerous freshwater fishes (Neumann et al., in press). Table 7.1 provides stock and quality lengths for common pond fishes discussed in this chapter.

PSD serves a valuable purpose by summarizing the size distribution of a population with a single number; for the astute student, PSD should create a simple and general image of the population. For example, 60% of the stock-length (i.e., those ≥200 mm) largemouth bass are ≥300 mm when PSD = 60, but only 30% of the stock-length largemouth bass are ≥ 300 mm when PSD = 30. Clearly, larger (quality-length) bass are relatively more abundant in the population with higher PSD.

Although PSD effectively summarizes the proportion of fish greater than quality length, there are virtually infinite ways for a population to have a particular PSD. Consider the three largemouth bass population samples in the following figure. All three of these largemouth bass samples have the same sample size and a PSD of 43. Despite the differ-ences among the population size structures, PSD is the same, indicating that it is a rather coarse index of size structure.

(Box continues)


BOX 7.1. CONTINUED

The concept of relative stock density (Gabelhouse 1984a) expanded on the utility of PSD by providing measures of the proportion of the stock-length fish that exceeded lengths greater than quality length. Gabelhouse (1984a) proposed three categories of lengths larger than quality length—preferred, memorable, and trophy—and a protocol for establishing length thresholds for each of the length categories. Accepted lengths for preferred, memo-rable, and trophy fish discussed in this chapter are provided in Table 7.1. The proposed change in nomenclature of PSD by Guy et al. (2007) also applied to relative stock density, and these population size-structure descriptors are now categories of PSD. These catego-ries are calculated as:

PSD-P = (number of fish ≥ preferred length) / (number of fish ≥ stock length) ×100,PSD-M= (number of fish ≥ memorable length) / (number of fish ≥ stock length) ×100, andPSD-T= (number of fish ≥ trophy length) / (number of fish ≥ stock length) ×100.

(Box continues)

188 Chapter 7

BOX 7.1. CONTINUED

Standardized length categories are useful for describing length distributions, compar-ing changes in a population’s length distribution over time (e.g., years), and comparing length distributions among different populations. Using standardized length categories is recommended, but may not provide the best approach for assessing and developing man-agement recommendations for a particular pond. Given that PSD-M for largemouth bass is the same as PSD-510, pond managers may choose to use population-specific size cat-egories. For example, a largemouth bass >560 mm would be considered a “very large” or “trophy” bass in many northern ponds, yet this fish is 50 mm less than trophy length by standardized classification. A northern pond with a PSD-560=10 would be considered to have an excellent population of trophy bass even though PSD-T=0. Throughout this chapter, categorical PSD values will follow the notation of PSD-X, where X is the mini-mum length of a length group; e.g., PSD-400 is the number of fish ≥400 mm divided by the number of stock-length fish multiplied by 100. Proportional size distribution without a numerical designation is the PSD based on quality-length fish (i.e., percentage of 200-mm and longer largemouth bass that also exceed 300 mm).

Gabelhouse (1984a) also proposed an incremental method as a companion technique for describing fish population structure. Incremental PSD values are measures bounded by the length categories: stock-quality (S-Q) are the fish that are ≥ stock length but < quality length; quality-preferred (Q-P) are the fish that are ≥ quality length but < preferred length; preferred-memorable (P-M) are the fish that are ≥ preferred length but < memorable length; and mem-orable-trophy (M-T) are the fish that are ≥ memorable length but < trophy length. Thus,

PSD S-Q= (number of fish of S-Q length) / (number of fish ≥ stock length) ×100,PSD Q-P= (number of fish of Q-P length) / (number of fish ≥ stock length) ×100,PSD P-M= (number of fish of P-M length) / (number of fish ≥ stock length) ×100, andPSD M-T= (number of fish of M-T length) / (number of fish ≥ stock length) ×100.

The utility of incremental PSD values is quantitative description of the relative pro-portion of specific length ranges of fish in a population. Paralleling population-specific PSD values (e.g., PSD-450, PSD-500), a pond manager may also elect to use population-specific incremental PSDs (e.g., PSD 350–450) to more precisely describe population size structure.


ment is known or suspected. Seasonal changes in size structure of samples can be caused by differential behavior and habitat use by different sizes of fishes (Willis et al. 1993; Pope and Willis 1996). For example, PSD values from largemouth bass electrofishing samples collected during midsummer likely will be lower than those collected during spring when larger adult bass might be concentrated in the shallows to spawn. Similarly, PSD values collected at night likely will differ from those collected during the day because larger bass move to shallow water at night to prey on the sunfish seeking shelter there.

The precision of a PSD estimate, as any other population metric, depends on sample size. Determining sample size before sampling is conducive to efficient and effective management. For PSD values ranging from 20 to 70, estimating PSD within ±10% confidence intervals at α = 0.05 requires a sample of 62–96 fish (Table 7.2). A sufficient sample usually can be col-lected from most productive ponds larger than 1 ha by boat electrofishing. Gustafson (1988) provided formulae and tables that allow calculation of 80 and 95% confidence intervals for PSD values that are useful when sample size is not determined before sampling or sampling fails to collect the prescribed number of fish (Table 7.3).

The use of PSD values in pond fish community assessment transforms the intuitive ap-proach of the Swingle seine-sample method described in Section 7.2.1 to a quantitative deci-sion process. The use of PSD also is prescriptive in the sense that the pond manager knows what proportional changes need to occur in the largemouth bass and sunfish populations to achieve management targets. Further, the quantitative PSD approach allows the manager to determine if or when the management target has been achieved. The PSD approach embodies the same conceptual basis as the Swingle seine-assessment approach—maintaining appropri-ate population size structures of predator and prey populations. However, it is the prescriptive capability that sets the PSD assessment apart from the seine assessment. Swingle’s assess-ment of reproduction and recruitment ended with a diagnosis of the status of the bass and sunfish populations; it left to the knowledgeable manager to determine whether a problem existed and what management strategy might remedy the problem. The PSD approach allows the manager to visualize and estimate changes needed in the relative abundance and size structure of the predator and prey populations.

7.2.2.2 Relative Abundance Indices

Relative abundance is an index of fish population density. Because density and biomass estimates are time-consuming and expensive, the catch of a particular fish species per unit of sampling effort with a gear often is used as an index of density. For example, the number of stock-length (≥200 mm) largemouth bass caught per hour of night electrofishing may provide interpretive information about that particular bass population.

Table 7.1. Established minimum length (mm) categories for fish species commonly used in rec-reational fishing ponds (from Anderson and Neumann 1996).

Species Stock Quality Preferred Memorable Trophy

Largemouth bass 200 300 380 510 630Bluegill 80 150 200 250 300Redear sunfish 100 180 230 280 330

190 Chapter 7

d (%)PSD 2.5 5.0 10 15 20 25

α = 0.055 292 10 554 139 15 784 196 49 20 984 246 62 28 25 1,153 289 72 32 30 1,291 323 81 36 21 35 1,399 350 88 39 22 40 1,476 369 93 41 23 1545 1,522 381 96 43 24 1650 1,537 385 96 43 24 1655 1,522 381 96 43 24 1660 1,476 369 93 41 23 1565 1,399 350 88 39 22 70 1,291 323 81 36 21 75 1,153 289 72 32 80 984 246 62 28 85 784 196 49 90 554 139 95 292 α = 0.205 125 10 237 60 15 336 84 20 421 106 27 25 493 124 31 30 552 138 35 35 598 150 38 17 40 631 158 40 18 45 651 163 41 19 50 657 165 42 19 11 55 651 163 41 19 60 631 158 40 18 65 598 150 38 17 70 552 138 35 75 493 124 31 80 421 106 27 85 336 84 90 237 60 95 125

Table 7.2. Approximate sample sizes to estimate proportional size distribution (PSD) with a speci-fied one-sided confidence interval (d) at significance levels (α) of 0.05 and 0.20. For example, at α = 0.05 and d = 10, the table predicts that 81 stock-length fish would be needed to be 95% certain that PSD = 30 ± 3 (i.e., ±10%). Values in the table are from Miranda (1993).


PSDN 5 10 15 20 25 30 35 40 45 50

80% confidence level

10 3015 22 22 22 2220 16 17 18 18 18 1925 13 14 15 15 16 16 1630 12 13 13 14 14 14 1435 10 11 12 12 13 13 13 1340 9 10 11 11 12 12 12 1250 7 8 9 9 10 10 10 11 1160 6 7 8 8 9 9 9 9 1070 6 6 7 8 8 8 9 9 980 5 6 7 7 7 8 8 8 8100 3 5 5 6 6 7 7 7 7 7120 3 4 5 5 6 6 6 6 6 6

95% confidence level

N 5 10 15 20 25 30 35 40 45 50

10 4815 34 35 35 3620 26 27 28 29 29 2925 21 22 23 24 25 25 2530 19 20 21 21 22 22 2235 15 17 18 19 20 20 20 2040 14 15 17 17 18 18 19 1950 11 12 13 14 15 16 16 16 1660 9 11 12 13 14 14 14 15 1570 9 10 11 12 12 13 13 13 1380 8 9 10 11 12 12 12 12 12100 5 7 8 9 10 10 11 11 11 11120 5 6 7 8 9 9 9 10 10 10

Table 7.3. Approximate 80% and 95% confidence intervals (±) for proportional size distributions (PSD) as a function of sample size (N). Confidence intervals have been shown only for PSD 5–50. The confidence intervals are symmetrical. Confidence intervals for values of PSD > 50 can be determined using the PSD value confidence interval of 100 minus estimated PSD. Table modi-fied from Tables 1 and 2 in Gustafson (1988).

192 Chapter 7

The utility of relative abundance indices has been, and continues to be, debated by fisher-ies professionals (Hubert 1996). Lacking scientific comparisons of catch rate and actual abun-dance, measured as density or biomass, the debate is fueled by the fact that many factors affect catchability of a fish species with a particular gear and catchability—the proportion of the population captured by a unit of effort—may not be constant. Consider electrofishing as an example. Seasonal changes in size structure of a sample of largemouth bass captured by elec-trofishing should be expected because their behavior changes throughout the year and differs among different sizes (Pope and Willis 1996). Comparing electrofishing catch per hour among locations can be difficult, as factors such as water conductivity (Reynolds 1996; Miranda 2005) or day versus night sampling (Dumont and Dennis 1997; McInerny and Cross 2000) can sub-stantially affect catches and must be accounted for before data comparisons are possible. Dif-ferent electrofishing boats may have greater or lower effectiveness that affects catch rates and observed size distributions of fishes (Heidinger et al. 1983). The number of netters on the front of the boat, or even the experience level of a netter or the boat driver, can substantially affect largemouth bass catch rate (Hardin and Connor 1992). Further, weather and water conditions (e.g., waves or turbidity) also can substantially affect electrofishing catches. In light of all these variables, relative abundance data must be interpreted cautiously (Hubert 1996).

Despite the potential sources of error or bias, relative abundance data tend to be more comparable when collected within a limited geographic location, in similar habitat types, and with similar electrofishing equipment. Largemouth bass population density has been positive-ly correlated with electrofishing catch per hour, especially in small waters (e.g., Gabelhouse 1984b, 1987; Coble 1992; Hill and Willis 1994). Thus, a pond management biologist with her or his own equipment, functioning in one geographic location, likely will be able to determine whether the electrofishing catch rate for largemouth bass in a pond is low, moderate, or high by the standards of that location.

Relative abundance data are typically used in two ways. When sampling at a relatively stan-dard time of year, time of day, and with similar electrofishing gear, trends in relative abundance over time inform fishery managers about changes in fish populations and alert them about needs for management action or changes in actions. Alternatively, biologists may want to compare data from one pond to others. Such an approach requires more caution, as differences in pond water quality, pond morphometry, etc., can complicate such comparisons. The bottom line on the utility of relative abundance indices is that despite high variability among catches, this tool can be useful for fish population and community assessment, especially if comparisons are lim-ited to ponds that are not greatly different with respect to geography, habitat, or morphometry.

7.2.2.3 Fish Condition Indices

Condition indices are used to assess fish relative plumpness and are assumed to be a mea-sure of well being. Although many factors (e.g., water quality, parasites) can affect condition, it is generally used to infer the availability of food. If most fish in a population, or most fish in one particular length-group, are thin, perhaps the population density is high and food is limit-ing. If the fish are too plump, then food apparently is abundant, so a management strategy to increase population density might be appropriate.

While several procedures are available for estimating condition (Box 7.2), the relative weight (Wr) index is most commonly used by North American fishery professionals and rec-ommended for use in pond assessments. As with relative abundance estimates, the use and


BOX 7.2. CALCULATION AND INTERPRETATION OF RELATIVE WEIGHT (Wr)

Condition of a fish traditionally has been regarded as an index of well-being—a fish that is relatively heavy bodied is considered a healthy and well-fed fish. Three types of condition indices have been developed: Fulton’s K; relative condition factor (Kn); and relative weight (Wr) (Blackwell et al. 2000; Neumann et al., in press). Fulton’s K is sim-ply a ratio of weight to length cubed; as such, it tends to increase with fish size because most species exhibit allometric growth—weight increases faster than length at larger sizes. Therefore, K cannot be compared throughout a wide range of fish lengths. Kn ac-commodates allometric growth and allows comparison of condition across a range of lengths within a fish species by comparing the observed weight of the specimen to a length-specific predicted weight for the population. The predicted weight is estimated from a regression model of log10(weight) = log10(length) of the population. The length of the specimen is entered into the population-specific weight-length regression model to obtain the predicted weight for a fish of that length, and Kn is calculated as the ratio of the observed weight of the specimen to its predicted weight. Wr is similar to Kn except that a standard weight (Ws) is predicted from a log10(length) = log10(weight) regression that considers populations throughout North America. The Wr condition index is most com-monly used by North American fishery professionals.

The Wr index, developed by Wege and Anderson (1978) is calculated as:

Wr = (Wo / Ws) ×100,

where Wo is the measured (observed) weight of an individual fish, and Ws is the length-specific weight (standard weight) predicted by a standard weight-length regression de-veloped for the species. Note that even though Wr is a percentage, it is unitless, and, by convention, no percentage symbol should be used.

The standard weight (Ws) is calculated as:

log10(Ws) = a′ + b • log10(L),

where a′ is the intercept value, b is the slope of the log10(weight)–log10(length) regression equation, and L is the total length of the fish. Most standard weight equations were devel-oped using 75th percentile fish weights at a given length, meaning that a Wr value of 100 is not an average but that the Ws equation represents fish in greater than average (i.e., 75th percentile) condition (Neumann et al., in press). Relative weight values above 100 for an individual or a length group suggest a surplus of prey, while Wr values below 90 can suggest a scarcity of food or problems with feeding conditions (Blackwell et al. 2000).

Standard weight equations have been proposed for a variety of fishes, and those for largemouth bass, bluegill, and redear sunfish are provided in Table 7.4. See Neumann et al. (in press; Table 14.5) for the most recent summary of available Ws equations and for background on the development of Ws equations.

Trends or patterns in Wr can be evaluated by plotting individual Wr values as a function of fish length or by calculating mean Wr values for specific length groups. Calculating mean

(Box continues)

194 Chapter 7

BOX 7.2. CONTINUED

Wr for an entire sample can mask important length-related trends in fish condition and should be avoided (Murphy et al. 1991). The incremental length groups defined by the five-cell PSD model (Gabelhouse 1984a)—S-Q, Q-P, P-M, M-T, and T—provide a biologically and managerially meaningful basis for determining mean Wr values, although any length groups can be used.

For example, the following data set provides weight and length data for sample of largemouth bass collected by electrofishing from a 40-ha impoundment in central South Dakota during May; only a portion of all largemouth bass were weighed.

Total length (mm) Wo(g) Ws(g) Wr

157 38.8 45.6 85 164 43.7 52.6 83 171 48.3 60.3 80 199 74.3 99.1 75 204 87 107.5 81 215 98 127.7 77 230 115 159.2 72 234 115 168.4 68 251 170 211.9 80 252 155 214.7 72 266 190 256.2 74 278 228 296.1 77 305 321 401.0 80 333 438 534.5 82 345 540 600.2 90 368 697 741.3 94 380 848 823.4 103 381 922 830.6 111 393 1103 919.3 120 402 1079 990.0 109 422 1346 1160.5 116 456 1765 1495.5 118 491 2000 1905.1 105 515 2695 2227.1 121

(Box continues)


BOX 7.2. CONTINUED

The Wr values for each individual largemouth bass were plotted as a function of fish length to assess trends in condition.

Patterns in the Wr data over the range of fish lengths often provide useful data for a pond management specialist. The Wr values for smaller largemouth bass in this popula-tion sample were lower than those for the larger fish, suggesting that the prey supply for the smaller bass may be limiting. The other sampling indices for this sample helped confirm that interpretation. The mean number of stock-length largemouth bass caught per hour of night electrofishing was 110, which was considered high for that particular geographic location and the equipment used. These Wr data represent only the sample of fish that were weighed; the PSD for the entire largemouth bass sample was 23, which is also indicative of a high density, slow-growing bass population. Together, the three sampling indices help confirm the diagnosis that largemouth bass smaller than 300 mm are too abundant and food for these fish apparently is limiting. In turn, it is likely that the growth of S-Q largemouth bass will be slow. The higher Wr of the low number of larger largemouth bass in the population suggests that their food resources are more plentiful.

196 Chapter 7

interpretation of Wr has been debated among fishery professionals. Much of the controversy arose from attempts to use Wr in lieu of other population variables, particularly growth rate (e.g., Gutreuter and Childress 1990), which were more time consuming to assess. Although Wr may at times be correlated with fish growth, that is not always the case, as condition is more indicative of short-term environmental conditions (weeks or months); whereas growth rate is commonly evaluated on an annual basis. Slow-growing fish that encounter a temporar-ily abundant food supply may have high Wr if sampled then but lower Wr at other times of the year when prey is more limiting or environmental conditions are more stressful. Similarly, a fast growing population may hit a feeding bottleneck for a few weeks or a month; if a biolo-gist happens to sample at the end of that bottleneck, Wr may be low despite the fact that an-nual growth is fast. Relative weight should be expected to change seasonally, such as in the short time period from pre- to postspawn (Pope and Willis 1996; Blackwell et al. 2000), and Wr may change with time of day if fish exhibit a strong diel periodicity in feeding activity because there is no established protocol for weighing fish with or without stomach contents. Finally, the accuracy and precision of Wr values are dependent on the accuracy and precision of measurement devices for length and weight (Gutreuter and Krzoska 1994).

Despite the potential for error and bias, pond management specialists often find Wr useful for assessment of pond fish populations. For example, Wege and Anderson (1978) found that growth of age-2 largemouth bass was highly correlated with their Wr values in Midwestern USA ponds. Perhaps just as importantly, Wege and Anderson (1978) also found a positive correlation between mean Wr for 200–299 mm largemouth bass and the prey biomass in the same ponds. Similarly, multiple authors have reported positive correlations between prey abundance and Wr values for a variety of fish species, such as pumpkinseed (Liao et al. 1995), walleye (Marwitz and Hubert 1997; Porath and Peters 1997; Hartman and Margraf 2006), flannelmouth sucker (Paukert and Rogers 2004), and northern pike (Paukert and Willis 2003). Although prey supply was not specifically measured, Otis et al. (1998) reported that bluegill Wr increased as abundance of stock-to-quality length (80–149 mm) bluegill declined in a 28.8-ha Wisconsin lake, a situation that probably resulted in greater food supply for individual fish.

7.2.2.4 Harvest Strategies Based on Size Structure, Relative Abundance, and Condition

Paralleling the interpretation of fishes collected by shoreline seine samples, PSD allows interpretation of electrofishing catch data to diagnose the probable status of the bluegill and largemouth bass populations. In addition, the PSD values for bluegill and largemouth bass also provide guidance for establishing a balanced predator–prey community or bluegill or largemouth bass populations with desired characteristics.

Table 7.4. Intercept (a’) and slope (b) parameters for standard weight (Ws) equations for blue-gill, largemouth bass, and redear sunfish.

Species a′ b Minimum applicable total length (mm)

Bluegill –5.374 3.316 80Largemouth bass –5.528 3.273 150Redear sunfish –4.968 3.119 70


Using data assembled by the Central States Pond Management Work Group, Reynolds and Babb (1978) found that largemouth bass PSD in ponds with balanced largemouth bass–bluegill fisheries and desirable largemouth bass population metrics (i.e., moderate population density and biomass, moderately high growth rate, low mortality, and consistent year-class production) were in the middle third (34–66) of the overall PSD range. Similar assessments of the same data found that the most desirable demographic metrics for bluegill populations occurred at a bluegill PSD of 20–60 (Novinger and Legler 1978). The higher bluegill PSD would be desirable in ponds in which high-quality bluegill fishing (a high proportion of bluegill ≥150 mm) was the target, but would not necessarily provide a sufficient prey base for fast growth rate of largemouth bass. Combining their findings with those of Reynolds and Babb (1978), Novinger and Legler (1978) proposed that largemouth bass PSD of 40–60 and bluegill PSD of 20–40 would be good targets for a balanced bass-bluegill pond (Figure 7.1). Although these targets have been proven effective to produce good, sustainable largemouth bass and bluegill fisheries, deviations from conventional PSD targets may be appropriate to achieve trophy bluegill (Section 7.2.2.6) or trophy largemouth bass (Section 7.2.2.7) fisher-ies.

Objective or target ranges also have been proposed for Wr. For example, Anderson (1980) first recommended a Wr target range of 95–105 for balanced fish populations. This range re-mains an effective indicator of adequate food supply for a bluegill or largemouth bass popula-tion (or certain length ranges of the population), but some variation is expected. Further, Wr values above or below the 95–105 range should be expected when trophy bluegill or trophy largemouth bass are the management objectives.

When accurate PSD estimates for bluegill and largemouth bass populations are available, these data can be plotted in a PSD decision model (Figure 7.1; often referred to as the ‘tic-tac-toe diagram’ for obvious reasons) to diagnose current predator–prey dynamics and provide clear direction for management actions. Based on the desired ranges proposed by Novinger and Legler (1978), bluegill and largemouth bass PSD each can fall into three categories (low, desirable, high). Thus, there are nine possible predator:prey PSD size structure scenarios,

Figure 7.1. Possible population size structures measured by proportional size distribution (PSD) of bluegill and largemouth bass populations in a largemouth bass-bluegill pond.

198 Chapter 7

each designated by Roman numeral (I–IX) in Figure 7.1. Explanations for each scenario and recommended management actions are presented below, organized by largemouth bass PSD category.

7.2.2.4.1 Largemouth bass PSD low (PSD<40; cells I, IV and VII)

Low largemouth bass PSD can result from angler overharvest of >300 mm (quality) bass or a high density of S-Q (200–300 mm) bass. Detecting overharvest of quality-length bass is relatively straightforward. Low electrofishing catch rates by the standards of that region and the equipment used (perhaps <10 quality-length bass per hour) and high Wr (perhaps ≥95) of the S-Q bass collected would suggest overharvest of quality-length largemouth bass. Low largemouth bass PSD could also result from high density and slow growth of S-Q large-mouth bass. Young largemouth bass are produced in excess in most well-designed ponds. The young largemouth bass may grow quickly to 150–200 mm on a mixed diet of invertebrates and sunfish fry, but at larger sizes these overabundant S-Q bass can quickly deplete their prey supply. This results in slow growth and, hence, low recruitment to quality length. Low Wr (<90) of S-Q bass is an indicator of overabundant, food-limited, and slow-growing S-Q bass. Electrofishing catch rates will be high by the standards of that geographic location and equipment used. This situation is referred to as a “bass crowded” population, and the slow growth through the S-Q size range results in “stockpiling” of S-Q bass (even though the term stockpiling is a misnomer because those bass are not being “saved” for anything). Bluegill PSD can provide important additional information that aids prediction of the abundance of S-Q bass, as discussed below.

7.2.2.4.1a Bluegill PSD high (PSD>40; cell I)

Probable situation: Few bluegill <150 mm because of abundant largemouth bass less than quality length (bass crowded). As a result, the S-Q largemouth bass eat most of the smaller bluegill, and the surviving bluegill grow quickly to quality length (>150 mm). This could be desirable if the management goal is high-quality bluegill fishing (see Section 7.2.2.6) and if all sizes of bluegill in the S-Q (80–150 mm) range are sufficiently abundant to indicate that recruitment to quality length is expected to continue. Bluegill that exceed 200 mm are also expected to be relatively abundant (e.g., PSD-P > 20) and bluegill Wr will be greater than 100.

Recommendation: Harvest S-Q largemouth bass if the management objective is a bal-anced fishery. Harvest may need to be as great as 150 S-Q bass per hectare for a severely bass-crowded pond that has high productivity. High annual harvest rates should continue until Wr values of S-Q largemouth bass improve and bluegill PSD declines.

If the management objective is a high-quality bluegill fishery, continue to monitor the abundance of S-Q bluegill to ensure continued bluegill recruitment to quality size; harvest of S-Q largemouth bass should be increased if the electrofishing catch rate of 50–100 mm bluegill is less than the catch rate of 100–150 mm bluegill, a sign that bluegill recruitment may be overly reduced.


7.2.2.4.1b Bluegill PSD desirable (PSD = 20–40; cell IV)

Probable situation: Quality-length largemouth bass may be overharvested. Alternatively, bass could be overcrowded and the expected high bluegill PSD not evident because angler harvest may have negatively affected the size structure of the bluegill population by excessive removal of quality-length fish.

Recommendation: Reduce harvest of largemouth bass >300 mm to increase bass PSD to 40–60. Monitor PSD and Wr values of S-Q largemouth bass; if Wr of S-Q bass is below 95, bass density may be sufficiently high to reduce growth rates and slow the progression of quality largemouth bass to larger sizes. Harvest of S-Q largemouth bass as recommended in 7.2.2.4.1a may be necessary. Alternatively, if harvest of the adult bluegills has been sufficient to negatively affect size structure, reduce or eliminate harvest and determine if bluegill PSD increases within 1 year.

7.2.2.4.1c Bluegill PSD low (PSD<20; cell VII)

Probable situation: Bluegill may be overabundant and slow growing due to insufficient pre dation on sub-stock and stock-length, particularly 75–125 mm, sunfish. Ponds with low habitat suitability (e.g., high clay turbidity, low productivity, excessive shallow areas, and excessive vegetation) can exhibit these characteristics of unusually low PSD for both the bass and bluegill. Alternatively, larger bluegills may have been excessively harvested by anglers.

Recommendation: If habitat is unsuitable, consider habitat improvement strategies (see Chapters 11 and 12). If habitat appears suitable and largemouth bass overharvest seems likely, stop harvesting largemouth bass >300 mm. If bass PSD does not increase after 1 year and few sub-stock (<80 mm) bluegill are present to provide food for S-Q largemouth bass, stocking bass large enough to consume the most abundant length-groups of sub-quality (<150 mm) bluegill may be necessary. As a general rule, the stocked largemouth bass should be at least three times as long as the lengths of bluegill that need to be reduced; for example, stock largemouth bass at least 360 mm long to control abundant 100–120 mm bluegill. Finally, if harvest of the adult bluegills has been sufficient to negatively affect size structure, reduce harvest and determine if bluegill PSD increases within 1 year.

7.2.2.4.2 Largemouth bass PSD desirable (PSD = 40–60; cells II, V, or VIII)

The largemouth bass population may be in balance, but a desirable size structure of the bluegill population is needed to maintain fast growth of all sizes of largemouth bass and to provide sustained quality bluegill fishing.

7.2.2.4.2a Bluegill PSD high (PSD>40; cell II)

Probable situation: Pond may be in balance and supporting a relatively abundant popula-tion of quality bluegill. For example, perhaps a strong year-class of bluegill recently recruited into quality length. However, bluegill spawning or recruitment may be limiting. In time, this could result in insufficient prey for largemouth bass and reduction in the bluegill population.

200 Chapter 7

Recommendation: Determine if bluegill spawning and recruitment are adequate by shore-line seining during late summer or early autumn to assess the abundance of sub-stock (<80 mm) bluegill. Make no changes in harvest strategies if sub-stock bluegill are moderately abundant. If few sub-stock bluegill are present and summer water temperature is suitable for bluegill spawning (>24°C for at least 2 months), gravel spawning areas and the addition of brush to increase bluegill reproduction and recruitment may be needed (consider this technique experimental and document results). If recently spawned (<25 mm) bluegill are present, but 25–80 mm bluegill are scarce, the abundance of largemouth bass may need to be reduced. Start by removing 30–50 of the 200–400 mm largemouth bass per hectare; monitor bluegill PSD to determine whether bass harvest should be increased (if bluegill PSD remains >40) or decreased (if bluegill PSD changes to <20). Also, monitor largemouth bass PSD. If bluegill PSD remains >40 and the bass PSD declines below 40, bass harvest should focus on S-Q bass as the population is moving toward a trophy bluegill option.

7.2.2.4.2b Bluegill PSD desirable (PSD = 20–40; cell V)

Probable situation: A balanced predator–prey system.

Recommendation: Continue present harvest regime if the management objective is a bal-anced fishery.

7.2.2.4.2c Bluegill PSD low (PSD<20; cell VIII)

Probable situation: Possibly a temporary situation as a result of high bluegill spawning and survival in the present and previous year. However, this scenario may also be an indica-tion of insufficient largemouth bass predation that could lead to a bluegill-crowded condition. Alternatively, anglers could be overharvesting large bluegills.

Recommendation: A definitive recommendation is difficult, but the objective should be to increase bluegill PSD. However, because the biomass of fish that any pond can support varies widely, as does the catchability of the largemouth bass by electrofishing, there is no specific electrofishing catch rate of bass that indicates bass abundance is sufficient. As a coarse gen-eralization, largemouth bass are scarce if electrofishing captures less than 25 stock-length bass/h and bass Wr values are 105 or above. Conversely, bass are sufficient if electrofishing captures more than 50 stock-length bass/h and Wr is 90–100. Monitor bluegill PSD, and if it does not increase within a year, bass harvest should temporarily cease. If angler harvest of bluegills is suspected to be sufficient to impact size structure, then reduce or eliminate bluegill harvest and assess potential PSD increases over time.

7.2.2.4.3 Largemouth bass PSD high (PSD>60; cells III, VI, and IX)

High largemouth bass PSD can result from an abundance of large bass or a scarcity of small bass. Relatively abundant large bass can be desirable if the management objective is to produce a high-quality or trophy bass fishery (see Section 7.2.2.7). The scarcity of small largemouth bass may result from poor spawning success or lack of recruitment by largemouth bass. The high bass PSD also could result from high harvest of S-Q bass, which may be pur-poseful in an effort to improve the growth rate of larger bass.


7.2.2.4.3a Bluegill PSD high (PSD>40; cell III)

Probable situation: This rare condition may occur in an unfished pond or one in which no large fish are harvested. This is not necessarily a problem, but it can be a forewarning of an unstable condition.

Recommendation: Continue present harvest regime and enjoy it while it lasts. However, closely monitor the largemouth bass population and be ready to take action. Most pond fish communities will naturally tend toward cells I or IX, depending on the pond habitat and re-cruitment patterns for largemouth bass.

7.2.2.4.3b Bluegill PSD desirable (PSD = 20–40; cell VI)

Probable situation: A desirable predator–prey system for producing a high-quality largemouth bass population. Expect largemouth bass Wr values to be high (e.g., 105 or higher for most of the year).

Recommendation: Continue the current largemouth bass harvest regime (including no har-vest if that is the current harvest regime) if the management objective is the big bass option (Gabelhouse et al. 1982; see Section 7.2.2.7). Continue to monitor the bluegill population to en-sure that a diversity of bluegill sizes remains available to support growth of the largemouth bass.

7.2.2.4.3c Bluegill PSD low (PSD<20; cell IX)

Probable situation: This condition may result from intentional efforts to produce high-quality largemouth bass by high harvest of <300 mm bass. This may be an acceptable, even desirable, condition if bluegill PSD is 15–20. However, a fish community in this cell may indicate an overcrowded, slow-growing bluegill population that potentially can impede bass spawning and eventual recruitment. This can be quickly checked by shoreline seining to de-termine whether sub-stock or age-0 largemouth bass are present.

Recommendation: Stop harvest of all largemouth bass to increase predation on small bluegill. If the management objective is a trophy bass option, do nothing if largemouth bass recruitment is occurring. If largemouth bass are scarce (<25 stock-length bass/h electrofish-ing), no recruitment of largemouth bass is occurring, and the community remains in cell IX, stocking adult largemouth bass nonvulnerable to bass predation (>250 mm) may be necessary.

7.2.2.5 Integration of PSD and Wr for Population Interpretation

While the previous section involved one-time community assessment for largemouth bass–bluegill ponds, fish communities should be tracked through time to monitor fish popula-tions and evaluate responses of the fish populations to management (harvest) actions. This can be done easily and effectively by sequentially plotting the largemouth bass and bluegill PSDs in the PSD decision model. In addition, annual electrofishing samples for largemouth bass might be tracked over time to monitor changes in PSD and Wr that might be related to a management action. The data in Figure 7.2 are from a 2.9-ha private pond in western South Dakota. The pond originally contained a high density, slow-growing largemouth bass

202 Chapter 7

population with Wr and PSD values below those for a balanced population (Willis 2010). The management strategy was removal (harvest) of sub-300 mm largemouth bass in an effort to reduce bass density and increase growth rates and size structure. By years 4 and 5, Wr and PSD had both increased, although not quite to the target range for balanced populations (the center box in the PSD decision model). No further management actions were undertaken at the pond and no angling occurred after year 5. When the pond was sampled again in years 12 and 13, the largemouth bass population had nearly returned to its original state of low Wr and PSD values. Without continued harvest of 200–299 mm largemouth bass, the bass returned a dense population of slowly growing individuals.

7.2.2.6 Managing for Trophy Bluegill (Panfish Option)

Producing a population with relatively abundant large (≥200 mm) bluegill (high bluegill PSD, high Wr, cells I and II in Figure 7.1) is a consequence of abundant food and conservative harvest of large bluegill. Although large adult bluegill may switch to feeding on large crusta-cean zooplankton if this resource is available (Osenberg et al. 1988; Werner and Hall 1988; Schramm and Jirka 1989), bluegill of all sizes prey upon, and therefore potentially compete for, benthic invertebrates (Keast 1978; Mittelbach 1981; Olson et al. 2003). Harvest of large male bluegills can decrease a population’s average length at maturity and cause a slowing of growth at the point in time when energy is diverted from somatic growth to growth of the gonads. See Chapter 8 for further information on the behavioral ecology of bluegills and its effect on management strategies.

Enhancing the abundance of large bluegill requires abundant food for all stock-length bluegill to increase growth rate and recruitment to large sizes. This is accomplished by in-creasing the abundance of S-Q bass (largemouth bass PSD will decrease) to reduce the abun-dance of <100 mm bluegill. Southern ponds in general and northern ponds with 20–50% submergent vegetation coverage tend toward high abundance of S-Q largemouth bass, so reducing harvest of S-Q largemouth bass will usually achieve the increased abundance of

Figure 7.2. Decision model indicating management targets (dotted lines) for largemouth bass proportional size distribution (PSD) and relative weight (Wr). These data are from a 2.9-ha pri-vate pond in western South Dakota. The numbers represent the year the pond was sampled. No management or sampling occurred in years 6–11 (dashed line).


S-Q largemouth bass. In northern ponds, harvesting 10–20 largemouth bass >400 mm per hectare usually increases the abundance of smaller largemouth bass, and in turn, reduces the abundance of bluegill less than quality length. Largemouth bass harvest should be reduced if bluegill PSD declines below 50. In northern ponds, the presence of 400 mm and longer largemouth bass likely indicates a low to moderate bass density, which may be the result of limited (e.g., 10% or less) submergent vegetation coverage. Such habitat is inappropriate for high recruitment of largemouth bass in northern ponds, and a different management objective should be selected (trophy bass).

The outcome of managing ecological systems, even when as simple as one predator-one prey, is not perfectly predictable. Although increasing the density of S-Q largemouth bass (largemouth bass PSD <40) is a recommended strategy to produce large bluegill, it is not fool-proof. Gabelhouse (1987) found that an overly dense largemouth bass population can com-pete with bluegill. Lacking sufficient prey fishes, small largemouth bass consumed aquatic insects and their larvae, which are the primary prey resource for bluegill. Relative abundance of larger bluegill increased after the abundance of 200–300 mm largemouth bass was reduced to evaluate the effectiveness of a 300–380 mm protected slot limit for largemouth bass in a small impoundment.

Feeding prepared feeds (Berger 1982; Porath and Hurley 2005) or fertilizing and liming (Chapter 5) also may help produce larger bluegill. Fertilization or feeding increases the blue-gill carrying capacity and, in the short term, bluegill usually respond with increased growth rate. However, with time, the bluegill population will grow in numbers, and growth rates of individual bluegill will predictably decline as the population approaches the pond’s carrying capacity. Thus, the numbers of bluegill <100 mm must still be controlled by largemouth bass predation or pond owner management efforts to channel the energy in the enhanced food re-source to the larger bluegill. Although desirable results can be achieved, managers should be aware that adding nutrients, whether as formulated feeds or inorganic nutrients, increases the organic matter load, thereby elevating the risk of oxygen depletion during summer and, for ice-covered northern ponds, in the winter (see Chapters 5 and 10).

Some success has been achieved with feeding programs to improve the quality of bluegill populations in southern USA ponds that are managed for a low to moderate density of large largemouth bass. Bluegill on a feeding program tend to be in better body condition, which results in more reproduction and, in turn, more prey for the bass.

7.2.2.7 Managing for Trophy Largemouth Bass (Predator Option)

Every pond has a carrying capacity for largemouth bass. That carrying capacity is ulti-mately determined by the trophic status or available nutrients in the pond that, in turn, affect the biomass of the prey base in the pond. The “natural” trophic status of a pond can be in-creased, to a point, by fertilizing or feeding sunfishes to increase forage production, or possibly by adding an additional and controllable prey fish, such as threadfin shad, to more efficiently transfer energy to the largemouth bass. Nevertheless, the carrying capacity, even if elevated by management activities, still dictates the biomass of largemouth bass a pond will support. Increasing the number of large bass in a pond—the goal of trophy bass management—results in fewer largemouth bass per acre than a pond managed for a more natural diversity of sizes of largemouth bass (viz., more Q-P bass than P-M bass and more P-M bass than M-T bass). Pond owners and managers also should recognize that largemouth bass biomass may be lower

204 Chapter 7

in ponds with high bass PSD (Reynolds and Babb 1978), the target condition when manag-ing for trophy bass. Thus, a pond managed for trophy bass will support relatively few large largemouth bass and still maintain fast growth of those bass.

Managing a pond for trophy largemouth bass is accomplished by shifting a larger portion of the largemouth bass biomass to large fish. Therefore, it is an ecological reality that the bio-mass of smaller bass must be reduced. More large bass and fewer small bass will be reflected by a higher bass PSD. A reasonable bass PSD target for trophy bass management would be 50–80 with high bass Wr values (>105); bluegill PSD should decline to approximately 15–20 to provide more prey-size bluegill (Table 7.5). However, a largemouth bass PSD >75 and most quality-length bass >450 mm (PSD-450 > 40) risks insufficient predation on small bluegill and the possibility of bluegill becoming overcrowded and interfering with large-mouth bass reproduction, a concern if bluegill PSD declines below 20. On the other hand, low natural rates of largemouth bass recruitment may actually be desirable if the pond owner or private sector biologist has been investing substantial time in harvest (either via angling or electrofishing) of the sub-300 mm bass.

Largemouth bass PSD is increased by harvesting S-Q bass, which simultaneously reduces predation on sub-stock bluegill, thereby providing more prey for the larger bass and stimulat-ing faster growth. In southern ponds, harvest of even larger largemouth bass, perhaps up to 350 or even 400 mm, may be necessary. As a starting point, harvest largemouth bass up to 300 mm if the largemouth bass PSD-350 is <20; harvest bass up to 350 mm if PSD-350 is ≥20. As a rule of thumb, reduce the size range of the bass population that are most abundant because these fish are reducing the prey available to larger bass.

The number of largemouth bass to harvest will depend on the bass biomass and thus, the productivity of the pond. Greater largemouth bass biomass is expected in ponds with greater fertility; however, specific relationships between pond trophic state and largemouth bass biomass have not been established, and largemouth bass harvest at this time can only be determined by trial and error. The length of the growing season is probably important. As a starting point, harvest 75 largemouth bass per hectare per year from southern or eutrophic ponds and 50 largemouth bass per hectare per year from less fertile or northern ponds. Moni-tor the bluegill PSD in successive autumns to refine largemouth bass harvest the succeeding year. A bluegill PSD ≥25 indicates bass harvest should be increased; a bluegill PSD <15 sug-gests largemouth bass harvest should be decreased.

Pond owners desiring very large trophy largemouth bass (>4.5 kg in the south, >2.7 kg in the north) may oppose harvesting large (>450 mm) bass, but harvesting some bass >400

Table 7.5. Proportional size distribution (PSD; Q = quality length, P = preferred length, M = memo-rable length) management targets for largemouth bass and bluegill under three different man-agement strategies (from Willis et al. 2010).

Largemouth bass Bluegill

Management strategy PSD PSD-P PSD-M PSD PSD-P

Trophy sunfish 20–40 0–10 50–80 10–30Balance 40–70 10–40 0–10 20–60 5–20Trophy bass 50–80 30–60 10–25 10–50 0–10


mm may be necessary to maintain fast growth of large bass. It is essential to recognize that a few trophy bass can fill the carrying capacity of the pond. For example, a bass standing crop of 50 kg/ha is a reasonable biomass for a moderately productive pond. Only six, 4-kg bass per ha would comprise almost half of the bass carrying capacity. In Midwestern USA ponds, Reynolds and Babb (1978) found that largemouth bass biomass declined from 50 kg/ha in ponds with bass PSD of 34–66 to 25 kg/ha in ponds with bass PSD > 66; thus, even fewer trophy bass would comprise the carrying capacity in a pond managed for trophy bass. Exactly how many large bass to harvest is difficult to determine. As a rule of thumb for southern and Midwestern ponds, harvest no large bass if few or no bass ≥450 mm are caught by angling or bass PSD-450 is <40. If largemouth bass ≥450 mm are frequently caught by angling or bass PSD-450 is ≥40, harvest several bass ≥450 mm per hectare annually. Condition also can be an indicator of the need to harvest large fish. For instance, harvest several bass ≥450 mm annu-ally if the bass ≥450 mm have Wr values less than 90. However, in northern ponds, be mindful that 510 mm largemouth bass should be considered trophies.

An unresolved question is the long-term maintenance of a trophy largemouth bass popu-lation in a pond that previously contained a crowded bass population. After fish have been removed to restructure a bass-crowded population with low PSD into a population dominated by 380–510 mm largemouth bass, will the large bass provide sufficient predation on the an-nually produced cohort of young bass? The alternative would be the return to a bass-crowded population if no further management efforts are applied. In one case of a South Dakota pond, the population reverted to a crowded largemouth bass population after electrofishing removal of small bass ceased (Willis 2010; Figure 7.2). Further research is still needed on this topic. In southern ponds where crowded largemouth bass populations are common, annual harvest of S-Q bass is required to prevent bass crowding and maintain abundant prey fishes for larger bass.

Finally, one untested method for trophy largemouth bass management would involve har-vest of mature male bass, either by angling or electrofishing removal, while females are re-leased. Females typically reach larger maximum sizes than males; this has been documented for Florida largemouth bass (Schramm and Smith 1987) and is commonly observed for north-ern largemouth bass. External determination of gender in largemouth bass is difficult, but can be reliably done during the prespawn time period (Parker 1971; Benz and Jacobs 1986). Further research is needed on this strategy.

7.3 LATITUDINAL VARIATION

The principles and general assessment and harvest guidelines described in this chapter apply across broad climatic conditions and wide geographic scales. However, latitudinal variation in predator–prey dynamics has been well documented in the literature, and pond managers will need to make some adjustments to accommodate local conditions. Guy and Willis (1990) found predator–prey relations between largemouth bass and bluegill, after both populations are established and recruiting, in northern ponds were quite similar to those in Midwestern and southern USA ponds. Thus, some potential problems can be avoided by adjusting the stocking procedures. For example, excessive populations of <150 mm bluegill (sunfish crowded) ponds were once a common problem in northern climates (Modde and Scalet 1985). One suggested cause for bluegill overcrowding in northern ponds was spawn-

206 Chapter 7

ing chronology during the first 2 years after stocking fingerling largemouth bass and bluegill. Bluegill typically spawn at age 1, but largemouth bass do not reproduce until age 2 in north-ern ponds (Bennett 1944; Dillard and Novinger 1975; Stone and Modde 1982). Thus, there is limited predation on the bluegill produced the year after stocking. A solution is to stock largemouth bass fingerlings and then stock intermediate or adult bluegill after the fingerling bass have grown to a size (approximately 300 mm) at which they are expected to spawn for the first time (Willis et al. 1990). In this manner, the age-0 largemouth bass will have a supply of age-0 bluegill for a prey source, and predation will control the abundant age-0 bluegill. A vulnerable prey fish, such as fathead minnows, should be stocked with the fingerling bass to stimulate growth (Stone and Modde 1982) and reduce cannibalism even though long-term es-tablishment of small prey species should not be expected. The fingerling largemouth bass can be expected to reach 300 mm and sexual maturity in 1–2 years depending on largemouth bass stocking rate, prey supply, system productivity, and length of the growing season. Although this stocking strategy can be effective, it can also be limited by the availability of adult sunfish for stocking.

To further determine how latitude might relate to differences in bluegill production and largemouth bass consumption, production for age-1 and 2 bluegill and consumption for age-1 and 2 largemouth bass were estimated using bioenergetics models (Hanson et al. 1997). In-put data were regional average length-at-age statistics for bluegill and largemouth bass from northern (Michigan, Minnesota, South Dakota, Wisconsin) and southern (Georgia, Texas) populations obtained from Carlander (1977) and thermal regimes for northern (Lardy Lake, South Dakota [Justin VanDeHey, University of Wisconsin–Stevens Point, unpublished data] and Pelican Lake, Nebraska [Jeffrey Jolley, U.S. Fish and Wildlife Service, unpublished data], and southern waters (hatchery ponds in Mississippi [Justin Wilkens, Mississippi Department of Wildlife, Fisheries and Parks, unpublished data]). Assuming no mortality and fish assem-blages containing only largemouth bass and bluegill, 2.4 times more age-1 largemouth bass are needed to consume age-1 bluegill production in South Dakota ponds than in Mississippi ponds. Similarly, 1.7 times as many age-2 largemouth are needed to consume age-2 blue-gill production in South Dakota ponds than in Mississippi ponds (Table 7.6). Although these models are simplistic and do not consider the many abiotic and biotic factors that affect large-mouth bass and bluegill populations, particularly mortality and density-dependent effects on growth and recruitment, these approximations indicate that management of northern ponds for quality bluegill fisheries likely requires maintenance of higher largemouth bass densities than ponds farther south.

Relatively stable reproduction and recruitment, high production, fast growth rate, and de-sirable size structure of predator and prey populations are maintained by appropriate harvest regimes. Regardless of the ecological force—spawning chronology, growth rates, production and consumption rates, or a combination of these factors—it is apparent that largemouth bass harvest should be lower in northern ponds than in southern ponds. Conservative largemouth bass harvest strategies should be employed in northern ponds.

A second aspect of latitudinal variation that can affect size structure-based (i.e., PSD-based) management is the designation of sizes associated with categories of larger fishes. Although growth and sizes attained by bluegill are rather similar along a latitudinal gradient, growth and sizes attained by largemouth bass are widely different (Neal and Noble 2006). As such, PSD targets for larger size categories of largemouth bass probably should not be ap-plied uniformly throughout the geographic and climatic range in which ponds are managed


for largemouth bass–bluegill assemblages. Further, the expectations of anglers and managers should be tempered by sizes that largemouth bass can attain in a reasonable period of time, say less than 8 years. For example, a PSD-600 of 10 may be attainable for southern ponds managed for trophy largemouth bass, but is not achievable in northern ponds under most con-ditions. The latitudinal variations in growth rate, maximum sizes attained, and angler expec-tations are reasons managers frequently have deviated from established size categories (i.e., PSD-P, PSD-M, and PSD-T) and expressed PSD categories in terms of actual length.

7.4. RESEARCH NEEDS

In several instances, values for catch rates of fishes have been provided that can be used to diagnose whether largemouth bass, or a particular length range of largemouth bass, are scarce or abundant. These numbers are targets based on limited published information about

Table 7.6. Production of age-1 and age-2 bluegill and consumption by age-1 and age-2 large-mouth bass estimated by bioenergetics models for northern and southern USA ponds.

Bluegill Largemouth bass Age 1 Age 2 Age 1 Age 2

Northern ponds Initial total length, mm 45 86 94 184Final total length, mm 86 115 184 255Initial weight, g 1.3 11.0 8.5 76.7Final weight, g 11.0 28.8 76.7 223.2P-value 0.677 0.640 0.571 0.514Production per 1,000 bluegill, g 9,700 17,800 Consumption per largemouth bass, g 279 637Number of largemouth bass needed to consume bluegill production 348 279 Southern ponds Initial total length, mm 53 95 166 256Final total length, mm 95 128 256 315Initial weight, g 2.2 15.3 54.7 226.0Final weight, g 15.3 41.1 226.0 445.6P-value 0.715 0.735 0.488 0.433Production per 1,000 bluegill, g 13,100 25,700 Consumption per largemouth bass, g 888 1,525Number of largemouth bass needed to consume bluegill production 147 169

208 Chapter 7

electrofishing catch rates of largemouth bass in Midwestern USA ponds (Novinger 1990), for spring nighttime boat electrofishing in small lentic waters (Brouder et al. 2009), or observa-tions from the chapter authors throughout their years of field experience. Electrofishing catch rate will vary with abundance of largemouth bass, which is a function of pond trophic status and bass population size structure, and with catchability, which is related to water conductiv-ity, pond morphometry (e.g., depth), habitat (e.g., macrophytes, large woody materials), time of year, boat design, crew experience, and other factors. Further, numbers of largemouth bass to harvest have been suggested. These numbers are, at best, approximations. The number of bass to harvest is affected by largemouth bass standing crop, which is a function of pond trophic status and population size structure. The general relationships between fertility or tro-phic state and fish standing crops are well established, but relatively precise predictive mod-els have not been developed for small impoundments. Databases for small impoundments that integrate electrofishing catch rate, trophic status, habitat conditions, water temperature regime, and largemouth bass and bluegill size structure and standing crops are needed to fur-ther develop and refine such models. Within this quantified background of biotic and abiotic conditions, validation of the suggested harvest and PSD targets are needed to further move pond management from art to science. Intuitively, population size structure should be inde-pendent of trophic status, and therefore, useful for measuring the status of largemouth bass and bluegill populations across wide ranges of pond trophic conditions. However, some pond managers have found that supplemental feeding of bluegill can increase forage production for largemouth bass. Clearly, research is needed to test the hypothesis that population size structure is independent of trophic status across a wide range of pond conditions in various geographic locations.

Predator–prey dynamics are known to vary along latitudinal gradients. The output of bio-energetics models presented in this chapter indicates that species-specific food consumption and production may account for some of the latitudinal variation in predator–prey balance. In other words, the effect of thermal regimes on predator–prey dynamics may be predictable, which presents a hypothesis that also needs to be tested. A finding that thermal regime has a predictable effect on predator–prey dynamics would warrant development of climate-specific harvest recommendations. This research also may shed light on how pond fisheries manage-ment will be affected by continued climate change, which has become a fertile area for future research in many disciplines.

Latitudinal variations in climate that affect growing season and fish growth also affect age at sexual maturity. Alternative stocking schedules in new or renovated ponds may suc-cessfully accommodate these variations in growth and onset of sexual maturity and prevent undesirable predator and prey dynamics. Willis et al. (1990) suggested delayed stocking of bluegill can be effective in northern ponds. Evaluations of this and other stocking strategies are warranted.

Another important need is developing the ability to diagnose pond predator–prey rela-tionships using angler catch data. Green et al. (1993) provided an example of using angler-collected data to make fishery management decisions for New York ponds. Because the PSD approach to pond assessment and management has proven valid both for diagnosing predator and prey population dynamics and for developing management recommendations, a logical first step would be to evaluate similarities and differences between angler-catch PSD and electrofishing PSD. Angling has repeatedly been shown to be size-selective (e.g., Gabelhouse and Willis 1986; Santucci and Wahl 1991; Prentice et al. 1993; Miranda and Dorr 2000; Is-


ermann et al. 2005). However, when lure size was purposely varied in an attempt to capture representative samples of largemouth bass, size structure and catch rate from angler-collected and electrofishing samples for largemouth bass were significantly and positively related in South Dakota ponds (Isaak et al. 1992). Research is needed to fully evaluate the comparability of angler- and electrofisher-collected samples of fish populations from ponds and to assess the utility of angler-generated measures of population size structure for assessing predator–prey dynamics and developing management recommendations.

A final research need is comprehensive evaluations of “new” pond stocking combina-tions or management strategies other than the traditional largemouth bass-bluegill systems de-scribed in this chapter. Willis et al. (2010) noted that many private pond owners have become interested in diversity in both species combinations and fish sizes. Examples of such preda-tor–prey combinations include largemouth bass-crappie (e.g., Gabelhouse 1984b; Boxrucker 1987), largemouth bass-yellow perch (Guy and Willis 1991), and the smallmouth bass-redear sunfish (Gabelhouse 1978). Direct predator management strategies also stir substantial in-terest, such as the use of hybrid striped bass, and feeding programs for the hybrid striped bass and for feed-trained largemouth bass. Pond stocking combinations for coldwater fishes should also receive attention, especially given the growing tendency of fishery biologists to use fishes native to specific geographic locations. Pond managers also have demonstrated success with supplemental prey fish stocking (e.g., threadfin shad) and the use of selectively bred or single-sex predators. The evaluations of these new management strategies should be sufficiently rigorous to understand the predator–prey dynamics such that management actions have predictable outcomes and harvest can be specified as has been done for largemouth bass and bluegill in this chapter.

7.5 CONCLUSION

Recreational fishing ponds are popular and valuable additions to private properties that, when built, stocked, and managed correctly, provide years of enjoyable recreation and, for many people, the challenge of managing a fish community to achieve a desired goal. Although habitat is always an issue in any fishery, correct management to achieve sustained quality fishing in a properly designed pond largely equates to correct harvest. Given the importance of harvest in maintaining balance between predator and prey populations, the angler is the manager and influences the size structures of the predator and prey populations by judicious harvest of predators—the largemouth bass. Implementing appropriate harvest strategies pays the compound dividends of enjoying quality fishing in the present while, at the same time, maintaining or improving the quality of future fishing.

7.6 REFERENCES

Anderson, R. O. 1976. Management of small warm water impoundments. Fisheries 1(6):5–7, 26–28.

Anderson, R. O. 1980. Proportional stock density (PSD) and relative weight (Wr): interpretive indices for fish populations and communities. Pages 27–33 in S. Gloss and B. Shupp, editors. Practical fisheries management: more with less in the 1980’s. Proceedings of the 1st Annual Workshop of the New York Chapter American Fisheries Society, July 14–16, 1980, Cazenovia, New York. (Available from New York Cooperative Fishery Research Unit, Ithaca).

210 Chapter 7

Anderson R. O., and R. M. Neumann. 1996. Length, weight, and associated structural indices. Pages 447–482 in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

Bennett, G. W. 1944. The effects of species combinations on fish production. Transactions of the Ninth North American Wildlife Conference 9:184–190.

Benz, G. W., and R. P. Jacobs. 1986. Practical field methods of sexing largemouth bass. The Progres-sive Fish-Culturist 48:221–225.

Berger, T. A. 1982. Supplemental feeding of a wild bluegill population. North American Journal of Fisheries Management 2:158–163.

Blackwell, B. G., M. L. Brown, and D. W. Willis. 2000. Relative weight (Wr) status and current use in fisheries assessment and management. Reviews in Fisheries Science 8:1–44.

Boxrucker, J. 1987. Largemouth bass influence on size structure of crappie populations in small Okla-homa impoundments. North American Journal of Fisheries Management 7:273–278.

Brouder, M. J., A. C. Iles, and S. A. Bonar. 2009. Length frequency, condition, growth, and catch per ef-fort indices for common North American fishes. Pages 231–282 in S. A. Bonar, W. A. Hubert, and D. W. Willis, editors. Standard methods for sampling North American freshwater fishes. American Fisheries Society, Bethesda, Maryland.

Carlander, K. D. 1977. Handbook of freshwater fishery biology. Volume two. Iowa State University Press, Ames.

Carline, R. F., B. L. Johnson, and T. J. Hall. 1984. Estimation and interpretation of proportional stock density for fish populations in Ohio impoundments. North American Journal of Fisheries Manage-ment 4:139–154.

Coble, D. W. 1992. Predicting population density of largemouth bass from electrofishing catch per ef-fort. North American Journal of Fisheries Management 12:650–651.

Dillard, J. G., and G. D. Novinger. 1975. Stocking largemouth bass in small impoundments. Pages 459–474 in H. Clepper, editor. Black bass biology and management. Sport Fishing Institute, Wash-ington, DC.

Dumont, S. C., and J. A. Dennis. 1997. Comparison of day and night electrofishing in Texas reservoirs. North American Journal of Fisheries Management 17:939–946.

Gabelhouse, D. W., Jr. 1978. Redear sunfish for small impoundments? Pages 109–123 in G. D. No-vinger and J. G. Dillard, editors. New approaches to the management of small impoundments. North Central Division, American Fisheries Society, Special Publication Number 5, Bethesda, Maryland.

Gabelhouse, D. W., Jr. 1984a. A length-categorization system to assess fish stocks. North American Journal of Fisheries Management 4:273–285.

Gabelhouse, D. W., Jr. 1984b. An assessment of crappie stocks in small Midwestern private impound-ments. North American Journal of Fisheries Management 4:371–384.

Gabelhouse, D. W., Jr. 1987. Responses of largemouth bass and bluegills to removal of surplus large-mouth bass from a Kansas pond. North American Journal of Fisheries Management 7:81–90.

Gabelhouse, D. W., Jr., and D. W. Willis. 1986. Biases and utility of angler catch data for assessing size structure and density of largemouth bass. North American Journal of Fisheries Management 6:481–489.

Gabelhouse, D. W., Jr., R. L. Hager, and H. E. Klaassen. 1982. Producing fish and wildlife from Kansas ponds. Kansas Fish and Game Commission, Pratt.

Green, D. M., E. L. Mills, and D. J. Decker. 1993. Participatory learning in natural resource education: a pilot study in private fishery management. Journal of Extension 31:13–15.

Gustafson, K. A. 1988. Approximating confidence intervals for indices of fish population size structure. North American Journal of Fisheries Management 8:139–141.

Gutreuter, S., and W. M. Childress. 1990. Evaluation of condition indices for estimation of growth of


largemouth bass and white crappies. North American Journal of Fisheries Management 10:434–441.

Gutreuter, S., and D. J. Krzoska. 1994. Quantifying precision of in situ length and weight measure-ments of fish. North American Journal of Fisheries Management 14:318–322.

Guy, C. S., and D. W. Willis. 1990. Structural relationships of largemouth bass and bluegills in South Dakota ponds. North American Journal of Fisheries Management 10:338–343.

Guy, C. S., and D. W. Willis. 1991. Evaluation of largemouth bass-yellow perch communities in small South Dakota impoundments. North American Journal of Fisheries Management 11:43–49.

Guy, C. S., R. M. Neumann, D.W. Willis, and R. O. Anderson. 2007. Proportional size distribution (PSD): a further refinement of population size structure index terminology. Fisheries 32:348.

Hanson, P. C., T.B. Johnson, D. E. Schindler, and J. F. Kitchell. 1997. Fish bioenergetics 3.0. University of Wisconsin Sea Grant Institute, Madison, Wisconsin.

Hardin, S., and L. L. Connor. 1992. Variability of electrofishing crew efficiency, and sampling re-quirements for estimating reliable catch rates. North American Journal of Fisheries Management 12:612–617.

Hartman, K. J., and F. J. Margraf. 2006. Relationships among condition indices, feeding and growth of walleye in Lake Erie. Fisheries Management and Ecology 2006 13:121–130.

Heidinger, R. C., D. R. Helms, T. I. Hiebert, and P. H. Howe. 1983. Operational comparison of three electrofishing systems. North American Journal of Fisheries Management 3:254–257.

Hill, T. D., and D. W. Willis. 1994. Influence of water conductivity on pulsed AC and pulsed DC electrofishing catch rates for largemouth bass. North American Journal of Fisheries Management 14:202–207.

Hubbard, W. D., and L. E. Miranda. 1988. Competence of non-random electrofishing sampling in as-sessment of structural indices. Proceedings of the Annual Conference of the Southeastern Associa-tion of Fish and Wildlife Agencies 40(1986):79–84.

Hubert, W. A. 1996. Passive capture techniques. Pages 157–192 in B. R. Murphy and D. W. Willis, edi-tors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

Isaak, D. J., T. D. Hill, and D. W. Willis. 1992. Comparison of size structure and catch rate for large-mouth bass samples collected by electrofishing and angling. The Prairie Naturalist 24:89–96.

Isermann, D. A., D. W. Willis, D. O. Lucchesi, and B. G. Blackwell. 2005. Seasonal harvest, exploita-tion, size-selectivity, and catch preferences associated with winter yellow perch anglers on South Dakota lakes. North American Journal of Fisheries Management 25:827–840.

Keast, A. 1978. Feeding relationships between age groups of pumpkinseed sunfish (Lepomis gibbosus) and comparison with bluegill sunfish (Lepomis macrochirus). Journal of the Fisheries Research Board of Canada 35:12–27.

Liao, H., C. L. Pierce, D. H. Wahl, J. B. Rasmussen, and W. C. Leggett. 1995. Relative weight (Wr) as a field assessment tool: relationships with growth, prey biomass, and environmental conditions. Transactions of the American Fisheries Society 124:387–400.

Marwitz, T. D., and W. A. Hubert. 1997. Trends in relative weight of walleye stocks in Wyoming res-ervoirs. North American Journal of Fisheries Management 17:44–53.

McInerny, M. C., and T. K. Cross. 2000. Effects of sampling time, intraspecific density, and environ-mental variables on electrofishing catch per effort of largemouth bass in Minnesota lakes. North American Journal of Fisheries Management 20:328–336.

Miranda, L. E. 1993. Sample sizes for estimating and comparing proportion-based indices. North American Journal of Fisheries Management 13:383–386.

Miranda, L. E. 2005. Refining boat electrofishing to improve consistency and reduce harm to fish. North American Journal of Fisheries Management 25:609–618.

Miranda, L. E., and B. S. Dorr. 2000. Size selectivity of crappie angling. North American Journal of Fisheries Management 20:706–710.

212 Chapter 7

Mittelbach, G. G. 1981. A study of optimal diet and habitat use by bluegills. Ecology 62:1370–1386.Modde, T., and C. G. Scalet. 1985. Latitudinal growth effects on predator-prey interactions between

largemouth bass and bluegills in ponds. North American Journal of Fisheries Management 5:227–232.

Murphy, B. R., D. W. Willis, and T. A. Springer. 1991. The relative weight index in fisheries manage-ment: status and needs. Fisheries 16(2):30–38.

Neal, J. W., and R. L. Noble. 2006. A bioenergetics-based approach to explain largemouth bass size in tropical reservoirs. Transactions of the American Fisheries Society 135:1535–1545.

Neumann, R. M., C. S. Guy, and D. W. Willis. In press. Length, weight, and associated structural indices. In A.V. Zale, D.L. Parrish, and T.M. Sutton, editors. Fisheries techniques, 3rd edition. American Fisheries Society, Bethesda, Maryland.

Novinger, G. D. 1990. Slot length limits for largemouth bass in small private impoundments. North American Journal of Fisheries Management 10:330–337.

Novinger, G. D., and R. E. Legler. 1978. Bluegill population structure and dynamics. Pages 37–49 in G. D. Novinger and J. G. Dillard, editors. New approaches to the management of small im-poundments. North Central Division, American Fisheries Society, Special Publication 5, Bethesda, Maryland.

Olson, N. W., C. P. Paukert, D.W. Willis, and J. A. Klammer. 2003. Prey selection and diets of blue-gills Lepomis macrochirus with differing population characteristics in two Nebraska natural lakes. Fisheries Management and Ecology 10:31–40.

Osenberg, C. W., E. E. Werner, G. G. Mittelbach, and D. J. Hall. 1988. Growth patterns in bluegill (Lepo-mis macrochirus) and pumpkinseed (L. gibbosus) sunfish: environmental variation and the impor-tance of ontogenetic niche shifts. Canadian Journal of Fisheries and Aquatic Sciences 45:17–26.

Otis, K. J., R. R. Piette, J. E. Keppler, and P. W. Rasmussen. 1998. A largemouth bass closed fishery to control an overabundant bluegill population in a Wisconsin lake. Journal of Freshwater Ecology 13:391–403.

Parker, W. D. 1971. Preliminary studies on sexing adult largemouth bass by means of an external char-acteristic. The Progressive Fish-Culturist 23:55–56.

Paukert, C. P., and D. W. Willis. 2003. Population characteristics and ecological role of northern pike in fish communities of shallow Nebraska natural lakes. North American Journal of Fisheries Man-agement 23:313–322.

Paukert, C., and R. S. Rogers. 2004. Factors affecting condition of flannelmouth suckers in the Colora-do River, Grand Canyon, Arizona. North American Journal of Fisheries Management 24:648–653.

Pope, K. L., and D. W. Willis. 1996. Seasonal influences on freshwater fisheries sampling data. Re-views in Fisheries Science 4:57–73.

Pope, K. L., R. M. Neumann, and S. D. Bryan. 2009. Warmwater fish in small standing waters. Pages 13–27 in S. A. Bonar, W. A. Hubert, and D. W. Willis, editors. Standard method for sampling North American freshwater fishes. American Fisheries Society, Bethesda, Maryland.

Porath, M. T., and K. L. Hurley. 2005. Effects of waterbody type and management actions on bluegill growth rates. North American Journal of Fisheries Management 25:1041–1050.

Porath, M. T., and E. J. Peters. 1997. Use of walleye relative weights (Wr) to assess prey availability. North American Journal of Fisheries Management 17:628–637.

Prentice, J. A., B. W. Farquhar, and W. E. Whitworth. 1993. Comparison of volunteer angler-supplied fisheries catch and population structure data with traditional data. Proceedings of the Southeastern Association of Fish and Wildlife Agencies 47:666–678.

Reynolds, J. B. 1996. Electrofishing. Page 221–253 in B. R. Murphy and D. W. Willis, editors. Fisher-ies techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

Reynolds, J. B., and L. R. Babb. 1978. Structure and dynamics of largemouth bass populations. Pages 50–61 in G. D. Novinger and J. G. Dillard, editors. New approaches to the management of small im-


poundments. North Central Division, American Fisheries Society, Special Publication 5, Bethesda, Maryland.

Santucci, V. J., Jr., and D. H. Wahl. 1991. Use of a creel census and electrofishing to assess centrarchid populations. Pages 481–491 in D. Guthrie, J. M. Hoenig, M. Holliday, C. M. Jones, M. J. Mills, S. A. Moberly, K. H. Pollock, and D. R. Talhelm, editors. Creel and angler surveys in fisheries management. American Fisheries Society, Symposium 12, Bethesda, Maryland.

Schramm, H. L., Jr., and K. J. Jirka. 1989. Epiphytic macroinvertebrates as a food resource for bluegills in Florida lakes. Transactions of the American Fisheries Society 118:416–426.

Schramm, H. L., Jr., and D. C. Smith. 1987. Differences in growth rate between sexes of Florida large-mouth bass. Proceedings of the Annual Conference Southeastern Association Fish and Wildlife Agencies 41:76–84.

Stone, C. C., and T. Modde. 1982. Growth and survival of largemouth bass in newly stocked South Dakota ponds. North American Journal of Fisheries Management 4:326–333.

Swingle, H. S. 1950. Relationships and dynamics of balanced and unbalanced fish populations. Ala-bama Polytechnic Institute, Agricultural Experiment Station Bulletin 274. Auburn.

Swingle, H. S. 1956. Appraisal of methods of fish population study, part 4: determination of balance in farm fish ponds. Transactions of the North American Wildlife Conference 21:298–322.

Wege, G. J., and R. O. Anderson. 1978. Relative weight (Wr): a new index of condition for largemouth bass. Pages 79–91 in G. D. Novinger and J. G. Dillard, editors. New approaches to the manage-ment of small impoundments. North Central Division, American Fisheries Society, Special Publi-cation 5, Bethesda, Maryland.

Werner, E. E., and D. J. Hall. 1988. Ontogenetic habitat shifts in bluegill: the foraging rate–predation risk trade-off. Ecology 69:1352–1366.

Willis, D. W. 2010. A protected slot length limit for largemouth bass in a small impoundment: will the improved size structure persist? Pages 203–210 in B. R. Murphy, D. W. Willis, M. L. Davis, and B. D. S. Graeb, editors. Instructor’s guide to case studies in fisheries conservation and management: applied critical thinking and problem solving. American Fisheries Society, Bethesda, Maryland.

Willis, D. W., B. R. Murphy, and C. S. Guy. 1993. Stock density indices: development, use, and limita-tions. Reviews in Fisheries Science 1:203–222.

Willis, D. W., M. D. Beem, and R. L. Hanten. 1990. Managing South Dakota ponds for fish and wild-life. South Dakota Department of Game, Fish and Parks, Pierre.

Willis, D. W., R. D. Lusk, and J. W. Slipke. 2010. Farm ponds and small impoundments. Pages 501–543 in W. A. Hubert and M. C. Quist, editors. Inland fisheries management in North America, 3rd edition. American Fisheries Society, Bethesda, Maryland.

chapter 7 · 181 assessment and harvest of largemouth bass–bluegill ponds harold l. schramm,...

Documents