WORKING PAPER SERIES

FISHERIES STOCK ASSESSMENT TITLE XI1

Collaborative Research Support Program

Fisheries Stock Assessrnent CRSP Management Office Internationai Programs, College of Agriculture

The University of Maryland, College Park, Maryland 20742

In cooperation with the United States Agency for International Development (Grant No.DAN-4146.G-SS-5071-,)0) the Fisheries Stock Assessment CRSP involves the following participating institutions:

The Univeis-t, of Maryland-Center for Environmental and Estuarine Studies The University of Rihode Island- International Center for Marine Resource DevelopmentThe University of Washington--Center foi Quantitative Sciences The University of Costa Rica-Centro de Investigaci6n en Ciencias del Mar y LimnologiaThe University of the Philippines.-Marine Science Institute (Diliman)--College of Fish­

eries (Visayas)

In collaboration with The University of Delaware: The University of Maryland-Collegeof Business and Management; The University of Miami; and The International Center forLiving Aquatic Resources Management (ICLARM).

Working Paper Series

Working Paper No. 9 "Hydrcacoustics and Ground Truth"

by Richard E. Thorne

School of Fisheries University of Washington

May, 1987

Fisheries Stock Assessment Title XII

Collaborative Research Support Program

The Fisheries Stock Assessment CPSP (sponsored in part by USAID GraiL No.DAN-4146-G-SS-5071-00) is intended to support collaborative research betweenU.S. qnd developing countries' universities and institutions on fisheries stock assessment and managenent stratrjies.

This Working Pdoer has been produced by the collaborative efforts of TheUniversity of Washington and The University of Costa Rica-Centro deInvestigacion en Ciencias del Mar y Limnologia (CIMAR) in association with TheUniversity of Delaware. Additional copies are available from the CRSP Management Office and from:

Dr. Vincent Gallucci, Director Center for Quantitative Science HR-20

School of Fisheries University of Washington

3737 15th Avenue, N.E., Room 304 Seattle, Washington 98195

HYDROACOUSTICS AND GROUND TRUTH

Richard E. Thorne

School of Fisheries

University of Washington

Seattle, WA 98195

Abstract

One of the most difficult problems in hydroacousticapplications is the acquisition of ground truth data. A major incentive for the use of hydroacoustics is the deficiencies of the same alternate techniques that areavailable for such ground truth data. However, such data areoften required for biological information including speciescomposition. In addition, since hydroacoustic techniques are not universally accepted, ground truth information issometimes needed to establish confidence in the results. Theauthor has been involved in over 2000 hydroacoustic surveysof various species in a variety of locations. Many different approaches were used to obtain ground truth data. Examination of these results provides some interestinginsights into the characteristics of both the hydroacousticand the ground truth techniques and suggests some principlesfor ground truth efforts in conjunction with hydroacousticsurveys. A major conclusion is that the appropriate role of ground truth efforts is not verification, but is to aid interpretation of the hydroacoustic data.

2

HYDROACOUSTICS AND GROUND TRUTH

Richard E. Thorne

Introduction

I had an occasion in 1980 to compile a list of the

number and type of hydroacoustic surveys in which I had

participated during the previous decade. The total came to

1025 (Thorne 1983). In the subsequent seven years, the total

has probably doubled. These represent a considerable variety

of habitat and species. Virtually all have had some type of

ground truth effort in conjunction with the surveys. The

type and effectiveness of the ground truth efforts were also

highly variable. The purpose of this paper is to summarize

these results and to develop some general principles for

ground truth programs. It should be emphasized that the

results represent my particular experiences. Even 2000

surveys are a small fraction of the potential interactions

among habitats, species and ground truth techniques. Other

investigators may have differing experiences. Nevertheless,

I think the results can provide vaiuable insight into ground

truth techniques.

Ground Truth and the Laws of Physics

Different investigators have differing definitions of

the concept of ground truth. One commonly held concept is

that of verification. Under this definition, cround truth is

an alternate technique that can be used to determine if the

3

hydroacoustic techniques are providing the "right" answer.

This was the concept underlying my initial research in this

field nearly 20 years ago (Thorne 19*!0, L971). One

difficulty with this concept is that there are very few

circumstances where alternate techniques can provide an

adequate standard. The glaring deficiencies of these

techniques are part of the motivation to use hydroacoustics

in the first place. In addition, most fisheries acousticians

have come to realize in the past two decades that the

question is not whether hydroacoustics are "right" or

"wronq", but the appropriate question is, "how can the

information contained in the physics of the acoustic data be

most effecti.rely processed and interpreted?" This concept

starts with the realization that the informaLion contained in

the acoustic data already limits the scope of possibilities

for interpretation. The data already contain considerable

information on the location and nature of targets. The role

of ground truth should be to facilitate interpretation of

this information. This is the concept of ground truth which

forms the basis of this paper.

Scope of Paper

The major techniques that have used in association with

my hydroacoustic surveys have been various types of trawls,

surrounding nets, gill nets, fyke nets, visual techniques,

hand lines, electroshocking and cove rotenone. In addition

to these fishery independent techniques, valuable insight

4

into the interpretation of hydroacoustic data can often be

obtained from comparisons with commercial catch data. In the

remainder of this paper I will discuss results with these

various techniques individually, then discuss multiple

techniques, and finally close with some general principles.

Direct Capture Techniques

Trawling

Trawling techniques have often been used for ground

truth efforts in association with hydroacoustic surveys. A

trawl provides an output similar to that from a mobile

hydroacoustic survey, that is, a density estimate in a depth

strata over a distance. I have previously reported many

examples of comparisons between trawl catches and

hydroacoustic estimates (fnorne 1971, 1973, 1977, 1983b,

1983c). The general conclusion is that synoptic trawl and

hydroacoustic observations are often higoly correlated (Figs.

I and 2). However, that conclusion must be treated

cautiously. First, trawls, like virtually all techniques,

are selective. They provide good correlation with the

acoustic data when the predominate species are suitable for

the selectivity characteristics of the net. The acoustic

data can often provide information for evaluation of the

appropriateness of the trawl. For example, McClain (1987)

demonstrated correlation between dual beam target strength

measurement of two juvenile salmon cohorts in Lake Tustumena,

5

Alaska, and corresponding trawl catch proportions. However,

both cohorts were relatively small and not greatly dissimilar

(mean lengths 47 and 75mm). The small mesh trawl was

suitable and the glacially turbid water resulted in an

unsually high catch efficiency of about 70% (Thorne and

Thomas, 1984). The same trawl would be ineffective on the

adults of that same species. Further, other comparisons have

been made between the estimates of relative year class

proportions from trawls and those from subsequent

outmigrat 'n data. These often indicate underestimation of

the larger cohort by the trawl data (Gary Kyle, Alaska Dept.

of Fish & Game, personal communication.

The second caution is that the efficiency of the trawl

is greatly affected by the environmntal conditions. For

example, the same type of trawl that effectively caught fish

in the glacially turbid Lake Tustumena was extremely

inefficient for the same size groups in clear water nursery

lakes. Further, Robinson and Barraclough (1978) showed

changes in trawl catch efficiency with changes in moonlight

and cloud cover conditions.

The limitations caused by untrawlable habitats are well

recognized and will be further discussed later. A recent

example is reported in Marino (1987). In this case the

hydroacoustic data clearly identified two di.3tributions: one

limnetic and one littoral. The trawl appeared adequate for

the first, but could not sample the fish in the near-shore,

near-bottom locations.

Surrounding Nets

Surrounding nets are more difficult to correlate with

hydroacoustic observations than trawls, but are often

effective for near surface fishes. Surrounding nets are

generally less selective than most other direct capture

techniques and are often very efficient. I have used

surrounding nets (lampara seines) for ground truth data in

two studies, one in the Southern California Bight and the

second in the nearshore Beaufort Sea. In the Beaufort Sea

study, estimates of capture efficiency were made on several

species. The results indicated catch efficiencies varied

between 20 and 29% (anon. 1984). The Southern California

study was the most extensive. It concerned an evaluation of

fish entrapment by offshore water intakes of coastal power

generating plants. Some of the :esults are reported in

Thomas (1982). The survey design was unusual. The sampling

area consisted of a 300m radius around a water intake. The

circle was divided into 4 quadrants, in- and off-shore and

up- and down-coast. Randomly selected radial transects were

run in each quadrant, then replicated On the replicate

rouiid, a lampara set was made in one of the quaarants

immediately following the run. This procedure was repeated

at hourly intervals. The lampara data were used to allocate

the fish density by species. In order to evaluate the

effective(ness this technique, the resulting acoustic

7

estimates of fish density were compared with the

corresponding net catches. The results showed high

correlation between the density estimates and the net catches

for all the major species and all species combined (Table 1).

An earlier, similar study also showed good correlation

between acoustics and lampera net catches. However, this

study only used a simple echogram analysis to evaluate catch

effectiveness. The resul-s showed good correlation (Fig. 3),

but also noted two anlolous points in which fish escapement

from the net was observed. Finally, a third -t'idv during a

period where large mackeral schools were Present showed very

poor correlation between acoustic data and net catch because

of poor catching efficiency on these fish (Thomas et al.

1980).

Gill Nets

I have used gill nets in many studies. Gill nets are

very selective, but that problem can be partially overcome

with the appropriate application of multiple mesh sizes.

However, there are two other major difficulties. Tne is that

the abundance of fish captured by gill nets is difficult to

relate to acoustic measurements of density, because gill

nets measure the flux of fish movement rather than density.

One impact of this characteristic of gill net catchability is

that gill nets are more effective on more active and faster

swimming fish. This causes a selection against small fish

(which swim slower). The selection against small fish is

8.

accentuated by the fact that momentum plays an important role

in the catching process, and momentum is a function of both

swimming speed and mass. I conducted a comparison of

acoustic detections, swimming speed and gill net catches in

the nearshore Beaufort Sea during 1982. The results showed

considerably greater gill net catchability relative to

acoustic detections for larger, faster swimming fish (Thorne

1983c).

While gill nets provide an index which is difficult to

compare with the density measurements from mobiJe acoustic

surveys, they do provide an good index for comparison with

stationary transducer deployment, especially for study of

fish migration rates. Stationary deployments; including

slant angle deployment, provide an estimate of fish passage

through an area, or flux, which is similar to the measurement

provided by a gill net. This was the type of transducer

deployment used in the Beaufort Sea study cited above.

A second difficulty with gill is the strong affectsnets

of such environmental parameters as water clarity, ambient

light and current on catch efficiency. Considerable

improveinelt in our understanding of gill net catchability

characteristics could be obtained by synoptic comparisons of

catch with stationary transducer deployment, including dual

beam and slant angle. Unfortunately, very little research

has been conducted in this area despite extensive use of gill

nets in fisheries research.

An advantage of vertical gill nets in conjunction with

9

hydroacoustic observations is that they can provide detailed

vertical distributional information for comparison with the

hydroacoustic data. A variation of this capability was used

to examine the potential near-surface and near-bottom bias of

acoustic estimates (Thomas et al. 1980). In this case the

vertical distribution from the gill nets was used to correct

for the proportion of fish in depth intervals that could not

be acoustically sampled (Fig. 4).

Other Direct Capture Techniques

Four other direct ci; )ture techniques that have been used

in conjunction with my acoustic surveys are fyke nets,

electroshocking, hand lines and cove rotenone. The

application of fyke nets and the electro,hocking were part of

multiple technique studies and will be discussed later. Hand

lines are difficult to quantify, but in some cases can

provide a rapid confirmation of acoustic targets. Jackson

and Thomas (1979) used hand lines to rapidly identify large

schools thaL were detected by naval sonars. In a recent

survey of Crater Lake, Oregon (Marino 1987), limited hand

line data were the only source of species identification

because of the difficult access to the lake and lack of

histcrical investigations.

The cove rotenone effort was associated with three

reservoirs in Texas that are used for cooling water purposes.

Hydroacoustic estimates of fish abundance for tb- thr~e

reservoirs were compared with corresponding cove rotenone

10

results. In all three cases, the hydroacoustic estimates

were far higher. The cove areas were simply not

representative of the areas of major fish biomass, which were

limnetic (Fig. 5).

Visual Techniques

There are a wide variety of visual techniques used in

fisheries. My experience has included comparisons of

hydroacoustic observations with video cameras, surface

observations and diver observations. One of the major studi?s

involved synoptic use of acoustics and a.video camera around

the water intake for the Southern California Edison Steam

lights for

Generating Plant at Redondo Beach, California (Thorne 1980).

The combination was effective during daytime. However,

observations at night required use of artificial

the video camera. The synoptic acoustic observations showed

major pertubation (fish attraction) by the artificial lights.

A similar light attraction was observed near an artificial

reef in the Gulf of Nicoya, Costa Rica (Fig. 6). This study

also demonstrated another limitation of visual observation,

this time from divers. Hydroacoustic observations from a

stationary transducer on the reef showed high concentrations

of fish near surface above the reef. The abundance of these

fish was considerably underestimated by the divers,

apparently because of the distance from the reef to the

surface combined with active avoidance by the fish.

Despite these limitations, diver observations can be

very helpful. In several instances, diver observations have

served to identify fish and also to note fish on the bottom

that were not detected by the acoustics. In one case, diver

observations were used to identify a very large acoustic

target that turned out to be a dense school of fish that was

associated with a breakwater and could not be acoustically

resolved from the structure.

Occasionally ground truth data can be obtained from

surface visual observation. Visual counting techniques were

used to verify acoustic estimates of the adult sockeye salmon

escapement into Lake Washington (Thorne 1979). The two

techniques differed by less than 2% over a four-year period.

Surface visual techniques were helpful in a recent survey of

fish in several reservoirs in eastern Texas. In this case,

the hydroacoustic data indicated predominance of small fish.

The gill net and cove rotenone data available were clearly

biased against capture of the size class of fish indicated by

the acoustic data. Visual observations, including attraction

of fish to the surface with lights, verified the presence of

huge numbers of minnows of various species.

Another case where acoustic data dictated a ground truth

approach was an evaluation of fish migration past a

hydroelectric dam via a sluiceway. The particular

hydroacoustic approach assumed individual fish passage.

However, examination of the acoustic data suggested schooled

targets. Subsequent visual observations, although inadequate

for accurate enumeration, verified passage of fish in small

12

dense schools, thus dictating an alternate approach to the

acoustic data processing (Llew Johnson, Associated Fisheries

Biologists, personal communication).

Comparisons with Fishery Catch Data

A common objective of hydroacoustic surveys is to

provide data to oid the management of a commercial fishery.

In this case, the actual catch of the fishery can often aid

interpretation of the acoustic data. In one of my first

studies, analysis of the annual variation of the acoustic

estimates, combined with the catch data, demonstrated flaws

in the acoustic technique, which later turned out to be

inadequate areal coverage (Thorne et al. 1971, Thorne 1973).

Comparisons of acoustic estimates and subsequent commercial

captures for several herring stocks in Alaska provided

considerable input to improvements in the acoustic techniques

(Thorne et al 1.983). Commercial fishing data, in conjunction

with hydroacoustic surveys, can provide valuable information

on the adequacy of survey coverage, input to stratified

efforts, species composition information and other necessary

biological data. An example of the use of commercial catch

data is presented in the next section.

While commercial catch data can provide data for

interp'-etation of acoustic surveys, the inverse is also true:

acoustic data can provide insight into the characteristics of

the commercial catch data that can aid interpretation of that

data. This potential is greatly underutilized, at least in1

13

the U.S. We have an unfortunate tendency to overuse,

overmassage and overmodel fishery catch data regardless of

its quality or biases.

Multiple Techniques

Sometimes the application of hydroacoustics is part of a

program for the development of optimal sampling tools for a

oarticular habitat. An example is a study I participated in

on the Mississippi River, 2ool 18. The objective of the

study was to evaluate several techniques in order to

determine the best technique, or combination of techniques,

for use in studies of fish abundance and behavior in this

particular habitat (Peterson 1983). The main techniques, in

addition to hydroacoustics, were gill nets, trawls and

electrofishing. The comparative study demonstrated major

differences in performance among the three capture

techniques. For example, in one location the electroshocking

indicated predominance of emerald shiner (49%) and gizzard

shad (48%) , while trawling in the same area suggested

predominance of drum (54%) and channel catfish (29%), and the

gill nets suggested that longnose gar (a species not even

caught with the other two techniques) was a major component.

Some of the differences are illustrated in the comparison of

minimum and m, :imum lengths of various species from the total

effort (Table 2). Overall conclusions included: (1) gill

nets were relatively poor indicators of species composition;

(2) trawls were 'ess selective, but were very limited by

14

untrawlable habitats, and (3) electrofishing sampled the

largest diversity and the largest sample size and was clearly

the best in shallow water, but the technique was difficult to

quantify either for its selectivity or efficiency.

A second multiple gear study took place under ice in the

nearshore Beaufort Sea near Prudhoe Bay. This study involved

comparison of fyke nets, gill nets and diver observations, as

well as fixed aspect hydroacoustic transducers. The nets and

acoustics operated day and night; diver operations were

limited to daytime. The fyke nets captured 19 Arctic cod and

2 snailfish; gill nets captured no fish; divers observed 29

snailfish, 7 sculpins, 5 Arctic cod and 1 eelbleeny. Only

the Arctic cod were observed in the water column. All others

were in contact with the bottom or kelp. The acoustics

detected 498 fish targets. Detection rates at night were

about 5 times higher. The results indicate that the fyke net

is most efficient for the more mobile cod, whereas the divers

more often observed the more sedentary fish. The diel

variation in the acoustic data indicated that the sedentary

fish were more active at night, but the lack of catch of

these species in the fyke net indicated that the activety was

locally oriented. The lack of success with the gill nets was

probably due to the clear water combined with ice formation

on the meshes.

One final example of the use of a combination of

techniques, including commercial catch data, is the

procedures developed for management of the herring roe

15

fishery in the Strait of Georgia (Trumble et al. 1982). The

combina:ion was hydroacoustic surveys, midwater trawling,

commercial catch data and spawning ground surveys. The

hydroacoustic surveys provided a time series of estimates of

the fish biomass as the herring moved into the area prior to

spawning. The midwater trawling effort provided data on the

species composition and the percentage of mature females.

The commercial catch data provided an accounting of the fish

removed by harvest, while the spawning ground surveys

estimated the number of fish that subsequently spawned and

left the area. Once the last herring is recruited into the

area, the combined techniques provide a total accounting of

the population size (Fig. 7). Although the acoustic data

provide an early indication of the population, the entire

combination is required to provide the real time accounting

of the total fishery that is needed for the management. No

lesser combination could have provided adequate information.

Conclusions - Some General Principles

The most important principle in field investigations of

fisn abundance, distribution and behavior is that all gear

types, including hydroacoustics, have some bias. This aspect

is clearly pointed out in several of the results reported

here, especially the multiple gear studies. Witn this

prinicple in mind, it is important to again point out that

the proper context of a ground truth program associated with

hydroacoustics is not to determine the "right" or "wrong" of

16

the acoustics, but to determine which complementary technique

or techniques can provide the information needed to most

effectively interprete the acoustic data. The primary

advantage of hydroacoustic techniques is the ability to

rapidly determine the location of fish targets. In addition,

acoustic data contain considerable information on the nature

of the targets, including abundance. No other technique

approaches the capability of hydroacoustics in this regard.

The capability to "see" fish one ofis the major advantages

of hydroacoustic techniques, and it is easier to catch a

target when you can see it (Fig. 8).

The second principle, which follows from the first, is

that ground truth techniques can be most effectively used

when the characteristics of the environment are well

understood. This is a variation of the principle in survey

design that the best statistical design can be achieved when

you already know all the distributional characteristics of

the fish to be surveyed. In practice there is always a

learning experience in every study. The more you learn about

the environment, the better you can monitor it. It is naive

to believe you can go into an environment the first time and

accomplish an effective study. I have observed many failures

in hydroacoustic assessments that were the result of

incorrect assumptions about the nature of the target species

and that could have been successful if properly designed.

The third principle, which again follows from the first

two, concerns the role of the acoustics in the selection of

17

ground truth techniques. The initial choice when entering a

new environment has to rely on assumptions based on the best

information available. However, the subsequent acoustic data

usually adds considerably to this knowledge and should be

used to reconsider and possibly redesign the ground truth

appoach. Fxamples of the type of information include depth

distribution, horizontal distribution, patchiness, schooled

or layerc-d distribution, near-boundary orientation, size of

targets and diel changes in distribution and behavior.

This capaui Iity leads to the fourth pi.nciple: that

ground truth t.echniques are most effective when they are

directed by the acoustic observations. Since the appropriate

role of ground truth is to provide information to interprete

the acoustic data, it can be most effective when the ground

truth efforts are directed to answer specific questions asked

by the acoustic (oata. Correlations between acoustic

observat ions are always best when they are synoptic. It

follows that the information value of the ground truth data

is greatest. when it can be directly compared to the synoptic

acoustic data. Whenever possible I use a two boat operation:

an acous-ic boat followed by a direct capture boat.

Finally, it should be apparent that a single ground

truth technique may not be adequate. If the acoustic data

are used to direct ground truth efforts, it follows that the

characteristics of the targets and the habitat that are

identified by the hydroacoustics should be used to determine

the best techniques to sample those targets in that habitat.

18

In many circumstances, that will require multiple ground

truth techniques.

Acknowledgments

I am grateful to many individuals and agencies for support of the studies summarized here. Initial preparationof this manuscript was supported by the Washington Sea Grant Program. I am indebted to the U.S. Agency for International Development (AID) for the funds for its completion and publication.

Literature Cited

Anon. 1984. Prudhoe Bay Waterflood Project Fish ManagementProgram 1983. Final Report, BioSonics Inc., Seattle.

Jackson, D.R. and G.L. Thomas 1979. Acoustic measurements of fish schools using array phase information. Proc. Oceans 79:59 (abstract).

Marino, D.A. 1987. An investigation of the summertime spatial and distribution behavior of kokanee (Oncorhynchus nerka) in Northwest lakes using dual beam hydroacoustic techniaues. Paper # 83, Internat. Symp. on Fish. Acoustics, Seattle.

McClain, J. 1987. A comparison of cohort proportions obtained by dual beam techniques and by tow netting in a sockeye salmon nursery lake. Paper # 85, Internat. Symp. on Fish. Acoustics, Seattle.

Peterson, G.A. 1983. A pilot study to evaluate the winter fishery biology of Pool 18, Upper Mississippi River. Final Contract Report, U.S. Fish and Wildlife Service, Rock Island Ecological Services Field Office. 13p + 4 Appendices.

Robinson, D.G. and W.F. Barraclough 1978. Population estimates of sockeye salmon in a fertilized oligothrophic lake. J. Fish. Res. Bd., Canada 35:851-860.

Thomas, G.L. 1982. Complementary hydroacoustic and net sampling techniques for determining the vulnerabilityof fish to power plant entrapment. Paper # 102, Symp.

19

on Fish. Acoustics, Bergen, Norway, 12p.

Thomas, G.L., R.E. Thorne, W.C. Acker, T.B. Staples, A.S. Kolok, L. Johnson, K. Miller, J. Yuge, B. Kulik and S. Shiba 1980. The effectiveness of a velocity cap and decreased flow in reducing fish entrapment.Final Contract Report, FRI-UW 8027, Univ. Wash. Fish Res. Inst. 22p + 9 Appendices.

Thorne, R.E. 1970. Investigations into the integrator for measuring pelagic fish aThesis, Univ. Wash., ll7pp.

use bunda

of an nce.

echo Ph.D.

Thorne, R.E. 1971. Investigations into the relation between integrated echo voltage and fish density. J. Fish. Res. Bd., Canada 28:1269-73.

Thorne, R.E. 1973. Acoustic assessment of hake, 1969-1973. Proc. IEEE' Symp. on Eng. in the Ocean Environ., 249-252.

Thorne, R.E. 1977. Acoustic assessment of hake and herringstocks in Puget Sound, Washington, and southeastern Alaska. ICES Rap. et Proc.-v. 170:265-278.

Thorne, R.E. 1979. Hydroacoustic estimates of adult sockeyesalmon in Lake Washington, 1972-1975. J. Fish. Res. Bd. Canada 36:1145-49.

Thorne, R.E. 1980. Application of stationary hydroacoustic systems for studies of fish abundance and behavior. Proc. Oceans 80:381-385.

Thorne, R.E. 1983. Assessment of population abundance byhydroacoustics. J. Biol. Ocean. 2:253-262.

Thorne, R.E. 1983b. Application of hydroacoustic assessment techniques Lo three lakes with contrasting fish distributions. FAO Fish. Rep. 300:269-277.

Thorne, R.E., J.E. Reeves and A.E. Millikan 1971. Estimation of the Pacific hake (Merluciusproductus) population in Port Susan, Washington, using an echo integrator. J. Fish. Res. Bd., Canada 28:1175-84.

Thorne, R.E., R. Trumble, N. Lemberg and D. Blankenbeckler 1983. Hydroacoustic assessment and management of herring fisheries in Washington and southeastern Alaska. FAO Fish. Rep. 300:217-222.

Thorne, R.E. and G.L. Thomas 1984. Recent applications of hydroacoustics to assessment of limnetic fish abundance and behavior. Proc. NALMS 1983 Internat. Symp. on Lake and Reservoir Management. USEPA

20

400/5/84-001, pp. 305-309.

Trumble, R., R. Thorne and N. Lemberg 1982. The Strait of Georgia herring fishery: A case history of timely management aided by hydroacoustic surveys. Fish. Bull. 80:381-388.

List of Tables

1. Spearman rank correlation coefficients between nightly mean larpera catch per set and acoustic estimates of densityfor queenfish, white croaker, north)ern anchovy and all species combined, Huntington Beach 1979-80.

2. Minimum and maximum lengths (mm) of various species caughtby gillnet, trawl and electrofishing, Mississippi River, Pool i8.

List of Figures

1. Comparison of actual catches of sockeye salmon in trawls with predicted catches based on hydroacoustic estimates of density, iLake 'Tustumena, Alaska.

2. Comparison of acoustic estimates of abundance and averagetrawl net catches of hake in Port Susan, Washington, 1969-1 973.

3. Comparison of acoustic echogram records and subsequent lampara net catches.

4. The vertical distribution of white surfperch and walleyesurfperch from vertical gill nets compared with The depthincrement of hydroacoustic observations.

5. Echogram from transect across cove rotenone area and into limnetic area of Monticello Reservoir, Texas.

6. Echogram illugftrating fish attraction to lights, Gulf of Nicoya, Costa Rica.

7. Biomass estimates of adult roe-herring in the Strait of Georgia, 1977, from various assessment techniques.

8. Cartoon illustrating principle that it is easier to catch organisms when you can see them.

(%,

1. Spearman rank correlation coefficients between nightly mean lampera catch per set and acoustic estimates of density for queenfish, white croaker, northern anchovy and all species combined, Huntington Beach 1979-80.

r n Significances

All species 0.5055 32 0.002

Queenfish 0.3221 32 0.018

White croaker 0.6328 32 0.001

Anchovy 0.3867 32 0.015

2. Minimum and maximum lengths (mm) of varicus species caughtby gillnet, trawl and electrofishing, Mississippi River, Pool 18.

Gillnet Trawl .1ectrofishing Species Min fin Max Min ­-Max Max

Sauger 254 490 -- ­ 385 420 Gizzard shad 140 381 121 -- 106 368 Mooneye 253 343 -- 216 330 Threadfin ;had -- 386 .. ... --Smallmouth buffalo 152 -- -- 121 440 Drum 114 445 122 276 114 38 Channel catfish 229 38) 67 425 211 406 Carp -- 356 -- -- 334 566 White bass 165 --. 94 493 White crappie 89 191 .. .-- 174 Shortnose gar 561 646 .. ...--Sturgeon ... .. 240 262 .... Silver chub . . 10-1 - -- --

Red horse .. .-- 481 247 483Madtom - - 60 ...--

Carpsucker (2 sp.) .. .. 320 367 296 441 Bluegill -- - 174 -- 92 183 Bigmouth buffalo .. ...-- . 325 508 Shiner (3 sp.) .. ... .. 64 114 Pumpkinseed .. ... .... 184 Longnose gar .. .. .. .. 396 622 Spotted sucker .. .... .. 123 --Largemouth bass .. .. .. . 29989 Black crappie .. .. .. .. 89 213

Total species i1 10 23

I 0 <701 . 60

so S

0 /I0

40

30 /0

20 /-,

10

I I I

40 60 100 120 Predicted Citck

I. Comparison of actual catches of sockeye salmon in trawls with predicted catches based on hydroacoustic estimates of density, Lake Tustumena, Alaska.

1225 -1969,-"

A ;20

0 -. 1971 =15 - 1972..

CE10 ­,,1970e

1973

- - - - I I 1 100 200 300 400 500 600

Average Not Catch (Ib)

2. Comparison of acoustic estimates of abundance and averagetrawl net catches of hake in Port Susan, Washington, 1969-1973.

'20­

100

80

60

z0t

ki 40

204. see 0 1.3 Small wqau ' L.. e

School Scrooi Sc":: NUMBER OF TARGETS (ECHOGRAPMI

OSChoo of lwu.Sfl oflr'h0y th(al #COQSCI Ml'S troUgP' mjeptI Oes oll mo ,-gt Id-wlojr &crOol m.lsd e'lfrqly by iomporo n,"erl

Fig. 3. Comparison of icoustic echogram records and subsequent lampara

net catches.

rm [src}1 " '"(SURFACE) '

N "'N

3

4

z LU

2 5 LLU

U

LU - ," :,,,

\\''k""\\"' " \LU l0/0>

.. ":\. , , 4 R:SEP ~N ,JZ, ,.

,9'"'"-"

\\',',>,&,

K' 0"

2 4 6 8 101214 16 18202224 2 4 6 8 i0 2 1416 '82022 VERTICAL PROFILE */ CAPTURED '1 CAPTURED OF HBGS INTAKE

WHITE SURFPERCH WALLEYE SURFPERCH n,-31 n 58

4. The vertical distribution of white surfperch and walleye surfperch from vertical gill nets compared with the depth increment of hydroacoustic observations.

p1

t- ACHAfi-0 CC

-- 5-- --­ lO .. .. ...........

and intoFig. 5. Echogram from transect across cove rotenone area

1innetic area of Monticello Reservoir, Texas.

, , •c~" ' "i

VN

Fig. 6. Echogran illustrating fish attraction to 1lights, Gui f of

Nicoya, Costa Rica.

--- -- - - -- - - -- - -

12

~~ 8 ~ COU~r:C TPA.VVL -"CLVLATI E

~ 6 ~2CAPEMENT 0 'L. dl ~~ 2 . '" '" - --- -------------..

4

2 a- UP4UL~rIVE

---- 4H 05 10 '~ 20 2,5 !.C 5 0 15 3'~T 40

7. Biomass estimates of adult roe-herring in the Strait of

Georgia, 1977, from various assessment techniques.

Q0 NK

8. Cartoon illustrating principle that it is easier to catch

organisms when you can see them.