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Larval Fish Diets in Shallow Coastal Waters off San Onofre,California
William Watson and Raymond L. Davis, Jr.
ABSTRACT: Stomach contents were analyzedfrom the larvae of six common coastal fish taxa(Atherinopsis californiensis, Leuresthes tenuis,Paralabrax spp., Genyonemus lineatus, Seriphuspolitus, and Paralichthys californicus) collectednear San Onofre, California. Samples were collected at night at approximately monthly intervalsbetween September 1978 and September 1979 dur-ing a study of ichthyoplankton distributions inthese shallow coastal waters.
Paralabrax spp. and Paralichthys californicuslarvae apparently did not feed at night, but highfeeding incidences for the atherinids and especiallythe sciaenids suggested that these larvae did feedduring early evening hours. Important componentsof the diets of all six taxa included the tintinnidgenus Stenosomella, mollusc veligers, and espe-cially the copepod Euterpina acutifrons.
The vertical distributions of the fish larvae dif-fered from the reported distributions of some oftheir principal prey taxa, suggesting that factors inaddition to, or other than, specific feeding habitsare important determinants in the nearshore distri-butions of fish larvae. The avoidance of seawarddispersal away from the relatively productive andstable nearshore zone may be an important factorinfluencing larval distribution.
Most studies on the feeding habits of fish larvaein the Southern California Bight have focused onspecies whose larvae occur primarily beyond thecontinental shelf, or are broadly distributedacross the shelf and beyond (Arthur 1956, 1976;Hunter and Kimbrell 1980; Lasker 1975; Sumidaand Moser 1980, 1984; Theilacker 1986). Larvalfish feeding in the shallow coastal zone (depth:575 m) has, until recently, received relativelylittle attention. Lasker (1975, 1981) examinedthe requisite conditions for the successful first
William Watson, MEC Analytical Systems, Inc., 2433Impala Drive, Carlsbad, CA 92009; present address: South-west Fisheries Center La Jolla Laboratory, National MarineFisheries Service, NOAA, P.O. Box 271, LaJolla, CA 92038.Raymond L. Davis, Jr., MEC Analytical Systems. Inc.,2433 Impala Drive, Carlsbad, CA 92009; present address:Sea World, Aquarium Department, 1720 South ShoresDrive, San Diego, CA 92109.
Manuscript accepted May 1989.Fishery Bulletin, U.8. 87: 569--591.
feeding of larval northern anchovy and sug-gested that the shallow nearshore zone may pro-vide a better larval feeding environment thanoffshore waters, largely because of the morestable nature of the nearshore zone.
It has become increasingly apparent in recentyears that this shallow nearshore zone is aunique area supporting distinctive, stable as-semblages of fish larvae and zooplankters(Brewer et a1. 1981, 1984; Gruber et al. 1982;Barnett et al. 1984; Brewer and Kleppel 1986;Petersen et a1. 1986; Barnett and Jahn 1987;Walker et al. 1987). Feeding studies are begin-ning to be reported for some of the fish larvaethat are largely restricted to this zone (Brewerand Kleppe11986; Jahn et a1. 1988).
The purpose of this report is to document thefood habits of the larvae of six fish taxa in theshallow coastal waters off southern California.These six taxa include larvae occupying all levelsof the water column: larval jacksmelt, Ather-inopsis californiensis, and grunion, Leu,resthestenuis, are largely restricted to the neuston andupper water column; California halibut, Para-lichthys californicus, and kelp and sand bass,Paralabrax spp., larvae occur throughout thewater column but tend to be most abundant inmidwater; and larval queenfish, Seriphus pol-it'u.s, and white croaker, Gen.yonemus lineatus,occur principally in the lower water column andepibenthos (Schlotterbeck and Connally 1982;Barnett et al. 1984; Jahn and Lavenberg 1986).All six taxa occur principally near shore through-out life (Frey 1971; Miller and Lea 1972; Barnettet a1. 1984; Lavenberg et a1. 1986;).
Plankton samples were collected between 25July 1978 and 23 September 1979 near SanOnofre, CA (lat. 33"20'N, long. 11730'W). Theplankton sampling methodology and rationaleare detailed by Barnett et al. (1984) and Walkeret al. (1987) and are only briefly summarizedhere.
Two sample sets, both of which provided com-plete water column coverage, were utilized inthis study. A small sample set, used to make arough approximation of feeding chronology, con-sisted of plankton samples collected twice duringthe day and twice at night within a 24 h period,on two occasions (25 July and 21 September1978). These samples were collected along the 8m isobath 1 km south of the San Onofre NuclearGenerating Station (SONGS) (July) and alongthe 13 m isobath just north of SONGS (Septem-ber). A larger sample set, used to examine larvaldiets, consisted of plankton samples collected atnight at approximately monthly intervals be-tween 6 September 1978 and 23 September 1979,along a randomly selected isobath within each offive offshore blocks. These blocks were definedby depth contours: (A) 6-9 m, (B) 9-12 m, (C)12-22 m, CD) 22--45 m, and (E) 45-75 m. Theblocks were arrayed between 0.5 and 7.2 kmfrom shore, approximately 1 km south ofSONGS.
SONGS Unit I, a 500 megawatt power plant,operated throughout the study period. Unit 1has been shown to have had only very localizedeffects (Marine Review Committee 19791) and itis unlikely to have influenced the results of thisstudy.
Three different types of gear were used tocollect both sample sets: a Brown Manta net(Brown and Cheng 1981), to sample the neuston(top 16 cm); a Brown-McGowan opening-closingbongo net, to sample the midwater column; andan Auriga nee, to sample the epibenthos (withinapproximately 67 em of the bottom). All threetypes of nets were const.ructed of 0.333 mm meshNitex3, fitted with flowmeters, and towed at ca.1 m/s to sample a target volume of 400 m3 Allsamples were fixed in 10% seawater-formalin.
In the laboratory, the plankton samples weresubsampled with a folsom plankton splitter andthe fish larvae were sorted from the subsamplesat 6-lOx magnification under dissecting micro-scopes. Larvae utilized in the feeding studies
IMarine Review Committee. 1979. Interim report of theMarine Review Committee to the California Coastal Com-mission part 1: General summary of findings, predictions.and recommendations concerning the cooling system of theSan Onofre Nuclear Generating Station. Mar. Rev. Comm.Doc. 79--02, p. 1-20. Marine Review Committee of the Cali-fornia Coastal Commission, 631 Howard Street, San Fran-cisco, CA 94105.
2MBC Applied Environmental Sciences, 947 NewhallStreet, Costa Mesa. CA 92627.
3Reference to trade names does not imply endorsement bythe National Marine Fisheries Service, NOAA.
FISHERY BULLETIN: VOL. 87, NO.3, 1989
were randomly selected from among thosesorted from a subsample; a maximum of 100specimens was selected from any subsample.These larvae were measured to the nearest 0.1mm notochord or standard length, separated bydevelopmental stage (preflexion = Pr; notochordflexion plus postflexion = FP), placed in aglycerin-water solution, and dissected with fineinsect pins. The gut contents of each specimenwere identified to the lowest possible taxon us-ing a dissecting (50x) or compound (100-450 x )microscope, as appropriate, and enumerated. Thenumber of specimens dissected is listed byspecies, survey, and sample in Table 1.
Feeding incidence (%FI = percentage oflarvae examined that contained at least one fooditem) was calculated with 95% confidence limitsfor each larval stage of each taxon. The 95%confidence limits were approximated as 1.96(pq/n)Jj.~ + 112'n, where p = the proportion contain-ing at least one food item, q = 1 - p, and n = thesample size. Percent frequency of occurrence(%FO) and percent of the total number (%N) ofprey ingested by each larval fish stage were cal-culated for each prey type.
Feeding incidence was calculated for Seri.phuspolit/ts, Paralabrax spp., and Paralichthys caJi-fornic'Us which were collected in the day/nightsample sets in order to examine feeding chro-nology (Table 2). Larval Genyonemu.s Uneatusand Atherinopsis ca.lijo-rniensis did not occur inthese samples, and too few Le/tresthes ten:/tiswere available to wan'ant examination.
During the day, 82% of the S. politus larvaecontained at least one food item, while at night,72% contained food. Feeding incidence increasedfrom the morning through the evening, reachinga maximum of 94% for the larvae collected be-tween 2003 and 2101 PST. However, since thefeeding incidences were all quite high, and the95% confidence limits about %FI broadly over-lapped for all three morning through eveningsampling episodes, it seems likely that therewere no real differences in feeding incidenceover this period. After midnight, feeding inci-dence was reduced to 33%, and the 95% confi-dence limits did not overlap with either themorning or evening values, indicating that feed-ing incidence indeed was reduced after midnight(Table 2).
Pa.ra.labrax spp. feeding incidence was 68%
WATSON and DAVIS: LARVAL FISH DIETS IN SHALLOW COASTAL WATERS
TABLE 1.-Number of fish larvae dissected on each survey date. Pr = preflexion stage larvae; FP =flexion and postflexion stage larvae.
Atherinopsis Leuresthes Paralichthys Paralabrax Genyonemus Seriphus
Surveycalifomiensis tenuis ca/ifomicus spp. lineatus politus
date Pr FP Pr FP Pr FP Pr FP Pr FP Pr FP
197806 Sept. 0 0 0 24 2 3 30 9 0 0 107 8602 Oct. 1 0 0 10 15 1 0 0 39 4 13 2601 Nov. 0 0 0 0 49 1 1 3 17 5 3 226 Dec. 2 5 0 0 31 7 0 0 89 33 0 0
197929 Jan. 0 0 0 0 10 0 0 0 138 94 0 026 Feb. 2 31 0 0 41 2 0 0 146 98 0 026 Mar. 20 21 0 0 0 0 0 0 161 180 23 025 Apr. 7 19 7 13 0 0 0 0 40 86 18 023 May 0 8 17 20 0 0 0 0 32 49 19