FISHERY BULLETIN; VOL. 87, NO. 3. 1989 



its importance at San Onofre is unknown. Eiiter- 

 pina acutifrons may be more abundant near San 

 Onofre than elsewhere (mean density 10,640/ 

 m^— range 1,078-37,314/m^— between the 9 and 

 100 m isobaths during a microzooplankton study 

 conducted at San Onofre during the year prior to 

 the feeding study), or it might have been un- 

 usually abundant during the year when the feed- 

 ing studies were done, but appropriate data from 

 long-term and larger scale studies that would 

 allow evaluation of these suggestions are un- 

 available. Other particularly important copepods 

 were the cyclopoid Oitliona oculata and the 

 calanoid Labidocera trispinosa. However, cope- 

 pods were not the only important food items in 

 the nearshore zone and were not the dominant 

 prey for some of the Pr stage larvae. Other con- 

 sistently important prey included tintinnids, 

 especially Stenosomella spp., and mollusc 

 veligers (principally bivalves, but also gastro- 

 pods in some cases). Older sciaenid larvae con- 

 sumed appreciable numbers of mysids. The diets 

 of the older larvae did not exclude small items 

 such as mollusc veligers or copepod nauphi; in- 

 stead, the small items continued to be consumed, 

 and larger items such as larger copepod species 

 (e.g., Barnett and Jahn 1987: table 3) were 

 added as well. This is consistent with Hunter's 

 (1981) observation that although the maximum 

 prey size selected increases more or less rapidly 

 with increasing larval fish size, the minimum 

 prey size increases very slowly. Thus larger lar- 

 vae can select from among a wider range of prey 

 sizes, consuming the energetically more valuable 

 larger items when those are available, and per- 

 haps maintaining on smaller items when large 

 prey are unavailable (Hunter 1976; Hunter and 

 Kimbrell 1980). 



Concurrent plankton sampling that would 

 allow comparisons of the spatial distributions of 

 the fish larvae and their prey species was not 

 part of the present study. However, other 

 studies did examine the distribution and abun- 

 dance of the zooplankton during the day in the 

 same area from 1977 through 1980 (Barnett and 

 Jahn 1987), and spatial patterns of the fish larvae 

 and their prey can be compared in a general way 

 on the basis of these studies. The majority of the 

 most important prey categories occurred in high- 

 est concentrations near shore (e.g., Barnett and 

 Jahn 1987). For example, Oithona oculata was 

 most abundant in the epibenthos shoreward of 

 the 13 m isobath (Barnett and Jahn 1987), while 

 Paracalanus parvus was abundant throughout 

 the water column shoreward of the 30 m isobath 



(Fig. 1). The Marine Review Committee's un- 

 published count data, from samples collected at 

 San Onofre on 31 October 1978 indicated that 

 Euierpina acutifrons nauplii were approxi- 

 mately 4-34 times more abundant in samples 

 taken at the 9, 13, and 30 m isobaths than in 

 samples from the 100 m isobath (maximum 

 abundance 141,200/m^, averaged over the water 

 column at 13 m), while the copepodites and 

 adults were 1.5-19 times more abundant at the 

 shallow stations than at the 100 m station 

 (maximum abundance 11,600/m^, averaged over 

 the water column at 13 m). Labidocera tris- 

 pinosa nauplii were restricted to the very near- 

 shore zone, shoreward of the 13 m isobath, 

 where they occurred throughout the water 

 column (Fig. 1). Bivalve veligers were abundant 

 throughout the water column between the 13 

 and 30 m isobaths, while gastropod vehgers oc- 

 curred throughout the nearshore zone and sea- 

 ward to at least the 100 m isobath (Fig. 1). The 

 most frequently occurring mysid taxa in the 

 larval diets — Holmesimysis costata, Neomysis 

 rayii, and Neomysis spp. juveniles — all were 

 most abundant in the epibenthos shoreward of 

 the 15 m isobath (Bernstein and Gleye 1981'*). 

 Clutter (1967) reported that H. costata, as well 

 as several other mysid species, was restricted to 

 the nearshore zone off La Jolla, C A. 



Barnett et al. (1984) described the cross-shelf 

 and vertical distributions of the larvae of five of 

 the six fish taxa considered here. All five were 

 most abundant shoreward of the 45 m isobath; 

 larvae of the sixth taxon, Paralabrax spp., occur 

 principally shoreward of the 36 m isobath 

 (Lavenberg et al. 1986). The atherinid larvae are 

 almost exclusively neustonic; Paralichthys cali- 

 fornicHS and the Paralabrax spp. larvae occur 

 throughout the water column (especially in mid- 

 water); and the Genyonemus lineatus and Ser- 

 iphus politus larvae are located mainly in the 

 lower water column and epibenthos (Schlotter- 

 beck and Connally 1982; Barnett et al. 1984; Jahn 

 and Lavenberg 1986). Ontogenetic redistribu- 

 tions occur during the larval phase for at least 

 some of the taxa: the flexion and postflexion 

 stage larvae of G. lineatus and S. politus are 

 more nearshore and epibenthic than the preflex- 

 ion stage larvae (Barnett et al. 1984), while the 

 transforming postflexion larvae of Paralichthys 

 californicus occur most frequently and in 



^Bernstein, B. B. and L. G. Gleye. 1981. The ecology of 

 mysids in the San Onofre region. Volume II: New reports. 

 Rep. Mar. Rev. Comm., Rep. No. MEC01281999. 



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