FISHERY BULLETIN: VOL. 82, NO. 1 



San Onofre Nuclear 

 Generating Station 



18 m 



37 m 

 55m 



74 m 



13 m it- A 



'"oV-iT- San Onofre Kelp 



c 



D 



Long Beoch^ 



N 



16 km 

 Pacific Ocean 



FIGURE 1.— Chart of the sampling area and its position off the 

 southern California coast. The one- and two-dimensional pattern 

 analyses were based on samples taken at a randomly selected 

 isobath in each of the five sampling blocks (A-E) on each sampling 

 date. The study of daily vertical migration was based on samples 

 taken along the 8 and 13 m isobaths (dotted lines). 



size, and sampling time for the ensuing full-scale 

 program. The results of this brief study indicated 

 that 



1. Filtration efficiency was at least 85% for all nets 

 and lengths of tow. 



2. Samples of 400 m 3 were adequate to attain 

 asymptotes of numbers of taxa per tow. A sampled 

 volume of 400m 3 from the epibenthos was the max- 

 imum that could be handled economically. 



3. The 12 most abundant larval fish taxa were 

 neither randomly nor evenly distributed with respect 

 to the three vertical strata. Half the taxa were prin- 

 cipally epibenthic, while 25% were neustonic and 

 25% were most abundant in midwater. 



4. Only one of these taxa showed a daily vertical 

 migration; Paraclinus integripinnis, not a top-ranking 

 species in the ensuing study, tended to descend from 

 midwater to the epibenthic layer at night. 



5. Size of individuals and apparent abundance of 

 most taxa increased at night, probably because of 

 visual avoidance during the day. 



6. Nitex netting of 0.333 mm mesh retained more 

 fish eggs and smaller anchovy larvae than did 0.505 

 mm mesh. 



From the preliminary results, it was clear that the 

 bongo net alone would undersample significant frac- 

 tions of many larval populations. Since our goal was 

 to estimate the density and distribution of nearshore 

 ichthyoplankton, we decided to use all three types of 

 gear with 0.333 mm mesh and to filter a target volume 

 of 400 m 3 . 



METHODS 

 Preliminary Study 



In shallow depths, interfaces at the sea surface and 

 seabed comprise a substantial portion of the water 

 column. In addition, concentration of a species at 

 either interface would necessitate sampling the 

 epibenthic and neustonic layers as well as the mid- 

 water column to obtain quantitative abundance 

 estimates. 



Neustonic, midwater, and epibenthic samplers 

 were used in a preliminary study 5 between Septem- 

 ber and November 1977, to verify their effectiveness 

 and to select mesh size, net design, standard sample 



! Barnett, A. M.,J. M. Leis, and P. D. Sertic. 1978. Report to the 

 Marine Review Committee on the preliminary ichthyoplankton 

 studies. Marine Ecological Consultants of Southern California, 53 1 

 Encinitas Boulevard, Encinitas, CA 92024. 



Sampling Gear 



A bongo net was selected for sampling the midwaters, 

 as recommended by Smith and Richardson (1977). 

 An opening-closing 71 cm Brown-McGowan bongo 

 net (total mouth area = 0.79 m 2 ) was used. A General 

 Oceanics 6 (GO) flowmeter was mounted in the star- 

 board frame. The bongo net, as conventionally used, 

 is placed on the wire some distance above a weight 

 and towed astern. The geometry of this arrangement 

 and the circular net mouths make the gear ill-suited 

 for sampling the plankton in the neustonic and epi- 

 benthic strata near the sea surface and seabed, re- 

 spectively. Therefore, specially designed samplers, 

 described below, were used to sample these 

 layers. 



We chose the brown manta net (Brown and Cheng 



6 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



98 



