FISHERY BULLETIN: VOL. 81, NO. 3 



METHODS 

 Field Sampling 



Two longshore locations were sampled in the 

 nearshore waters (0.5-3.0 km offshore) between San 

 Onofre and Oceanside in southern California (Fig. 1). 

 Fish abundances at these locations were monitored 

 as part of an environmental impact assessment of the 

 San Onofre Nuclear Generating Station (SONGS), 

 located about 5 km downcoast of San Clemente, per- 

 formed for the Marine Review Committee of the 

 California Coastal Commission. The upcoast loca- 

 tion is situated several kilometers downcoast of 

 SONGS and the downcoast location ~18 km 

 downcoast (Fig. 1). The sand and sand-cobble bot- 

 tom in the area slopes gradually from shore with an 

 increase in depth of about 5 m/km. The upcoast loca- 

 tion is ~0.5-1.5 km downcoast of the San Onofre kelp 

 bed (designated by stippling, Fig. 1). 



Samples (net-hauls) were taken at randomly chosen 

 positions within each of three depth blocks (shallow: 

 5-11 m; mid: 12-16 m; and deep: 18-27 m) at both 

 locations during day (1-6 h after dawn) and night (1-6 

 h after sunset) periods from September 1979 to 

 March 1981, inclusive. (Samples could not be taken 

 in January-February 1980, when our sampling vessel 

 was drydocked for repairs.) The three depth blocks 

 used were chosen as most appropriate for partition- 

 ing onshore/offshore variation in catches, based on 

 the results of prior (May 1978-August 1979) lampara 

 sampling at various depths in the general area. The 

 number of cruises (N = 1-4) and net-hauls (N= 4-8) 

 per month differed between diel periods and depth 

 blocks, with most samples allocated to the daytime 

 period and shallow depth block wherein catches were 

 most variable. Because we suspected a significant 

 date (cruise) effect on our catches, a paired sampling 

 design was established in which the same depth 

 blocks were sampled during the same diel period at 

 both longshore locations on each cruise. 



Two sizes of lampara net (semipursing round haul, 

 Scofield 1951) were used: 1) A small net with 

 each of two wings 118 m long of 15 cm stretch mesh, 

 tapering to a bag of 1 .25 cm mesh, was used to sample 

 surface-to-bottom within the 5-11 m and 12-16 m 

 depth blocks. The small net sampled about 4,600 m : 

 of sea surface area. 2) A large net with wings each 

 136 m long of mesh identical to the small net was used 

 to sample the 18-27 m depth block, wherein it also 

 fished surface-to-bottom. The large net sampled 

 about 6,200 m 2 of sea surface area. Catch was stan- 

 dardized to the area of the small lampara net. Both 

 nets took about 10 min to set and retrieve, using a 



commercial fishing vessel. The same vessel and pro- 

 cedures of net deployment were used for the duration 

 of the study. 



Fishes collected in net-hauls were transferred by 

 dip net to a holding tank on the vessel and were then 

 identified and counted. Subsamples of major species 

 were taken for life history analysis, and other fishes 

 were returned to the sea as soon as possible. Large 

 catches were subsampled with standard bait 

 brailers. 



In order to evaluate the potential effects of variable 

 net catch efficiencies under varying water clarity con- 

 ditions during the day, an index of water clarity 

 (visibility to shipboard observer of 30 cm Secchi 

 disk) was measured immediately following most net- 

 hauls. Potential diel differences in catch efficiency 

 were evaluated on the basis of the percentage recap- 

 ture of marked Seriphus politus in net- hauls made 

 during a pilot (June-September 1978) study. A con- 

 stant number (50) of fin-clipped adult S. politus, cap- 

 tured on the previous net-haul, were released within 

 the center of the area being encircled as the net was 

 deployed. Test releases were made in all depth 

 blocks, both at the surface and near bottom (via a 

 messenger-tripped holding cage), and during both 

 day and night. Secchi disk indices of water clarity 

 were measured at night between test net-hauls, using 

 a standard shipboard light source. 



Data Analysis 



Analyses were carried out using the Statistical 

 Analysis System (SAS) installed at the Marine 

 Review Committee's Computer Center in Solana 

 Beach, Calif. 



Preliminary tests (Ntest for paired comparisons, P 

 >0.05) failed to detect significant differences be- 

 tween locations in all but a few of the common species 

 using log-transformed catch data. Log transforma- 

 tion (log 10 X + 1 ) of catch data was necessary to satis- 

 fy the parametric assumptions of normality and 

 equality of variances within depth blocks and diel 

 periods. The general lack of longshore differences 

 allowed us to pool the data at both locations for sub- 

 sequent analyses. 



Catch per unit effort (CPUE) was calculated by 

 month based on log-transformed catch data for in- 

 dividual depth blocks and diel periods. Combined 

 CPUE of all three depth blocks was expressed as the 

 grand mean and associated standard error of depth 

 means. 



Comparisons of untransformed catch data between 

 depths, diel periods, and dates were made by using 

 Wilson's nonparametric analysis of variance (Wilson 



570 



