FISHERY BULLETIN: VOL. 81, NO. 3 



DISCUSSION 



The nearshore pelagic ichthyofauna between San 

 Onofre and Oceanside, Calif., was dominated by 

 silvery-sided, schooling fishes. Engraulis mordax, the 

 dominant pelagic species offshore (Mais 1974), was 

 also the most abundant species nearshore. Seriphus 

 politus and G. lineatus, the two abundant sciaenids in 

 this assemblage, are best characterized as bottom 

 associated fishes which rise into the water column. 

 Both of these species are well represented in bottom- 

 trawls in the area. 5 Genyonemus lineatus is generally 

 more abundant in trawls, indicating that it is more 

 closely associated with the bottom than 5. politus. 

 The three species above, together with P. simillimus 

 and atherinid spp., constituted species Group I. 

 Members of this group were abundant and ubi- 

 quitous within the area and accounted for >98 C A of 

 the total individuals collected. Species Groups II and 

 III represented periodic components (Tyler 1971) 

 within the assemblage. Group II comprised three 

 species of higher carnivores that generally occurred 

 in the offshore portion of the study area during the 

 warmer months (spring-summer). Group III, on the 

 other hand, contained four species that were more 

 abundant at shallow depths during the colder water 

 months (fall- winter). Two of these species, Anchoa 

 compressa and the sciaenid Umbrina roncador, are 

 known to occur in bay-estuarine habitats such as 

 Newport Bay during the summer months (Horn and 

 Allen 1981). Both A. compressa and U. roncador 

 belong to primarily tropical families. The presence of 

 these two species in the study area during fall-winter 

 suggests that they may seasonally migrate out of era- 

 bayments and into shallow coastal waters in response 

 to cool-water temperatures. The bottom-associated 

 species of Group IV were relatively rare in catches 

 with the exception of the bat ray, Myliobatis Califor- 

 nia (California bat ray). Myliobatis californica oc- 

 curred in about one-third of all net-hauls and ranked 

 sixth in number of total occurrences. Its relatively 

 large size (x — 2 kg) and high frequency of occurrence 

 makeM. californica a more important component of 

 this nearshore assemblage than numerical abun- 

 dance alone would indicate. 



Upcoast and downcoast locations were generally 

 similar in terms of total individuals, species counts, 

 and in the abundances of most common species. The 

 few exceptions (atherinids, Sphyraena argentea, 



! DeMartini, E. E., and L. G. Allen. Temporal and spatial patterns 

 of distribution and abundance of benthic, soft-bottom fishes at 

 shallow depths off San Onofre-Oceanside, California. Manuscr. in 

 prep. Marine Science Institute, University of California, Santa Bar- 

 bara, CA 93106. 



Trachurus symmetricus,Xenistius californiensis) that 

 were more abundant at the upcoast location probably 

 reflect the proximity of the San Onofre kelp bed. All 

 of these species are known to associate with kelp 

 beds or rocky reefs at some time during the year 

 (Feder et al. 1974; Hobson and Chess 1976; Mais 

 1974). 



Significant date effects found by Wilson's 

 ANOVA' s reflected a certain amount of temporal 

 variation within this assemblage of fishes. Some of 

 these date effects can be attributed to spatial patch- 

 iness and sampling error; other date effects un- 

 doubtedly reflect short-term, temporal changes in 

 the environment. Upwelling is probably a major fac- 

 tor contributing to short-term variation in the abun- 

 dance and distribution of these fishes. The waters 

 within the Southern California Bight can be subject- 

 ed to bouts of upwelling anytime during the year, 

 although upwelling is most likely to occur during 

 March- July (Parrish et al. 1981). Both short-term 

 temperature variations due to upwelling and long- 

 term seasonal warming and cooling of coastal waters 

 probably influenced the 10 observed correlations 

 between sea surface temperature and the abundance 

 of individual taxa. The abundances of only two of the 

 top five taxa however were significantly correlated to 

 sea temperature (Engraulis mordax, positive; 

 atherinids, negative). Peprilus simillimus, the fourth 

 most abundant species, varied significantly between 

 dates (ANOVA results), but showed no significant 

 relationship to temperature. Extremely patchy dis- 

 tributions and high vagility might account for the 

 observed short-term variations in the abundance 

 of P. simillimus. Neither Seriphus politus nor 

 Genyonemus lineatus varied greatly in seasonal abun- 

 dance although S. politus did show a significant date 

 effect (ANOVA) that was apparently unrelated to 

 temperature. These two sciaenids were largely re- 

 sponsible for the uniformity of catch seen when En- 

 graulis mordax was excluded from the catch totals. 

 The only major change in catches of S. politus and G. 

 lineatus occurred during the October-December 

 periods of 1979 and 1980 when CPUE was de- 

 pressed. During this time of year the adults of both 

 species presumably migrated out of our sampling 

 area into deeper water. 



Temporal distributions differed for Scomber 

 japonicus, Sarda chiliensis, and Sphyraena argentea, 

 the major higher carnivores of the assemblage. The 

 observed temporal differences probably reflect dif- 

 ferences in general longshore migratory patterns and 

 residence of juveniles within the study area (e.g., pres- 

 ence of juvenile S. argentea near San Onofre kelp bed 

 during fall-winter, authors' pers. obs.). A pos- 



582 



