SHENKER: OCEANOGRAPHIC ASSOCIATION OF NEUSTONIC MEROPLANKTON 



through early spring when net surface drift is 

 primarily northward and onshore. Oceanic lar- 

 vae, however, should be spawned following the 

 spring-summer transition when upwelling re- 

 sults in southward and offshore transport. 



The onshore/offshore distributions of several 

 abundant fish species in 1984 were similar to 

 those described earlier, and their seasonal occur- 

 rence usually coincided with the constraints dis- 

 cussed by Parrish et al. ( 1981). However, four spe- 

 cies had distributions that crossed the previously 

 described zonal boundaries (Fig. 10). Early 

 cabezon larvae appeared to disperse offshore as 

 they grew. In contrast, early juvenile brown Irish 

 lords were collected offshore in the early spring, 

 while the larger juveniles spread inshore across 

 all stations. Larval greenlings have only been col- 

 lected close to the coast in late fall (Bates 1984), 

 while the juveniles collected in this study were 

 found at all stations prior to upwelling. Juvenile 

 ronquils were also distributed along the transect, 

 during both non-upwelling and upwelling condi- 

 tions. 



The dispersion of organisms across the transi- 

 tion zone may have been accomplished by several 



mechanisms. Physical transport of the organisms 

 by mesoscale hydrographic events (e.g., eddies, 

 offshore jets, and meanders in the alongshore cur- 

 rents) (Ikeda and Emery 1984; Mooers and 

 Robinson 1984; Abbott and Zion 1985; Davis 

 1985) undoubtedly play important roles in the 

 onshore/offshore dispersal of planktonic organ- 

 isms. Transport with these events may be acceler- 

 ated or hindered by diel vertical migration into 

 water layers with different zonal flow patterns. 

 Additionally, several species (especially green- 

 ling and sablefish) are rapid swimmers whose mo- 

 bility can contribute to their dispersal or aggrega- 

 tion. 



The rapid change in the composition of the 

 ichthyoplankton fauna following the onset of up- 

 welling has not been previously observed. Fishes 

 abundant prior to upwelling may respond to the 

 change in the environment in different ways. The 

 disappearance of greenling and brown Irish lord 

 juveniles suggests upwelling triggered settle- 

 ment of these fishes to the demersal habitat uti- 

 lized by older juveniles and adults. A possible 

 stimulus for this transition is the breakdown of 

 the thermocline, which has been identified as a 



125° 

 00' 



124° 

 30' 



124° 

 00' 



Figure 10. — Summary of the zonal distributions of larval and juvenile neustonic fishes in 

 the pre- and early upwelling period (April through mid-June) and the strong upwelling 

 period (July). 



313 



