FISHERY BULLETIN: VOL. 73, NO. 2 



been studied extensively (see, for example, John- 

 son 1956, 1960; Wyllie 1966). During the summer 

 months the California Current system has a 

 generally southward trend, but displays retaining 

 eddies and a net northward onshore drift in the 

 northern range of P. interruptus larval distribu- 

 tion near the southern California coast and ad- 

 jacent Channel Islands. There is a net southerly or 

 offshore drift for water masses off most of Baja 

 California. Even the apparent swimming 

 capabilities of the puerulus stage probably would 

 not allow it to move against these strong, offshore 

 surface currents, particularly because an object in 

 the surface waters would be vectored at a 45° 

 angle, or westwardly, to the wind and current 

 forces. 



As a specific example of this problem, review of 

 mean geostrophic flow at the surface off Califor- 

 nia and Baja California for the months of June- 

 September during the typical period 1950-1964 

 (Wyllie 1966) reveals that there was a net surface 

 transport southward from Point Conception to 

 Cabo San Lucas offshore from approximately 

 80-320 km (50-200 miles). Northward flow near 

 shore during these summer periods occurred only 

 in the Southern California Bight (San Diego to 

 Ventura), while net offshore transport apparently 

 occurred from Bahia San Quintin south to Cabo 

 San Lucas as a precursor to the California Current 

 Extension. 



Thus, it appears very likely that a majority of 

 the late stage phyllosoma and puerulus larvae in 

 the surface layers in this region, more than about 

 40-95 km (25-60 miles) offshore, depending on 

 variations in the current system, were swept 

 seaward by geostrophic flows which averaged 

 greater than 46 cm /sec (0.9 knots) during this 

 typical 15-yr interval. Such individuals undoubt- 

 edly are lost to the population. On the other hand, 

 individuals present closer to shore, or in retaining 

 eddies near the Southern California Channel 

 Islands and the shallow Bahia Sebastian Viz- 

 caino-Isla Cedros area (Johnson 1960), are within 

 distances and ocean surface conditions which 

 would allow their nearshore recruitment by 

 directed swimming of the puerulus stage. 



The Significance of Phyllospadix in 

 the Settlement of the Puerulus Stage 



The strong preference by the puerulus stage for 

 the habitat traps containing Phyllospadix torreyi, 

 as compared to generally similar synthetic 



material in the Witham traps, seems particularly 

 significant in view of the fact that both Serfling 

 (1972) and Parker (1972) discovered numerous 

 early juvenile stages primarily in areas which had 

 thick growths of this surfgrass. Comparative 

 evaluations of habitat traps filled with Phyllo- 

 spadix and other substrates, such as giant kelp 

 {Macrocystis pyrifera) fronds and holdfasts, the 

 eelgrass {Zostera marina), and MytHns clumps, 

 might prove useful as a means of improving 

 collection success with the traps. 



Preference tests involving various substrates 

 typical of different nearshore habitats might also 

 suggest other areas of natural puerulus 

 settlement. In this regard, however, substrate 

 preference tests of the puerulus and postpuerulus 

 stages conducted in the laboratory by Parker 

 (1972) suggest that these stages favor Phyllo- 

 spadix over Macrocystis, Zostera, several species 

 of red algae, sand, and rock. 



Evaluation of the Natural Seaweed 

 and Artificial Habitat Traps 



In comparative tests conducted by Witham et al. 

 (1968), their Witham habitat trap proved 

 somewhat more successful than two other 

 seemingly poor refuges, a tire and a shingle (102 

 versus 77 and 57 pueruli collected, respectively, 

 over a 10-mo period). Phillips (1972), studying P. 

 longipes cygnus in Australia, found that his ar- 

 tificial seaweed habitat trap design collected more 

 pueruli than a modified Witham trap, but only by a 

 factor of approximately two. In contrast, the 

 results of our comparative evaluations (Table 2) 

 indicate that the average number of pueruli 

 caught by the two lighted natural seaweed habitat 

 traps (single and double seaweed frame) was 47 

 per trap, while on lighted Witham artificial sub- 

 strate trap caught only 5 pueruli over the same 

 time period and at the same location. This sug- 

 gests that the natural seaweed trap design was 

 approximately nine times more effective than the 

 Witham trap. Secondly, the lighted habitat traps, 

 regardless of the design, caught more pueruli than 

 did nonlighted ones at the Scripps Institution pier 

 during the same time period (33 and 7 pueruli re- 

 spectively), suggested that a lighted trap was 

 approximately four to five times more effective 

 than an unlighted one. Thus, the system developed i 

 in this study, utilizing a combination of both noc- 

 turnal illumination and natural seaweed, clearly is j 

 much more effective in collecting pueruli of P. in- " 



374 



