FISHERY BULLETIN: VOL. 87. NO. 3. 1989 



number of larval growth-related parameters, in- 

 cluding increased larval swimming speeds and 

 search volumes and increased conspicuousness of 

 larger larvae (Hunter 1981). It is possible that 

 increasing encounter rates between a suite of 

 predators and larger white seabass larvae in na- 

 tural systems would offset the observed steady 

 increase in detection and escape responses ob- 

 served in larger larvae in laboratory trials. This 

 could occur until larvae became invulnerable to 

 attacks. My laboratory data provide some hint of 

 this pattern in the slightly increased predation 

 rates on larvae in the 4.5-7.5 mm size range (see 

 Figures 2A, 3A). However, white seabass lar- 

 vae are relatively inactive and become increas- 

 ingly demersal during ontogeny, thus, they 

 might not be subject to significantly higher 

 encounter rates with predators. This remains 

 speculative, however, and is an area for future 

 investigation. 



Implications for White Seabass Early 

 Life History 



Compared with white seabass larvae, Cali- 

 fornia sardine, Sardinops sagax, and northern 

 anchovy larvae (co-occurring pelagic larvae in 

 nearshore southern California waters) appear 

 better able to detect and avoid attacks by adult 

 northern anchovy predators at comparable 

 stages of larval development (Folkvord and 

 Hunter 1986; Butler and Pickett 1988). These 

 two clupeoid species also exhibit schooHng be- 

 havior in the later larval stages. Many species 

 exhibit a combination of larval adaptations to 

 minimize fish predation, including long periods 

 of transparency (e.g., dover sole, Microstomus 

 pacificus; Hunter^), rapid development of avoid- 

 ance capabihties (northern anchovy and sardine) 

 and schooling (clupeoids). During early feeding 

 stages, white seabass larvae develop a robust, 

 highly pigmented body form and exhibit limited 

 mobility. During the early postflexion stage 

 (7-10 mm), white seabass start to abandon a 

 strictly pelagic distribution and become notice- 

 ably more demersal. By the late larval and early 

 juvenile stage, they are found almost exclusively 

 associated with submerged cover (often drift 

 algae) or near-bottom habitats (pers. obs.; Allen 

 and Franklin 1988; Orhun^; Kramer^). In near- 

 shore waters of southern California, other 



sciaenid larvae show a marked vertical size dis- 

 tribution during daylight hours, with larger 

 larvae (postflexion and larger) occurring in high- 

 est densities in suprabenthic habitats and 

 smaller larvae occurring higher in the water col- 

 umn (Love et al. 1984; Jahn and Lavenberg 

 1986). The suprabenthic distribution of larger 

 larvae has been characterized as a possible adap- 

 tation to high concentrations of food, for preda- 

 tor-avoidance or for maintenance of position on 

 the continental shelf. However, recent studies of 

 white croaker, Genyomenus lineatus, larvae in- 

 dicate that the suprabenthic distribution of older 

 sciaenid larvae is probably not related to feeding 

 (Jahn et al. 1988). 



My results indicate that this ontogenetic shift 

 deeper into the water column by older white 

 seabass larvae (and other sciaenids) may be re- 

 lated to their predator-avoidance capabilities. 

 The dominant planktivorous species encountered 

 in midwater habitats of nearshore southern Cali- 

 fornia waters are fast-swimming, shoaling 

 pelagics such as northern anchovy, sardine, and 

 Pacific mackerel. Scomber japonkus. Potential 

 planktivores in near-bottom habitats include 

 sciaenids, gobiids, embiotocids, chnids, ser- 

 ranids, and various flatfishes (Eschmeyer et al. 

 1983). All of these demersal species exhibit some 

 type of ambush, hovering, discontinuous, or 

 close-range mode of predatory behavior, similar 

 to tne attack behavior of juvenile white seabass, 

 and all attack at slower speeds than the shoaling 

 pelagics. Based on my experimental evidence, it 

 is likely that, as they drop out of the plankton, 

 older white seabass larvae maximize their preda- 

 tor-detection and avoidance capabilities when 

 encountering demersal predators. Remaining in 

 the plankton in later larval stages and being 

 exposed to pelagic, shoaling fish predators would 

 prolong a period of extreme vulnerability, while 

 shifting to a demersal distribution would place 

 white seabass in habitats to which they are bet- 

 ter suited developmentally. 



ACKNOWLEDGMENTS 



I would like to thank Refik Orhun, Chris 

 Donohoe, and Donald Kent of the Hubbs Marine 

 Research Center in San Diego for providing 



'J. R. Hunter. UnpubL data. Southwest Fisheries 

 Center La Jolla Laboratory, National Marine Fisheries Ser- 

 vice, NOAA, La Jolla, CA"92038. 



^R. Orhun. Unpubl. data. Hubbs Marine Research 

 Center, Sea World, San Diego, CA 92109. 



■'S. Kramer. Unpubl. data. Southwest Fisheries 

 Center La Jolla Laboratory, National Marine Fisheries 

 Service, NOAA, La Jolla, CA 92038. 



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