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Fishery Bulletin 89(2), 1991 



1967). Both occur along the shallow open coast as well, 

 but are most abundant in bays (Allen 1985). Staghorn 

 sculpin feed primarily on crustaceans (>50% by 

 weight), but small diamond turbot Hypsopsetta guttu- 

 lata have also been found in their stomachs (frequen- 

 cy of occurrence 0.5%) (Tasto 1975). Over 94% of the 

 diet by volume of round stingray is composed of mol- 

 luscs, polychaetes, and crustaceans, but gobies--also 

 have been found in their stomachs (Babel 1967). 



Other predators found both in the bays and on the 

 open coast include barred sand bass Paralabrax 

 nebulifer, spotted sand bass P. maculatofasciatus, and 

 kelp bass P. clathratus. Spotted sand bass occur 

 predominantly in bay habitats, barred sand bass occur 

 ubiquitously in the bays and on the open coast, and kelp 

 bass are associated with rock reef and kelp bed habitats 

 on the open coast, but also have been taken as juveniles 

 in bays (Allen 1985, Lane 1975). Kelp bass on the open 

 coast feed mostly on northern anchovies and crabs, and 

 have been found occasionally with flatfishes in their 

 stomachs (Quast 1968). The diet of barred sand bass 

 taken from bottom depths of 8-30 m on the open coast 

 indicates that they forage close to the substrate, 

 feeding on brachyuran crabs, mysids, pelecypods, and 

 epibenthic fishes (mostly Porichthys notatus) (Roberts 

 et al. 1984, Feder et al. 1974). Spotted sand bass oc- 

 cur predominantly in bay habitats, feeding on crabs and 

 other crustaceans, and on small kelpfish (Feder et al. 

 1974, Allen 1985). The juveniles of all three species are 

 found commonly in Mission Bay, and are considered 

 highly probable goby predators (Brothers 1975). The 

 sand basses probably eat juvenile halibut also, as gobies 

 and halibut share the same habitats. 



Comparison of predation risk must also include a 

 measure of abundance or biomass of predators by 

 habitat. The estimated density of the potential bay 

 predators (round stingray, Paralabrax spp., and stag- 

 horn sculpin) based on otter trawl surveys is 61/hectare 

 in Agua Hedionda Lagoon, and only 3/hectare on the 

 open coast (San Diego Gas and Electric 1980). The 

 estimated density of two open-coast predators, the 

 speckled sanddab and the thornback ray, is >1000/ 

 hectare (Ford 1965). Based on this scanty information, 

 it appears that predators are more abundant on the 

 open coast than in the bays. 



Thus the possible advantages of using bays as nur- 

 sery areas by juvenile halibut appear to be at least two- 

 fold: (1) Decreased risk of predation on newly-settled 

 juveniles, since fewer predators are known to occur 

 there; and (2) increased potential for faster growth of 

 juveniles >55mm SL because small fishes (gobies) are 

 more abundant in bays than on the open coast (Haaker 

 1975, Allen 1985). 



Migration to bays 



The migration of larvae from spawning areas over the 

 continental shelf to their juvenile nursery areas in em- 

 bayments is thought to consist of two phases (Boehlert 

 and Mundy 1988): Accumulation of larvae in the near- 

 shore zone (Boehlert and Mundy 1988, Miller et al. 

 1986), and location and entering of the bays by trans- 

 forming larvae and juveniles (Boehlert and Mundy 

 1988). The nearshore accumulation of larvae prior to 

 movement to the bays is probably facilitated by the 

 timing of spawning, the short duration of pelagic 

 stages, and the vertical distributions of the postflex- 

 ion and transforming larval stages. California halibut 

 spawn throughout the year, with peak spawning dur- 

 ing the winter and spring (Lavenberg et al. 1986, 

 Walker et al. 1987). The spawning peak coincides with 

 the period of minimum offshore transport of surface 

 water in the Southern California Bight (Parrish et al. 

 1981, Jackson 1986). Offshore transport increases in 

 late spring and summer due to increasing upwelling ac- 

 tivity (Parrish et al. 1981, Jackson 1986). The seasonal 

 shift in upwelling activity has been correlated with a 

 seasonal cross-shelf shift in the zooplankton assemblage 

 off San Onofre: from February to early April the com- 

 munity was shifted onshore, and from mid-April to July 

 the shift was offshore, corresponding to the period of 

 increased upwelling (Barnett and Jahn 1987). 



The size distribution of California halibut larvae 

 taken in plankton tows indicates that they move in- 

 shore as they approach metamorphosis. Preflexion and 

 flexion larvae (~2-6mm SL) occur in mid water >2km 

 offshore, whereas transforming larvae occur at night 

 in the neuston within 1km of shore (Moser and Wat- 

 son 1990). My collections indicated that transform- 

 ing larvae occur on the bottom during the day; thus 

 transforming larvae appear to undergo a daily vertical 

 migration, occurring at the surface at night and at the 

 bottom during the day. Larvae of other Paralichthys 

 species, yellowtail flounder Limandaferruginea, stone 

 flounder Kareius bicoloratus, and the larval stages of 

 several crustacean taxa have similar diurnal activity 

 patterns (Weinstein et al 1980, Tsuruta 1978, Shanks 

 1988, Penn 1975, Smith et al. 1978). 



Postflexion and transforming halibut larvae may be 

 transported shoreward by internal waves at night when 

 they are in the neuston, with very little movement dur- 

 ing the day while they are on the bottom, resulting in 

 accumulation of larvae nearshore (Moser and Watson 

 1990). Surface slicks associated with internal waves 

 may transport neustonic larval fishes and crustaceans 

 onshore (Shanks 1988, Kingsford and Choat 1986). 

 Recovery of drift bottles released <20 miles offshore 

 in the Southern California Bight region is greatest 



