Growth, Mortality, and Movements of Juvenile California Halibut Paralichthys californicus in Shallow Coastal and Bay Habitats of San Diego County, California

-Growth and mortality rates were compared for juvenile California halibut Paralichthys calif0rnicu.s from bay and open coast habitats. Growth was estimated by determination of size-at-age using daily increments in otoliths. No significant difference was observed in size-at-age for juvenile halibut between 6 and 41mm from the bays and open coast. However, age-spec& mortality rates estimated for halibut <70 days were highest for newlysettled halibut on the open coast. California halibut settled either in bays or on the open coast, but ultimately nearly all of the halibut that settled on the coast entered and xed the hays as nursery areas during their first year of life or else they died. The advantages of bays as nursery areas may be a decrease in risk of mortality of newly-settled halibut and an increase in growth of larger juveniles that feed upon the abundant small fishes in the bays. Manuscript accepted 12 December 1990. Fishery Bulletin, U.S. 89:195-207 (1991). Growth, Mortality, and Movements of Juvenile California Halibut Paralichthys californicus in Shallow Coastal and Bay Habitats of San Diego County, California Sharon Hendrix Kramer Southwest Fisheries Science Center National Marine Fisheries Sewice, NOAA P 0 Box 27 I , La Jolla. California 92038 Present address MBC Applied Environmental Sciences 947 Newhall Street, Costa Mesa, California 92627 The utilization of specialized nursery habitats by juvenile fish is a common phenomenon (Boehlert and Mundy 1988, Miller et al. 1986). Many of the fish species that utilize bays as nursery areas spawn in offshore waters, and move into bays as late larvae and early juveniles (Boehlert and Mundy 1988, Miller et al. 1986). The migration, location, and entry of larvae and juveniles into the bays involve complex behaviors that are particularly important on the Pacific coast of North America, where only 10-20% of the coastal habitat consists of estuaries and lagoons, compared with 80-90% on the Atlantic and Gulf coasts (Emery 1967). Possible consequences of the use of bays as nursery areas include faster growth because of high food production, warm temperatures, and decreased predation (Miller et al. 1986, Kneib 1987, Krygier and Pearcy 1986). The California halibut Para2ichthys calqornicus is a commercially important flatfish found in southern California coastal waters and bays (Frey 1971, Haaker 1975, Allen 1988, Love et al. 1986, Plummer e t al. 1983). Eggs and larvae occur over the shelf and seaward, with greatest densities in waters less than 75m deep and within 6km of shore (Frey 1971, Gruber et a]. 1982, Barnett et al. 1984, Lavenberg et al. 1986, Walker et al. 1987, Moser and Watson 1990). In past studies juvenile halibut rarely were taken on the open coast, suggesting that bays and lagoons might be the only significant nursery habitat (Plummer e t al. 1983, Allen 1982, Kramer 1990). The objective of this study was to determine the relative importance of bays as nursery areas and to evaluate the movements between bay and open coast habitats. To meet these objectives, I estimated habitat-specific distribution, abundance, and growth and mortality rates of juvenile halibut from both bay and open coast habitats. Materials and methods Distribution and abundance California halibut were collected during a 2-year survey (September 1986September 1988) of the open coast between Mission Bay and San Onofre, and two bays, Mission Bay and Agua Hedionda Lagoon (Fig. 1). A stratified random sampling design was used, consisting of four open coast blocks each with three depth strata(5-8m, gl lm, and 12-14m), and five blocks in Mission Bay and three blocks in Agua Hedionda Lagoon, each with three depth strata (0-lm, 1-2m, and 2-4m) (Fig. 1).