Linking juvenile habitat utilization to population dynamics of California halibut

We investigated the nursery role of four coastal ecosystems for the California halibut (Paralichthys californicus) using the following metrics: (1) contribution in producing the fish that advance to older age classes, (2) connectivity of coastal systems resulting from migration of fish from juvenile to subadult habitats, and (3) effect of nursery habitat usage and availability on subadult population size, specifically evaluating the concentration hypothesis. Potential nurseries were grouped using a robust classification scheme that segregated exposed, bay, lagoon, and estuarine environments. Assignment of nursery origins for individual subadult fish via elemental fingerprinting indicated that exposed coasts, bays, lagoons, and estuaries contributed 31%, 65%, 1%, and 3% of advancing juvenile halibut during 2003, versus 49%, 33%, 16%, and 2% during 2004, respectively. These results were remarkably similar to ‘‘expected’’ nursery contributions derived from field surveys, suggesting that in this system juvenile distributions were a good indicator of unit-area productivity of juvenile habitats and that densitydependent mechanisms during the juvenile phase did not regulate recruitment pulses. Elemental fingerprinting also demonstrated that individuals egressing from bays did not migrate far from their nursery origins (,10 km), resulting in reduced connectivity along the 110-km study region over the timescale of approximately one generation. Consequently, we observed considerably higher subadult densities at sites near large bays, while populations distant from large bays appeared to be more influenced by nursery habitat limitation. Over large (,100 km) scales, the location and availability of nursery habitat alternatives had significant effects on the population dynamics of an important member of the ichthyofaunal community of southern California. For coastal fish and invertebrate species, recruitment to an adult population is affected by a wide suite of spatially varying biotic and abiotic factors that operate throughout the pelagic larval phase (Checkley et al. 1988), at settlement (Allen 1988), or during advancement to older age classes (Modin and Pihl 1994). Many species are defined by life histories in which settled juveniles must select among nursery habitat alternatives that can affect the demography of adult populations through habitator site-specific growth or mortality (Sogard et al. 1992). Therefore, understanding the functional role that nursery habitats play in promoting population success is critically important for the proper management of coastal ecosystems and fish