Distribution of squid paralarvae, Loligo opalescens (Cephalopoda: Myopsida), in the Southern California Bight in the three years following the 1997-1998 El Niño

Abstract

Large numbers of paralarvae of the California market squid, Loligo opalescens (10,560 paralarvae from 422 plankton samples), were collected in the Southern California Bight in 1999, 2000, and 2001 during the spawning season. Paralarval abundance increased dramatically (P<0.0041) from 1.5 squid/1,000m3 in 1999 to 77.9 squid/1,000m3 in 2000, and 73.6 squid/1,000m3 in 2001, following the El Nino of 1997–1998. The effects on the squid fishery of the 1997–1998 El Nino were thus extended for two years, with larval abundance reduced until the 1999–2000 spawning season. Paralarvae were abundant close to shore for up to a month after hatching in 2000 (P<0.003), with tidal surface currents adjacent to shore in the Channel Islands strongly affecting paralarval abundance. Tidally reversing currents within 1–3 km of shore created a boundary layer of "sticky water" within which paralarvae remained entrained inshore immediately after hatching. Neritic currents farther from shore dispersed older paralarvae within the Southern California Bight. The greatest change in paralarval abundance, for all transects, was observed within 1 km of the transition between these two flow regimes. Age of paralarvae (from statolith increments) entrained within the Catalina Island boundary layer averaged 13–16 days, but some individuals remained nearshore for up to a month. Paralarvae in the boundary layer occurred above 80 m depth both day and night, and exhibited a statistically significant pattern of vertical diel migration (P<0.01). Paralarvae at sea were disproportionately abundant adjacent to fronts associated with uplifted isotherms.