Changes in the spawning environment of Sardinops caeruleus in the Gulf of California during El Niño 1997-1998

Abstract

The Sardinops caeruleus fishery decreased drastically in the Gulf of California during the seawater heating generated by El Niño-Southern Oscillation (ENSO). Changes in the spawning environment of this species and their relation with the larval abundance in the Gulf of California during the ENSO 1997-1998 are analysed. Plankton and water samples and CTD data were obtained from cruises made during (November 1997 and March 1998) and after the ENSO (November 1998 and March 1999), coinciding with the spawning period of the species. Higher values of sea surface temperature (SST) and lower values of the stratification parameter [phi] (water column stratification), zooplankton biomass, copepod nauplii, and integrated chla were recorded in November 1997 (ENSO) than in November 1998. Higher values of SST and copepod nauplii were recorded in March 1998 (ENSO) than in March 1999. The differences in zooplankton biomass and chl a were not significant. Principal component analysis recognized two large zones during and after the ENSO; the big island zone (BIZ) and the central Gulf. Low SST values and high of plankton levels were at the BIZ in both Novembers, whereas in the March cruises they were in the central Gulf.Sardinops caeruleus larvae were almost absent during the ENSO, whereas in November 1998 high larval abundance concentrated in the BIZ was recorded. In March 1999 the larval abundance decreased again. The results showed changes in the spawning environment of the species during the cruises influenced by the ENSO, which coincided with low abundance of S. caeruleus larvae. But these environmental changes were buffered more in March than in November, maintaining in the first similar levels of some plankton fractions during and after the event. In November 1998 at the BIZ, the interaction of a SST optimal range for the spawning species (from 18 to 21 °C) and availability of food indicated by the plankton abundance coincided with high abundance of S. caeruleus larvae. In addition, enrichment mechanisms occur in the BIZ (e.g. tidal mixing), that might contribute to generate favourable conditions for spawning of the species.