Fish larvae abundance and distribution in the central Gulf of California during strong environmental changes (1997-1998 El Nino and 1998-1999 La Nina)

The pelagic ecosystem of the Gulf of California was affected by the 1997-1998 El Nino warming event and the 1998-1999 La Nina cooling. Larval fish abundance and distribution were analyzed in the central Gulf during El Nino (November 1997 and March 1998) and La Nina (November 1998 and March 1999). Mean sea-surface temperature (SST) differed significantly between El Nino and La Nina (P<0.05), with variations up to 4degreesC. The lowest zooplankton biomass and larval abundance were recorded during El Nino, when species with tropical-subtropical affinity dominated. The Bray-Curtis Dissimilarity Index defined two persisting station groups. The oceanic group, located south of Islas Angel de la Guarda and Tiburon, was strongly co-dominated by Benthosema panamense, Engraulis mordax, and Vinciguerria lucetia larvae in November 1997, whereas larvae of these species together with Triphoturus mexicanus, Sardinops caeruleus, and Scomber japonicus larvae co-dominated in November 1998. Abundances of these last two species were drastically reduced during El Nino. Larval Diogenichthys laternatus, B. panamense, V. lucetia, and T mexicanus co-dominated the oceanic station group in March 1998, but were less prominent in March 1999, except for V lucetia, which co-dominated with E. mordax larvae. This situation was associated with the peak of maximum intensity of the La Nina. The second station group, located in the vicinity of Big Islands, was dominated by R panamense larvae in both Novembers and by E. mordax larvae in both Marches; in both cases this probably was more reflective of high larval abundance in the adjacent oceanic area than a preferential habitat in the Big Islands vicinity. Results suggest that the fish larvae abundance and distribution were altered in different ways by the environmental changes caused by the 1997-1998 El Nino and 1998-1999 La Nina. (C) 2004 Elsevier Ltd. All rights reserved.