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SUMMARY: Taxonomic composition of fish larvae was analysed from 464 plankton samples obtained during 10 oceanographic surveys in the Gulf of California between 1984 and 1988. We identified 283 taxa: 173 species, 57 genera, and 53 families. Tropical and subtropical species predominated except during the winter, when temperate-subarctic species were dominant. The most abundant species were the mesopelagic Benthosema panamense, Triphoturus mexicanus and Vinciguerria lucetia, but the coastal pelagic species Engraulis mordax, Opisthonema spp., Sardinops caeruleus and Scomber japonicus were also prominent. The taxonomic composition of the ichthyoplankton shows the seasonality of the Gulf as well as environmental changes that occurred between the 1984-1987 warm period and the 1956-1957 cool period previously reported. The presence of E. mordax larvae as one of the most abundant species in the Gulf provides evidence of the reproduction of this species two years before the development of the northern anchovy fishery and the decline of the sardine fishery in the Gulf of California.Key words: fish larvae, ichthyoplankton, Gulf of California. RESUMEN: LARVAS DE PECES DEL GOLFO DE CALIFORNIA. -Se analizó la composición taxonómica de las larvas de peces capturadas en 464 arrastres de plancton obtenidos durante 10 cruceros oceanográficos en el Golfo de California entre 1984 y 1988. Se identificaron 283 taxones: 173 especies, 57 géneros y 53 familias. Los organismos de afinidad tropical y subtropical fueron los más numerosos excepto durante el invierno, periodo en el que las especies templado-subárticas fueron dominantes. Las especies más abundantes fueron los mesopelágicos Benthosema panamense, Triphoturus mexicanus y Vinciguerria lucetia, pero las especies pelágico-costeras como Engraulis mordax, Opisthonema spp., Sardinops caeruleus y Scomber japonicus fueron también importantes por el número de organismos recolectados. La composición taxonómica del ictioplancton refleja la variabilidad estacional del Golfo, así como los cambios ocurridos entre el periodo cálido de 1984-1987 y el periodo frío de 1956-1957 previamente registrado en la literatura. La presencia de larvas de E. mordax como una de las especies más abundantes en el Golfo, aporta evidencia de la reproducción de esta especie dos años antes del desarrollo de la pesquería de la anchoveta norteña y el desplome de la pesquería de sardina del Golfo de California.

Seasonal assemblages of mesopelagic fish larvae and changes related with environmental factors (plankton biomass, sea surface temperature anomaly, upwelling, and the multivariate El Niñ o index) were investigated. From 1982 to 1987, 16 oceanographic cruises were carried out along the Pacific coast of Baja California Sur, Mexico. Larvae of 42 mesopelagic fish taxa were collected. Larval abundance was highly variable during the studied period, but summer months coincided with higher abundance (>200 larvae under 10 m 2 ). Larval assemblages were dominated by three of the most common species of tropical (Vinciguerria lucetia, Diogenichthys laternatus) and subtropical affinity (Triphoturus mexicanus). A group of species of tropical affinity (Diplophos proximus, Diaphus pacificus, Benthosema panamense) was useful for distinguishing the 1982-84 El Niñ o event, and an assemblage of larvae of temperate affinity (Symbolophorus californiensis, Melamphaes lugubris, Bathylagus ochotensis, Leuroglossus stilbius, Protomyctophum crockeri) characterized 'normal' years (mid-1984 to mid-1987).

The distributional diversity and assemblages of fish larvae in the Gulf of California indicated two main seasonal stages and two transitional periods: in winter, the tropical water mass is confined to the south-east portion of the mouth of the Gulf and larval fish assemblages are dominated by subtropical and temperate-subarctic species; in summer; tropical water invades the Gulf and assemblages are dominated by tropical species. Both seasonal stages are separated by transitional periods coinciding with strong latitudinal temperature gradients. During the autumn and spring transitional periods, the Gulf of California splits into three regions: a northern region where temperate and subarctic species spawn from autumn to spring, a southern region dominated by tropical and subtropical species year round and a central region where tropical and temperate assemblages merge. Seasonal changes in the location of the regions, as well as the borders between them, show expansion and contraction of the northern and southern faunas related to the general oceanic circulation patterns during the year. # 2004 The Fisheries Society of the British Isles

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