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Habitat characterization provides predictive information about the distribution of species and is useful for as­sessing habitat quality and population stability. Larval abundance of six frequent and abundant demersal species and the relationship of each with the environment were analysed through generalized additive models to determine their preferential distribution and predictive response to the environmental variables in the southern part of the California Current (25-31°N) between two periods of data collection: 1997-2000 and 2006-2010. Essentially, the main associated variables governing the distribution patterns were related to common and oceanographic characteristics of the water column (temperature and salinity at 50 m depth, dynamic height and degree of water column stratification); however, the set of variables and their ranges are usually species-specific. Species of northern distribution, Sebastes sp. and Citharichtys stigmaeus, were recorded mainly in newly emerged, relatively unstratified waters characterized by a shallow mixed layer and low temperatures. Low dynamic height values were the most significant predictor of larval distribution for Merluccius productus. Citharichthys xanthostigma and Symphurus atricaudus were widespread, distributed across the study area mainly in autumn in unstratified or stratified waters and at a shallow mixed layer. Particularly C. Xanthostigma and S. Lucioceps were related to high dynamic height val­ues, likely influenced by a coastal flow towards the pole, as evidenced by counter-currents.

Resumen.-Se analiza la variabilidad estacional de los ensambles de larvas de peces en relación con las con diciones hidrográficas, durante 4 cruceros en la región norte del Golfo de California (GC). De acuerdo a las propiedades termohalinas y fauna asociada se identificaron 2 periodos: un periodo frío, cuando la temperatura disminuye y la corriente costera fluye en dirección al ecuador en invierno y primavera (circulación anticiclónica), dominado por especies de afinidad templada y subtropical (e.g., Engraulis mordax y Merluccius productus); y un periodo cálido, caracterizado por la intrusión de agua tropical superficial en verano y otoño (circulación ciclónica), con alta diversidad de especies de a finidad subtropicaltropical (e.g., Benthosema panamense y Anchoa spp.). La variabilidad estacional se identifica como el elemento principal en la estructuración de los ensambles de larvas de peces. Sin embargo, la hidrodinámica incide en lo s patrones de agregación y el predominio de la biota pelágico costera, demersal y mesopelágica a lo largo del año.Palabras clave: Larvas de peces, masas de agua, hidrografía, Golfo de California Abstract.-This paper analyzes the seasonal variability on larval fish assemblage structure and the relationships to hydrographic conditions during 4 seasonal surveys in the northern Gulf of California. Two periods were identified according to thermohaline properties and associated fauna: a cold period, when temperature drops and the coastal current flows equatorward in winter and spring (anticyclonic circulation), dominated by species of temperate and subtropical affinity (e.g., Engraulis mordax and Merluccius productus); and a warm period, characterized by poleward intrusion of Tropical Surface Water in summer and autumn (cyclonic circulation), with a high diversity of tropical-subtropical species (e.g., Benthosema panamense and Anchoa spp.). Cluster analysis defined 2 groups of stations and associated taxa: a Northern Group, located in the Delfín Basin, including mainly demersal taxa; and a Mainland-Insular group, of species with various affinities (demersal, coastal-pelagic, mesopelagic). Seasonal variability is identified as the main element in the structuring of larval fish assemblages. However, hydrodynamic changes influence the aggregation patterns and the prevalence of the coastal pelagic, demersal and mesopelagic biota throughout the year.