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Although the Gulf of California is probably one of the most studied regions in México due it high productivity, zoogeographic complexity, and economical relevance, copepod studies have been focused mostly on studies of distribution and abundance based on Bongo net collection. This is the first study of vertical distribution of epipelagic copepods in the Gulf of California. Zooplankton was collected using opening closing nets at five depth strata (0, 25, 50, 75 and 100 m) during 12-31 Jan 2007 (n=20 stations). From a total of 44 species identified, Pleuromamma gracilis, Calanus pacificus, Rhincalanus nasutus and Scolecithrix danae accounted >65% of the total copepod abundance. Independently of the day/night collection, the highest copepod abundance was observed in the first 50m depth, including species frequently recorded in mesopelagic habitat. This suggests short or non-migratory vertical behavior, closely associated with the maximum Chlorophyll-a depth. Vertical distribution of environmental conditions showed a well mixed water column (average 90 m depth) and relatively deeper oxygen minimum layer depth ( < 1.5 mg O₂ L^-1, 90-120 m depth) indicating that near surface distribution of most copepod species was not related with thermo-haline vertical structure or hypoxic conditions. Our results suggest that the water mass circulation prevailing during upwelling season is the main driving force that structures the copepod spatial distribution. The presence of high density copepod populations, particularly P gracili

Palabras clave: vertical distribution; Specialist; copepods; winter season

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