CENTRO INTERDISCIPLINARIO DE CIENCIAS MARINAS

Resumen

The assemblages of fish larvae in Bahia Concepcion were identified, during June and November of 1997 and their relation to the hidrographic variability. The data of temperature, salinity and depth were measured with a CTD Inter Ocean S4 at each one of the 35 sampling stations. The analysis of these physical factors indicates that differences exist between both months, coincident with the two marked climatic seasons as much for the bay as for the Gulf of California. The period from March to October is characterized by Southwest winds, presents a stratified water column and a strong thermocline. In the period from November to February Northwest winds prevail and water column presents homogeneous characteristics from the surface until the bottom. A total of 3,435 larvae was collected during both seasons by using a conical net of 333 μm through superficial haulages in circular trajectory. The ichthyoplankton community was represented by 88 species in 36 families. The most abundant families in June were Gerreidae (62%), Clupeidae (15%) and Sciaenidae (9%) and in November they were Mullidae (27%), Gobiidae (20%) and Clupeidae (9%). The biggest abundance of fish larvae ocurred in June and the highest species richness in November. Three major groups of sampling stations in June were defined by cluster analysis employing the Bray-Curtis Index. The first group denominated “the mouth” characterized by species of the families Gerreidae and Clupeidae; the second group was located in the “center” of the bay and it was characterized by the families Sciaenidae, Clupeidae, Pomacentridae and Gerreidae, while the third group denominated “head” presented to the family Sciaenidae as dominant. For the month of November were defined two major groups of sampling stations, the first group located in the area of the “mouth”, was characterized by the families Mullidae and Clupeidae, while the second group, called “center-head”, showed as dominant the families Mullidae, Gobiidae, Sciaenidae, Pomacentridae and Bleniidae. The differences in the definition of groups of stations and the species that characterize them are associated to the two climatic periods defined in the bay: the stratification time (June) and the time of homogeneity (November). In this last period, an increment is favored in planktonic biomass that coincides with a high diversity of species as well as the definition of a great group of stations that almost include the whole bay. The composition in both seasons showed a mixture of species, in its majority of coastal environment and in less percentage of oceanic areas due