A seasonal survey of the fish larvae community of the central Pacific coast of Mexico

Larval fish abundance off the coasts of the central portion of the Mexican Pacific was studied during a year cycle. Zooplankton samples were collected during 11 sampling cruises carried out between December 1995 and December 1996 using a bongo net. A total of 63,342 larvae were collected. The most a bundant families were Bregmacerotidae 94.6%, Eleotridae 1.19%, Sciaenidae 0 .67%, and Engraulidae 0.64%. Abundance values were significantly higher (P < 0.005) at near-shore stations, suggesting a potential ecological use of a djacent coastal environments as nursery areas. Fish larvae were most abunda nt during January-May, a period with the lowest average sea temperature, wh ich is related to the seasonal influence of the California Current (CC). In these months, advective processes are active along the outer shelf favorin g upwelling of colder, relatively nutrient-richer waters which in turn allo w an overall local increase of zooplankton activity and populations. The hi gh variability of abundance values in the surveyed area suggest episodic, l ocalized processes enhancing the local productivity. Lowest abundance occur red in October-December, when the CC is weak and the area is influenced by tropical oligotrophic waters. Highest abundance values were consistently fo und at nearshore stations, this is probably related to ( 1) the extraordina ry dominance of the coastal species Bregmaceros bathymaster and (2) the ins horeward transport of larvae into potential nursery areas. B. bathymaster w as the most abundant larvae during the entire survey period. It is suggeste d that this species has a year-round breeding cycle, with moderate month-to -month but sharp seasonal variations. The absence of adult individuals of t his species in the surveyed area suggest that it probably spawns in the oce an and its larval stages are transported inshorewards into potential nurser y zones.