Tuna larvae (at flexion, postflexion, and transformation
stages) were collected by dip net and light traps at night in the northwestern Panama Bight during the season of
reduced upwelling (June−September) of 1990, 1991, 1992, and 1997. The larvae were identified as yellowfin tuna (Thunnus albacares) by mtDNA analysis. Ichthyoplankton data from
bongo and Tucker trawl tows were used to examine the potential prey abundance in relation to the mean
size-at-age and growth rates of the yellowfin tuna larvae and their otoliths. The most rapid growth rates occurred during June 1990 when plankton volumes were at their
highest levels. The lowest plankton volumes coincided with the lowest growth rates and mean sizes-at-age during the August−September 1991 period. High densities of larval fish
were prevalent in the ichthyoplankton tows during the 1991 period; therefore intra- and interspecific competition
for limited food resources may have been the cause of slower growth (density-dependent growth) in yellowfin
tuna larvae The highest mean seasurface temperature and the lowest mean wind stress occurred during an El Niño-Southern Oscillation (ENSO) event during the 1997 period. There
appeared to be no clear association between these environmental factors and larval growth rates, but the higher temperatures may have caused an increase in the short-term growth of otoliths in rela