Seasonal growth of small pelagic fish off Talcahuano, Chile (37 degrees S,73 degrees W): a consequence of their reproductive strategy to seasonal upwelling?

Is the seasonal growth of Strangomera bentincki (Clupeidae) and Engraulis r ingens (Engraulidae) a consequence of their reproductive strategy to adapt to the seasonal upwelling ecosystem they inhabit? This question is addresse d by analysing monthly length-frequency data, gonadosomatic index and condi tion factor of the species in relation with the seasonal patterns of enviro nmental variables. Modal progression analysis of mean length-at-age of coho rts along the time axis was used to study the growth in the period 1990-199 7. A seasonally oscillating growth curve was estimated for both species, wi th the slowest growth rate occurring between April and May, a few months be fore the higher reproductive activity occurring in August-September. The re productive strategy is to spawn when environmental conditions are related w ith onshore transport in winter (August), favouring the concentration and r etention of eggs and larvae. One month later, a moderate upwelling determin es an enrichment in food particles and the spawning area is transformed in a nursery area for juveniles. The reproductive strategy is combined with an 'energy storage strategy' during the period of upwelling. The energy store d is used for reproduction several months later, affecting the growth proce ss of the species. It is concluded that the regularity in the seasonal grow th in both species is a response, from an evolutionary point of view, of a long-term reproductive adaptation to the seasonal upwelling ecosystem of th e central southern area off Chile. (C) 2001 Ifremer/CNRS/Inra/IRD/Cemagref/ Editions scientifiques et medicales Elsevier SAS.