Note Llanos-Rivera and Castro: Egg-size variation of Engraulis nngens 



211 



are not necessarily always associated with latitude (i.e. 

 north Atlantic herring stocks) because local environmen- 

 tal conditions that trigger spawning (i.e. specific tempera- 

 ture or others) may have a stronger effect in some species 

 (Chambers, 1997). Because of the extremely wide distri- 

 bution range of the anchoveta (4-42°S) and its residence 

 along an almost linear coast oriented exactly north-south, 

 we proposed that any potential differences in egg size due 

 to specific local conditions is probably over-driven by the 

 larger scale changes in environmental conditions associ- 

 ated with latitude. 



The strong latitudinal gradient in egg size of the ancho- 

 veta may be an adaptive measure if different egg sizes are 

 favored at different latitudes or if there is a correlation 

 between egg size and adult life history traits that maximize 

 net reproductive output. Unfortunately, an analysis of the 

 anchoveta in which fecundity, age of first reproduction, 

 longevity, or other adult traits are compared in relation 

 to latitude has not yet been carried out. The timing and 

 length of the spawning season seem to be similar for the 

 northern (Iquique, 20°S) and southern (Talcahuano, 36°S) 

 stocks along Chile, despite the different temperatures at 

 which anchoveta spawn (Castro et al., 2001 ). The decrease 

 in egg size coincides with known temperature effects on 

 physiological rates (Houde, 1989) and on ecological factors 



related to the need of anchoveta at early life stages to re- 

 main in nearshore environments (Bakun. 1996). At lower 

 latitudes, the sea temperature is higher and the seaward 

 surface Ekman transport is stronger and therefore eggs 

 and larvae in such conditions would likely develop rapidly. 

 Alternatively, anchovy egg and larvae at higher latitudes 

 are retained nearshore in winter (because the Ekman 

 transport is negative, Castro et al., 2000) but are exposed 

 to lower temperatures and to strong turbulence that may 

 not facilitate the first feeding of recently hatched larvae 

 and subsequent rapid larval development. Larger eggs, 

 larger larvae at hatching, and more energy reserves may 

 be the favored early life history strategy in southern popu- 

 lations. How the latitudinal variations in environmental 

 characteristics affect the rest of the life history traits of the 

 different populations of Engraulis ringens, one of the most 

 important fish species in the world in terms of catches, 

 remains to be assessed. 



Acknowledgments 



We acknowledge help from R. Escribano (U. Antofagasta), 

 G. Claramunt (U. Arturo Prat), and F. Balbontin (U. of 

 Valparaiso) who facilitated ichthyoplankton collections. 



