207 



Latitudinal and seasonal egg-size variation of the 

 anchoveta (Engraulis ringens) off the Chilean coast 



Alejandra Llanos-Rivera 



Leonardo R. Castro 



Laboratorio de Oceanografia Pesquera y Ecologia Larval 



Departamento de Oceanografia 



Universidad de Concepcion 



Casilla 160-C, Concepcion, Chile 



E-mail address (for L. R Castro, contact author) lecastro@udeccl 



occur among populations of E. ringens 

 along its distribution. In this study, we 

 1 ) report changes in egg size through- 

 out the anchoveta spawning season 

 as well as for the peak months of the 

 spawning season, 2) evaluate whether 

 egg size varies with respect to latitude, 

 and 3 ) evaluate whether differences in 

 larval length and yolksac volume occur 

 in hatching larvae from the two major 

 spawning stocks along Chile (central 

 and southern stocks). 



The anchoveta Engraulis ringens is 

 widely distributed along the eastern 

 South Pacific (from 4° to 42°S; Serra et 

 al., 1979) and it has also supported one 

 of the largest fisheries of the world over 

 the last four decades. However, there 

 are few interpopulation comparisons 

 for either the adult or the younger 

 stages. Reproductive traits, such as 

 fecundity or spawning season length, 

 are known to vary with latitude for 

 some fish species (Blaxter and Hunter, 

 1982; Conover, 1990; Fleming and 

 Gross, 1990; Castro and Cowen, 1991). 

 and latitudinal trends for some early 

 life history traits, such as egg size and 

 larval growth rates, have been reported 

 for others clupeiforms and other fishes 

 (Blaxter and Hempel, 1963; Ciechom- 

 ski. 1973; Imai and Tanaka, 1987, 

 Conover 1990, Houde 1989). However, 

 there is no published information on 

 potential latitudinal trends during the 

 adult or the early life history of the 

 anchoveta, even though this type of 

 information may help in understand- 

 ing recruitment variability, especially 

 during recurring large scale events 

 ( such as El Nino or La Nina) that affect 

 the entire species range. 



Egg volume has been found to vary 

 widely among species and among popu- 

 lations of the same species. For fish that 

 broadcast planktonic or benthic eggs, 

 egg size often varies as the spawning 

 season progresses (Bagenal, 1971), and 

 the magnitude of this variation depends 

 on the species. For instance, the egg vol- 

 ume of the pelagic spawners Engraulis 

 anchoita and Solea solea decreases 23% 

 and 38%. respectively, throughout the 

 spawning season (Ciechomski, 1973; 

 Rijnsdorp and Vingerhoed, 1994). Ma- 

 ternal and environmental factors may 

 also affect egg volume (Bagenal, 1971; 



Thresher, 1984; Rijnsdorp and Vinger- 

 hoed, 1994; Chambers and Waiwood. 

 1996; Chambers, 1997). Variations in 

 size of the spawning females and shifts 

 in energy allocation from reproduction 

 to growth as the spawning season pro- 

 gresses may influence the egg volume 

 (Wootton, 1990). Alternatively, seasonal 

 variations in photoperiod, seawater 

 temperature, and food supply during 

 the spawning season may affect the 

 reproductive output (Wootton, 1990). 



Scarce information exists on the 

 variability of egg sizes for fishes in the 

 Humboldt Current. In this extensive 

 area, the heavily exploited anchoveta 

 Engraulis ringens is the dominant 

 small pelagic species. Throughout this 

 range, three major stocks are recog- 

 nized: the northern stock off northern 

 Peru ( the largest ); the central stock off 

 southern Peru and northern Chile (mid- 

 size), and the southern stock off central 

 Chile (the smallest of the three). For 

 the entire distribution of anchoveta, 

 the main spawning season is from July 

 through September, but may extend to 

 December or January (Cubillos et al., 

 1999). The wide latitudinal range and 

 prolonged spawning period suggest the 

 possibility of egg-size variation, as ob- 

 served in other clupeifoms (Blaxter and 

 Hempel, 1963; Ciechomski, 1973; Imai 

 and Tanaka, 1987). Egg size correlates 

 with larval characteristics such as lar- 

 val length at hatching, the time to first 

 feeding, and time before irreversible 

 starvation (Shirota, 1970; Ware, 1975; 

 Hunter, 1981; Marteinsdottir and Able, 

 1992). To explore whether differences 

 in potential early-life-stage survival 

 would exist among populations and (or 

 seasons ), the objective of our research 

 was to determine whether variations 

 in some early-life-stage characteristics 



Materials and methods 



We collected anchovy eggs from four 

 locations along the coastal zone (<20 

 nmi offshore ) off northern and central 

 Chile during the austral winter and 

 spring spawning seasons 1995-97 

 (Fig. 1). Eggs were collected with a 

 Calvet net (150 urn mesh) in Iquique 

 and Antofagasta (northern Chile), 

 with a standard conical net (330 um) 

 in Valparaiso and with either a Tucker 

 trawl (250 ;<m mesh) or a standard 

 bongo net ( 500 um) in Talcahuano. The 

 shorter axis of the anchovy eggs varied 

 from 0.563 mm (SD=0.032) in Iquique 

 to 0.657 mm (SD=0.027 ) in Talcahuano. 

 Consequently, egg extrusion from the 

 nets was ruled out as a potential source 

 of variation in our collections. Egg size 

 (length and width) was measured with 

 an ocular micrometer on a dissecting 

 microscope at 25x magnification. Upon 

 collection, all eggs were preserved in 

 5% buffered formalin. Previous studies 

 on anchoveta eggs have reported no egg 

 size shrinkage or shape changes with 

 formalin preservation (Fisher, 1958). 

 Similarly, reports on this species and 

 other anchovies show that egg-size 

 variations throughout their develop- 

 ment do not occur iEngr-aulis ringens, 

 Fisher. 1958; Engraulis japonica, Imai 

 and Tanaka, 1987). We tested this 

 hypothesis using eggs that we col- 

 lected in northern Chile and found no 

 size differences among different egg 

 stages (ANOVA. n=535, P=0.1176). 



Manuscript approved for publication 

 12 August 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish. Bull. 102:207-212 (2004). 



