Milton et al.: Reproductive biology and egg production of three species of Clupeidae 



1 15 



in other parts of their range (Table 3). We found few 

 differences within Kiribati, but both species became 

 sexually mature and spawned at much shorter body 

 lengths than at other locations. Herklotsichthys 

 quadrimaculatus did not grow as large in Kiribati 

 as elsewhere (Milton et al., 1993). but the propor- 

 tion of maximum size at which this species matured 

 was similar throughout its range. Milton and Blaber 

 ( 1991) found regional differences in length at sexual 

 maturity in other small tropical clupeoids; they sug- 



gested these differences were consistent with the 

 hypothesis of Longhurst and Pauly (1987) that fish 

 of any species living in cooler water will grow to and 

 mature at a larger size through the interaction of 

 oxygen supply and demand. Our data on H. 

 quadrimaculatus is consistent with this hypothesis 

 — the other studies were all at sites at higher lati- 

 tudes than Kiribati, where the water temperature 

 is lower. Also, the proportion of maximum size at 

 which fish matured was similar at all locations, 

 despite the absolute differences in size at maturity 

 in Kiribati. 



By comparison, A. sirm matured at a smaller size 

 and grew to a larger size in Kiribati than at other 

 locations (Milton et al., 1993). The proportion of 

 maximum size at which fish matured was also lower 

 than found in previous studies and was less than the 

 proportion common to a wide range of clupeoids 

 (70%; Beverton, 1963). In response to severe fishing 

 pressure, the size and age at sexual maturity of 

 several sardine species have been found to decline 

 (Murphy, 1977). Presumably, this is because any 

 density-dependent effects are reduced during early 

 growth (Beverton and Holt. 1957; Ware, 1980). 

 Amblygaster sirm can have high or variable adult 

 mortality in Kiribati (Rawlinson et al., 1992), 

 favouring early maturation (Stearns and Crandall, 

 1984). 



Length at first spawning was a similar proportion 

 of maximum size for the three species and was con- 



