104 



Fishery Bulletin 92(1), 1994 



173°E 



I 

 175°E 



177°E 



Butaritari 



Abaiang 

 > Tarawa 



Gilbert Is 



2°N- 



(D 



.Abemama 



$><0 



o°- 



<%> <^ 



100 



kms 



1S0°E 



Gilbe rt Is 



,-, < *.r ^Solomon 



Australia 



N 



^Tuvalu 



Fiii 



% 



Figure 1 



Map of Gilbert Islands, Kiribati showing the four study sites 

 (Butaritari, Abaiang, Tarawa, and Abemama). Inset shows the ter- 

 ritorial boundary of Kiribati, the Gilbert Islands, and their posi- 

 tion in the Pacific. 



and 1990 were obtained from the Kiribati Govern- 

 ment Meteorological Division. 



Sampling 



Fifty to 1,000 Amblygaster sirm, Herklotsichthys 

 quadrimaculatus, and Spratelloides delicatulus were 

 collected monthly at one or more of four sites in 

 Kiribati (Butaritari, Abaiang, Tarawa, and 

 Abemama; Fig. 1) between August 1989 and May 

 1991. Additional samples of A. sirm and H. 

 quadrimaculatus were collected in November 1988 



and January 1989 from Tarawa. Fish 

 were caught by several methods at 

 each site. Most samples were collected 

 from the commercial tuna baitfish 

 catches each month at each site. 

 Supplementary samples were ob- 

 tained by beach-seining (H. 

 quadrimaculatus and S. delicatulus), 

 cast-netting (H. quadrimaculatus) in 

 shallow water during the day, or gill- 

 netting (25- and 38-mm stretched 

 mesh) at night near baitfishing opera- 

 tions. All fish were preserved in 70% 

 ethanol. 



Reproductive biology 



Laboratory studies All fish collected 

 from commercial baitfish sampling 

 were measured (standard length in 

 millimetres), and a subsample of 20 to 

 60 specimens weighed (±0.005 g). Go- 

 nads, otoliths, liver, and viscera were 

 removed and the amount of visible fat 

 subjectively estimated. Both ovaries 

 from the first 20 females of each spe- 

 cies at each site for each month were 

 dried of surface moisture, weighed 

 (±0.001 g) and stored in 4% formalin- 

 seawater for histology. Testes, ovaries 

 of other fish, liver, and the soma were 

 dried at 60°C to a constant weight. 

 Otoliths were used to estimate the 

 age (in days) of each fish by methods 

 outlined in Milton et al. ( 1993). Addi- 

 tional samples offish caught by other 

 methods were treated separately, but 

 in a similar way. We report only on 

 results of studies offish collected from 

 commercial samples unless otherwise 

 stated. 



For histological preparations, go- 

 nads were embedded in paraffin, sec- 

 tioned at 9 mm, and stained with Ehrlich's 

 haemotoxylin and eosin (McManus and Mowry, 

 1964). Gonad maturation stages were defined follow- 

 ing Cyrus and Blaber (1984) and Hunter and 

 Goldberg (1980), and were similar to those of 

 Moussac and Poupon (1986) for H. quadrimaculatus 

 from the Seychelles. We staged each gonad accord- 

 ing to the relative numbers of cells at each develop- 

 mental stage (Young et al., 1987; Table 1), and the 

 presence of any post-ovulatory follicles was noted. 

 The percentage of each histological section that cor- 

 responded to each developmental stage was subjec- 



2°S- 



