Abstract. — The spawning 

 seasonality, fecundity, and daily 

 egg production of three species of 

 short-lived clupeids, the sardine 

 Amblygaster sirm, the herring 

 Herklotsichthys quadrimaculatus, 

 and the sprat Spratelloides 

 delicatulus were examined in 

 Kiribati to assess whether vari- 

 able recruitment was related to 

 egg production. All species were 

 multiple spawners, reproducing 

 throughout the year. Periods of 

 increased spawning activity were 

 not related to seasonal changes in 

 the physical environment. Spawn- 

 ing activity and fish fecundity 

 were related to available energy 

 reserves and, hence, food supply. 

 The batch fecundity of A. sirm and 

 S. delicatulus also varied inversely 

 with hydrated oocyte weight. 



The maximum reproductive life 

 span of each species was less than 

 nine months and averaged two to 

 three months. Each species had a 

 similar spawning frequency of 

 three to five days, but this varied 

 more in A. sirm and S. delica- 

 tulus. Amblygaster sirm had the 

 highest fecundity and potential 

 lifetime egg production, but the 

 number of eggs produced per ki- 

 logram of fish was highest in the 

 small sprat S. delicatulus. 



Monthly estimates of the daily 

 egg production of each species 

 varied with the proportion of the 

 population that was spawning. 

 Estimates of egg production 

 showed little similarity to the fre- 

 quency distribution of birthdates 

 back-calculated from length-fre- 

 quency samples. The distribution 

 of back-calculated birthdates con- 

 firmed that fish spawned in all 

 months, but the proportion born 

 each month varied widely from 

 species to species and year to year. 

 The reproductive strategy of these 

 species ensures that successful 

 spawning is likely, and so the 

 level of recruitment is more de- 

 pendent on post-hatching survival 

 rates than on egg production. 



Reproductive biology and 

 egg production of three species of 

 Clupeidae from Kiribati, 

 tropical central Pacific 



David A. Milton 

 Stephen J. M. Blaber 

 Nicholas J. F. Rawlinson 



CSIRO Division of Fisheries. Marine Laboratories, 

 RO. Box 1 20, Cleveland, Queensland 4 1 63, Australia 



Manuscript accepted 24 September 1993 

 Fishery Bulletin 92:102-121 (1994) 



The sprat Spratelloides delicatulus, 

 the herring Herklotsichthys quadri- 

 maculatus, and the sardine Ambly- 

 gaster sirm are the dominant tuna 

 baitfish species in the Republic of 

 Kiribati (Rawlinson et al., 1992). 

 All three species inhabit coral reef 

 lagoons and adjacent waters. 

 Sprats school in shallow water 

 around reefs and adjacent seagrass 

 during the day. Herring also form 

 dense schools in shallow water 

 along the shoreline and among 

 reefs during the day (Williams and 

 Clarke, 1983). Unlike the other 

 species, sardines school near the 

 bottom of the lagoon during the day 

 (Conand, 1988). All species disperse 

 into the mid and upper waters of 

 the lagoon during the night to feed 

 and become available to the com- 

 mercial fishery. 



A major source of lost fishing 

 time by pole-and-line vessels in 

 Kiribati has been irregular baitfish 

 catches (Maclnnes, 1990). These 

 important tuna baitfish species 

 have shown large seasonal and 

 interannual fluctuations in abun- 

 dance since they were first re- 

 corded during the 1940s (McCar- 

 thy, 1985 1 ; Rawlinson et al., 1992). 

 Both A. sirm and H. quadrima- 

 culatus disappear from baitfish 

 catches for variable periods and 

 can be absent for months or years 

 (Kiribati Fisheries Division, 1989 2 ). 



Changes in abundance may be 

 related to variable or irregular re- 

 cruitment, because many clupeoids 

 (especially clupeids and engraulids) 

 have little capacity to compensate 

 for environmental variation during 

 the period of peak spawning and egg 

 production (Cushing, 1967, 1971). 



Most clupeids, including some 

 tropical species, are multiple 

 spawners (Alheit, 1989). Multiple 

 spawning should be advantageous 

 for short-lived species because it 

 enables them to maintain rela- 

 tively stable population sizes in 

 unpredictable environments 

 (Armstrong and Shelton, 1990). 

 Multiple spawning has been estab- 

 lished for few tropical clupeids 

 (e.g., Sardinella brasiliensis; Isaac- 

 Nahum et al., 1988). Of the three 

 major baitfish species in Kiribati, 

 only S. delicatulus has been shown 

 to be a multiple-spawner (Milton 

 and Blaber, 1991). All three species 

 are subject to high natural mortal- 

 ity in Kiribati (Rawlinson et al., 

 1992), thus lifetime egg production 



1 McCarthy, D. 1985. Fishery dynamics and 

 biology of the major wild baitfish species 

 particulary Spratelloides delicatulus, from 

 Tarawa, Kiribati. Kiribati Fisheries Div., 

 Tarawa, Kiribati, 53 p. 



2 Kiribati Fisheries Division. 1989. Fisher- 

 ies Division 1989 Annual Rep., Ministry 

 of Natural Resources Development, 

 Tarawa, Kiribati, 38 p. 



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