REPRODUCTIVE-BIOLOGY AND EGG-PRODUCTION OF 3 SPECIES OF CLUPEIDAE FROM KIRIBATI, TROPICAL CENTRAL PACIFIC

The spawning seasonality, fecundity, and daily egg production of three species of short-lived clupeids, the sardine Amblygaster sirm, the he rring Herklotsichthys quadrimaculatus, and the sprat Spratelloides del icatulus were examined in Kiribati to assess whether variable recruitm ent was related to egg production. All species were multiple spawners, reproducing throughout the year. Periods of increased spawning activi ty were not related to seasonal changes in the physical environment. S pawning activity and fish fecundity were related to available energy r eserves and, hence, food supply. The batch fecundity of A sirm and S. delicatulus also varied inversely with hydrated oocyte weight. The max imum 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 . delicatulus. Amblygaster sirm had the highest fecundity and potentia l lifetime egg production, but the number of eggs produced per kilogra m of fish was highest in the small sprat S. delicatulus. Monthly estim ates of the daily egg production of each species varied with the propo rtion of the population that was spawning. Estimates of egg production showed little similarity to the frequency distribution of birthdates back-calculated from length-frequency samples. The distribution of bac k-calculated birthdates confirmed 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 t hat successful spawning is likely, and so the level of recruitment is more dependent on post-hatching survival rates than on egg production.