Blue sprat Spratelloides robustus (Clupeidae: Dussumieriinae): a temperate clupeoid with a tropical life history strategy?

Abstract

This article describes the life-history strategy of the blue sprat Spratelloides robustus in South Australia and compares the demographic traits observed with those of other clupeoids. Validation studies that involved marking the sagittae of captive fish with oxy-tetracycline suggested that growth increments are deposited daily. The oldest fish examined was 82 mm caudal fork length and 241 days old, which suggests S. robustus may live for less than 1 year. Growth rates were high during larval stages (0.34 mm day )1 ) and remained high throughout juvenile (0.33 mm day )1 ) and adult stages (0.19 mm day )1 ). S. robustus reached 50% ma- turity at approximately 60 mm caudal fork length after approximately 135 days. Spawning occurred from Oc- tober to February (spring to late summer) and larvae were found mainly in Spencer Gulf, Gulf St Vincent, and Investigator Strait. Females spawned multiple batches of demersal eggs every 1-2 days. Batch fecundities were low (mean=756, SD=341) and increased linearly with length and weight. The life history of S. robustus is dissimilar to other small to medium-sized temperate clupeoids, but similar to those of many small sub-trop- ical and tropical clupeoids, including other Spratelloides species. Gulf St Vincent and Spencer Gulf may be considered to be ''seasonally subtropical systems'' in an otherwise temperate region that support a suite of species, including S. robustus, that have life-history strategies similar to those of sub-topical and tropical taxa.