The life history of the protandrous tropical shad Tenualosa macrura (Alosinae : Clupeidae): Fishery implications

Tenualosa macrura is a tropical shad that was previously found throughout t he estuaries and coastal waters of Sumatra and Borneo where it formed the b asis of flourishing fisheries. The only viable fishery today has contracted to the Riau Province of Sumatra, Indonesia. To provide information for con servation and fisheries management, a two-year study of the biology, ecolog y and life history characteristics of T. macrura was conducted. The evidenc e from sizes of sexes, sex ratios and histology is that T. macrura is a pro tandrous hermaphrodite. It changes from male to female mainly between 14 an d 20 cm SL (standard length) (six months to one year in age), after the mal e has spawned.. Almost all fish in their second year are females; the speci es does not appear to live beyond two years. There is a regular movement of spawning males and females between the Strait of Malacca (salinity 28-30) and the spawning grounds in the sheltered straits (salinity 20-28) of Riau Province on each new and full moon. Their occurrence in the inshore straits leads to heavy fishing during these moon phases. The main nursery areas ap e the shallow coastal waters of the Strait of Malacca. The decline in catch es of T. macrura has probably been as a result of fishers intensively targe ting aggregations of spawning females. Furthermore, most are caught before spawning. It is postulated that the protandrous habit of this species, and its likewise endangered congener of Sarawak, T. toll, renders them more vul nerable to overfishing than is the gonochoristic and more widespread T. ili sha that is heavily fished from Burma through the Indian sub-continent to K uwait. (C) 1999 Academic Press.