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 the estuaries and coastal waters of Sumatra and Borneo where it formed the basis of flourishing fisheries. The only viable fishery today has contracted to the Riau Province of Sumatra, Indonesia. To provide information for conservation and fisheries management, a two-year study of the biology, ecology and life history characteristics of T. macrura was conducted. The evidence from sizes of sexes, sex ratios and histology is that T. macrura is a protandrous hermaphrodite. It changes from male to female mainly between 14 and 20 cm SL (standard length) (six months to one year in age), after the male has spawned.. Almost all fish in their second year are females; the species 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 ape the shallow coastal waters of the Strait of Malacca. The decline in catches of T. macrura has probably been as a result of fishers intensively targeting 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 vulnerable to overfishing than is the gonochoristic and more widespread T. ilisha that is heavily fished from Burma through the Indian sub-continent to Kuwait. (C) 1999 Academic Press.