Reproductive Biology of Penaeus Esculentus (Haswell, 1879) and Metapenaeus Endeavouri (Schmitt, 1926) in Torres Strait

J. A. Keating, R. Watson, D. J. Sterling, (1990). “Reproductive Biology of Penaeus Esculentus (Haswell, 1879) and Metapenaeus Endeavouri (Schmitt, 1926) in Torres Strait.,” Torres Strait prawn project: A review of research 1986-88 (Queensland Fisheries, Brisbane, Australia)

In the past, management of the Torres Strait Prawn Fishery has relied on the reproductive biology and larval and juvenile abundance information on Penaeus esculentus, brown tiger prawn, from the Northern Prawn Fishery and the Queensland East Coast Prawn Fishery. Seasonal trawling closures in Torres Strait are adjusted to coincide with the main seasonal closure in these areas (Section 1 ). Metapenaeus endeavouri, endeavour prawn is often taken in association with P. esculentus (Grey et al. 1983). Although M. endeavouri is a major contributor to the commercial prawn landings of Torres Strait, very little information on its reproductive biology is available compared with P. esculentus. As the commercial catch of the Torres Strait Prawn Fishery increases (Section 2), knowledge of the reproductive biology of the penaeid prawns present in Torres Strait is required for management purposes. The reproductive biology of P. esculentus has been investigated in the Gulf of Carpentaria (Northern Prawn Fishery) (Buckworth 1985, Robertson et al. 1985, Crocos 1987b), Exmouth Gulf (Western Australia) (Penn and Caputi 1986) and the Low Isles (Queensland East Coast Fishery) (O’Connor 1979). Somers et al. (1987), investigated the reproductive activity of P. esculentus and M. endeavouri in Torres Strait. Interpretation of this study was restricted due to the three-monthly interval between sampling periods (Courtney and Dredge 1988). To enable documentation of the reproductive patterns and spawning seasons for the commercial prawn species in Torres Strait, an egg production index or a PFI (Population Fecundity Index) has been estimated. Population fecundity is the sum of the fecundities of all the females in a population (Bagenal 1973) and can be expressed in terms of an index of population fecundity (PFI) which is the number of eggs produced or potentially produced by a population. This measure has been used in combination with estimates of spawning frequency to document spawning seasons (Penn 1980). Past calculationsof a PFI for penaeid species (Penn 1980, Crocos and Kerr 1983, Crocos 1987a and 1987b, Courtney and Dredge 1988) have incorporated the proportion of female spawners in the population, their length distribution and the relationship between an individual female’s fecundity with its carapace length. The PFI calculated in this study does not incorporate the proportion of female spawners in the population but uses the number of female prawns with mature ovaries per square metre of seabed swept by trawl nets as estimated from our surveys. This method is equivalent to the methods used in other reproduction studies on P. esculentus (O’Connor 1979, Buckworth 1985, Robertson et al. 1985), except these studies identified spawning peaks from the proportion of females with mature ovaries in a population (Crocos 1987a). To assess the true reproductive potential of a female prawn, the probability that it will be inseminated and therefore have fertile eggs must be determined. Crocos and Kerr (1983), Crocos (1987a and 1987b) and Courtney and Dredge (1988) studied the proportion of inseminated female penaeids but did not, however, incorporate this information into their egg production index or PFI. In this study, probability of insemination of ripe females has been incorporated into the PFI calculations. The aim of this report is to investigate the reproduction dynamics of both species to facilitate study of spawning seasonality and spawning areas for future management of the Torres Strait Fishery.