Seasonal, spatial and interannual variability in the reproductive dynamics of the grooved tiger prawn Penaeus semisulcatus in Albatross Bay, Gulf of Carpentaria, Australia: the concept of effective spawning

Abstract

An index of population fecundity based on the abundance and fecundity of spawners was used to describe the spawning patterns of a population of Penaeus semisulcatus de Haan in the Albatross Bay region of the Gulf of Carpentaria, Australia. Between March 1986 and March 1992, 66 monthly sampling cruises were completed and a total of 133238 prawns were caught in 1986 trawls. Subadult females from the spring (August–November) spawning recruit to the offshore population in summer (December–January). Some of these mature and spawn in late-summerautumn (January–March) at ∼6 mo old, but most spawn in spring (August–November) at ∼12 mo old. The subadult females from the late-summer-autumn spawning recruit to the population in May–July, and some spawn in spring (August–November) at ∼6 mo old. As a result there is a mixture of 6 and 12-mo-old spawners in spring. The effective spawning periods for stock renewal, based on subsequent larval, postlarval and juvenile abundances, and recruits, are spring (August to November) and late summer (January–February). In 2 of the 6 yr, the spring and late-summerautumn spawning patterns were clearly bimodal; in the other years the late-summer-autumn peak was less distinct, although spawning continued over this whole period. Both the absolute and relative sizes of the seasonal peaks varied between years. Population fecundity was found to be a function of the complex interactions of the abundance and size structure of the females and the proportion of spawners. P. semisulcatus moves offshore and disperses between February and May. By May, most of the adults that recruited the previous summer are located offshore in depths >40 m. After July, they move to shallower waters (<40 m). In September–October they spawn, together with the component of autumn recruits, in depths of 20 to 35 m. The variation in seasonal, spatial and size composition patterns of the spawners provides the basis for description of the subset of the overall spawning stock (“effective spawners”) that contributes to subsequent recruitment.