Seasonal, interannual and spatial variability in the reproductive dynamics of Penaeus merguiensis

Abstract

Penaeid prawns (shrimp) are short-lived and fecund, with a complicated life cycle that includes offshore spawning followed by a coastal or estuarine postlarval and juvenile phase. Factors affecting survival during the early life-history stages, and during movement between these stages, will affect variability in recruitment to the nursery ground, the offshore subadult and adult population, and, ultimately, catch. The inability to predict recruitment, and ultimately commercial offshore catch, has been complicated by an incomplete understanding of these factors. The reproductive dynamics of Penaeus (Fenneropenaeus) merguiensis were investigated by simultaneous adult and larval sampling on 66 lunar-monthly surveys from March 1986 to March 1992 in Albatross Bay, northeastern Gulf of Carpentaria, Australia. Egg production was seasonal, with the highest production from 6-mo-old newly recruited spawners, and another peak from 12mo-old spawners. Larval abundance (no. m-2) followed the same seasonal pattern as the abundance of eggs. However, interannual variation in egg and larval abundance was large, and there was a weak correlation between monthly egg and larval abundance. Larval abundance appeared to be further influenced by fluctuations in chlorophyll a concentration, a measure of food availability. There was evidence of a match/mismatch relationship between larval abundance and episodic chlorophyll increases. While there was no direct spawner (egg production)-fishery recruit relationship in P. merguiensis over the 6-yr study, there was a strong relationship between total larval abundance in spring and the size of the commercial catch 3 to 6 mo later. Therefore, factors affecting larval survival, including food availability, have significant implications for fishery production.