Fishery ecology and oceanography of the prawn Penaeus merguiensis (de Man) in the Gulf of Papua: estimation of maximum sustainable yield and modelling of yield, effort and rainfall

Abstract

Annual fishing effort for banana prawns, Penaeus merguiensis (de Man), in the Gulf of Papua increased from low levels in 1974 to around the optimum level in 1978 and peaked at 95000 trawl-hours in 1989 before decreasing after the introduction of effort controls in 1988. Maximum sustainable yield of P. merguiensis was estimated at 559 ± s.e. 25 t (of tails) by linear regression of CPUE (U) on effort using the Schaeffer model. Optimum effort was estimated at 84·0 (± s.e. 11·8) 10³ trawl-hours, and an equation for the yield (C_E) for a given effort (E) was derived as C_E = 13·5E – (8·31 10^-2)E². Application of the CLIMPROD program to Gulf of Papua yield and effort and seasonal rainfall inputs resulted in validated modelling of the fishery. CLIMPROD selected a Schaeffer model for the CPUE–effort relationship (U = a + bE). When CLIMPROD incorporated rainfall (V), the model used was = UaV^(b+c) + dV^(2b)E (linear–exponential–exponential), where rainfall influences abundance and catchability. For 1974–93 overall, effort was by far the chief determinant of yield. The model using regionally averaged total rainfall in the fourth quarter and unstandardized effort data explained only an extra 5% of the variation in the following year’s catch over the model using effort alone. Standardization of effort data by 3% probably approximates the real effort applied more accurately than does recorded effort.