Factors affecting year-to-year variation in the catch of banana prawns (Penaeus merguiensis) in the Gulf of Carpentaria, Australia

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Abstract
Annual catch of banana prawns (Penaeus merguiensis de Man) from the Gulf of Carpentaria, Australia, varied six-fold (range 1677–9705 t) over the period 1970 to 1979, although fishing effort remained relatively constant. Relationships between prawn catch and seasonal rainfall, river discharge, air temperature, wind speed and direction, numbers of spawning adults, and numbers of juveniles were determined for six regions of the Gulf using both single variable correlation analyses and multiple regression techniques. Spring, summer, and autumn rainfall were positively correlated with regional catches in the southern regions of the Gulf whereas summer rainfall was inversely related to catch in one northern region. In northern regions, wind and temperature were more closely related to prawn catches than rainfall. However, because the causal mechanisms for temperature and wind effects are unknown, descriptive regression models were developed for all areas using only rainfall variables. These models explained between 35% and 67% of the variation in regional catches. Because rainfall affects the emigration of juvenile prawns, estimates of the abundance of earlier life history stages were of little value in explaining subsequent catches. Predictive models based on rainfall data could provide estimates of catches in the southern regions of the Gulf up to six weeks prior to the prawn season each year. In northern regions, where annual variations in catches are less than those in southern regions, the most reliable estimate at this stage of data collection is the mean catch for the past seven years in each region. No long-term trends in prawn catches over the last decade have occurred that cannot be explained by variations in environmental variables over the same period, although recruitment overfishing cannot be completely ruled out.

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