Environmental influences on stock abundance and fishing power in the silver-lipped pearl oyster fishery

Abstract

Abstract Hart, A. M., Thomson, A. W., and Murphy, D. 2011. Environmental influences on stock abundance and fishing power in the silver-lipped pearl oyster fishery. – ICES Journal of Marine Science, 68: . Stock variability, fishing power, and the contributing environmental factors were examined for the Australian silver-lipped pearl oyster, Pinctada maxima. The approach was to compare the longer-term time-series of stock abundance derived from catch per unit effort against the shorter-term 0+ spat-settlement index to seek agreement on causal factors. Indices of stock abundance were established with generalized linear models that simultaneously examined the influence of technological and environmental factors, resulting in a predictive model with a 3-year forecast. The advent of global positioning systems caused a 30% increase in fishing power. A negative relationship between abundance and rainfall, and a positive relationship between abundance and temperature, was detected for both spat settlement and fishery abundance. Northerly winds (negative northings) from December to February significantly enhanced settlement, but easterly winds (negative eastings) in the main fishing month of May influenced fishing power positively. After standardizing for the effects of fishing power, a 150% increase in stock abundance of the exploited component of P. maxima stocks was detected between 2004 and 2009. A major contributor to this increase was an exceptionally high settlement of spat in 2005, associated with a rare combination of environmental conditions. Once this year class grows beyond the target size classes, abundance is predicted to decrease to the normal levels.