Improved forecasts of recreational western rock lobster ( Panulirus cygnus) catches in Western Australia, by predicting licence usage

Abstract

Recreational rock lobster fishers in Western Australia are required to purchase an annual licence. Between 3000 and 4000 randomly selected fishers are surveyed about their fishing activity at the end of each season. The responses are used to estimate the annual western rock lobster ( Panulirus cygnus) recreational catch and fishing effort. Catch has previously been shown to be significantly correlated with licence usage (the number of licences sold multiplied by the proportion used) and abundance of puerulus (the post-larval settling stage of rock lobster) settlement 3–4 years earlier and these variables have been used to predict future catches, with licence usage being assumed to have remained the same as the most recently completed season. In this study, a multiple regression incorporating the long-term trend (1986/1987 to 2001/2002 seasons) and puerulus settlement indices, found puerulus indices at Alkimos (Western Australia) 3–4 years earlier to be highly correlated with licence usage ( R 2=0.91). Based on this relationship it is predicted that licence usages will be approximately 31 000 in 2002/2003, 34 500 in 2003/2004, 34 000 in 2004/2005 and 32 000 in 2005/2006. The ability to predict licence usage means that future effort trends can now be used to forecast catch more accurately than has been possible in the past. Future recreational catch based on the predicted usage figures is forecast to increase from 545 t in 2001/2002 to 750 t in 2002/2003, 950 t in 2003/2004, and then decrease to 860 t in 2004/2005. Licence sales were strongly correlated with licence usage ( r=0.97), but were considered to be more complicated to reliably model than licence usage.