Use of charter boat data to infer the annual availability of black marlin, Makaira indica, to the recreational fishery off Cairns, Australia

Abstract

Catch data, recorded in daily diaries kept by the captains of charter boats in the recreational fishery that targets black marlin (Makaira indica) in the Cairns/Lizard Island region off north-eastern Australia, were used to calculate annual indices of fishing success (catch per day). Generalized Linear Models were used to investigate factors likely to influence catch rates, such as captain, area fished, water temperature, moon phase and the strength and direction of prevailing currents. Despite a high degree of inter-annual variability in the catch, results indicate that there has been a long-term decline of between 20–30% in estimated availability between 1970 and 1997. Models fitted to the data for the period 1987–1996 indicate that several environmental factors can have a significant influence on availability in any given year, with higher catch rates occurring close to a half moon and associated with water temperatures around 26.0–26.5°C. Catch rates for the period 1980–1997 were also found to be negatively correlated with longline effort levels within the inshore region close to the recreational fishery, though this correlation was not found to be significant.