Biology of fish associated with moored fish aggregation devices (FADs): implications for the development of a FAD fishery in New South Wales, Australia

Abstract

Abstract The number of pelagic fish were counted around fish aggregation devices (FADs) moored 3 (inshore) or 10 km (offshore) from the coast on the continental shelf off Sydney, Australia. Visual counts were made on 81 separate days periodically from April 1999 to April 2002 to estimate abundance and size of dolphinfish (Coryphaena hippurus) and kingfish (Seriola lalandi). Dolphinfish were also collected from around FADs off Sydney and Port Stephens for analysis of sex ratio, stomach contents, age and spawning period. Occurrence of both species at FADs was seasonal. Abundance of dolphinfish was 2–8 times higher at offshore than inshore FADs in summer and autumn, respectively. Attraction of kingfish was the greatest in summer but was not affected by cross-shelf position. Size and age data indicated most FAD-associated dolphinfish and kingfish were immature juveniles. Sex ratios of dolphinfish captured at FADs were significantly skewed; over two females were captured for every male, probably due to behavioral differences in attraction to FADs. Based on the biological data, the most effective FAD deployment strategy to enhance the fishery for dolphinfish would be to place FADs offshore in summer and autumn. As large catches of dolphinfish are frequently made at FADs, two females are caught for every male, and limited information exists to estimate dolphinfish stocks, establishment of a bag limit would be a conservative management option. Moreover, management strategies to minimize by-catch of juvenile kingfish that aggregate at FADs should be considered.