Effects of environmental variables on catch rates of yellowfin tuna (Thunnus albacrares) in waters near Cook Islands

Abstract:

To better understand the effects of environmental variables on catch rate of yellowfin tuna (Thunnus albacrares) is beneficial to increasing the yellowfin tuna catch rate and reducing the bycatch rates of other non-target species in the longline fisheries. In this study, the catch rate of yellowfin tuna and environmental variables were collected from longlining surveys in waters near Cook Islands from Sep. 8^th, 2013 through Dec. 31^th, 2013, including hook depth data, temperature, chlorophyll-a concentration, current, operating parameters, and catch data. Stepwise regression of DPS was used to develop the hook depth calculation model. Statistics and clustering analysis were used to analyze the effects of environmental variables on yellowfin tuna catch rate. Results showed that the depth, temperature, chlorophyll-a concentration, east-west direction current, south-north direction current, vertical and horizontal direction current related with the high catch rate of yellowfin tuna were 120-160 m, 21-22℃, 0.32-0.36 μg/L and 0.40-0.44 μg/L, -0.20-0.10 and 0.00-0.20 m/s, -0.10-0.20 m/s, -0.10-0.06 m/s and 0.02-0.06 m/s, 0.20-0.30 m/s, respectively. Results suggest that the hook numbers should be increased in ranges of the water depth, temperature, chlorophyll-a concentration, and current related with the high yellowfin tuna catch rate when fishing in the waters near Cook Islands and targeting yellowfin tuna.