Characteristics of the habitat depth for swordfish in the central Atlantic Ocean

Abstract:

Based on hook number information collected by scientific observers on the Chinese tuna longline vessels in the central Atlantic Ocean from 2007 to 2008 and from 2010 to 2011, the distribution of capture depth of swordfish (Xiphias gladius) was estimated by using catenary curve method. The depth range of the captured swordfish was from 124.6 to 280.5 m, with an average of 215.2 m and standard deviation of 46.5 m. With the increase of depths of hooks ,the proportion of swordfish in total catch increased to a maximum at the depth of 220 m to 250 m and then decreased. The proportion of female swordfish in catch increased with depths of hooks and then remained stable. The mean fork length of swordfish tended to increase with depths of hooks. This paper provided important information for improving our understanding of swordfish habitats and bycatch mitigation in the pelagic tuna fisheries.