Quantifying the distribution of swordfish (Xiphias gladius) density in the Hawaii-based longline fishery

Abstract

The Hawaii-based longline fishery targeting bigeye tuna and swordfish is the most economically important fishery in Hawaii. An improved understanding of the distribution of swordfish within this fishery and how it changes in response to environmental conditions is critical for predicting potential climate change impacts to the fishery. The multi-species Vector-Autoregressive Spatio-Temporal (VAST) model was used to estimate abundance and density of swordfish within the Hawaii-based longline fishing grounds. Swordfish and bigeye tuna catch per unit effort were used in a spatial dynamics factor analysis to help estimate swordfish density in time periods when the swordfish fishery was closed. Although the model was unable to account fully for the significant changes in fishery regulations in 2000, it provided quantified estimates of swordfish density and distribution and information on how those distributions may change in response to environmental variables. Swordfish density center of gravity was found to correlate with the Southern Oscillation Index (SOI) averaged during the swordfish spawning season (April – July), with densities centered further north and east during positive SOI (cooler sea temperatures) and further south and west during negative SOI (warmer sea temperatures).