Movements and habitat utilization of two longbill spearfish Tetrapturus pfluegeri in the eastern tropical South Atlantic Ocean

The longbill spearfish Tetrapturus pfleugeri Robins and de Sylva, 1963, is a small istiophorid billfish found in the Atlantic Ocean and adjacent seas that occurs as an infrequent by-catch in recreational and commercial pelagic fisheries. Although some data exist on diet and reproduction based on dead specimens, little is known of the species' habitat preferences or individual movement patterns. In 2004, two longbill spearfish were tagged with pop-up satellite archival tags (PSATs) near Ascencion Island in the South Atlantic for 11 d and 45 d. Individual movement tracks derived from light-based geolocation estimates suggested little relationship with sea surface temperature fronts, although both animals demonstrated a clear preference away from the west African subsurface hypoxic plume. Overall temperature at depth distributions for both fish were narrow; between 22-26 °C for 97% and 82% respectively of the total time at liberty durations. Almost all of the 8-h time-at-depth periods for both day and combined periods showed that these two fish remained within 150 m of the surface. However, time at depth utilization analyses suggest a slightly bimodal distribution, with the majority of the time at depths < 25 m and a secondary grouping at 50-100 m. Depth utilization data are consistent with the hypothesis that interactions between this species and deep-set pelagic longline fisheries for bigeye tuna in the eastern tropical South Atlantic occurs primarily at set and retrieval of the gear.