Determining summer residence status and vertical habitat use of sailfish (Istiophorus platypterus) in the Arabian Gulf

Abstract

Pop-up satellite archival tags (PSATs) were deployed on 18 sailfish in the Arabian Gulf between 2001 and 2005 to determine summer geoposition and habitat preference. Programmed releases following periods ranging from 110 to 156 d provided an aggregate total of 533 monitoring days of data. Three PSATs failed to report and nine released prematurely after periods ranging from 3 to 93 d. Four were recovered in gillnets after periods ranging from 39 to 90 d, and two transmitted after programmed releases of 127 and 128 d. Pooled archival data from recovered PSATs showed a cumulative mean distribution of 83.9% for total time spent in the upper 10 m, with no significant difference between day and night (χ24 = 0.84, p = 0.93). Depth ranged from 0 to 61 m, and ambient water temperature from 19.7°C to 30.1°C. Linear displacements ranged from 11 to 543 km and were all located inside the Gulf. Satellite- and light-level-derived geopositioning suggested that all fish remained in the Gulf. The two PSATs releasing on schedule validated summer residence inside the Gulf, providing further evidence in support of genetic analyses and conventional mark-recapture studies, which suggested that this billfish population confines itself year-round within a shallow marginal sea area. Preference for near-surface depths suggests a great susceptibility to capture by gillnets and other surface gears, raising concern for the effectiveness of regional management and conservation of the species. © 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.