Abstract
Swordfish, Xiphias gladius (Linnaeus, 1758), is a commercially important species that is widely distributed throughout three oceans. This species inhabits oceanic waters with preferred environmental ranges and migrates vertically to the surface layer for feeding. However, the spatial distribution pattern and habitat preferences of swordfish have been rarely studied in the Pacific Ocean due to the wide geographic range of this species. This study examined the spatial distribution and preferred ranges of environmental variables for swordfish using two approaches, generalized additive models and habitat suitability index methods, with different spatio-temporal data resolution scales. Results indicated that sea surface temperature is the most important factor determining swordfish spatial distribution. Habitat spatial pattern and preferred environmental ranges, estimated using various modeling approaches, were robust relative to the spatio-temporal data resolution scales. The models were validated by examining the consistency between predictions and untrained actual observations, which all predicted a high relative density of swordfish in the tropical waters of the central Pacific Ocean, with no obvious seasonal movement. Results from this study, based on fishery and remote sensing data with wide spatial coverage, could benefit the conservation and management of fisheries for highly migratory species such as swordfish and tuna.
Highlights
Xiphias gladius (Linnaeus, 1758) is a highly migratory swordfish species that is widely distributed in the open waters of the three oceans outside of polar areas; it is occasionally found in the coastal waters of the Pacific Ocean [1]
Swordfish were discovered to aggregate in waters with high prey density that corresponded to preferred ranges in mixed layer depth (MLD) and sea surface height (SSH) [9]
Catch data were in terms of the number of fish caught in the longline fisheries, whereas effort was in terms of the number of hooks employed by these fleets
Summary
Xiphias gladius (Linnaeus, 1758) is a highly migratory swordfish species that is widely distributed in the open waters of the three oceans outside of polar areas; it is occasionally found in the coastal waters of the Pacific Ocean [1]. As an oceanic apex predator, this large species grows up to 450 cm in fork length and more than 650 kg in weight [2]. They inhabit waters deeper than 400 m during daytime and migrate vertically to the surface layer of the ocean, shallower than 100 m, for feeding during nighttime [3]. Rooker et al [7] and Hsu et al [8] demonstrated that the spatial pattern of high catch rates is related to various oceanographic variables, such as sea surface temperature (SST), sea surface salinity (SSS), and chlorophyll-a concentration (CHL). Swordfish were discovered to aggregate in waters with high prey density that corresponded to preferred ranges in mixed layer depth (MLD) and sea surface height (SSH) [9]
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