Abstract
Fisheries bycatch is a critical source of mortality for rapidly declining populations of leatherback turtles, Dermochelys coriacea. We integrated use-intensity distributions for 135 satellite-tracked adult turtles with longline fishing effort to estimate predicted bycatch risk over space and time in the Pacific Ocean. Areas of predicted bycatch risk did not overlap for eastern and western Pacific nesting populations, warranting their consideration as distinct management units with respect to fisheries bycatch. For western Pacific nesting populations, we identified several areas of high risk in the north and central Pacific, but greatest risk was adjacent to primary nesting beaches in tropical seas of Indo-Pacific islands, largely confined to several exclusive economic zones under the jurisdiction of national authorities. For eastern Pacific nesting populations, we identified moderate risk associated with migrations to nesting beaches, but the greatest risk was in the South Pacific Gyre, a broad pelagic zone outside national waters where management is currently lacking and may prove difficult to implement. Efforts should focus on these predicted hotspots to develop more targeted management approaches to alleviate leatherback bycatch.
Highlights
Populations of leatherback turtles, Dermochelys coriacea, have declined precipitously in recent decades in the Pacific Ocean [1,2], resulting in their listing as critically endangered by the International Union for the Conservation of Nature
Direct comparison of East Pacific (EP) and West Pacific (WP) nesting populations revealed that location, size and timing of predicted bycatch hotspots differed considerably, reflecting their use of different areas of the Pacific and further underscoring the need to approach these populations as separate management units [16]
Though this area was predicted to be of moderate bycatch risk, it occurred along a persistent migration path for nesting leatherbacks [14,17], representing a potential chronic threat during a critical phase in the life cycle of reproductive adult turtles
Summary
Populations of leatherback turtles, Dermochelys coriacea, have declined precipitously in recent decades in the Pacific Ocean [1,2], resulting in their listing as critically endangered by the International Union for the Conservation of Nature. Leatherbacks are the most widely distributed of sea turtles in the Pacific, and can be found in pelagic and neritic waters in tropical and temperate regions, both in the Northern and Southern Hemispheres [5] Their broad distribution and widespread occurrence in waters of numerous countries and international commons (i.e. high seas) complicates conservation and management efforts. Leatherbacks are captured in gillnet, trawl and longline gear in both largescale industrial and small-scale artisanal fisheries [8,9] Such assessments are typically made from observer and logbook data, which are sometimes voluntary and not always conducted with sufficient rigour to identify locations, timing and environmental conditions of bycatch [9]. We integrate information on leatherback distribution with ocean-wide data on industrial longline fishing effort to predict areas and times of potential interaction, with the aim of informing management and alleviating bycatch of this imperilled turtle. Even though bycatch in smaller-scale artisinal longline fisheries may have a significant impact on leatherback populations [20], here we focus only on largescale industrial longlines owing to the relative availability of public data covering broad spatial and temporal scales comparable with our turtle tracking data
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