PIFSC Sea Turtle Longline Research EA June 1, 2009
from the hook, often avoiding the hook. However, when squid is used as bait, they line up the squid with their flippers and gulp it down whole, along with the hook. Even turtles hooked or entangled but released alive may subsequently die due to internal injuries and/or secondary infections. The risk of mortality for sea turtles captured in pelagic longline fisheries is affected by the level of hook ingestion, with fully ingested hooks believed to cause mortality and handling while removing turtles from the line either in the water or after being brought on board increasing the risk (Watson et al. 2003, Watson et al. 2004a, Gilman et al. 2007, Read 2007).
Although adult leatherback and juvenile loggerhead turtles are the species most at risk worldwide for interaction with shallow-set longline gear in mid-ocean because they spend more of their lives in pelagic habitats than other sea turtles, other species are caught as well (Polovina et al. 2003, Gilman et al. 2006, NMFS 2008a). In temperate waters such as around the Hawaiian Islands, olive ridley turtles are often the species of turtle most frequently caught by deep-set longline gear targeting tuna. In the tropics, olive ridley capture rates are especially high in many artisanal fisheries off the Pacific coast of Latin America (Arauz et al. 2000, Largacha et al. 2005, Swimmer et al. 2005, Swimmer et al. 2006). Approximately 75% of the olive ridley turtles taken in the Hawaii deep-set longline fishery originate in the eastern Pacific Ocean (NMFS 2005, 2008b).
Beverly and Chapman (2007) compiled the results of various studies to identify the following Bycatch per Unit Effort (BPUE; catch of sea turtles per 1,000 hooks). A selection from this table (eliminating those with missing data and/or selecting studies with the highest number of hooks) indicates that BPUE in the Mediterranean Sea is comparatively high, BPUE in an artisanal fleet (smaller boats fishing along the coastline of Costa Rica) is also high, and BPUE in the U.S. fleets in both the Atlantic and Pacific Oceans prior to 2004 (before regulations requiring large circle hooks baited with fish were implemented) was also relatively high (Table 1). The summary of sea turtle bycatch studies compiled by Beverly and Chapman (2007) found that the Hawaii-based longline fishery bycatch (measured in terms of bycatch per unit effort; BPUE) of all sea turtle species was 0.06 compared to foreign longline fishery fleets, which had much higher BPUE, varying from 0.3 to almost 20 turtles per 1,000 hooks. The major finding of a study conducted by Bartram and Kaneko (2004) was that Hawaii’s longline fishery has a lower CPUE/BPUE ratio of finfish to sea turtles compared to most competing pelagic longline fisheries.
Some attempts to conserve Pacific sea turtles have focused on unilaterally closing commercial fisheries or areas to commercial fishing. However, with transboundary species such as turtles migrating across many nations’ EEZs and the high seas, fish formerly caught in Hawaii-based fisheries with high levels of regulation and low levels of bycatch are likely to be caught by other nations with higher levels of bycatch and imported back into the nation with the closed fishery (market transfer effect). If U.S. demand for swordfish remains high and fewer fish are caught by the Hawaii-based fishery because of closures, reliance on imports from nations having higher bycatch rates would most likely increase. The main sources of imports during the 2001 to 2004 closure of the Hawaii-based shallow-set longline fishery were Mexico, Panama, Uruguay, Brazil, Costa Rica, New Zealand/Cook Islands, Viet Nam, and South Africa, all of which have higher sea turtle bycatch (in terms of BPUE). A study of the market transfer effect during the closure of the Hawaii-based shallow-set longline fishery resulted in an estimated transfer of 1,602 mt of