Studies of the Costa Rican mahi mahi longline pelagic fishing fleet have shown that even though incidental capture of sea turtles is extremely high, the observed death rate upon catch of hooked turtles is almost zero.  Nevertheless, when the turtles are released from the hooks, injuries are sustained which can lead to death.

Yonat Swimmer and Richard Brill, researchers at the University of Hawaii, who develop methods to mitigate the impact of longline fishing on sea turtles, became interested in the opportunities Costa Rica offers for studying sea turtle post hooking mortality: the presence of a fishery where many sea turtles are captured, a longline fleet that is open to research and willing to collaborate (Papagayo Seafood and Nutria Marina S.A.), and a team of local researchers with experience in the issue of incidental capture of sea turtles (PRETOMA).
To conduct the research, sea turtles captured during longline operations, which had the hook deeply embedded in their throats, were tagged with satellite trackers.  Additional free swimming turtles were tagged with satellite trackers to be used as controls.

The satellite trackers are known as Pop Up Satellite Archival Tags (PSATs).  They record depth, temperature, and geographic position, to determine migratory patterns and associated environmental surroundings.  This data can provide the basis for improving management policies, and increasing acceptance of these measures on behalf of the fishermen.

The preliminary results of this study were presented during the 2nd International Fishers Forum in Honolulu, Hawaii, November 2002.  To quote these preliminary results, please use the following source:

Swimmer, Y., R. Brill, R. Arauz, L. Mailloux, M. Musyl, K. Bigelow, A. Nielsen, and J. Sibert. 2002. Use of pop up archival satellite tags to quantify mortality of marine turtles incidentally captured in longline fishing gear. 2nd International Fishers Forum, November, 2002. Western Pacific Fisheries Council. Honolulu, Hawaii.

Since November 2001, 9 sea turtles (olive ridleys and Pacific greens) have been tagged with PSATs.  Six were tagged after they were captured by longline gear, with the hook deeply embedded in their throat, while the other three were control turtles, captured while swimming freely.  The tags fell off after 6-8 weeks, much less than the expected one year.

These are the most probable routes of the 3 Olive Ridley control turtles based on the raw data provided and adjusted for error.  The daily diving patterns of the control olive ridleys show that these turtles normally dive to depths greater than 250 meters (almost 900 feet).

These are the most probable routes of 2 olive ridleys that had been captured by longline gear with hooks deeply embedded in their throats, and then released.  The daily diving patterns of one of these turtles shows it diving to depths no greater than 90 meters (300 feet).

Different methods of attaching the PSATs to the turtles’ carapaces are currently being study.  Furthermore, there are plans to study the effectiveness of devices known as “deehookers” which have been designed to remove hooks from turtles and reduce injury.

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