Researchers studying Loggerhead Turtles, Caretta caretta, have found that most adult turtles forage in the open ocean, with only the very largest foraging in coastal waters. This is different to what was previously thought, and has profound implications for the conservation of these turtles.
The study, published in the latest issue of Current Biology, says that although tbe protection of coastal areas may be attainable, the ocean-going turtles are dispersed over more than half a million square kilometers. So the largest turtles may be protected but the more numerous smaller adult turtles are at a very great risk from being caught by fisheries in the east Atlantic. Not deliberately, but as by-catch.
Previously it was thought that only juveniles foraged in the open ocean. Using satellite tracking, the new research shows that the majority of adults are also exposed to longline fisheries. The scientists conclude that fisheries in the east Atlantic will likely require complex and regionally tailored actions to protect the turtles.
Experiments over the last few years have shown that large “G”-shaped circle hooks effectively reduce turtle by-catch rates compared to smaller “J”-shaped hooks. Large circle hooks are effective without compromising commercial viability for some target species. Studies comparing small circle hooks (5.1 cm width or smaller) to smaller (4.1 cm width or smaller) J-shaped hooks found no significant difference in turtle bycatch rates. Other strategies include setting gear below the depths where turtles are in relatively high densities, using fish instead of squid for bait, single hooking fish bait versus threading the hook through the bait multiple times, timing the retrieval of line to minimize gear soak during the daytime and area and seasonal closures.
According to the WWF, some 260,000 loggerhead turtles are caught annually on longlines set for tuna, swordfish, and other fish.
Journal Source: Current Biology Volume 16, Issue 10 , 23 May 2006
Photo copyright Pedrín López, http://www.seaturtle.org/