A dichotomy in migration patterns found for sea turtles in east Atlantic

May 22, 2006

Studying members of a large population of loggerhead sea turtles that nest on the Cape Verde islands off of West Africa, researchers have found an unexpected dichotomy in turtle behavior: While some turtles leave the nesting grounds to feed on bottom-dwelling sea life in shallow coastal waters, others leave Cape Verde to roam the much deeper open ocean along the African coast and exhibit a distinct feeding strategy. Interestingly, while adults compose both groups, the coastal feeding strategy correlates with larger animal size. These new findings revise our understanding of the turtle's life history and indicate that a multifaceted approach to fishing regulation--in both coastal and oceanic waters--will be required to effectively conserve these animals.

The findings are reported by Brendan Godley and colleagues at the Marine Turtle Research Group at the University of Exeter in Cornwall, Michael Coyne of the Marine Geospatial Ecology Lab at Duke University, and other members of an international team of researchers. The paper appears in the May 23rd issue of Current Biology.

Past studies had indicated that the loggerhead sea turtle (Caretta caretta), which reaches sexual maturity at about 30 years of age, typically undergoes a shift from an oceanic juvenile stage to a shallow-water, coastal adult stage. But the new findings--obtained by newly-improved methods for satellite tracking of the adult turtles' geographical movements and diving patterns--show that the sexually mature adult population also includes oceanic animals and thereby reveal that adults in the eastern Atlantic occupy very different habitats and undertake two distinct foraging strategies.

The differing strategies correlate with body size, which may be linked to the different diets of the two groups. Turtles migrating to shallow coastal waters-the so-called neritic environment-were larger, and they feed on the arthropods and mollusks that are normally abundant in this food-rich ecosystem. In contrast, adults foraging in the open ocean are smaller, have a more limited capacity for diving, and most likely feed on a somewhat different set of prey that includes small, floating plants and animals.

Importantly, the correlations in animal size and foraging strategy suggest that the majority of adults in the Cape Verde population may undertake the oceanic strategy, rather than the primarily coastal existence previously thought to characterize adulthood. This means that two adult populations will need to be monitored for conservation efforts. And critically--because commercial and artisanal fishing occur in both the open ocean and coastal waters--the findings indicate that appropriate measures will be needed to regulate fishing efforts to reduce by-catch in the different environments. The fact that the oceanic adults were found in a large area, including international waters and waters from Mauritania to Guinea Bissau, indicates that efforts toward regulation and population monitoring will need to take place on a large scale.
The researchers include Lucy A. Hawkes, Annette C. Broderick, and Brendan J. Godley of the University of Exeter, Cornwall Campus in Penryn, United Kingdom; Michael S. Coyne of Duke University in Durham, NC; Matthew H. Godfrey of the North Carolina Wildlife Resources Commission in Beaufort, NC; Luis-Felipe Lopez-Jurado, Pedro Lopez-Suarez, and Nuria Varo-Cruz of Universidad Las Palmas de Gran Canaria in Las Palmas de Gran Canaria, Spain; Sonia Elys Merino of the Instituto Nacional de Desenvolvimento das Pescas in Sao Vicente, Islas de Cabo Verde.

L.A.H. is supported by a University of Exeter Postgraduate Scholarship and the Anning-Morgan Bursary. B.J.G. and A.C.B. acknowledge the additional support of the Darwin Initiative, European Social Fund, and the Overseas Territories Environment Programme. Additional support was provided by the Large Pelagics Research Center at the University of New Hampshire through National Oceanographic and Atmospheric Agency award NA04NMF4550391.

Hawkes et al.: "Phenotypically Linked Dichotomy in Sea Turtle Foraging Requires Multiple Conservation Approaches." Current Biology 16, 990-995, May 23, 2006. DOI 10.1016/j.cub.2006.03.063 www.current-biology.com

Author Contact:
Brendan J. Godley, University of Exeter, Cornwall Campus in Penryn, United Kingdom at +44 01326 371 861; bgodley@seaturtle.org
Michael S. Coyne, Duke University in Durham, NC at +919-613-8119; out of hours +301-221-9952; mcoyne@seaturtle.org.

Cell Press

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