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.
-end-
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

Related Turtle Articles from Brightsurf:

Sea turtle nesting season winding down in Florida, some numbers are up and it's unexpected
Florida's sea turtle nesting surveying comes to a close on Halloween and like everything else in 2020, the season was a bit weird.

Mystery over decline in sea turtle sightings
The number of sea turtles spotted along the coasts of the UK and Ireland has declined in recent years, researchers say.

Scientists develop new way to identify the sex of sea turtle hatchlings
A new minimally invasive technique greatly enhances the ability to measure neonate turtle sex ratios.

What can be learned from the microbes on a turtle's shell?
Research published in the journal Microbiology has found that a unique type of algae, usually only seen on the shells of turtles, affects the surrounding microbial communities.

Extinct giant turtle had horned shell of up to three meters
Paleobiologists from the University of Zurich have discovered exceptional specimens in Venezuela and Colombia of an extinct giant freshwater turtle called Stupendemys.

One single primitive turtle resisted mass extinction in the northern hemisphere
Sixty-six million years ago, in the emerged lands of Laurasia -now the northern hemisphere- a primitive land tortoise, measuring about 60 cm, managed to survive the event that killed the dinosaurs.

Turtle tracking reveals key feeding grounds
Loggerhead turtles feed in the same places year after year - meaning key locations should be protected, researchers say.

Trace Metals in Leatherback Turtle Eggs May Harm Consumers
Leatherback turtle eggs in the Panamanian Caribbean may be harmful to the health of consumers, due to the concentrations of trace metals found in them.

Fossil research unveils new turtle species and hints at intercontinental migrations
A multi-institution research team working with fossils archived at the Arlington Archosaur Site (AAS) of Texas has described four extinct turtle species, including a new river turtle named after AAS paleontologist Dr.

Turtle embryos play a role in determining their own sex
In certain turtle species, the temperature of the egg determines whether the offspring is female or male.

Read More: Turtle News and Turtle Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.