Referee 2's review:

I find this a worthwhile piece of work, well overdue.

Introduction. I think the work could have been better embedded within the literature and I provide some examples below.

Most importantly, this is not the first study of isotopes in leatherbacks. In addition to that of Wallace et al, the authors are somewhat remiss in not citing Godley B.J., Thompson, D.R. Waldron, S. & Furness, R.W. 1998. The trophic status of marine turtles determined by stable isotope analysis. Marine Ecology Progress Series 166: 77-284. Which was the first such published work.

To say that there are only two strategies in N Atlantic leatherbacks may be somewhat of an over-simplification. I would point the authors to three forthcoming papers, freely avaialble online at

http://www.int-res.com/jo...

Doyle TK, Houghton JD, O'Súilleabháin PF, Hobson VJ, Marnell F, Davenport J, Hays GC Leatherback turtles satellite-tagged in European waters Clearly shows one individual moving from NE to tropical

Fossette S, Corbel H, Gaspar P, Le Maho Y, Georges JY
An alternative technique for the long-term satellite tracking of leatherback turtles. Makes the dichotomy in the northern turtles

Godley BJ, Blumenthal JM, Broderick AC, Coyne MS, Godfrey MH, Hawkes LA, Witt MJ Satellite tracking of sea turtles: Where have we been and where do we go next? Suggest that there are three strategies that females may show fidelity to within the Atlantic

An additional point re methods. I feel that the authors by trying to suggest that egg sampling is "less stressful" they are by inference suggesting that blood sampling is "stressful". I doubt that this is the case in the strictest sense. I would like to see this deleted.

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N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication the manuscript has been revised in light of these comments and to address other editorial requirements.