Review of potential line-transect methodologies for estimating abundance of dolphin stocks in the eastern tropical Pacific

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Cleridy E. Lennert-Cody
Stephen Terrence Buckland
Tim Gerrodette
Andrew Webb
Jay Barlow
Peter Fretwell
Mark N Maunder
Toshihide Kitakado
Jeffrey E. Moore
Michael D. Scott
Hans Julius Skaug

Abstract

A twelve-year hiatus in fishery-independent marine mammal surveys in the eastern tropical Pacific Ocean (ETP), combined with a mandate to monitor dolphin stock status under international agreements and the need for reliable stock status information to set dolphin bycatch limits in the tuna purse-seine fishery, has renewed debate about how best to assess and monitor ETP dolphin stock status. The high cost of replicating previous ship-based surveys has intensified this debate. In this review, transect methods for estimating animal abundance from dedicated research surveys are considered, with a focus on both contemporary and potential methods suitable for surveying large areas for dolphin species that can form large, multi-species aggregations. Covered in this review are potential improvements to the previous ship-based survey methodology, other ship-based methods, alternative approaches based on high-resolution imagery and passive acoustics, and combinations of ship-based and alternative approaches. It is concluded that for immediate management needs, ship-based surveys, with some suggested modifications to improve precision, are the only reliable option despite their high cost. However, it is recommended that a top research priority should be development of composite methods. Pilot studies on the use of high-resolution imagery and passive acoustics for development of indices of relative abundance to be used in composite methods should be part of any future ship-based survey efforts.

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How to Cite
1.
E. Lennert-Cody C, Terrence Buckland S, Gerrodette T, Webb A, Barlow J, Fretwell P, N Maunder M, Kitakado T, E. Moore J, D. Scott M, Julius Skaug H. Review of potential line-transect methodologies for estimating abundance of dolphin stocks in the eastern tropical Pacific. JCRM [Internet]. 2023 Jan. 24 [cited 2023 Feb. 8];19(1):9-21. Available from: https://journal.iwc.int/index.php/jcrm/article/view/411
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