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Changes in diel diving patterns accompany shifts between northern foraging and southward migration in leatherback turtles

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Abstract:

Diel diving patterns have been widely documented among plankton-feeding marine vertebrates. In many cases, these patterns have been interpreted as a response to the diel vertical migrations of prey. The leatherback turtle, Dermochelys coriacea (Vandelli, 1761), is a large marine predator that exploits gelatinous plankton in disparate foraging areas. Individuals of this species spend extended periods at northern latitudes before moving southward through pelagic waters. To identify and compare potential diel patterns of diving behaviour in temperate areas, where foraging has been observed, versus during southward migration, 15 subadult and adult leatherbacks were equipped with satellite-linked time–depth recorders off Nova Scotia, Canada. We observed variation in nocturnal versus diurnal behaviour, both at northern latitudes and during migration; however, diel differences in both diving and surface activity were much less pronounced while leatherbacks were in the north. We interpret the difference in leatherback diel diving regimen to reflect a response to changing resource conditions at these times, with leatherbacks foraging throughout the day and night at high latitudes, then changing to a bimodal pattern of diving during southward migration, with generally longer, deeper diving occurring during the night versus during the day. By quantifying diel changes in leatherback behaviour, we provide the first surface time correction factors based on multiple individuals for use in estimating abundance from aerial surveys.

Les patrons journaliers de plongée chez les vertébrés marins planctonophages ont été bien étudiés. Souvent, les patrons sont interprétés comme des réactions aux migrations verticales journalières des proies. La tortue luth, Dermochelys coriacea (Vandelli, 1761), est un prédateur marin de grande taille qui exploite le plancton gélatineux dans des aires d’alimentation disparates. Les individus de cette espèce passent de longues périodes dans les latitudes nordiques avant de se déplacer vers le sud dans les eaux pélagiques. Dans le but d’identifier et de comparer les patrons journaliers potentiels du comportement de plongée dans les zones tempérées où on observe de l’alimentation (par rapport aux patrons observés durant la migration vers le sud), nous avons muni 15 tortues subadultes et adultes d’enregistreurs de temps et de profondeur reliés à des satellites au large de la Nouvelle-Écosse, Canada. Nous avons observé une variation entre les comportements nocturne et diurne, tant dans les latitudes nordiques que durant la migration; les variations journalières d’activité en plongée et en surface sont, cependant, beaucoup moindres lorsque les tortues sont dans le nord. Nous interprétons les différences dans le régime journalier de plongée des tortues luth comme des réactions aux conditions changeantes des ressources à ce moment; aux latitudes élevées, les tortues s’alimentent tout au long de la journée et de la nuit; durant la migration vers le sud, elles adoptent un patron bimodal de plongée, avec généralement des plongées plus profondes et plus prolongées durant la nuit que durant le jour. En quantifiant les changements journaliers du comportement des tortues luth, nous fournissons les premiers facteurs de correction du temps passé en surface basés sur l’observation de plusieurs individus pour servir à estimer l’abondance à partir d’inventaires aériens.

Document Type: Research Article

Publication date: May 1, 2006

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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