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Estimation of mortality of juvenile blacktip sharks, Carcharhinus limbatus, within a nursery area using telemetry data

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Abstract:

A population of young blacktip sharks (Carcharhinus limbatus) was monitored over three years to determine their mortality rates using a series of acoustic listening stations. Based on these data it was possible to use several mortality estimators, including indirect life history based methods and direct methods such as the Kaplan-Meier and SURVIV methods, to estimate natural, fishing, and total mortality. Kaplan-Meier (61–91%) and SURVIV (62–92%) methods provided nearly identical total mortality rates during the first six months of life. This agreement suggests that these estimates are accurate for this population. All natural and fishing mortality occurred within the first 15 weeks of the study. This suggests that young sharks are most vulnerable to all types of mortality during this period. Sharks that survived beyond the first 15 weeks successfully left the nursery and were presumed to have migrated southward during fall months. These results provide critical information concerning the early life history of sharks and the importance of nursery areas to the survival of young animals.

Un réseau de stations d'écoute nous a permis de suivre une population de jeunes requins bordés (Carcharhinus limbatus) pendant 3 ans pour en déterminer les taux de mortalité. Il a été possible avec ces données acoustiques d'utiliser divers estimateurs de la mortalité, en particulier des méthodes démographiques indirectes et des méthodes directes, telles que celle de Kaplan-Meier et SURVIV, pour estimer la mortalité naturelle, la mortalité due à la pêche et la mortalité totale. Les méthodes de Kaplan-Meier (61–91 %) et SURVIV (62–92 %) donnent des estimations presque identiques de la mortalité totale durant les premiers 6 mois de vie. Cet accord laisse croire que ces estimations sont exactes pour cette population. Toute la mortalité naturelle et la mortalité due à la pêche se sont produites pendant les 15 premières semaines de l'étude, ce qui fait penser que les jeunes requins sont vulnérables aux diverses causes de mortalité durant cette période. Les requins qui survivent au-delà de cette période initiale de 15 semaines quittent la zone d'alevinage et migrent sans doute vers le sud durant les mois d'automne. Ce sont là des renseignements essentiels sur les premières étapes du cycle biologique des jeunes requins et sur l'importance des zones d'alevinage pour la survie des jeunes.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2002

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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