An age- and sex-structured assessment model for American eels (Anguilla rostrata) in the Potomac River, Maryland
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چکیده
American eel (Anguilla rostrata) and European eel (Anguilla anguilla) populations have declined since the 1980s prompting concern about their status and the causes of decline, but stock assessment approaches to estimate effects of fishing on these populations are lacking. Since 1964, 16% of United States commercial American eel harvest came from the Potomac River, yet American eel abundance, production, and fishing mortality is poorly understood in this system. We developed an ageand sex-structured assessment model for 1980–2008 and compared results with the F50% biological reference point (BRP). The model included natural mortality, fishing mortality, and sexand age-specific maturation mortality and selectivity. Between 1980 and 2008 estimated recruitment, biomass, and abundance decreased 82%–89%. In all years since 1993, the exploitation rate exceeded the F50% BRP. The model was moderately sensitive to changes in natural mortality, standard deviation for fishery and recruitment catch-per-unit-effort indices, and initial fishing mortality. The multidecadal decline in recruitment in Chesapeake eels matches those reported elsewhere for American and European eels, suggesting large-scale processes have affected anguillid eel recruitment in the North Atlantic. Résumé : Les populations d’anguilles d’Amérique (Anguilla rostrata) et d’Europe (Anguilla anguilla) ont décliné depuis les années 1980, ce qui a généré des préoccupations sur leur statut et les causes de leur déclin; il n’existe, néanmoins, pas d’études d’évaluation des stocks pour estimer les effets de la pêche sur ces populations. Depuis 1964, 16 % de la récolte commerciale américaine d’anguilles d'Amérique s’est faite dans le fleuve Potomac, bien que l’abondance, la production et la mortalité due à la pêche dans ce système restent mal comprises. Nous avons mis au point un modèle d’évaluation structuré d’après l’âge et le sexe pour 1980–2008 et comparé nos résultats aux points de référence biologiques (BRP) F50%. Le modèle inclut la mortalité naturelle, la mortalité due à la pêche, ainsi que la mortalité reliée à la maturation et la sélectivité spécifiques à l’âge et au sexe. Entre 1980 et 2008, le recrutement, la biomasse et l’abondance estimés ont décru de 82–89 %. Au cours de toutes les années depuis 1993, le taux d’exploitation a dépassé le BRP F50%. Le modèle est modérément sensible aux changements dans la mortalité naturelle, la déviation standard dans les indices des pêches et de capture par unité d’effort du recrutement et la mortalité initiale de la pêche. Le déclin sur plusieurs décennies du recrutement des anguilles dans la baie de Chesapeake correspond à ceux signalés ailleurs pour les anguilles d’Amérique et d’Europe, ce qui laisse croire que des processus à grande échelle affectent le recrutement des anguilles de la famille des Anguillidae dans l’Atlan-
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