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Role of disease in abundance of a Pacific herring (Clupea pallasi) population

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Disease significantly affects population abundance of Pacific herring (Clupea pallasi). Comprehensive epidemiological study of the Pacific herring population of Prince William Sound, Alaska, U.S.A., from 1994 to 2000 included complete necropsy examination of 230–500 fish each spring and 40–160 fish each fall (total n = 2983 fish). Mortality is best estimated, through modifications of an age-structured assessment model, using a disease index that combines the prevalence of viral hemorrhagic septicemia virus (VHSV) with the prevalence of ulcers. Risk factors for an epidemic include poor body condition and abundant recruitment before spawning in the spring. Prevalence of the pathogen Ichthyophonus hoferi increased as fish aged, but changes in I. hoferi prevalence were not related to changes in population abundance. Disease that caused an epidemic in 1998 (VHSV and ulcers) nearly disappeared from the population when changes in abundance were detected by traditional stock assessment methods in 1999. Disease significantly affects recruitment — the two lowest recruitment estimates on record, in 1994 and 1999, followed increased natural mortality of adults in 1993 and 1998.

La maladie affecte de façon significative l'abondance des populations de harengs du Pacifique (Clupea pallasi). Notre étude épidémiologique détaillée de la population des harengs du Pacifique du détroit du Prince William, Alaska, États-Unis, de 1994 à 2000, comprenait l'examen complet par nécropsie de 230–500 poissons chaque printemps et de 40–160 poissons chaque automne, pour un total de 2983. La mortalité s'estime le plus précisément par un modèle d'évaluation structuré d'après l'âge qui utilise un indice de morbidité combinant la prévalence du virus de la septicémie hémorragique virale (VHSV) à celle des ulcères. Les facteurs de risque d'une épidémie incluent une mauvaise condition physique et un recrutement important avant la fraye au printemps. La prévalence de l'agent pathogène Ichthyophonus hoferi augmente avec l'âge des poissons, mais les changements dans la prévalence du pathogène ne sont pas reliés aux changements d'abondance de la population. La maladie (VHSV et ulcères) qui a causé une épidémie en 1998 avait presque disparu de la population lorsque des changements d'abondance de la population ont été détectés par des méthode classiques d'évaluation des stocks en 1999. La maladie affecte de façon significative le recrutement; en effet, les estimations de recrutement les plus faibles enregistrées l'ont été en 1994 et 1999 suivant une augmentation de la mortalité naturelle des adultes en 1993 et en 1998.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2003

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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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