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The importance of recruitment for the production dynamics of stream-dwelling brown trout (Salmo trutta)

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Abstract:

The objective was to highlight the role of recruitment for production dynamics of stream brown trout (Salmo trutta). The analysis of 51 cohorts (hatched in 1986–1999) at four sites of Rio Chaballos (northwestern Spain) showed sinusoidal growth patterns with more intense growth in spring and summer and reduced growth in winter. Survivor abundance described two-phase trajectories over the lifetime (1000–1400 days after emergence). A first phase of negligible or no mortality was prolonged for 500–650 days. Severe mortality during the second phase differed among cohorts and among sites. Spatiotemporal variations in growth, mortality, density, spawner abundance, biomass, and production underlay variations in recruitment. Increased recruitment affected growth negatively (except at one site) and mortality positively. Cohort production decreased with increased growth at three sites but increased with increased growth at another site. Greater mortality typified the most productive cohorts. However, 90.8% and 83.6% of the variations in density and production, respectively, were explained by variations in recruitment. Thus, cohort size and production appeared to be determined by recruitment in which postrecruitment processes played a minor role. Recruitment reset the cohort's numerical and productive capacity, and increments in recruitment continued to increase cohort size and production over the recruitment magnitudes observed across sites and years.

Le but de cette étude est de mettre en évidence le rôle du recrutement sur la dynamique de la production de truites brunes (Salmo trutta) dans les cours d'eau. L'analyse de 51 cohortes (écloses en 1986–1999) à 4 sites du Rio Chaballos (nord-ouest de l'Espagne) révèle des patrons de croissance sinusoïdaux avec une croissance plus intense au printemps et en été et une croissance ralentie en hiver. L'abondance des survivants décrit une trajectoire en deux phases au cours de la vie (1000–1400 jours après l'émergence). Une première phase de mortalité nulle ou négligeable dure 500–650 jours. La mortalité importante durant la seconde phase diffère d'une cohorte à l'autre et d'un site à l'autre. Les variations spatio-temporelles de croissance, de mortalité, de densité, d'abondance des reproducteurs, de biomasse et de production sont sous-jacentes aux variations du recrutement. Une augmentation du recrutement a un effet négatif sur la croissance (excepté à un site) et un effet positif sur la mortalité. La production des cohortes diminue lorsque la croissance augmente à trois des sites, mais elle augmente en fonction de la croissance à l'autre site. Une mortalité plus importante caractérise les cohortes les plus productives. Cependant, respectivement 90,8 % et 83,6 % de la variation de la densité et de la production s'expliquent par des variations du recrutement. Ainsi, la taille et la production d'une cohorte semblent déterminées par le recrutement; les processus subséquents ne jouent qu'un rôle secondaire. Le recrutement rétablit le potentiel numérique et productif de la cohorte et les augmentations du recrutement continuent de faire augmenter la taille et la production de la cohorte dans la gamme des valeurs de recrutement observées au cours des années dans les divers sites.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2005

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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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