Interactive effects of substrate sand and silt contents, redd-scale hydraulic gradients, and interstitial velocities on egg-to-emergence survival of Atlantic salmon (Salmo salar)

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Abstract:

We conducted laboratory incubation experiments with Atlantic salmon (Salmo salar) eggs to test a number of hypotheses concerning the relative sensitivity of the incubating eggs to variations in silt (diameter < 0.063 mm) in interaction with sand (0.63 mm < diameter < 2 mm) fractions in the incubating gravels, as well as to different strengths of local hydraulic gradients pushing flow across the egg pocket. Our results show that variations of only a few percent of silt content can strongly degrade survival to emergence. Higher silt loadings (>0.5%) are detrimental to survival for all substrate mixtures, except those that are very sparse in sands (<5%). For sand contents over 10%, an increment of 1% silt has over three times the effect on survival as a 1% increment in sand. Increasing hydraulic gradients had a positive effect on median survival, but the effect depended both on the details of the fines composition and on the gradient level. Our results suggest that silt loadings over 1.5% in redds cannot easily be mitigated by stronger gradients. Our data conclusively show that there is no single threshold interstitial flow velocity that insures survival to emergence. Even when maintaining a constant interstitial velocity, survival tended to reduce in higher fines-content substrate.

Nous avons effectué en laboratoire une étude d'incubation d'œufs de saumon atlantique (Salmo salar) afin de tester la sensibilité relative des œufs aux variations du pourcentage de limon (le diamètre < 0,063 mm) et de sable (0,63 mm < le diamètre < 2 mm) dans le substrat d'incubation, ainsi qu'aux variations du gradient hydraulique. Nos résultats indiquent que des variations très faibles du contenu en limon réduisent fortement la survie à l'émergence. Des contenus en limon élevés (>0,5 %) réduisent la survie pour tout les substrats étudiés, sauf ceux ayant de très faibles contenus en sable (<5 %). Lorsque le contenu en sable est supérieur à 10 %, une augmentation de 1 % des limons a un effet sur la survie plus de trois fois supérieur à une augmentation comparable de sable. L'augmentation du gradient hydraulique augmente la survie médiane mais l'ampleur de l'effet dépend de la composition exacte en sédiments fins et du gradient hydraulique. Nos résultats suggèrent que des teneurs en limons supérieurs à 1,5 % sont difficilement compensables par un gradient hydraulique élevé. Les données montrent aussi l'inexistence d'un seuil unique de vitesse d'écoulement interstitiel permettant d'assurer la survie des œufs; même à vitesse intersticielle constante, la survie des œufs tend à diminuer avec une augmentation du contenu en fines.

Document Type: Research Article

Publication date: December 1, 2004

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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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