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Individual variability in activity patterns of juvenile Atlantic salmon (Salmo salar) in Catamaran Brook, New Brunswick

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Abstract:

The activity of juvenile salmonids in streams varies between seasons, age classes, and times of day, but few studies have quantified the magnitude of individual variation in the behaviour of wild individuals. We monitored the activity patterns of 35 young-of-the-year (YOY) (fork length: 25.6–34.6 mm) and eight 1+ (fork length: 68.2–78.7 mm) Atlantic salmon (Salmo salar) over an 8-week summer field season. Age 1+ salmon were more active at night than during the day, whereas YOY fish were almost exclusively active during the day. However, daytime activity did not peak at 16–20 °C, the optimal water temperature range for growth determined in laboratory studies. Rather, the activity of 1+ fish peaked at 21 °C, whereas the activity of YOY fish continued to increase until 23 °C and then leveled off between 23 and 27 °C. There was also considerable individual variability within an age class in how fish responded to environmental variables that was often obscured by the average patterns. In a multiple logistic regression analysis for the activity of the 35 YOY, 18 responded significantly to time of day, 17 to water temperature, and 16 to day of the year. The causes of this individual variability and the consequences for growth and mortality deserve further study.

L'activité des jeunes salmonidés dans les cours d'eau varie en fonction des saisons, des classes d'âge et de l'heure de la journée; peu d'études ont cependant mesuré l'importance de la variation individuelle du comportement des poissons sauvages. Nous avons suivi les patrons d'activité de 35 jeunes saumons atlantiques (Salmo salar) de l'année (YOY) (longueur à la fourche: 25,6–34,6 mm) et de huit saumons d'âge 1+ (longueur à la fourche: 68,2–78,7 mm) durant une saison de terrain de huit semaines en été. Les saumons d'âge 1+ sont plus actifs la nuit que le jour, alors que les poissons YOY sont presque exclusivement actifs de jour. Cependant, l'activité de jour n'atteint pas son maximum à 16–20 °C, l'étendue des températures optimales de l'eau pour la croissance déterminée dans les études en laboratoire. Au contraire, l'activité des poissons d'âge 1+ est maximale à 21 °C, alors que celle des poissons YOY continue à augmenter jusqu'à 23 °C pour atteindre un plateau entre 23 et 27 °C. Il existe aussi au sein d'une même classe d'âge une importante variation individuelle de la réaction des poissons aux variables du milieu, qui est souvent camouflée par les patrons moyens. Dans une analyse de régression multiple logistique de l'activité des 35 poissons YOY, 18 réagissent significativement à l'heure de la journée, 17 à la température de l'eau et 16 au jour de l'année. Les causes de cette variabilité individuelle et ses conséquences sur la croissance et la mortalité requièrent des études additionnelles.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2007

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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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