Extreme Salmo: the Risk-Prone Life History of Marine-Phase Atlantic Salmon and its Implications for Natural Mortality
Although life history variation in Atlantic salmon (Salmo salar) has been examined in scores of scientific papers, the most remarkable features of the species ' life history have been ignored in the literature. This paper examines marine growth and pre-spawning fasting in Atlantic salmon, two t...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.618.953 http://www.npafc.org/new/publications/Technical Report/TR4/page 73-75(Cairns).pdf |
| Summary: | Although life history variation in Atlantic salmon (Salmo salar) has been examined in scores of scientific papers, the most remarkable features of the species ' life history have been ignored in the literature. This paper examines marine growth and pre-spawning fasting in Atlantic salmon, two traits which set Atlantic salmon radically apart from other fish species. Atlantic salmon pre-fishery abundance in the Northwest Atlantic has decreased markedly since the 1980s due to increased marine mortality (Cairns 2001). Understanding the life history strategies behind the Atlantic salmon's growth and fasting patterns may be the key to explaining the species ' decline. Juvenile Atlantic salmon grow at rates typical of other stream fishes, but growth rates increase dramatically after sea entry. Salmon in the Northwest Atlantic increase in weight 75-fold between river exit and return after 1 sea winter, and> 200-fold between river exit and return after 2 sea winters. These growth rates are two orders of magnitude faster than those of other fish (herring, mackerel, capelin) which occupy the same pelagic habitat (Fig. 1). Atlantic salmon typically return to natal rivers in early summer (early run) or in fall (late run). Adult Atlantic salmon stop feeding before they enter rivers, and continue to fast during their time in fresh water. The pre-spawning fast typically lasts about five months in early run fish. Late-run fish spend the summer at sea. Although they have the opportunity to feed during the pre-spawning summer, late-run fish are not larger than early-run fish (Fig. 2). This suggests that they either have a slower overall growth trajectory, or that they do not eat during the pre-spawning summer. Circulii spacing patterns in scales collected from late-run salmon returning to the Margaree River, Nova Scotia, suggest |
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