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Temporal changes in ascendance and in-season exploitation of Atlantic salmon, Salmo salar, inferred by a video camera array

Authors

  • R. BORGSTRøM,

  • J. OPDAHL,

  • M.-A. SVENNING,

  • M. LÄNSMAN,

  • P. ORELL,

  • E. NIEMELÄ,

  • J. ERKINARO,

  • J. B. DEMPSON


Reidar Borgstrøm, Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, 1432 Ås, Norway (e-mail: reidar.borgstrom@umb.no)

Abstract

Abstract  Weekly exploitation rates of Atlantic salmon, Salmo salar L., in the River Utsjoki, Finland, were estimated from catch reports during the 2003, 2004, 2006 and 2007 seasons, and recordings of all Atlantic salmon ascending the river using a submerged video camera array. In all years, mean weekly fishing mortality rates were significantly higher in June than July to August, with a falling trend throughout the fishing season. Owing to overlap in size between one-sea-winter (1SW) and multi-sea-winter (MSW) salmon, the estimated fishing mortality rates were based on all sea-age categories combined. By the second week in June, 18.3–34.7% of large salmon (only MSW) had ascended, compared with 2.2–6.4% of small salmon (1SW and some MSW). Indirectly, the earlier start of ascent of large salmon to River Utsjoki indicated that in-river fishing mortality of MSW salmon is higher than for 1SW salmon. A later opening of the fishing season may be used to reduce the in-river fishing mortality, especially for the MSW component.

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