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Aquaculture Environment Interactions

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AEI 11:417-427 (2019)  -  DOI:

Swimming with the fishes: validating drift diving to identify farmed Atlantic salmon escapees in the wild

S. Mahlum1,2,*, H. Skoglund1, T. Wiers1, E. S. Norman1, B. T. Barlaup1, V. Wennevik3, K. A. Glover2,3, K. Urdal4, G. Bakke3, K. W. Vollset1

1NORCE Norwegian Research Centre, LFI, Nygårdsgt. 112, 5008 Bergen, Norway
2Department of Biology, University of Bergen, Thormøhlensgate 53 A & B, 5006 Bergen, Norway
3Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway
4Rådgivende Biologer AS, Edvard Griegs vei 3, 5059 Bergen, Norway

ABSTRACT: Escaped farmed Atlantic salmon Salmo salar interbreeding with wild conspecifics represents a threat to the genetic integrity and viability of wild populations. Therefore, it is necessary to accurately quantify escapees in riverine systems to monitor and mitigate interactions with wild conspecifics. Drift diving surveys are presently used in Norway to quantify the number of wild and escaped farmed salmon in rivers. However, limited information is available on the validity of the method for distinguishing escapees from wild conspecifics. Comparing the proportion of escapees calculated from drift diving (mean = 8.5%) and net captures (mean = 8.6%), we found that drift diving was well correlated with net captures (adj. r2 = 0.79). Furthermore, scale analysis from an independent data set demonstrated a 98% true positive rate when identifying and capturing farmed escapees during drift diving. The results of this study indicate that drift diving is an accurate and robust method for quantifying escaped farmed salmon, at least in rivers where observation conditions are adequate for snorkeling. In general, drift diving can be a valuable tool for stakeholders to quickly assess broad spatial extents with limited time and resources.

KEY WORDS: Snorkeling · Domesticated salmon · Aquaculture · Bayesian · Method comparison · Escaped farmed salmon · Mitigation

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Cite this article as: Mahlum S, Skoglund H, Wiers T, Norman ES and others (2019) Swimming with the fishes: validating drift diving to identify farmed Atlantic salmon escapees in the wild. Aquacult Environ Interact 11:417-427.

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