Domesticated escapees on the run: the second-generation monitoring programme reports the numbers and proportions of farmed Atlantic salmon in &amp;gt;200 Norwegian rivers annually

Kevin A Glover ,Håkon Otterå ,Øyvind Kanstad-Hanssen ,Monica Favnebøe Solberg ,Øystein Skaala ,Ola Håvard Diserud ,Peder Fiske ,Rune Muladal ,Ingrid Solberg ,Anders Lamberg ,Bjørn Torgeir Barlaup ,Kurt Urdal ,Kjetil Hindar ,Håvard Lo ,Bjørn Florø-Larsen ,Gunnar Bakke ,Harald Sægrov ,Sten Karlsson ,Mikko Heino ,Tor F Næsje ,Helge Skoglund ,Ove Skilbrei ,Tonje Aronsen ,Vidar Wennevik

doi:10.1093/icesjms/fsy207

Abstract

Abstract Norway is the world’s largest producer of farmed Atlantic salmon and is home to ∼400 rivers containing wild salmon populations. Farmed escapees, a reoccurring challenge of all cage-based marine aquaculture, pose a threat to the genetic integrity, productivity, and evolutionary trajectories of wild populations. Escapees have been monitored in Norwegian rivers since 1989, and, a second-generation programme was established in 2014. The new programme includes data from summer angling, autumn angling, broodstock sampling, and snorkelling surveys in &gt;200 rivers, and &gt;25 000 scale samples are analysed annually. In 2014–2017, escapees were observed in two-thirds of rivers surveyed each year, and between 15 and 30 of the rivers had &gt;10% recorded escapees annually. In the period 1989–2017, a reduction in the proportion of escapees in rivers was observed, despite a &gt;6-fold increase in aquaculture production. This reflected improved escape prevention, and possibly changes in production methods that influence post-escape behaviour. On average, populations estimated to experience the greatest genetic introgression from farmed salmon up to 2014 also had the largest proportions of escapees in 2014–2017. Thus, populations already most affected are those at greatest risk of further impacts. These data feed into the annual risk-assessment of Norwegian aquaculture and form the basis for directing mitigation efforts.

Highlights

Aquaculture represents one of the fastest growing food production sectors and plays a major role in the global blue revolution
Escape of farmed salmon is regarded as one of the two most critical issues influencing the environmental sustainability of Atlantic salmon aquaculture, in addition to sea lice infections (Taranger et al, 2015; Forseth et al, 2017)
Genetic introgression is widespread in Norwegian salmon populations (Glover et al, 2013; Karlsson et al, 2016; Diserud et al, 2017), and differences in age and size at maturation between wild and admixed individuals have been reported in native populations (Bolstad et al, 2017)

Summary

Introduction

Aquaculture represents one of the fastest growing food production sectors and plays a major role in the global blue revolution. The aquaculture of Atlantic salmon (Salmo salar L., hereon referred to as salmon) represents the most economically significant global aquaculture product (Bostock et al, 2010). Salmon aquaculture started in Norway in the late 1960s and thereafter established as a significant industry in several countries. Farmed escapees (fish that are domesticated but for simplicity are hereon referred to as farmed), which interact ecologically (Jonsson and Jonsson, 2006) and genetically (Glover et al, 2017) with wild conspecifics, represent one of the most persistent issues. Farmed escapees and genetic interactions with wild conspecifics continues to be a long-standing topic of concern (Hindar et al, 1991; Ferguson et al, 2007; Glover et al, 2017)

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