A biological risk assessment for an Atlantic salmon (Salmo salar) invasion in Alaskan waters

• Published in: Aquatic Invasions
• Main Authors: Piccolo, John, Orlikowska, Ewa H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Karlstads universitet, Institutionen för miljö- och livsvetenskaper (from 2013) 2012
• Subjects: Atlantic salmon; salmon farming; biological invasion; Alaska; British Columbia; Ecology; Ekologi; Canada; Pacific; Salmo salar
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-9141; https://doi.org/10.3391/ai.2012.7.2.012

We present an event-tree biological risk assessment for a non-native Atlantic salmon (Salmo salar) invasion into Alaskan waters. Atlanticsalmon farming is prohibited in Alaska, USA, but large numbers of them are reared in ocean net-pens in Washinton (WA) USA, and BritishColumbia (BC), Canada. Large numbers of Atlantic salmon escape each year, and they have been recovered in both saltwater and freshwaterin WA, BC, and Alaska. There is limited evidence of successful spawning and rearing in BC, but none from Alaska. No stream-reared smoltsare known to have returned successfully from ocean migrations, but survey efforts for escaped adults and reared juveniles in streams havebeen very limited in time and space. Given recurring, large-scale escape events, propagule pressure could be great enough in any given yearfor a successful invasion. To date, such large numbers of adults have not been recorded ascending Alaskan streams, but again, monitoring isvery limited. Atlantic salmon could most likely successfully spawn and rear in Alaskan streams, so successful ocean migration appears to bethe factor most likely to limit their success. Successful invasion of BC waters, where propagule pressure is greater, followed by a subsequentinvasion of a pre-adapted stock by straying to Alaskan waters, may pose the greatest risk. The lack of adequate surveys, under-reporting ofescapes and recoveries, and inherent ecosystem variation, make it impossible to assign meaningful probabilities to the risk of an invasion ofAlaskan waters. We conclude that the short-term risk of invasion generally appears low, but that it might increase over time. We also notethat invasion is only part of the ecological risk of Atlantic salmon farming in Pacific waters. Disease, parasites, and pollution may also poserisks to local ecosystems – we do not assess these risks here.