Sammendrag

As a result of an escape incident from a fish farm in Patreksfjörður in August 2023, measures to monitor ascendance of escaped farmed salmon in rivers and to remove any farmed salmon from the rivers were implemented. The Icelandic Directorate of Fisheries (Fiskistofa) planned, in dialog with river owners, activity in rivers and watercourses on the west and north-west coast. Drift diving and underwater hunting was chosen as the preferred methodology, based on being proved as a valuable and effective method to monitor and remove escaped farmed salmon in Norway. Therefore, Norwegian biologists with extensive experience with the methods were engaged to carry out the planned work.

Scandinavian Nature Surveillance undertook surveys in a total of 31 rivers on the west and north-west coast during four work sessions from mid-September to early November. The results showed that escapees from the Patreksfjörður incident had spread widely, mostly in a northerly direction, and ascended rivers in high numbers even far from (>300 km) the escape site. Escaped farmed salmon were observed in 65% of the surveyed rivers, and the mean estimated incidence of farmed salmon was 20,9 %. Removal of observed farmed salmon was a primary goal of the assignment from Fiskistofa, and 90% of all observed escapees were removed (shot with spearguns). As a result, the mean estimated incidence of farmed salmon was reduced to 3,5%. However, in most rivers the surveys had the character of sampling, i.e. only selected stretches or pools likely to hold escaped farmed salmon were surveyed. To some extent this may have led to results overestimating the overall incidence of farmed salmon. These high estimates, both initially and after countermeasures, are partly a result of low numbers of wild Atlantic salmon in many rivers.

Even though drift diving and underwater hunting proved to be effective, and many escapees were removed, only selected stretches and pools were surveyed in most rivers. Moreover, there were many rivers that were not surveyed. Thus, it is likely that escaped farmed salmons were able to spawn together with wild salmon. Moreover, the percentage of immature individuals among the escapees not seeking towards river mouths in 2023 is not known due to the lack of recaptures in the sea. When maturing, such fish may try to ascend rivers in 2024, and there should be a contingency plan both for detecting return of escapees in 2024 and removal from the rivers.

Rivers

Hiterá / Haffjarðará / Straumfjarðará / Midá / Haukadalsá / Laxá í Dölum / Flekkudalsá / Búðardalsá / Staðarhólsá / Hvolsá/ Djúpadalsá / Fjarðarhornsá / Vatnsdalsá / Arnarbýlá / Osá/ Botnsá / Fossá / Dynjandisá / Mjölká / Laugardalsá/ Ísafjarðará / Langadalsá / Hvannadalsá / Staðará / Selá/ Húsadalsá / Viðidalsá / Hrófá / Miðfjarðará / Laxá í Refasveit / Fnjóská

Forfattere

Øyvind Kanstad-Hanssen / Vidar Bentsen / Emil Jamtfall / John Birger Ulvund

Adresse

Skandinavisk Naturovervåking AS
Vestre Rosten 81
7075 TILLER

Telefon

+(47) 905 97 904

Mail

post@skandnat.no