Following the discovery of non-native humpback salmon in the River Ness and in other rivers on Scotland’s east coast, Professor Eric Verspoor, Director of the Rivers and Loch Institute, explains how the species came to Scotland and highlights implications for Scotland’s native salmon populations.
The “humpback” salmon being caught in some of Scotland’s east coast rivers in the last few days are probably what are more commonly known as pink salmon and scientifically referred to as Oncorhynchus gorbuscha. They are most likely strayers from naturalised populations in the Russian Kola Peninsula and White Sea regions to the north of Scotland. These populations established from the stocking of millions of eggs from Pacific Ocean rivers in eastern Russia in the mid-1950s. They may also come from rivers in adjacent northern Norway where small populations have become established by natural straying. The species is native to rivers on both sides of the Pacific Ocean in temperate and sub-arctic areas and has also been found to stray into adjacent parts of the arctic. The species has also been introduced into the Great Lakes of North America where a number of self-sustaining populations have been established and now flourish. However, that they are pink salmon needs to be confirmed and this is something we are currently looking at using DNA analysis.
If it is confirmed, this suggests that the species, like some other salmonid species (e.g. brown and rainbow trout) has the ability to adapt successfully to new environments when transplanted outside its native range and to expand to adjacent areas. It clearly has a solid foothold in the Kola-White Sea region of Russia where it has historically sustained a small local fishery. Thus the presence of multiple individuals in Scottish rivers gives rise to the concern that these strayers may eventually be able to establish self-sustaining populations in Scotland as well.
What the implications might be for the native Atlantic salmon is far from clear as the two species are not naturally found together, but exotic species seldom establish themselves without some impact on local species and biodiversity. It might be argued by some that another salmon species might be desirable in Scotland’s rivers. However, the potential for negative impacts on native species and the fact that they are the least desirable of the Pacific salmon from an angling and commercial fishery perspective suggests there are unlikely to be any positives from their doing so.
The fact that they are running up Scottish rivers is worrying as that suggests a spawning intention – the species normally spawns from July to October across its native range. Furthermore, the numbers of pink salmon caught in UK rivers appears to be on the increase over the last decade. What would be interesting to know is whether the fish caught encompass males and females, and whether they are reproductively mature or not. It is a situation which should be closely monitored in respect of the threat it poses to Scotland’s native salmon, given the latter’s great socio-economic value and biological uniqueness.
Professor Eric Verspoor
Director of the Rivers and Lochs Institute at Inverness College UHI
University of the Highlands and Islands
Scotland’s Salmon Festival 2017 takes place from Tuesday 29 August to Saturday 2 September. Organised by Inverness College UHI with support from a range of partner organisations, the event includes lectures, workshops, casting tournaments and a family fair. For more information visit http://scotlandsalmonfestival.org