TO its list of invasive plant and animal species, the impoverished Scottish ecosystem may soon have to add the pink, or humpback salmon, oncorhynchus gorbuscha. Averaging around four and a half pounds and significantly smaller than the Europe’s native Atlantic salmon, pink salmon naturally run the rivers of western North America and eastern Russia where they spawn in huge numbers. Despite anglers first reporting catches of the fish in east coast rivers around six years ago, the numbers were few, providing no significant worry that a breeding population would become established.

This summer, however, there has been a far greater cause for concern. The Ness District Salmon Fishery Board’s well documented video and photographic evidence has shown more pink salmon running the River Ness than ever before, and at least twenty pairs have spawned already. With females producing between eight hundred and two thousand eggs each, this could, provided environmental conditions such as water temperature that are conducive to their survival, mean an increasing run of fish in following years and the prospect that they could come to compete with native Atlantic salmon.

Whether via the colonial philosophy which saw emigrants bring to foreign continents their own part of Europe — starlings to New England, Loch Leven trout to New Zealand — or the crashingly naive belief that cane toads thousands of miles and evolutionary steps distant could control beetle populations on Australian sugar plantations, intervention in ecosystems has a pattern: species are introduced in arrogance by homo sapiens, alone on Earth possessed with a certainty that it should have dominion over the rest. Unaware of this divine superiority apparently bestowed upon humans, the rest subsequently set about surviving any way they can in their new environment. Momentous impact on native ecosystems is generally the result.

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First introduced to the seas of northern Russia in the fifties from their native range in far east of the country, pink salmon have also been found in Swedish, Norwegian, and Irish waterways. Should they spawn successfully in Scotland disentangling them from the ecosystem could prove problematic, if not impossible — particularly given the government’s attitude to eradication and control of existing destructive invasive species such as Himalayan balsam, North American mink, and signal crayfish.

Distinct differences between oncorhynchus gorbuscha and Atlantic salmon may however mean less competition between the species than could have occurred should a different Pacific salmonid have arrived in its stead. Pinks, while utilising the same spawning habitat as Atlantics — beds of fist-sized gravel into which the female cuts a nest known as a redd — tend to spawn in the lower reaches of rivers, while Atlantic salmon utilise their whole length provided there is suitable habitat.

Unless there is a change in the behaviour of these fish in Scottish waters then Atlantic salmon will continue to find successful spawning areas, albeit with more competition in the lower reaches. Chris Conroy, director of the River Ness DSFB and former biologist for River Naver Fisheries.

“Generally pink salmon spawn in the lower system of rivers. They have spawned five miles up the Ness, and although they may of course be further up we have not seen them. Where they spawn in the same locations, the Atlantic salmon — which is larger — will cut over the redds of the pinks so there may be some disruption (to the developing eggs of pink salmon) there as well.”

Upon hatching in spring, the young pink salmon, or fry, leave the river for the sea immediately. Atlantic salmon, meanwhile, can spend up to four years in fresh water as parr before smolting, the stage whereupon they themselves leave freshwater for the feeding grounds on the fringes of the Arctic Circle.

Direct competition for food sources between the species while in freshwater will then exist for only a limited period, and it could be posited that competition for spawning habitat aside, the Atlantic salmon’s Pacific cousin may be less harmful than seemingly innocuous invasives such as the minnow, phoxinus phoxinus, which was introduced to Scottish watercourses in the belief that it would provide feeding for trout, and which is now direct competition with young salmonids for for the duration of its six year lifespan.

However as Chris Conroy explains, should pink salmon find their way to the same maritime feeding grounds as Atlantics, there may be a more significant impact.

“It is also about where pink salmon go at sea. Atlantic salmon are struggling to feed, and should pink salmon compete here then it may impact our native species even more severely.” Yet as many of our Atlantic salmon discovered from the industrial revolution onwards, Scots can be downright determined when it comes to stopping their progress. Dams, weirs, fords. Tunnels, mills, the wrong tap turned in a factory and thousand of litres of poisonous chemicals down a river. It is an irony, but not an unexpected one, that the largest barrier to the pink salmon’s expansion could prove to be Scotland’s own environmental negligence.

While in its naivety the pink salmon may believe the gravel beds it selects to be healthy, their evolution did not count for Scottish farming practice nor SEPA’s lack of vigour in curtailing even the worst of it. Hyporheic sampling, a procedure in which the riverbed is tested for oxygen and conductivity levels down to around 300mm — the maximum depth to which salmon cut their redds — has shown the lower reaches of some rivers, such as the Lugar in Ayrshire, to be utterly suffocated by sediment, mainly from the cumulative effects of intensive farming practices upstream.

While the survival rate of Atlantics which push on to the headwaters to spawn can be excellent, fry and parr numbers are in many cases drastically reduced the further one progresses towards the lower reaches, and in some instances they are non-existent. Should pink salmon follow their traditional spawning patterns, then they may only become firmly established in the cleanest of our rivers. Where little is known, however, can only exist conjecture and speculation. At present, as Conroy admits, a tentative, hopeful analysis of the pink salmon’s progress is all that can be done.

“For us it is a steep learning curve, and basically at the moment the honest truth is that we do not know what the impacts will be.”

What is certain is that Salmo salar, the great leaper, anadromous king of European rivers, is for this season at least not alone in his kingdom.