Title Image Credit: Earl Steele, CC BY-NC-ND 2.0, Image Cropped

Every time fighter jets fly overhead here in Central Norway, either my wife or I nearly always make a dry remark about the Russians finally invading. It’s a slightly dark reference to former Norwegian occupations, but not something that’s likely to occur anytime soon.

Yet this summer, the papers were filled with constant sensational references to very real and ongoing Russian invasions. Luckily, they’re referring to the pink (or humpback) salmon, and not to any human army marching across the borders.

Quick recap: the pink salmon were introduced into the White Sea by the Russian fishery industry in the 1950s. It took a long time for the fish to take to Russian rivers, with the populations only surviving through constant restocking until the 1980s, at which point the fish started to spread through the north of Norway as well. The species has a distinct two-year life cycle, which means that the numbers of salmon travelling up the rivers varies on a bi-annual basis. The numbers are going up though, resulting in record numbers these last few months, with over 13,000 caught all along the Norwegian coastline, and catches even being reported in Ireland.

Read More: The Pink Salmon

You said invasive. They must have a pretty negative effect on the local species then?

You’d think so, given how extensively I’ve written about the problems with wanton labelling of species as invasive. But at the moment it’s still up for debate as to how the pink salmon affects the local salmonids that the Nordic countries hold so dear. There are a few valid theories among local biologists, with some claims that the pink salmon will aggressively chase away locals, and that the carcasses left behind after they spawn and die will result in lower oxygen levels. Others have suggested that the slightly different timing of spawning in the local salmonids means that the pink salmon should have a minimal effect on the locals.

The reason I’m going against the message I’ve previously extolled is the sheer numbers of pink salmon that Norway and Finland are seeing in their rivers, and the speed at which the salmon seem to be spreading.

One of the better metrics for interpreting a species’ “invasiveness” is used here in Norway, by the institute Artsdatabanken. ADB use a table (shown below) that employs two main metrics, a) how quickly a species spreads, and b) its potential effect on local biodiversity.

This introduces a bit more nuance into the definition of invasive, rather than the binary approach invasive ecologists have often been guilty of taking. It acknowledges that even if a species isn’t thought to be capable of spreading by itself, it’s still a problem if it has a pronounced negative effect on the local ecosystem. Maybe changing environmental conditions will allow its spread in the future!

Conversely, and more appropriate to the pink salmon situation, it also acknowledges that a fast spreading and fast growing species can be a potential problem, even when it doesn’t seem to be affecting the species around it severely. While some species will exert pressure on locals directly after arriving, many invasive species have only started to affect locals once they are firmly established, or reached high enough densities, which the pink salmon are certainly approaching. If that’s the case, things could be particularly disastrous. For instance, if their spawning does result in huge drops in oxygen levels, that could lead to huge ecosystem upheaval at certain times of the year.

So what’s next?

Unfortunately there’s little that can be done from a management perspective. Destroying spawning grounds for the pink salmon would likely result in the destruction of spawning grounds for other species. The slightly different timing of the pink salmon’s migration mean that catching as many adults as possible before spawning could do some good.

What I’m more interested in is seeing whether or not public attitudes to the species change over the coming decades. Attitudes to species often depend on our familiarity with them, and right now the pink salmon represent the unfamiliar, and a potential threat to the species many people have been fishing for generations. A stark contrast to this is the Red King Crab, also introduced by Russian fisheries, which the Norwegian market took to almost instantly.

How long it will take local fishers to adapt to a new salmonid species is anyone’s guess. The pink salmon aren’t helped by the fact that the timing of the catch matters greatly, as when they’ve completed their spawning journey they’re almost at the end of their lifetime, and are basically already rotting.

As I’ve written before, the labelling of a species as invasive is a complicated act, but one that is definitely warranted here. Funnily enough, a year ago I got into an argument with a NINA employee about this very issue, before I did a 180 on the subject. Given that this year, more fish turned up in two rivers alone than every other river in the country two years prior, I have to admit I was wrong.

---

Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology and recalls fondly drunken conversations with NINA employees about the nature of fish. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

Some lakes near where I currently live have been wiped free of freshwater cyrpinid roach before the larger invader pike was even known to be there.