Forecasting Foreign Fishy Futures

Forecasting the future establishment of invasive alien freshwater fish species (2021) Perrin et al., Journal of Applied Ecology,

The Crux

I know I write a lot about whether or not we should jump to conclusions about non-native species, but the fact is that there are lots of situations in which invasive species need to GO. Giving them the boot, however, can be a right pain, and more often than not it’s impossible.

But an ounce of prevention is worth a pound of cure (I don’t know the imperial system well so I assume that makes sense), and figuring out where an invader is likely to turn up means you can take measures to stop it happening in the first place. This saves a lot of hassle (and money) down the road.

So how do we figure out where invasives are likely to show up? That’s what this paper, which made up the first chapter of my thesis, aimed to find out, by looking at where invasive freshwater fish species have been popping up in Norway over the last 100 years.

What We Did

We were lucky enough to have access to an enormous survey carried out almost exactly a century go. This survey mapped out the distribution of different freshwater fish species back then, which we considered the ‘native’ distribution (read this post to see why that’s a bit of a tricky term though).

We then used the Global Biodiversity Information Facility (GBIF), which compiles studies showing species occurrences, to find records of species in lakes outside of their native range. These were considered establishment events. We then modelled the likelihood of establishment in a lake, by considering the environmental (like lake size or temperature) and human-related characteristics (like nearby human activity and distance to the nearest road) of lakes where fish had established, and ones in which they hadn’t.

We then used this model to forecast establishments over the next 50 years, looking at which lakes were likely to see invasive species (check the image below for the species we looked at) establish in them, and which lakes those established species were likely to spread to.

Species modelled were (from top to bottom) the common roach, the common rudd, the European perch, the European whitefish, and the northern pike (Image Credit: Sakke Yrjola)

Did You Know: Predictive Modelling Potential

Predictive modelling like this can be dangerous. When you say that species A is likely to turn up in a like, there’s an implicit expectation that something be done to prevent it. If the data is dicey, or the model is poorly thought out, this can be an issue. Check out my article from last week on some of the quandaries ecologists face when publishing a paper like this.

Read more: Forecasting the Fate of an Ecosystem: The Double-Edged Sword of Predictive Modelling

What We Found

Although climate change might help species spread in the near future, at the moment human spreading of fish is still the big problem here. Lakes with lots of populations nearby, even where those population weren’t connected via a river, were far more likely to see invasive species move in, indicating that humans were probably moving species around. Lakes closer to roads and to areas with higher levels of human activity were also hotspots for invasion.

Pike (Esox lucius) and perch (Perca fluviatilis) are the two fish who showed the most potential to spread. Of the five species shown above, these are the two thought to be most often moved around for the purpose of creating a new fishing stock in a lake. Roach and rudd, which usually get into lakes when they’re used as bait, showed very little spread.


What we were looking at here was establishment, since it’s very hard to figure out when exactly a species first arrived in a lake. We made the assumption that the fish were recorded shortly after their population grew large enough to be noticed, but it’s a tricky assumption and comes with a lot of uncertainty.

So What?

This study is an important reminder that while climate change might have an effect on species ranges and extinctions, there are a lot of local actions humans undertake which can have more drastic consequences for species. Freshwater populations would benefit a lot more in the short term from people not taking it upon themselves to move fish around wherever they see fit.

But in the bigger picture, studies like these need to be undertaken more often if we want to improve our ability to keep out invasive species. We have a wealth of data lying around in resources like GBIF, and it should be put to use.

Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology who finds the fact that he’s publishing his second paper eight months after finishing his PhD and it’s not even that weird from an academic sense WORRYING. 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.

Title Image Credit: pxfuel, CC0 1.0, Image Cropped

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