Fishing for Invaders

Image Credit: California Department of Fish and Wildlife, CC BY 2.0, Image Cropped

Angling as a source of non-native freshwater fish: a European review (2019) Carpio, De Miguel, Oteros, Hillstrom & Tortosa, Biological Invasions, doi.org/10.1007/s10530-019-02042-5

The Crux

People love fishing. It’s an intrinsic part of some people’s lives, whether as a livelihood or a past-time. People who have grown up fishing often have specific species that they enjoy fishing for. Nothing wrong with that.

Yet people’s desire to go after one fish species will often lead them to move that species around. This can happen on a small scale, with people moving a species from one lake to another slightly closer to their homes. Or it can happen on a massive one, with a species being transported to new continents.

This has shaped entire freshwater communities in modern-day Europe, where 195 species now reside that have no natural range in the continent. Most of these have been introduced since the nineteenth century, which is around the time that fishing became a popular recreational activity. This week’s authors wanted to find out what the role of recreational fishing was in shaping the make-up of today’s invasive freshwater fish populations in Europe.

What They Did

The authors searched literature to find the reason for introduction of all fish species previously alien to Europe. Fish species were then narrowed down to those whose main reason for introduction was fishing in at least one country. The authors also looked at similarities between different countries, grouping countries based on the similarities between the introduced fish species that were present. They then took a number of characteristics of each country, including GDP, size, percentage of the population living in rural areas, to see if they were related to the numbers of introduced species in the country.

Did You Know: The Concept of “Native”

The concept of a species as native or non-native may seem straightforward, but it can be dicey. Many species are spreading through Europe slowly, and whilst they may be native to a country, they may now be present in areas of that country they were previously absent from. Methods of introduction vary too. Some species are spreading further north as temperatures rise in line with climate change. Should these species be considered ‘alien’ in the same way that those introduced for sport-fishing are?

What They Found

Almost a quarter of fish species that have been introduced to Europe were introduced for the purpose of recreational fishing. The cyprinids (includes carps, minnows among many) and salmonids (salmon, trout) were over-represented, making up two thirds of the total species.

The grouping of countries with similar invasive communities yielded surprising results. Whilst some groups turned out as expected (Norwegian, Swedish and Finnish alien communities are all quite similar, as are Belgian, Swiss and French), the Netherlands had quite a similar invasive community to the Balkan countries, and the UK was grouped with Romania, Bulgaria, and Denmark. Larger countries with higher GDPs were likely to have more invasive species, as were countries found further south.

Problems?

In a study that leans so much towards social practices, I expected to see more social science present. Attitudes to introduced species can vary enormously depending on the country and the species. Opinions on the quality of a species for eating can vary enormously throughout Europe, so different species status by country would have made an interesting addition here. Admittedly, this is a big stretch when considering 46 different fish species.

The Rainbow trout is classed as one of the world's 100 worst invasive species, but is a favourite among anglers

The Rainbow trout is classed as one of the world’s 100 worst invasive species, but is a favourite among anglers (Image Credit: US Fish and Wildlife Service Headquarters, CC BY 2.0)

So What?

This study highlights the varying reasons for fish introduction, even among those introduced for sport fishing. Salmonids are popular as trophy fishes, yet many cyprinids are often used instead as bait, and the two are both widespread throughout Europe. Additionally, the cyprinids are an incredibly diverse group, so their overrepresentation here may not be all that surprising. The sometimes odd grouping of countries by fish communities also shows that patterns of introduction do not necessarily always follow strict geographical rules.

I think my take-home message here is that whilst we can come up with some indicators of where introductions are likely to occur, local social practices and geographical features mean that the onus will be on local governments to try and cut down on more fish introductions. Invasive fish species are particularly damaging to freshwater ecosystems, and steps need to be taken to reduce their negative effects. But the variation in invasive communities shown here mean that one blanket strategy across Europe won’t be effective.

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