Invasive Fish Species- What are they, and why should we care?

Invasive Fish Species- What are they, and why should we care?

Hello everyone, I thought I would take the time to discuss an interesting topic that I get lots of questions about- invasive species. There seems to be a lot of confusion when it comes to invasives… Why are some non-natives considered invasive, while others are not? What are the impacts of invasives? Can native species be invasive? So many questions, so little time. So lets dive right in.

I presently work for the Central Kootenay Invasive Species Society (CKISS), a non-profit organization helping efforts to control the impacts of invasive species in the Kootenay region. This exposure to the world of invasives is what prompted me to create this post (along with all the confusion I see out there, in forums and in general). CKISS generally deals with terrestrial invasive species (aka plants), however, invasive species come in many other forms; terrestrial and aquatic wildlife, insects, or even bacteria and microscopic invertebrates. In this post, we are going to focus specifically on invasive fish species in Alberta and BC.

So what is an invasive species?

To understand invasive species, one must understand several concepts.

Native species are those that have historically occupied a particular region or ecosystem naturally or have come to be present in an area through natural means. Essentially, the flora and fauna that were here before humans started tinkering.

Introduced species are those that have been introduced to a region or ecosystem by humans, either on purpose or by accident, through various means. There are hundreds of introduced species in western canada that we see all the time, and many are not considered invasive.

Invasive traits are traits present in a species that allows them to spread rapidly and colonize/establish in areas very quickly. These traits may be present in native species or introduced species.

These three definitions are critical in understanding invasive species. Essentially, to be considered an invasive species, the following criteria must be met:

  1. The species must be non-native
  2. The species must display invasive traits
  3. Those invasive traits must result in some sort of negative impact. This is the key point. It is only considered invasive if the invasive traits are negatively impacting some human value. These could be impacts to ecological, economic, or social values.

The most common impact of invasive species is loss of native biodiversity. Invasive species often out-compete native species and either reduce their distribution or replace them altogether. Other common impacts include reduced agricultural yields, impacts to infrastructure, or health concerns (toxic plants/insects). In fisheries, we are primarily concerned with invasive species displacing native species. However, there is a distinctive grey area when it comes to defining invasive species in fisheries. And that’s because the definition of an invasive species is filtered though human values.

The point being, the concept of invasive species are a human construct, and we often reflect that in our management practices. The fish species we define as invasive are those that hurt other ecologically (or socially valued) species, or those that reduce the quality of a recreational fishery.

Should this Brown Trout from a Central AB spring creek be considered invasive??

So what species are considered invasive?

The most common invasive fish species in western Canada is the brook trout. Brook trout are invasive because they reproduce much faster than native species, and they occupy the same habitat that our native species use to rear as juveniles. If brook trout have overtaken a small tributary, any native species that is hatched into that stream will struggle to survive until adulthood because they will have to compete against hundreds of brook trout. This will lead to a stream full of tiny brook trout. This impacts both the quality of fishing and the viability of native species.

While they are excellent sportfish, brook trout are highly invasive in western Canada.

The most recent invasion by an invasive species in Alberta is the Prussian carp. This is a species of carp that steals the sperm of native species (meaning it can reproduce without a mate) an therefore can reproduce very quickly. Albertans have seen first hand what can happen if these fish get into our waterways. Prussian carp should be killed and removed from any waterbody in which they are caught. They are similar to Goldfish or Koi fish, which can be introduced by pet owners releasing their aquarium pets into the wild. THIS SHOULD NEVER BE DONE. Always kill and dispose of pets and never release them into the wild.

The Prussian Carp poses a major threat to native fish in Alberta. Photo: Wikipedia

What are not invasive?

Pike in the Bow river and pretty much all other eastern slope streams are NOT invasive, despite what many people say in internet forums. Pike are native to Alberta (eastern slopes) and are an excellent sportfish for anglers. If you catch a pike in the bow river, it should be released like any other sportfish.

In BC however, pike are invasive. Pike are not native to British Columbia, however, they have found their way into the Columbia river system. A pike suppression program is being undertaken to try to eliminate them from these waterways as their predatory nature could have serious impacts on native fish populations.

I was surprised when I pulled this pike out of the headwaters of a central AB brown trout stream…. however, it makes sense. Pike are actually native to these central AB streams, while brown trout are introduced.

Recently, the idea that bull trout are invasive seems to have become more and more prominent. This is NOT true. Bull trout are native to pretty much every major river system in western Canada, and they occupy a niche at the top of the food chain as they have for thousands of years. They are predators, yes, so their presence doesn’t necessarily benefit other sportfish. And in systems that have been significantly altered, they may show invasive traits. This is NOT an argument to kill them in order to benefit non-native species like rainbow trout. These things will balance out over time. Data typically shows that having healthy bull trout will make the other fish populations healthier in the long run, by removing competition. Bull trout distribution is severely limited compared to historical data, and while they are making a comeback, they should not be killed unless specified in the regulations. Equilibrium between bull trout populations and other sportfish populations will be reached in time (this could be a blog post on its on).

Invasive ALERT: Zebra and Quagga Mussels

A major invasive species every angler (especially those who use boats) needs to be aware of is Zebra and Quagga Mussels (ZQM). ZQM are miniscule mussels that attach to watercraft, and once established in an area can have devastating impacts. They have currently not been detected in Alberta and BC, however, are found pretty much everywhere else across the continent. All anglers that use watercraft must Clean, Drain, and Dry their watercraft before moving between waterbodies. And the watercraft inspection stations located across both provinces are MANDATORY. Please stop and have your boat inspected, it could save taxpayers of BC and Alberta billions of dollars. This applies to ALL watercraft, including paddle boards, kayaks, belly boats, or anything else.

Zebra and Quagga Mussels can have devastating impacts on ecology and infrastructure. Don’t let them get into Alberta. CLEAN, DRAIN, DRY. Photo: CKISS

Managing Invasive Species through a Fisheries Lens

Fisheries managers are simultaneously managing for ecosystem health AND recreational opportunities. Therefore, many introduced species that have negative impacts on native trout are not considered invasive because they are increasing the recreational fishing opportunities. Consider the Bow river. Neither of the two primary sportfish, the brown trout and the rainbow trout, are native. They occupy a the niche that was traditionally occupied by bull Trout and cutthroat trout, both of which are essentially not present anymore. An ecologist would see this as a negative impact on the native Bow river species, which would mean that both species would be considered invasive. However, they are not considered invasive because they provide valuable sportfishing opportunities. The same is true in streams across the west. The brown trout in central Alberta springs creeks have displaced bull trout. The rainbows in the Oldman system encroach upon native populations of cutthroat. But none of these populations of trout are considered invasive? It’s understandable that many get confused about what is considered invasive.

I suppose that fisheries managers have always looked at these situations as tit-for-tat. Replacing one salmonid with another; so long as the system still has trout, then it wont have too much impact on the rest of the ecosystem. And if we can increase other values in the process, then that’s just a win, right? Sometimes, yes. It’s all about ecological niches. In the case of the Bow river and the brown trout streams of central Alberta, the native fish were already essentially gone by the time the new species were introduced. The introduced species took the place of a niche that was vacated, and needed to be filled.

To me, the ultimate goal is to have healthy streams with wild, self sustaining populations of trout. How much does it matter to you whether that is a cutthroat trout, a cuttbow, or a rainbow trout? All are great sportfish. This is a question I’ve grappled with for some time now, especially as cutthroat trout hybridization becomes more and more common and rainbows encroach ever higher into the native cutthroat trout streams. It appears this is now inevitable- within my lifetime, it is very likely the pure strain native cutthroat will be extirpated (regionally extinct) from all but the most remote and isolated headwater streams. It sounds scary…. but is it really so bad? This doesn’t mean there will be NO fish in our favorite streams, it just means we will be catching rainbow trout instead. Rainbows are exceptional sportfish, so what the big deal? Should we pump millions of dollars into preserving native cutthroat, who are less likely to thrive during the era of climate change, or should we just give in and accept that rainbow trout are the fish of the future?? I am genuinely very interested to know what you think. How important is it that our streams have native fish? There are many arguments in favor of native fish that can be found through this website- higher genetic variabilty, more diverse life strategies, greater ability to withstand change- but I want to know, how much will we miss cutthroat were they to disappear? How much will the rest of the ecosystem miss them? Surely, an eagle doesn’t have preference between a cutthroat and a rainbow. Are rainbow trout invasive, or just better adapted for a warmer future?

If we truly managed fisheries from a conservation perspective, then angling wouldn’t be allowed in many sensitive streams. We would close all angling and allow our fish to thrive, unaffected by humans. But what is the point of having fish if we can’t enjoy, experience, and utilize them? Angling is what gives our fish value, in many instances. It’s what adds tourism value to local economies, puts money in the pockets of guides, and provides an abundant and free food source. It’s also what prompts many citizens to care about trout conservation, and inspires people to want to protect these ecosystems. Therefore, I think it’s valid that we manage our fisheries with both conservation and recreation in mind.

The same goes for invasive species. If we only managed for ecosystem integrity, we would undermine hundreds of exceptional fisheries that contain introduced fish. If we only managed for fisheries quality, then we might lose an assortment of very rare, genetically pure native populations of fish. Where is the equilibrium? How do you think our fisheries should be managed?

A rainbow trout from an isolated stretch in the headwaters of a native cutthroat stream…. should this be considered invasive?

I hope this post clarified what we define as invasive, what definitely isnt invasive, and why there is a grey area in fisheries. I also hope it gave you something to think about. The conflicting nature of what is best for us as humans and what is best for the environment are always at the forefront for me- as an environmentalist angler, I see both sides of the argument. And I certainly enjoy hooking into a nice rainbow, even if its on a stream that used to have cutthroat. It’s complicated out there, and that is part of what makes fishing fun.

I would really, really appreciate any feedback any of you may have…. how much would we miss cutthroat trout? Do you think the definition of invasive needs to be changed? Should we manage our fisheries for ecological integrity, or for recreational value? I want to know what others think. Please comment or send me an email if you want to have a chat.

Thanks for reading, tight lines.

– KR

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