When it comes to discussing issues between native and nonnative species, there’s sometimes no way to say things simply. Rather than try to break this down into multiple short missives, I’m putting this out as one long post. I’m fully aware that this post exceeds the length most people are willing to commit to reading, but I wanted to put all of this in one place.
As the popularity of wild, or stream-born salmonids increases, I see the word “native” tossed around in some interesting ways these days. The noun native has a straightforward meaning according to Webster’s dictionary;
- 1: one born or reared in a particular place
- 2a: an original or indigenous inhabitant b: something indigenous to a particular locality
- 3: a local resident especially: a person who has always lived in a place as distinguished from a visitor or a temporary resident
2a & 2b here are important because of the word “indigenous”. Indigenous’ definition is also straightforward;
- 1a: produced, growing, living, or occurring natively or naturally in a particular region or environment indigenous plants the indigenous culture
- b: Indigenous or less commonly indigenous: of or relating to the earliest known inhabitants of a place and especially of a place that was colonized by a now-dominant group of indigenous peoples.
- 2: INNATE, INBORN
If we forget the word native for a moment and focus on indigenous, would anyone ever say “indigenous brown trout” when referring to a brown trout that was born in the wilds of Pennsylvania? Of course not, because Salmo trutta is not indigenous to the United States. Just to clarify, brown trout (Salmo trutta) are native to Europe, western Asia, and northern Africa. rainbow trout (Oncorhynchus mykiss) are native to the west coast of the United States from Alaska to Mexico, and cutthroat trout (Oncorhynchus clarkii) are native to the Pacific Northwest coast from Alaska through British Columbia into northern California, in the Cascade Range, the Great Basin and throughout the Rocky Mountains including southern Alberta.
I think where a lot of confusion comes from is the “born or reared in a particular place” or “a local resident” when we’re talking about fish. I see folks refer to brown trout in Pennsylvania (and elsewhere in the United States) as “native brown trout”. The same goes for “native rainbow trout” in places like West Virginia. While wild, stream-born brown and rainbow trout might be technically considered “native to the stream”, it’s disingenuous to refer to brown and rainbow trout as “natives” outside of their native range.
Here’s a simple way to look at this issue; My dog is native to Pennsylvania. She’s specifically native to Bedford County Pennsylvania. That said, I would never say; “I’m taking my native dog for a walk” or “my dog is a native”. It’s the same when talking about humans frankly. I’m native to Bedford County PA, but I have never, and never would refer to myself as simply “a native”.
This is where the context of the statement is important. I can say; “I’m native to Bedford County Pennsylvania”, and that’s fine. It’s not acceptable for me to go around referring to myself as “a native” even though I’m obviously native to a place. Everything and everyone is native to a place, but we don’t attach the word native to descriptions about things unless it defines the person or thing.
Brook trout (Salvelinus fontinalis) and lake trout (Salvelinus namaycush) are the only native salmonids in Pennsylvania and are char, not trout. Brown trout, rainbow trout, and cutthroat trout are nonnative to Pennsylvania. In just about every single scientific fisheries-related paper in the Northeast, brown trout and rainbow trout are referred to explicitly as “nonnative”. So science already defines those species as “nonnative”, which makes calling them “native” somewhat silly.
Personally, I believe a lot of this is an attempt to assign a higher value to these wild, stream-born nonnative fish. There has been a big push in the angling world to hold “wild trout” in higher regard than their hatchery-born cousins. I believe that the pursuit of escalating these species to a higher level of worth has led to folks misusing the word native. One of the most challenging issues here is that the basic premise of wild, stream-born fish being of greater value than their hatchery-raised cousins is true. Where those fish occur is equally important though.
To make matters worse, as I said above, technically people are correct in that an individual fish that is born in a particular stream is native to that stream. Again though, we don’t typically attach the word native to things when we describe them unless that’s the defining characteristic. In the case of nonnative fish, again, it’s completely counter to science to define something that is technically “nonnative” as “native”.
I believe this is an important issue in that misclassifying nonnative species as native dilutes the importance of native fish conservation. That problem is compounded when there is a mountain of scientific research that illustrates how these nonnative species have a deleterious effect on true native species (HERE). It should be obvious to see here that misidentifying nonnative species as native creates the potential for people to become confused about what we’re trying to save through conservation efforts across the eastern brook trout’s native range.
Organizations like Native Fish Coalition exist to protect, preserve, and restore native fish. It’s harmful when people conflate nonnative fish as native fish because it might cause some people to be confused about what Native Fish Coalition stands for, and which species they’re focused on protecting. When organizations like Native Fish Coalition talk about native fish, they’re referring to native fish species specifically.
“Q: WHAT DOES NATIVE FISH COALITION MEAN BY THE TERM “NATIVE”?
A: When NFC uses the term “native” we mean indigenous or historically present: “Indigenous: originating or occurring naturally in a particular place; native.” Unless otherwise noted we mean native to a given water not the state, region, etc. It is not meant to imply self-sustaining or genetically pure as some state fish and game agencies and conservation organizations are now using the term.”https://nativefishcoalition.org/faq
So why is “native” important when it comes to fish conservation? For the same reason, native plants are more important than nonnative or invasive plant species. Introducing species to an ecosystem they didn’t evolve in can lead to a “cascade” of system-wide problems. In a lot of cases, the introduced nonnative or invasive species tend to outcompete the native species. It’s true for plants, and it’s true for fish.
One of the best examples of how the entire native fabric of an ecosystem can be disrupted by the presence or introduction of nonnative species is a study that was conducted in 2010 that looked at the response of hellbenders to nonnative and native predators (Gall and Mathis 2010, pp. 51-54, DOI10.1111/j.1439-0310.2009.01718.x). There seems to be an indication that larval hellbenders don’t have the same instinctual (chemical) response to the presence of nonnative salmonids as compared to native predator fishes.
While the Eastern Hellbender is not currently listed on the federal endangered species list, or state endangered species list, it is listed as a species of special conservation need in Pennsylvania due to its decreasing population. There is a lawsuit that was introduced in 2021 calling for the federal government to list the hellbender on the federal endangered species list as well. It’s worth noting that Pennsylvania still stocks nonnative trout in areas known to be hellbender strongholds.
A big issue here is called Trophic Cascade, and there are plenty of examples of how trophic cascade has caused problems even beyond the aquatic landscape. Take Yellowstone Lake for example. The introduction of Lake Trout to Yellowstone Lake caused a “top-down” trophic cascade which caused the native cutthroat trout population to collapse. That species replacement had a ripple effect throughout the ecosystem of the lake down to a microscopic level.
In the illustration above, the graphic illustrates the impact on trees due to the removal of a top predator, a wolf in this case. The loss of the wolf results in an increase of elk, which causes the de-leafing of plant species. This could be expanded further down the food chain to show the impact on insect species due to the change in plant mass, or even soil disruption due to the decrease in leaf litter to the forest floor.
When we cause a reshuffling of the food web by replacing a keystone species in an ecosystem, it can have an impact on all of the species within that ecosystem. For example, in Yellowstone Lake, one of the species impacted by the disruption to the food web was a shift in zooplankton biomass and species composition. The lake’s zooplankton population shifted from being primarily dominated by copepods to being primarily dominated by cladocerans (water fleas). This then had an effect on the average size of the cladocerans in the system in that the average size of the cladocerans increased.
One of the more glaring impacts of this trophic cascade in Yellowstone Lake was the impact the shift in primary top-level fish species had on terrestrial wildlife around the lake. Native cutthroat trout mostly lived in the shallow sections of the lake and would run up tributaries to spawn. This life strategy made them available to land-based wildlife like osprey, eagles, otters, and bears. Lake trout on the other hand mostly live in deep water and rarely visit the shallow portions of the lake and the tributaries. There was a documented decline in the number of osprey and eagle nests near the lake and a decline in bear activity when they should’ve been there to eat migrating cutthroat trout.
The trophic cascade issue on Yellowstone Lake is far more complex than my brief summary here. You can read a more in-depth account of what happened at Yellowstone here: https://www.nps.gov/yell/learn/ys-25-1-non-native-lake-trout-induce-cascading-changes-in-the-yellowstone-lake-ecosystem.htm
With native fish (any native animal really), the species coevolved together alongside the numerous other native fauna in an ecosystem and developed a symbiotic relationship over millennia. Predator/prey relationships ebb and flow in a natural rhythm based on seasonal fluctuations in biomass but always find their balance because they’ve been doing it forever. While the cutthroat/lake trout example in Yellowstone Lake is glaring because of the difference in habitat preference between the two species, in other cases, the trophic cascade might be occurring on a much smaller scale and over a much longer timespan.
For example, native eastern brook trout and nonnative brown trout are similar in terms of habitat preference. Both live in cold, clean flowing streams and prefer similar in-stream habitats. Both are fall spawners. They are similar in size for most of their life until several years of age when brown trout outgrow brook trout. Both are potamodromous in that they spend their entire lives in freshwater (in landlocked southern states outside of New England) and migrate throughout river systems to spawn, over-winter, and find summer thermal refuge. So it might be easy to think that brown trout function as an analog to extirpated brook trout. However, the ultimate size difference, aggression, feeding preferences, fecundity, and intelligence are all vastly different than brook trout.
Again, on top of the differences noted above, we know from the Hellbender studies that native species that coevolved together likely have some genetic tools that they’ve built over millennia to help them identify the presence of native predators. So consider for a moment what the potential impacts to native fauna might be by removing the brook trout from a food web and replacing it with brown trout. The similarities between brook trout and brown trout might mean that the trophic cascade takes much longer to materialize, but that doesn’t mean it isn’t happening.
For the fly fisherman who might have made it this far, consider that introduced nonnative fish may be having an impact on mayfly communities. There is compelling research on the impact both brown trout and rainbow trout have on native aquatic macroinvertebrate communities. A study in New Zealand for example mentions the following:
“Furthermore, in some of the most ecologically notorious examples in New Zealand (McIntosh et al. 2011 662 chapter 19), negative effects of nonnative Brown Trout cascaded down food webs from mayflies to algae and even altered ecosystem function (McIntosh and Townsend 1996; Huryn 1998).”https://www.montana.edu/mcmahon/Paradox%20book%20chapter.pdf
Something that sets native species apart from nonnative species is genetic diversity. Native species evolved in a geographic place and developed genes specifically tailored to deal with environmental factors in their native environment. Native species in their native environment are better suited to deal with environmental pressures unique to their native geographic region.
Nonnative or introduced species come from a limited source population. This limited source stock means that there is limited genetic diversity in the population of nonnative species. Introduced species can never be as genetically diverse as native species.
The below excerpt explains the long-term issues with introduced species:
Introduced species can be prone to founder events and population bottlenecks imposed by filters in the invasion pathway, leading to declines in genetic diversity within nonnative populations as compared to their native, source populations. In a review of 80 species of animals, plants, and fungi, diversity of alleles and heterozygosity were significantly lower in introduced populations than in source populations, although decreases were less than 20% (Dlugosch and Parker, 2008; also see Wares et al., 2005). Furthermore, Dlugosch and Parker (2008) found a U-shaped relationship between genetic (allelic) diversity and time since first introduction, suggesting that selection and genetic drift continue the loss of genetic diversity during the first several decades after colonization. Over longer time scales, multiple introductions can cause genetic diversity to rise again via the mechanisms discussed below. Thus, it is perhaps not surprising that a lag phase often occurs between the colonization and spread stages in the invasion pathway (see Crooks, 2005), in which population growth and subsequent spread are inhibited either directly by low population sizes or by low level of genetic variation within the populations.https://doi.org/10.1016/B978-0-12-800049-6.00303-6
When we start manipulating nature by introducing species, we can’t expect to fully understand the impact throughout the food web or with the introduced species itself. There are issues with brown trout in the USA that stump biologists, but should we really be surprised when an introduced species population mysteriously collapses? Could it be that the lack of genetic diversity finally catches up with the population and causes a catastrophic collapse of the population? Could mysterious population stunting in places like Spring Creek in Pennsylvania be the result of limited source stock genetic diversity?
The quote below from a MTFW&P biologist in reference to the collapse of brown trout in Montana:
“While we try to figure out what’s really the root cause of this, we should certainly be doing something. I’m not the decision maker, but that’s how I feel based on what’s going on biologically — we should be doing something,” said Jim Olsen, Montana Fish, Wildlife & Parks fisheries biologist for the Big Hole River.https://mtstandard.com/news/local/brown-trout-decline-across-southwest-montana-rivers/article_8b26ffca-0295-5218-a3dd-61fef0e3b20f.html#:~:text=In%20the%20upper%20Clark%20Fork’s,low%20of%2082%20in%202019.
An issue with native vs nonnative fish specifically is the prioritization of conservation initiatives across the United States. The country has a diverse aquatic landscape with extensive negative impacts from industrial expansion, pollution, logging, and introduced species. Should we be devoting financial, human, or other resources to propping up nonnative species? What if we’re spending all this capital on protecting nonnative fish only to have them self-destruct due to some war-of-the-worlds style biological failure due to their inability to adapt to their introduced environment or to have them negatively impact some terrestrial species? 200 years is not enough time for a nonnative species to settle into a new environment. We really don’t know what will happen with brown trout in the US in the real long term.
When the Hebgen Dam failed recently in Montana causing the rapid dewatering of the Madison River, anglers and even the state Fish Wildlife & Parks biologists went into Defcon 1 to try to fix the “problem” and save the salmonids. There will no doubt be changes in the flow regime and release schedule at the dam to try to protect the nonnative fish that exist in the tailwater. Ironically, you’ll hear the same people advocating for the removal of the Snake River dams begging to make sure Hebgen remains fully operational and in good working order. Dams are a problem when they negatively impact fishing, and dams are essential when they create an artificial fishery. Aquatic organism passage is of utmost importance except when it’s not.
What if we redirected all this energy (and money) into protecting, preserving, and restoring our imperiled native fish? We should be prioritizing efforts in conservation to benefit native fish first. Biotic interactions are like a hot potato when anglers are involved. We seem unwilling to accept or address the fact that not all trout are equal, trout don’t need to be unlimited, and nonnative trout are not direct analogs for native trout.
We can’t continue riding the fence on species preferences. Not when time is running out, money is limited, and there’s only so much that can be done about some major environmental factors.
This is why Native fish deserve prioritization.
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