On The Brink
The Westslope Cutthroat Trout is a favourite for many anglers in Southern Alberta, me being one of them. They aggressively eat dry flies, are relatively easy to fool, and inhabit some of the prettiest streams in the province. They have a distinctive red slash under their jaw, a trait which gives them their name. They are a unique fish, and a major attraction for anglers across the west. However, they are presently listed as threatened under the provincial Wildlife act and by COSEWIC.
SPECIES AT RISK
What are the threats facing these trout? What is their status in the province and current management strategies? What are the impacts of angling, and what can you do about it?
A natural place to start when discussing the ecology of cutthroat trout is understanding some of the factors leading to speciation of different trout in Western North America. The story of cutthroat trout begins with the most recent ice age, which peaked around 20,000 years ago and ended around 11,500 years ago. During this time, there were a few places which served as refuge for trout and other species of fish.
BEFORE THE ICE AGE!
Rainbow Trout and the closely related species of pacific salmon occupied the oceans before the Ice age, and the Pacific Ocean served as a refugia for these species during this time. A second refugia was present in the interior of the United States, which also served as refugia to Onchorhynchus species similar to those found in coastal waters. Over the 10,000 years that followed, the isolation between the two populations led to speciation, with the inland Onchorynchus populations evolving into cutthroat trout. Following deglaciation, rainbow trout from the ocean recolonized the entire pacific seaboard, establishing themselves in all waterways without barriers. The newly formed Cutthroat trout began to colonize the Rockies from the interior.
Here is the key point when considering this evolutionary history: In all places where the two species converged, rainbow trout became the dominant species.
The two species do not coexist naturally in the wild, for rainbow trout have several advantages over cutthroat trout that allow them to outcompete them, except at the outer range of their thermal tolerance. Thus, any body of water in North America that is attached to the ocean and does not have impassable barriers contains rainbow trout.
Cutthroat trout were able to successfully colonize many streams in the eastern slopes of the Rockies (ie. east of the continental divide),.
Due to things like glacial lakes, ice dams, and other geomorphological processes during this time, they were also able to cross the divide and colonize many reaches west of the divide that were uninhabited by rainbow trout because of barriers.
The Cutthroat Trout’s expansion north went as far as the South Saskatchewan River drainage in Canada, including the two watersheds in Alberta where Cutthroat Trout naturally occur- the Bow River and the Oldman river systems. This is how we ended up with the species mosaic we had at the time just prior to European Settlement.
Making matters more confusing is the two species ability to interbreed with one another and produce viable (aka breeding) offspring. The result of this interbreeding over the long-term favor’s the establishment of rainbow trout and the elimination of cutthroat trout. Widespread stocking of rainbow trout into native cutthroat trout rivers has led us to where we are today.
Some notable examples of Southern Alberta fisheries that shifted from cutthroat trout streams to primarily rainbow trout dominated include the Bow River and the Crowsnest River. However, the loss of cutthroat trout goes far beyond these few streams. In fact, rainbow trout genes are now present in 95% of natural cutthroat populations across the province; meaning only 5 % of cutthroat trout populations in the province remain pure. Essentially, only the populations above waterfalls and barriers remain pure.
What are the implications of this? Essentially, all systems where rainbow trout are present will trend towards the establishment of rainbow trout and the extirpation of cutthroat trout. This is bad news for Alberta fisheries, as that suggests that close to 95 % of our cutthroat rivers are trending towards extirpation. This puts a great deal of emphasis on the remaining 5 % which contain pure cutthroat, as these will be the strongholds for this species moving forward.
Cutthroat Trout vs. Rainbow Trout
When comparing cutthroat trout vs. rainbow trout, there a few key differences between them. Firstly, rainbow trout have a faster metabolic rate- that is to say, they are less efficient compared to cutthroat. Furthermore, their metabolism changes more as temperatures change, where as cutthroat have similar metabolic rates throughout their thermal range. Functionally, what this means is that rainbow trout have an advantage in warmer, more productive conditions compared to cutthroat and can grow faster and reach maturity faster.
Secondly, they are more aggressive during spawning season, and defend themselves and their territories more rigorously compared to cutthroat. This gives them another advantage over cutthroat, with the later being less likely to defend a redd and successfully mate in the presence of rainbows.
There is much nuance when it comes to the impacts of hybridization, however, there is evidence to show that these interactions lead to rainbow trout dominated systems. However, these advantages disappear in systems that are very cold, as Cutthroat Trout are more metabolically efficient at these temperatures compared to Rainbows. The advance of rainbow trout in Alberta has therefore been contained by these thermal gradients, and many high mountain streams continue to be dominated by ‘mostly pure’ Cutthroat. However, data shows that stream temperatures have been consistently warming in the province due to climate change, allowing rainbows to advance further and further into cutthroat trout strongholds.
Hybrid Swarms
What commonly happens in hybridized systems is what is known as a ‘hybrid-swarm’. This pattern has been observed in many systems across North America, including in Alberta. In the lower reaches of a stream, there will be primarily rainbow trout as they dominate in warmer conditions. In the upper reaches, there will be mostly pure cutthroat, as they dominate in cold water. In the area in between these two ecozones, a hybrid zone will form. A hybrid-zone is a part of the stream where hybrids have the greatest advantage, as their blended traits give them an advantage over both species. This leads to reaches where there are essentially only hybrids, which then mate with each other, producing more hybrids which continue to push out other species from this area. This process, known as a ‘hybrid swarm’ can happen very quickly, and within the matter of a few generations pure cutthroat can be fully pushed out.
Westslope Cutthroat Trout Brood Stock
In the past few years, the provincial government has been working towards creating a brood stock of genetically pure Westslope Cutthroat Trout from local populations. Historically, stocked populations of cutthroat in the province have used non-local stocks of hatchery raised cutthroat. Creating a brood stock using local populations ensures the survival of the distinct genetic components that make up our local populations. These unique genetics are the best adapted to the watershed they are found and are more resilient compared to non-local stocks.
As part of this project, genetically pure Westslope cutthroat have been captured during spawning season. These fish remain in streamside holding tanks until enough trout are captured to ensure ample genetic diversity. At this point, the gametes are extracted and fertilized streamside, with different males being crossed with different females. These fertilized eggs are then brought back to the hatchery where the resulting trout are raised. This has been done for the past three years, and the result is a brood stock of genetically pure trout that can be used for stocking efforts, and to bolster populations that are becoming increasingly introgressed with rainbow trout.
Trickle Down Effect
In conjunction with these efforts, strides have been taken to identify areas suitable for cutthroat trout introductions. These are areas that are protected from rainbow trout invasion (ie. above barriers/culverts), have suitable habitat for cutthroat, and are within the native ranges of cutthroat. The hope is that places such as this can sustain healthy populations of pure cutthroat trout, whose genes will ‘trickle down’ into areas where hybridization occurs. Since the pure genes can move down but the hybridized genes can’t move up, these populations would continually infuse hybridized populations with pure genes.
What Can You Do As An Angler?
It is very important that we as an angling community do our part to protect these unique fish. Below I have compiled some key factors to consider before you head out on your next trip.
Follow Regulations
This one is the bare minimum for anglers, regardless of what species you are targeting or what body of water you are fishing. It is imperative that all anglers read the regulations for the stream they are fishing BEFORE they head out fishing. On top of that, make sure you pick up a fishing license, which renews yearly on April 1st.
In general, most Cutthroat steams open June 16th and close October 31st. If you see someone angling outside of this time window, you can report them by calling the report a poacher line.
Pinch your barbs and practice proper fish handling techniques!
Practicing proper safe fish handling techniques is important to ensure we limit the catch and release mortality from angling. This means pinching your barbs, keeping the fish wet at all times, promptly removing the hook, limiting time for photos, and reviving the fish in the water before letting it swim away when it is ready. Try to avoid squeezing it to hard, grabbing it by its gill plate, or damaging its eyes. All the above info is especially important when its hot outside or stream temperatures are warm.
Consider Putting the Camera Away
The angling community seems to be obsessed with photos nowadays. Photos are often the reason why anglers overhandle or damage fish— if a fish is not cooperating, a photo may not be in the cards. You may not get a photo of every fish. That’s OK. Don’t squeeze or damage a fish just to get a photo. To make matters easier, have your camera ready with the setting dialed before snapping your photo. If you are fishing by yourself, have your camera set-up on the shore or however you like to take photos. Even better— take your photos underwater using a go-pro or an underwater camera. While it’s great to capture memories on the water, don’t let photos be the reason a fish is mishandled or damaged— try to enjoy the moment and not focus so much on taking photos!
Don’t Fish when it’s too Hot!
This is the most important factor to consider when trying to limit your impact. As previously discussed, stream temps are higher than they used to be, and flows are lower. In hot temperatures, a fish’s metabolic rate goes up, meaning they must feed more to meet their energetic demands. This makes them vulnerable to angling. To compound issues, the dissolved oxygen in the stream goes down, meaning there is less oxygen available to meet these energetic demands. The last thing trout need in these conditions is to be caught by an angler, as this will drain them of all their energy reserves, and in these conditions, they may not be able to replenish them. Catch and release mortality sky-rockets in these conditions, and is the time when our angling has the highest impact.
The solution? Carry a thermometer. You can get one for a couple of bucks at the dollar store. In general, try not to fish if stream temperatures are above 16 o C, and absolutely don’t fish if temps are above 20 o C— in these temps, mortality may occur even without the added stress of angling. New daytime angling closures are in place across Southern Alberta, and its important to follow them.
A Bright Future— If We All Do Our Part
I believe Cutthroat Trout can remain a mainstay in Alberta if we all do our part to conserve them and enjoy angling for them responsibly. There truly is nothing quite like watching a big cutthroat dart up from the depths to smash a big, bushy dry fly. As the primary user group interested in these fish, it is up to us to stand up for them and to continue to advocate for them, now, and into the future. If we do so, we may yet be able to enjoy the satisfaction of catching a native trout, in its native environment— just the way it should be.