A very large and newly tagged cutthroat pushing 5 lbs! Photo: Mike McCulloch with the Province of BC.

The first recorded tagging of fish dates back to 1862, when wealthy Scottish landowners decided they wanted to find out what happened to the salmon and trout that lived in their streams. Where did they migrate to? What were the chances of recapturing them? Today, the reasons for tagging fish are not very far from the initial motives, but the technology and the science have changed radically.

In recent years, one specific application of tagging has been the wild cutthroat trout fisheries in Vancouver Island’s lakes. The Freshwater Fisheries Society of BC (FFSBC) started a tagging program for lake-run cutthroat trout that launched an investigation into mortality rates and sought to understand fish movement. Were fish dying due to angler retention, or from other causes including after spawning? Since 2016, these tracking programs have been revealing the hidden mysteries of the lake-run cutthroat trout.

Why Tag Cutthroat Trout?

Cutthroat trout on Comox, Cowichan, and Horne lakes are wild fisheries, meaning that there is no stocking program needed to support or enhance angler retention. According to FFSBC, Cowichan Lake is one of the busiest lakes on Vancouver Island and in all of BC. Despite these lakes being very popular fisheries, not much is known about lake-run cutthroat trout regarding their causes of mortality, how they spend their lives, how vulnerable they may be to angling pressure, and their migration behaviours. Therefore, little science informs the fishing regulations.

Recent survey data on Cowichan Lake suggests that angler effort has declined, with fewer and smaller fish being caught. Why are cutthroat trout getting smaller and less numerous in wild fishery lakes? Have unchanging regulations lessened fish numbers on this popular lake? Has spawning mortality increased?

What is a Cutthroat Trout?

The biology of a cutthroat trout or “cutty” is worth examining. What makes this fish worth the fuss? First of all, anglers rave about the great flavour and quality of meat in these wild fish. Cutthroat trout are a piscivorous fish, meaning a large component of their diet is eating other fish (as opposed to rainbow trout, which eat mainly insects). They often eat plugs and streamers, resulting in aggressive strikes, and are fished more actively as opposed to watching an indicator with a nymph. This piscivorous behaviour perfectly suits them in Horne, Comox, Cowichan, and other island lakes that support Kokanee populations, as cutthroat trout will gorge themselves on these small salmon. Kokanee not only provide an excellent food source for predatory cutthroat trout, but they may also influence the movements of cutthroat trout within the lakes.

Lake-run cutthroat trout differ from their sea-run counterparts in both appearance and habitat. Sea-run cutthroat trout, also called coastal cutthroat trout, spend much of their time in the ocean choosing to spawn in the rivers and streams near the coast. Lake-run cutthroat trout never migrate to the salt. Instead they push further into freshwater systems, spawning in or near the tributaries that spill into the lake. These lake-run fish have adjusted to their specific environment over countless generations, giving rise to genetically unique populations that exhibit lake-specific behaviours (fish community, spawning and feeding habitats, and temperature patterns). The more biologists understand these isolated and unique fish populations, the more evident it becomes that a conservation-based approach to regulations is needed to safeguard the species for generations.

Coastal BC Sea-Run Cutthroat Trout with scratches. Photo: Pat Demeester of Cutthroat Coast Company

This cutthroat was caught during the salmon spawn

Types of Fish Tags

What once were simple wire or copper tags that stuck out of the fish have evolved to encoded spaghetti, acoustic, or PIT (passive integrated transponder) tags.

An encoded spaghetti tag

Traditionally, when a fish was tagged, an angler or biologist had to catch the fish to record it. Now however, technology like acoustic receivers and PIT arrays monitor fish movement without the fish needing to be caught. From their humble origins in Scotland, tags are now in thousands of fish that navigate our waterways, from 9′ salmon sharks to 2″ salmon fry, all providing valuable information on fish movement and populations.

Slipping an acoustic tag into the stomach cavity. Photo: Mike McCulloch with the Province of BC.

Fish Tagging on Vancouver Island

Fisheries biologists at a tagging station. Photo: Mike McCulloch with the Province of BC

The lake-run cutthroat trout tagging program on Vancouver Island started in 2016 when the FFSBC funded a pilot project in Comox Lake to monitor the wild cutthroat trout population and the impact anglers have on the stock. Then, a more comprehensive project began in the fall and spring of 2016/17. In concert with tagging 93 fish (both acoustic and wire), FFSBC placed three electronic tag-detection stations in specific spawning tributaries around Comox Lake. The study aims to identify the total mortality rate for the population of cutthroat trout in Comox Lake. Eventually the collected data will be adequate to evaluate the balance of population gains and mortality. Following the implementation of the Comox Lake tagging program, provincial biologists teamed up with Kintama Research Services (industry forerunners in technological fish tracking) to attach acoustic tags onto catchable-size cutthroat trout in Cowichan Lake. Acoustic tags send out data for 2 to 3 years after they’re implanted, and an array of semi-permanent acoustic receivers track their movement. As of 2021, acoustic tags have been surgically implanted into 93 of these catchable-size cutthroat trout. This is critical for monitoring spawning mortality, as the receivers can pick up on when fish enter tributaries, and if they return to the lake. A handful of the acoustic tags also record the temperature and depth of each fish. The temperature-and-depth graph indicates how much the seasons dictate the movement of this cutthroat, which appears to have depth and temperature preferences.

The acoustic tag in this fish shows what depths the fish swam to and the temperature it favoured during the year. (Credit: FFSBC)

What the Cutthroat Tagging Program Data Tells Us

While the program is still relatively new, the data has provided a better understanding of this elusive fish’s habits. While a small percentage of spaghetti-tagged cutthroat have been caught (~10% each year), it appears that mortality connected to natural causes is more significant than angler harvest. The data collected essentially concludes that spring is a time for high mortality relating to the spawning events that weaken the fish, making them more susceptible to disease and predation (bears, birds, lamprey, and other fish), as well as being more vulnerable after being caught and released. Furthermore, the tracking data notes that fish chose to remain in the sub-basin after being captured and tagged. The movement of fish is available on Kintama’s website—you can even enter a specific fish’s tag code and watch its movements around the lake on an interactive monitor (in depth instruction can be found on FFSBC’s website).

Using Kintama’s open-source interactive tracking map, the viewer can this cutthroat’s journey all over Cowichan Lake

While undergoing tagging efforts an increasing number of fish were caught with lamprey marks and scars. Lamprey (click here for what is a lamprey) are native to both Cowichan and Mesachie lakes but they engage in a sinister, parasitic behaviour. After latching themselves onto a host’s body, they gnaw through the fish’s scales and skin to suck blood from their host.

A fresh lamprey bite on this newly tagged fish. Photo: Mike McCulloch with the Province of BC.

This fish has three healed lamprey marks that have caused significant stress. Photo: Mike McCulloch with the Province of BC

Since the biologists tagged 325 fish from 2019-2022, they noted high amounts of lamprey marks meant low numbers of caught cutthroats (suggested from angler surveys). Within this lamprey scarring analysis, biologists like Brendan Anderson, a senior fisheries biologist, began noting how cutthroat trout caught from different basins and locations meant different rates of scarring. According to Anderson, data increasingly shows that lampreys, a protected species, have a large impact on Cowichan Lake cutthroat trout populations. More data and research is required on both lamprey populations and this parasite’s effects on cutthroat trout. The years 2019 to 2022 could merely be a natural cycle of lamprey and cutthroat populations, but only time and research will tell if human intervention is needed on this wild fishery.

What Do Cutthroat Tags Mean For Anglers?

If you see a spaghetti tag on a fish, you can release it or, if legal, you can keep it. While much more data is needed for a more complete understanding of the fishery, it already has given some interesting insight for anglers. Anglers should keep in mind that spawning season (February – March) is when natural-cause mortality is already high, so be sure to set limits on fish that are caught and released, and always use proper catch-and-release measures (rubber net, wet hands, minimize the fish’s exposure to air and time out of the water, fingers away from gills, etc). The future iterations of this insightful tagging program will further the understanding of this mysterious wild fishery and the approach to regulations. While this program has produced great insight, Anderson notes the intricacy of this fishery as: “Cutthroat are complex fish operating in a complex system.”

The lake-run cutthroat tagging program will continue to help us understand the impacts fishing has on this wild fishery and how regulations could be tightened or loosened depending on what the coming data from the tagging program suggests.

This article appeared in Island Fisherman magazine, never miss another issue—Subscribe today!