I met my first Arctic grayling, the iconic freshwater salmonid of the North, the summer of 1990 while helping test climate change predictions as a young, impressionable research assistant for the Arctic Long Term Ecological Research (ArcLTER) project on the North Slope of the Brooks Mountain Range, Alaska. Since then, I have sampled, weighed, measured, tagged, and tracked thousands of Arctic grayling in order to assess biotic responses of Arctic aquatic ecosystems to rapid climate change. A recent 2022 study estimated the rate of Arctic warming at 4 times that of the global average, much faster than previously estimated, which could have strong repercussions for cold-adapted species, like Arctic grayling. Will Arctic grayling persist in a warmer Arctic through processes such as acclimation (phenotypic plasticity), moving to more suitable habitat (migration), or adaption (genetic trait evolution) given this rapid rate of change? My research team and I traveled to the remote headwaters of the Kuparuk River, Alaska to reassess the river's long-studied Arctic grayling population and to help answer questions regarding climate change and persistence of cold-adapted species.
Fig.1 Our remote field camp in the headwaters of the Kuparuk River, Green Cabin Lake, AK.
We hit the dusty "Haul Road" en route for Toolik Field Station after 8 days of quarantine in Fairbanks. We spent one extremely hectic day at the field station finding, weighing, and organizing our field gear into helicopter sling loads for deployment to our remote field camp in the headwaters of the Kuparuk River.
Fig. 2 Team Grayling at the Yukon River visitor center, free from quarantine and en route to Toolik Field Station via the Dalton Highway (aka the Haul Road, aka the Ice Road Truckers' road). From left to right: Dr. Linda Deegan, Dr. Heidi Golden (me), and Kathleen Lewis.
We had no time for photos while at Toolik Field Station or during our helicopter operations out to the Kuparuk headwaters, but I did snap one shot of Toolik Lake and the field station upon our approach the previous day.
Figure 3. Approaching Toolik Lake and Toolik Field Station.
The helicopter dropped our gear and us at Green Cabin Lake the next day. Once on the ground, securing shelter became the first priority for setting up field operations. Weather in the Arctic can move fast and I have personally experienced changes from warm, clear, and sunny to snowing sideways in minutes. Thus, our communal tent, a 12' x 12' Arctic Oven provided by NSF's Polar Field Services, went up first and provided a relatively warm, dry space for sheltering, meeting, and cooking.
Figure 4. Field camp priority number one: shelter! Linda and Kathleen choose a relatively flat, less-rocky site for the communal tent.
Once shelter was secure, priority shifted to capturing Arctic grayling. We used a fish weir comprised of black plastic mesh stretched across the lake outlet, anchored at the bottom with rocks, and held in place with metal reinforcement bar (rebar) pounded into the outlet bed. Setting up this weir provided a full-body workout beyond any available at the gym! Traps, situated on either side of the weir, helped funnel migratory grayling into temporary holding chambers. The traps included a foldable dog crate retro-fitted with a mesh entryway and a winged fyke net (added later). We added the fyke net to the weir system after watching fish approach and either enter the dog crate trap or stage in front of the weir. This additional net greatly improved our fish capture rate.
Figure 5. Fish weir and dog crate trap (left), and tagging station (center) and fyke net (right) at the outlet of Green Cabin Lake.
At least twice daily, we checked the traps and removed, measured, weighed, and PIT tagged (if the fish was not already tagged) each fish captured. This data, along with any other notable information on fish condition and health, was recorded by hand and later entered into our long-term database.
Figure 6. Arctic grayling within the dog crate trap, ready to add their data to our population assessment.
After collecting fish data for a couple of days, a few things became apparent based on our past experience. Not as many fish were entering the lake compared with past migration surveys, we seemed to be lacking the most common size class for this Arctic grayling population (the 30-something cm fish), and many fish showed signs of stress.
We alleviated concerns that we might have missed the fall migration during quarantine by visiting our downstream PIT antenna array, which had been collecting data throughout the summer including while we were in quarantine. The PIT antenna array (Kup2) recorded the date, time, and PIT tag number for every tagged fish that passed by the antenna. We hiked to the Kup2 antenna and downloaded then analyzed the data, which suggested that one pulse of incoming fish had passed into the lake just prior to our arrival but that the migration was still underway (Fig. 7).
Fig. 7 Kup2 antenna array (a. and b.) and data (c.). The Kup2 antenna consists of an on-shore, solar powered reader (a.) and an in-stream antenna-wire loop connected to a tuning box (b.). The data (c.) show the number of uniquely tagged fish detected at the antenna (y axis) for each day the antenna was functioning (x-axis) during the 2022 field season. Also indicated are the dates we were in Fairbanks (blue box), at Toolik (arrow), and at Green Cabin Lake (purple box).
However, concerns regarding our missing Arctic grayling size class were emphasized when we compared our 2022 data with our long-term migration survey records. Our 2022 fall migration survey data showed a bi-modal (two peaks) length distribution with lots of small fish (juveniles, less than 30 cm total length) and lots of very large adult fish (Fig. 8a). The 2022 adult fish length distribution was significantly different compared to previous migration studies. The 2022 length distribution showed a shift toward larger sized fish and lacked the usual 30-ish cm size class which normally comprised the bulk of the population in past surveys (Fig. 8b).
Fig. 8 Arctic grayling total length (cm) distributions: Fall 2022 survey data (A.) adults (pink) and juveniles (blue). Adult length comparison (B.) between fall 2022 survey data (pink) and previous fall survey data from 1988 to 2016 (grey).
Another interesting observation from our 2022 fall survey included the occurrence of notable pathology, such as wounds and other oddities, which might (or might not) be associated with environmental stress. Anecdotally, there seemed to be more fish than usual missing portions of their fins and opercula, and many that had wounds often associated with a white substance (Fig 9). We still need to compare our 2022 findings with past data to verify whether or not what we witnessed this past fall is significantly different from previous years.
Fig 9. Examples of Arctic grayling pathology noticed during the 2022 fall survey, including damaged operculum (A.), tumor on nose (B.), ulcer on operculum (C.), internal fatty tumor (D.), side wound associated with white substance (E.), and white spot on an otherwise healthy looking fish (F.).
As often occurs with scientific research, we are left with more questions to answer regarding the potential influence of climate change on persistence of cold-adapted species. Unfortunately, due to the COVID-19 pandemic, our Grayling Team was unable to conduct research or surveys of Arctic grayling on the North Slope since 2018 and it seems much has happened during this absence. Changes in the health and abundance of individuals within and to size structure of the Kuparuk River Arctic grayling population could be indicators of stressful underlying environmental shifts, possibly due to climate change. Going forward, we hope to revisit Green Cabin Lake to conduct a mark-recapture population estimate to determine whether or not this population is in decline. We might also collect samples of the wound-associated 'white substance' for pathogen identification. One certainty underscored during our 2022 survey is the continued need for long-term data, such as data set from the ArcLTER and other programs, which provide background for identifying and tracking change over time and hopefully help facilitate the ability to more effectively address and manage ecosystem disfunction.