In partnership with Takshanuk Watershed Council (TWC) and Chilkoot Indian Association (CIA), the STC Environmental Department has begun its 4th year of data collection on eulachon (Thaleichthys pacificus) and is excited to announce that this year’s run has commenced in both the Taiya and Skagway Rivers!
Reuben Cash, environmental coordinator, twisting closed a Whirl-Pak sample bag full of Taiya River water.
Little was known about the population structure of eulachon in Southeast Alaska until TWC and CIA launched a study in 2014, using mark-recapture statistical methodology and cutting-edge environmental DNA (eDNA) sampling techniques to gain a better understanding of the size and timing of the runs.
Traditional statistical methods like mark-recapture can estimate population size with high confidence, but are time-consuming, logistically complex, potentially stressful to the fish, and costly. In years past, STC staff partnered with Klondike Gold Rush National Park and set up a modified fyke net in the lower Taiya along with boat-based larval outdrift sampling to facilitate these methods, requiring multiple personnel to work long days for nearly a month. Conversely, eDNA sampling can be performed by a crew of two in a few hours, processed by a single lab technician in 1-2 hours, and does not require any fish handling. After several years of collecting both traditional and eDNA population data, it was established that eDNA methods offer a reliable index to actual run sizes. Therefore, in 2019 STC ditched the fyke net and switched solely to eDNA sampling.
The filtering setup at the STC lab.
Our field crew collects water samples daily from two locations on each river during the run – one near the estuary and another approximately 1-5 km upstream of the river mouth. These samples are vacuum pumped through a micropore filter which captures the eDNA, and then sent to Oregon State University for analysis. Additionally, the crew measures water quality, collects environmental data, and conducts daily wildlife censuses to track changes in diversity, total count, and behavior, information that can indicate both the initiation and conclusion of the run. Of course, STC’s environmental coordinator was ready with his GoPro to capture underwater video of these fish too.
Counting wildlife at the mouth of the Taiya River.
Collecting water quality data in the mainstem of the Taiya River.
eDNA sampling for population estimates is an amazing technique that has allowed our environmental department to continue participating in TWC and CIA’s ground breaking study, and has great potential for other wildlife applications too. Say hello or wave to our field crew if you see them out there!