Eulachon study abandons old techniques due to COVID-19
May 14, 2020
For the first time, this year’s eulachon run estimate will be calculated without using the “mark-and-recapture” technique. The change in the estimate conducted each year by the Chilkoot Indian Association is due to COVID-19 concerns.
The eulachon, or candlefish research project was initiated in 2010, spurred by a decline in the southern population located off the coast of Washington, Oregon and California, CIA fisheries specialist Ted Hart said. Eulachon aren’t a commercial fish, so traditionally they haven’t attracted a lot of research funding.
“It’s up to us to do our own monitoring,” Hart said. CIA initiated the study to document year-to-year eulachon population fluctuations and to establish a baseline and look for trends. The Chilkoot Indian Association partnered with Takshanuk Watershed Council to collect the data.
“(Eulachon) are a very, very important little fish,” Hart said. “They have major cultural significance. A big part of why we’re here is because of the eulachon.” Centuries ago, oil rendered from eulachon was traded between Tlingits in the Chilkat Valley and tribes in the Interior, giving rise to a trade route known as the “Grease Trail.” To this day, eulachon grease remains a coveted item exchanged between tribes.
The study monitors eulachon run size at rivers in the upper Lynn Canal including the Chilkoot, Chilkat, Ferebee, Katzehin, Taiya and Skagway Rivers.
In past years, the eulachon study has always employed a mark-and-recapture method to estimate run size. The technique involves setting a trap to collect fish. For the Chilkoot River, the trap is located near the bridge. Crew hired to conduct the study clip the adipose fin, located along the spine near the tail fin, to “mark” the fish. Fish are released back into the river. Upstream, between the weir and the lake, crew members wade into the water and capture eulachon, some with clipped adipose fins. The ratio between those with clipped fins and those without allows scientists to extrapolate an estimate of the total number of fish.
To conduct this portion of the study requires crew members working in relatively close proximity, Takshanuk Watershed Council executive director Meredith Pochardt said. “This year, it didn’t seem like a good idea.”
Since 2014, the eulachon study has employed a second method for estimating population size involving environmental DNA (eDNA) sampling. This technique is better suited to social-distancing practices since it can be done without additional staff. Pochardt collects water samples from the river before, during and after the run, and sends samples to a lab in Oregon for testing. A run estimate is reached based on the concentration of eulachon DNA in the water samples.
Mark and recapture is a “tried and true population estimate technique used by fisheries,” Pochardt said. Use of the eDNA technique to arrive at population estimates is a relatively new innovation. In recent years, the eulachon study has employed both techniques, comparing the results to establish the accuracy of the eDNA method. So far, the run estimates produced by the two techniques have been very similar, she said.
This year was the first year they did not employ both techniques, Pochardt said. The eventual goal is to rely on just the eDNA technique to reach a population estimate as it does not require handling the fish. However, next year, she said she expects the study will employ both techniques once again. She said they would like to get a few more years comparing the results of the two methods before shifting to eDNA as the sole method.
This year’s Chilkoot River eulachon run began April 23, the first day fish were observed in the river. By May 8, the run was essentially over. No fish were observed at the bridge and only a few remained upstream.
“I think it was a really good run. The fish seemed really big,” Pochardt said. She said she doesn’t think the run was quite as large as last year’s, which was the largest since sampling began in 2010.
Pochardt said it’s hard to know what causes runs to fluctuate from year to year. “We don’t understand enough about this species to say a whole lot definitively.”
Questions remain about where eulachon go when they leave the upper Lynn Canal. “They go out to the Gulf of Alaska, but as far as where exactly they end up, there hasn’t been much research,” Pochardt said.
In the future, data from the Chilkoot Indian Association’s study could be used to see how human activity in the area affects the run size or to inform decisions about population management, Hart said. Ketchikan began monitoring its eulachon populations a few years ago. The past two seasons, they haven’t been able to fish because the run has been too small.
“We feel pretty good about the (upper Lynn Canal) population right now,” Hart said.
In addition to their cultural significance, eulachon also play a role in the local marine ecosystem.
Eulachon provide an important food source to sea lions right before they give birth, Pochardt said. The females bulk up on eulachon, a nutritious, high fat food, to sustain them through the fasting period while they nurse their young.
“Without eulachon, I think we would quickly see a decline in the sea lion population,” Pochardt said.
CIA and Takshanuk are still waiting on an official run estimate for this year, Pochardt said. The eDNA estimate usually takes a couple of months, and it could take longer if social-distancing measures delay work at the Oregon lab.