Report: Big Hole grayling populations low despite voluntary efforts
Laura Lundquist
(Missoula Current) A recent analysis of the Big Hole River indicates that arctic grayling survival hasn’t improved over almost 20 years so some are saying voluntary water conservation doesn’t go far enough. Others say conditions are as good as they could be.
On Thursday, the Center for Biological Diversity, a wildlife advocacy nonprofit organization, released a 42-page report that analyzed almost 20 years of demographic and genetic data gathered from arctic grayling along with streamflow and temperature data in the upper Big Hole River.
The report authors found that low streamflow continues to be a chronic problem, particularly during hot summers, and that correlates with low recruitment of young fish into adulthood causing population numbers to remain flat when averaged over time.
The study team was led by Gary Rule, a recently retired fisheries biologist with NOAA Fisheries who specialized in Endangered Species Act species status reviews, critical habitat analyses and scientific permitting. The report was prepared for the Center for Biological Diversity.
“The weight of evidence from decades of monitoring shows that Big Hole grayling habitat conditions — and overall viability — have not improved. Low late-summer flows and elevated temperatures still squeeze rearing habitat, and adult abundance remains essentially flat since the historic lows documented in 2002,” Rule said in a release.
While agreeing that the recent multi-year drought has hurt streamflows and fish, Big Hole water users say voluntary conservation is working despite the drought.
“This study confirms the obvious. But I just returned from the annual Arctic Grayling working group meeting and the actual data about grayling numbers are impressive despite the terrible precipitation and flows we've been having,” said Pedro Marques, Big Hole Watershed Committee executive director.
Arctic grayling have been introduced into the Ruby River and 10 mountain lakes in Montana, but the report focused on arctic grayling in the Big Hole River since it’s the only native population that still uses river habitat. But since the 1980s, that habitat has become less hospitable.
Montana Fish, Wildlife & Parks recorded catching 111 fish per mile in the upper Big Hole in 1983. But after repeated dewatering of the river and a severe drought in 1988-1989, that dropped to a catch of 22 fish per mile in 1989. After that, grayling populations never recovered to those previous levels.
Most recently, the Fish and Wildlife Service decided in early 2020 that the Upper Missouri River grayling didn’t need endangered species protection, partly because of the lake populations being protected by federal land management, and partly because, in the Big Hole River, the CCAA has “addressed many past threats, and resulted in both improvements in habitat conditions and increases in the number of effective breeders.”
But some question whether the CCAA program is sufficient to preserve arctic grayling in the Big Hole River. To assess arctic grayling demographics, the report authors calculated the number of breeding individuals, which reflects how many fish are effectively reproducing each year, rather than how many fish are present in the river. Then they looked at the number of fish caught per kilometer using electrofishing in the fall.
The report found that the number of breeding individuals in the river has averaged about 175 over the past two generations. There’s been a slight increase in the average since 2007 but the report authors say it’s a weak tendency “driven in part by episodic high years rather than consistent improvement through time.” In 2013, there was a sudden jump to 450 breeding individuals followed by a drop to 100 in 2016.
When electrofishing in the river mainstem, technicians caught more first-year fry after 2016 - seven fry per kilometer compared to less than one before 2016 - but saw no associated increase in the number of older fish caught, indicating that only a small percentage of fish survived to their second year. A similar story was found in the Big Hole tributaries.
When the report authors looked at genetic data for the grayling, they found some gene variations called alleles have been lost due to population crashes and small population size. They also found that the effective population - the breeding population averaged over time - is smaller than what is needed to maintain genetic health in the river population.
Finally, the report analyzed streamflow and water temperature data and confirmed that the river often exceeds the heat stress temperature of 70 degrees Fahrenheit brought on by high air temperatures and low river levels.
“Seasonal instream-flow targets under the Big Hole River Candidate Conservation Agreement with Assurances are not met with sufficient frequency, and several segments show declining compliance over time,” the report authors wrote. “In our professional judgment, the weight of evidence supports listing the Upper Missouri River DPS under the Endangered Species Act.”
But the Big Hole Watershed Committee is pushing back against that conclusion, saying the Fish and Wildlife Service is about to renew the Big Hole CCAA program for another 50 years “to continue the progress we've made and all landowners are renewing their agreements.”
“The (Center for Biological Diversity) remain without a real answer to the problem and refuse to join those doing the real work for the fish- including every federal and state agency, numerous NGOs, universities and landowners all working together for a shared objective. Their attorney fees would be much better spent funding projects on the ground that make a difference for the resource,” Marques said in an email. “Mandating that the State ensure a mandatory minimum flow of water would require the State to violate or change Montana water law and private property rights or make a futile call on its in-stream Murphy water rights.”
Contact reporter Laura Lundquist at lundquist@missoulacurrent.com.