From 2000 to 2010 Wyoming Game and Fish Department and U.S. Fish and Wildlife Service biologists salvaged 240-2685 (average 853) burbot a year from the Pilot Butte Irrigation Canal in the Wind River Drainage, Wyoming. More than 70 percent of the fish were juveniles. As a result, biologists wanted to know where the trapped burbot came from and whether dam operations might be contributing to burbot entrapment in the irrigation canals.
Burbot are highly susceptible to the effects of dams and water diversions as they are weak swimmers, poor jumpers, and have a passive larval drift phase, which makes them unable to cope with both high flow releases and small anthropogenic barriers such as culverts and diversion dams.
During the first three decades of the 20th century, natural lakes on tributaries to the Wind River were augmented with dams and a large diversion on the Wind River was built to store and supply irrigation water to the region. The Wind River Diversion Dam can divert up to 70 percent of the Wind River into the irrigation system. In addition, high flow releases from dam-augmented natural lakes on tributary streams are suspected of flushing burbot out of lakes, making them susceptible to entrapment in the irrigation network.
The Wyoming Unit used three complementary approaches that addressed different time scales to test this idea. They used high throughput genomic sequence data to characterize the relationships between populations within the drainage, assessed where fish were born with otolith strontium microchemistry, and explored movement of burbot in response to dam releases with a PIT-tag, mark-recapture study. They expected to see increased fish movement during high flow dam releases and that the fish entrapped in the irrigation network would be genetically related to Bull Lake fish and have been born in Bull Lake.
Their results were surprising. They found evidence of entrapment of burbot from Bull Lake into the irrigation system coinciding with high flow dam releases, but the numbers were low and could not account for the large number of fish salvaged each year. The most surprising result was most fish trapped in Pilot Butte Reservoir Canal were genetically distinct from Bull Lake and were likely born within the irrigation system reservoir. This suggests the presence of a self-sustaining population within the irrigation network, contradicting the hypothesis that the irrigation populations are primarily sustained through entrapment from the Wind River and its tributary populations. Historically irrigation networks have been viewed as sink habitats, but in this case the construction of the irrigation network and the Pilot Butte Reservoir created a novel habitat that burbot were able to colonize. Pilot Butte Reservoir holds water year-round, but it was previously believed to be too shallow to support burbot reproduction.
Historically this type of study would have focused on tagging fish and observing their movement to see what proportion became trapped. This study used several new approaches in addition to tagging that allowed greater insight. For example, strontium otolith microchemistry uses the strontium isotope ratio in the fishes’ ear bone to assess where a fish was born and high throughput genomic sequence data allows differentiation of more recently diverged populations.
The more thorough and mechanistic understanding of the effects of dams and diversions achieved through this approach will enable resource managers to make more effective conservation plans to mitigate the effects of water development in the Wind River, Wyoming.
The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new, fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by: Annika Walters, Assistant Unit Leader-Fish, USGS Wyoming Cooperative Fish and Wildlife Research Unit.
