WEBER COUNTY — Over the weekend, visitors to Pineview noticed a significant number of dead fish along the shoreline of the reservoir.
The fish were almost all one species — black crappie — and most of them were young, about four inches long.
Chris Penne, aquatic biologist with the Utah Division of Wildlife Resources, said that DWR staff estimate that thousands of fish have died.
The dead fish are concentrated in the narrows by the dam, including some of the beach access areas, swim beaches and the port ramp area where boats launch, Penne said. Wind may also blow the dead fish to other parts of the reservoir.
But Penne said water quality is likely not to blame, though they can’t say for sure.
Penne said the Weber-Morgan Health Department has regularly taken samples for harmful algal blooms, and there have not any harmful blooms up to this point.
Following reports of dead fish, the health department took more samples, and those results are pending, Penne said.
The massive die-off has multiple causes, Penne said, including Pineview’s current water level, recent high temperatures, and a particularly large population of fish.
“The gist of it is summers are hard on fish,” Penne said. “Just like with humans, the temperature gets warmer than they like. In the case of some species, like crappie, when that water gets warmer, it holds less oxygen ... so that makes breathing it a little bit more of a challenge for them.”
Young black crappie like to have cover from predators, so they tend to live in flooded vegetation or brush, where they can safely eat, Penne said.
Pineview has dropped about five feet, so the young crappie have lost access to their vegetated habitat.
“Rather than going to ... live in the open water where the predators are, they’d rather take their chances along the shorelines in the shallow water,” Penne said.
The problem is that the shallow water is crowded, making it more likely for the fish to be affected by disease, infection or starvation, Penne said.
“We don’t really try and look for one (reason) because they’re all linked together,” Penne said. “Crowded, stressed fish are a lot easier to hit with disease, and so it could be one (thing) that killed them (or) it could be all of the above.”
Last year, there was a similar die-off event at Pineview, but hundreds of fish died then, compared to thousands killed this year.
However, those who like to fish should not conclude that they’ll be out of luck at Pineview.
“All things the same, if we didn’t have so many fish right now, I don’t think you’d be seeing this,” Penne said. “There’s no denying that temperature is part of it, but we’ve had these temperatures in other years and haven’t had this issue, so when you get this many fish, when they get a lot more crowded, that’s where you start getting problems.”
“They’re kind of the victim of their own success,” Penne continued. “Pineview’s got a lot of fish in it right now. While this may look like a lot, this is still a fraction of what’s out there.”
It’s difficult to say how many more fish will die. If temperatures stay hot, the die-off will likely continue. If it cools down, it will likely get better, Penne said.