By Mike Jaccarino
5 August 2012
Thousands – perhaps millions – of various types of fish, some endangered, have died in the Midwest, as record summer temperatures dry up rivers and raise water temperatures in some spots to nearly 100 degrees.
About 40,000 shovelnose sturgeon were killed in Iowa last week as the water reached 97 degrees. Meanwhile, Nebraska fishery officials said they've seen thousands of dead sturgeon, catfish, carp, and other species, including the endangered pallid sturgeon, in the Lower Platte River.
And Illinois biologists said the hot weather has killed tens of thousands of large – and smallmouth bass – and channel catfish, and is threatening the population of the greater redhorse fish, a state-endangered species.
So many fish died in Illinois's Powerton Lake two weeks ago that the carcasses clogged an intake screen near a power plant. A spokesman for the coal-fired plant said workers shut down one of its two generators for several hours because of the low water levels at the lake, which it uses for cooling.
'We're talking hundreds of thousands (killed), maybe millions by now,' said Dan Stephenson, a biologist with the Illinois Department of Natural Resources. 'If you're only talking about game fish, it's probably in the thousands. But for all fish, it's probably in the millions if you look statewide.'
'It's something I've never seen in my career, and I've been here for more than 17 years,' said Mark Flammang, a biologist with the Iowa Department of Natural Resources. 'I think what we're mainly dealing with (is) … extremely low flows and this unparalleled heat.'
Indeed, it seems the fish are victims of one of the driest and warmest summers in history.
The U.S. Drought Monitor shows nearly two-thirds of the lower 48 states are experiencing some kind of drought; while the Department of Agriculture has labeled more than half of the nation's counties - nearly 1,600 in 32 states - natural disaster areas.
More than 3,000 heat records were broken over the last month.
Iowa DNR officials said the sturgeon found dead in the Des Moines River were worth nearly $10 million, a value partly based on their highly sought eggs, which are used for caviar. The fish are valued at more than $110 a pound.
However, Gavin Gibbons, a National Fisheries Institute spokesman, added of the sturgeon deaths that they don't appear to have reduced the supply enough to hurt regional caviar suppliers.
Flammang, meanwhile, added that weekend rain improved some of Iowa's waterways and and lakes, but temperatures were on the rise once more, straining a sturgeon population that develops health problems when water temperatures climb into the 80s.
'Those fish have been in these rivers for thousands of thousands of years, and they're accustomed to all sorts of weather conditions,' Flammang said. 'But sometimes, you have conditions occur that are outside their realm of tolerance.'
In Illinois, heat and lack of rain has dried up a large swath of Aux Sable Creek, the state's largest habitat for the endangered greater redhorse, a large bottom-feeding fish.
Illinois biologist Stephenson said fish kills happen most summers in small private ponds and streams, but the hot weather this year has made the situation much worse. 'This year has been really, really bad - disproportionately bad, compared to our other years,' he said.
A stretch of Nebraska's Platte River has dried up, killing a 'significant number' of sturgeon, catfish, and minnows, as well as an unidentified number of endangered pallid sturgeon, said Daryl Bauer, fisheries program manager.
'It's a lot of miles of river, and a lot of fish,' Bauer said. 'Most of those fish are barely identifiable. In this heat, they decay really fast.'
Bauer worries dry conditions in his state will continue, causing a repeat of a memorable stretch in the mid-2000s that weakened local fish populations.
Kansas has also seen declining water levels that pulled younger game fish away from shore lines and forced them to cluster, making them easier targets for predators, said Doug Nygren, fisheries chief with the Department of Wildlife, Parks and Tourism.
Nygren said he expects a drop in adult walleye populations in the shallower, wind-swept lakes in southern Kansas. But he said other species, such as large-mouth bass, can tolerate the heat and may multiply faster without competition from walleye.
'These last two years are the hottest we've ever seen,' Nygren said. 'That really can play a role in changing populations, shifting it in favor of some species over others.
'The walleye won't benefit from these high-water temperatures, but other species that are more tolerant may take advantage of their declining population.' […]