Explosion of Gill Lice Besets Wisconsins Beloved Fish

As streams warm, a gruesome parasite is gaining the upper hand against Wisconsin’s iconic brook trout – and anglers bemoan the loss.

By Brian Bienkowski
The Daily Climate

Creepy critters are leaching onto the gills of Wisconsin’s brook trout and choking off their oxygen, stoking fears in anglers that the iconic fish may be on the outs in many streams.

Biologists fear warming waters may be behind the parasites’ recent surge, further hampering a cold-water fish already beset by a host of environmental changes.

gill-lice2“I would say it looks like little minute rice attached to their gills,” said Len Harris, a law enforcement retiree and outdoor writer who has been fishing Wisconsin streams for about 50 years. “It looks like they’re eating away at the gill plate.”

Gill lice aren’t aquatic versions of head lice, the bane of any elementary school teacher. They’re tiny crustaceans that attach to trout and char gills. They make breathing difficult, impede development and can slow sexual maturation – none of which is good news for fish. Worse, warmer water appears to give gill lice a boost. For the state’s only native trout, the brook trout, evidence points to yet another climate change concern.

“They’ve [gill lice] been here many years, but something seemed to change a few years ago,” said Matt Mitro, a fisheries research scientist at the Wisconsin Department of Natural Resources. “We started getting a lot of calls from anglers seeing more in the streams they fish.”

Harris was one of those anglers. Not only is Harris noticing more lice, he’s also catching almost no brook trout in some of his favorite spots, such as Crow and Plum creeks in Crawford County.

Decades ago on Crow Creek “it was nothing for me and my dad to catch 100 in a morning,” Harris said.

State biologists are seeing the same. They saw an “explosion” of gill lice after the unusually warm winter of 2011-2012 and following spring, Mitro said. In March, 2012, streams were experiencing temperatures historically common for June.

“Those conditions are ideal for the reproduction of gill lice,” Mitro said.

In southwestern Wisconsin’s Ash Creek, 95 percent of the 270 brook trout sampled in 2012 had gill lice. Officials estimated a 77 percent decline in brook trout recruitment – the number of new trout under 1 year old – in October 2012 compared to 2007-2011, according to a recent report.

Biologists fear warming waters may be behind the parasites’ recent surge, further hampering a cold-water fish already beset by a host of environmental changes.

Gill lice do not impact Wisconsin’s other inland trout species such as rainbows and browns, just the small, psychedelic-speckled “brookies” – the prize of many fly anglers.

“Brook trout are revered because they are the trout that belong in our streams, and also a bellwether concerning stream health,” said Henry Koltz, the state chair of Wisconsin’s Trout Unlimited.

Stream temperature changes pose other threats to brook trout, said Titus Seilheimer, a fisheries specialist with Wisconsin Sea Grant. Brook trout like cold water – preferring a temperature range of 53-57 degrees Fahrenheit.

Between 1900 and 2010, the average Midwest air temperature increased by more than 1.5 degrees Fahrenheit, and it increased three times that quickly from 1980 to 2010, according to the 2014 National Climate Assessment.

“Increasing air temperatures are correlated with water temperatures and this will shrink available habitat,” Seilheimer said.

Scientists added up the total length of Wisconsin streams and found 33 percent is suitable for brook trout. When they plugged that information into three climate models – best case, moderate case and worst case scenarios of rising air and water temperatures – the percent of suitable brook trout habitat declined by 43.6, 94.4 and 100 percent, respectively.

gilllice“The situation certainly doesn’t look good,” Mitro said.

Adding to the concern: Brown trout are “a larger, faster growing species and more tolerant to warmer temps,” Seilheimer said. Brown trout prefer a range of 65 to 75 degrees Fahrenheit.

It’s not just brook trout that are stressed – it’s the people who chase them.

“This is problematic because anything that threatens our trout populations can indicate systemic problems in our waters,” Koltz said. “This is a large
concern for Wisconsin Trout Unlimited as we view cold water streams as integral to a healthy environment and clean drinking water.”

Koltz added that invasive species, development and pollution are also concerns for the future of brook trout.

Harris admits he’s “been being a pest” to the Department of Natural Resources about it.

“I just don’t see them trying anything other than writing papers,” Harris said.

Mitro said unfortunately there’s not much that can be done to stop gill lice right now.

Wisconsin Trout Unlimited has a reporting form for anglers to contact the Department of Natural Resources when they find gill lice, and also encourage anglers to clean and disinfect their equipment to avoid transferring lice or any other aquatic species.

While those are good practices, when it comes to gill lice, “there’s reason to think they’re already present everywhere in [the]state,” Mitro said.

Brian Bienkowski is a staff writer for The Daily Climate and its sister publication, Environmental Health News. Follow him on Twitter @BrianBienkowski (http://twitter.com/BrianBienkowski).

Photos: Gill lice are tiny crustaceans that attach to the gills of trout and char, making it difficult for fish to breathe, impeding development and sometimes slowing sexual maturation. Courtesy Matt Mitro, Wisconsin Department of Natural Resources.

The Daily Climate is an independent, foundation-funded news service covering energy, the environment and climate change. Find us on Twitter@TheDailyClimate or email editor Douglas Fischer at dfischer [at] DailyClimate.org

The Daily Climate is an independent, foundation-funded news service covering energy, the environment and climate change. Find us on Twitter @TheDailyClimate or email editor Douglas Fischer at dfischer [at] DailyClimate.org