While the mild temperatures this winter have been a blessing to some, it resulted in an unexpected finding at last month’s winter stonefly searches: Terrestrial adult stoneflies, which normally don’t make an appearance until early spring.
“In past years, adults have only been seen in March,” said Sally Petrella, the Friends of the Rouge (FOTR) volunteer monitoring program manager. “Warmer water temperatures can speed up the transformation process from larvae to adult.”
“Our team at Mill Creek: Shield Road found a large number of stoneflies that had already emerged and were warming themselves in the sun,” said Paul Steen, an ecologist with the Huron River Watershed Council (HRWC). “This is a very early emergence and is connected to the warm temperatures that we are experiencing this year.”
Last month, three local watershed advocacy groups — the Clinton River Watershed Council (CRWC), the HRWC, and the FOTR — searched for winter stoneflies in their watersheds.
Winter stonefly nymphs develop in cold, clear running water. When they become adults, they climb out of the water and shed their skins. This normally occurs in late winter, which is why area watershed groups conduct stonefly searches in January.
Because they have stringent water quality requirements such as highly-oxygenated, clean water, winter stoneflies are ideal water quality indicators. The presence of stoneflies indicates good water quality, while their absence points to a potential problem.
The FOTR reported stonefly larvae were found with the help of 70 volunteers at 14 of 32 monitoring sites, which is an “average year,” according to Petrella.
“Most of the stoneflies were found in the Johnson Creek, the Rouge’s only coldwater tributary that flows through Salem Township, Plymouth and Northville,” Petrella said. “The rest were found in the lower branch, including two tributaries (Fellows and Fowler creeks). None were found in the upper branch, main branch or the middle branch downstream of Johnson Creek.”
In addition to searchers finding adult stoneflies for the first time this year, Petrella said there was another unusual finding.
“A type of stonefly called the broadback was found for the first time in the Johnson Creek,” she said. “Broadbacks have only been documented once before and this was in the main branch of the Rouge River at 8 Mile Road. Most stoneflies found are slender winter or perlodids.”
Meanwhile, the HRWC found stonefly larvae at 32 out of 50 sites checked this season. The watershed council also had a few surprising stories to tell after this year’s search, which included over 150 volunteers.
For the first time after four years of sampling, a stonefly was found at the Renton Road site.
Meanwhile, Mann Creek east of Brighton continued to be the best creek in the watershed for stoneflies.
“This is now the sixth year in a row where volunteers have found four stonefly families,” Steen said. “In way of comparison, most of our healthy creeks only have one or two stonefly families.”
A rare species of stonefly for the Huron River watershed was also found at Pettibone Creek on Livingston Road in Highland Township — the nemourid broadback, which is also known as a little brown stonefly.
“This is the first stonefly search in which a team found a stonefly at this site,” Steen said.
Insect populations at Davis Creek south of Brighton, on the other hand, saw a decline, which is consistent with fall and spring monitoring results, as well.
“The water quality of Davis Creek is declining slowly but consistently,” Steen said. “The HRWC is planning on exploring Davis Creek more this coming summer.”