January 23rd was a beautiful day for the annual Stonefly event. The weather hovered around 30 degrees and the sun shone nicely throughout the volunteers’ time outside. They were searching for stoneflies, an insect that only lives in the healthiest creeks and rivers. The absence and presence of stoneflies, and the trends in their population that we see after visiting a location over and over again, give us clues as to how the water is changing over time.
Unfortunately for the purposes of data analysis and clear-cut answers, stoneflies are affected by more than water quality, however. Strange weather can also play havok on their ecosystems, causing populations to drop off. Our volunteers came back with very low amounts of stoneflies this year, and while we can’t be certain, it is possible that our variable Michigan weather is to blame. You may recall that December was unseasonably warm in 2015, and wonder how that might affect the insects. However, in this case, it wasn’t a warm December that hurt the stoneflies, but instead February 2015, a month that was extremely cold. In fact, it was one of the coldest February’s on record. When streams and rivers are covered by thick ice, oxygen levels decline, which is bad for all aquatic life but particularly bad for stoneflies, who have high oxygen requirements. Also, February and early March are when winter stonefly adults are emerging, mating, and depositing eggs; all activities hampered by extreme cold and ice cover. In summary, the cold 2015 winter had direct consequences for the stoneflies in 2016.
Volunteers did not find stoneflies at many places this year, but five locations in particular that did not have stoneflies were noteworthy as all of them have a long (10+ years) history of always holding stoneflies. In addition, all of these locations have great insect populations at our other events and there are no indications of water quality issues, further strengthening the argument that this year was a weather-related population decline. These five locations were three places on the main branch of the Huron (White Lake, Zeeb, and Bell Roads), Arms Creek at Walsh Road, and Boyden Creek at Delhi Road. Many other locations had reduced numbers or family counts.
Those interested in all results can see them here: PDF report.
Prior to the event, I laid out several examples of things that we would watch for this year:
Davis Creek at Pontiac Trail: Stoneflies have been dropping off here for the past decade. Volunteers did come back with stoneflies this year, though not the winter stoneflies but rather a family that is more widely available. Still, this is good news.
Honey Creek at Wagner Road: Stoneflies were missing here in 2014 for the first time, and unfortunately volunteers did not find them this year either.
Woods Creek at Lower Huron Metropark: Just like Honey Creek at Wagner Road, stoneflies were not found here for the second year in a row.
Insect populations are resilient and can bounce back with good water quality and suitable weather conditions. While this year was disappointing, the mild winter we are experiencing right now may result in a bumper crop in 2017. Come next January, HRWC and its volunteers will be ready to check it out!