More Findings about the recent catastrophic decline in abundance of the green drake mayfly on the Credit River

I had an opportunity today to read Henry Frania's recent report, More Findings About the Recent Catastrophic Decline in Abundance of the Green Drake Mayfly, Ephemera guttulata Pictet (Ephemeroptera: Ephemeridae) on the Credit River. Last spring, I took part in the Green Drake survey on the Credit, to contribute data to Mr. Frania's research. The afternoon / evening I was on the stream, I saw almost no duns emerge. This, it seems, is consistant with the results discussed in the report. Here is a quote from the abstract, "Monitoring by volunteers last spring of "hatch" activity of the Green Drake mayfly on the Credit River indicated that in recent years, there has been about a 125 fold reduction in the number of subadults (duns) emerging on the Middle Branch and Main Stem of the river compared to the West Branch above the Willoughby Weir, or expressed another way, a stretch of the main river that at one time might have produced 10,000 duns during the "hatch" now yields only about 80 of them."

This is tremendously sad news. The Upper Credit River is a treasure in our midst. I can recall years when I was on stream for marvellous hatches.....and crazy spectactular coffin fly spinner falls, so many spinners that walking along Dominion street at dusk, it was difficult to avoid crunching the great white bugs underfoot.

There appears to be something in the substrate in the Credit that is causing part of the midgut of the nymphs to disintegrate. "Certain toxic chemicals, and various kinds of pathogenic microbes, when ingested by some insects are known to act by destroying the midgut epithelium"

Mr. Frania concludes, "There is now a considerable body of observational and experimental evidence that contamination of the river bottom along the entire upper part of the Credit River has led to the near disappearance of the Green Drake mayfly from much of the river. The Gordon Quill mayfly has evidently already gone extinct on the Credit River, undoubtedly because of pollution of the tributary creeks, but it is hoped that remedial efforts now underway will prevent the Green Drakes from also disappearing, perhaps to be followed by other environmentally sensitive species, such as the Brook Trout, Salvelinus fontinali (Mitchill)".

Henry E. Frania is an entomologist and consultant in Toronto, and Post-doctoral Research Associate, Entomology Section, Department of Natural History, Royal Ontario Museum.