As the spring begins in earnest and the regions lake and rivers begin to thaw, some area residents are concerned about the apparent die-off of a large number of fish and frogs at Tiny Marsh.
After taking photos of the hundreds of fish found on the shore along with a couple of frogs floating on small sheets of ice at the popular hiking spot, local resident Steve Davenport wondered what could be behind it.
But despite concerns, it seems to be a fairly natural phenomenon, according to local naturalists.
“Tiny Marsh is quite shallow and in many places can freeze right to the bottom,” explains Midland-Penetanguishene Field Naturalists president Bob Codd.
Codd, who’s also involved with the Marl Tiny Matchedash (MTM) Conservation Association, says that although this winter was not particularly cold, the region didn't get its customary ‘January thaw’ that allows ice to continue building up.
Fellow MPFN member Ken MacDonald, who serves as the club's program director and outing coordinator, says that this seems to be an annual occurrence at Tiny Marsh.
“Although with the heavy snow cover this year it may be a little worse this time,” he says. “ It has to do with a lack of oxygen in the water under the ice.”
Codd says that appears to be the case in this instance.
“The midwinter thaw allows a pulse of oxygen laden water to recharge the otherwise stagnant wetland,” Codd says. “Many species count on this normally reliable event. Nevertheless this winter fish kill is a reasonably common occurrence at Tiny Marsh.”
Codd says that in his experience, it’s never proven to be a “cataclysmic event.”
“Sufficient fish survive to maintain the population,” Codd says. “The dead fish will provide a feast for many other species at a critical time of year."
Orillia-based master naturalist Bob Bowles says that American Bullfrogs and Green Frogs overwinter in the mud at the bottom of the lakes and ponds.
“We had some cold days this winter and lots of snow,” Bowles tells MidlandToday. “Sometimes if the water levels drop in late fall, the cold and ice freezes to the bottom of locations where it would normally be deep enough not to freeze.”
Bowles says that every spring naturalists and those walking at marshes and other shallow bodies of wate often find dead fish and herps (herpetofauna) including frogs and turtles.
“This is usually due to a change in the water level allowing the frost and ice to form deeper than other years, killing the fish, frogs and turtles that have overwintered at this location in previous winters.
Naturalist David Hawke, who writes a weekly column for MidlandToday, says this time of year can be touch and go for a number of species.
“When the surface ice formed and began holding snow, the sunlight could no longer penetrate down through the water, making this aquatic world rather dark and bleak,” he wrote in a recent column.
“For a while the submergent vegetation continued to release oxygen (as all plants do) but after a while even these weakened shoots and stems failed to function.
"Without oxygen being added to the water, the living conditions for fish and insects can get pretty touch-and-go. For pond fish like the central mudminnow and brown bullhead (the later also called ‘catfish’) this lack of oxygen becomes a life-and-death struggle.”
Codd says it’s disturbing in a way that “our industrial world has conditioned us to see ourselves as the perpetrators” of these types of things and usually that's true.
“Interestingly, this past October we stumbled on an unusual species called Bryozoans in Tiny Marsh,” Codd says. “Evidently these colonies of microscopic animals need well oxygenated water to thrive.
“I'm comfortable that this die-off is a purely natural phenomenon and Tiny Marsh maintains good water quality.”