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Freshwater Mussels

Happy New Year and welcome back to my PEI wildlife track and sign series! Let’s start the year with a group of Island animals you may not have given much though to: Freshwater Mussels. Shown here is sign of our most common species, the Eastern Floater (Pyganodon cataracta, Photo 1).

Photo 1: Eastern Floater shell

Most people are familiar with PEI’s famous Blue Mussels (Mytilus edulus), considered a delicacy throughout North America. That’s a saltwater species, more closely related to Scallops and Oysters than to Freshwater Mussels. Freshwater Mussels are very different and – in my opinion – far more interesting! (Though not edible. Their taste is described variously as dirty shoe, mud, and garbage ).

As a group, Freshwater Mussels are among the most endangered animals in North America, for a few reasons. First, most species need clean water. As land clearing, development and population all increased, so too did discharge of sewage, nutrients, and other contaminants into our water. Today, there are laws limiting this, but many Freshwater Mussels are slow-growing, long-lived species – some can be as much as 100 years old! The actions of a century ago have impacts that extend to present-day.

Next, Freshwater Mussels rely on fish for reproduction. Fertilized mussel eggs are released into the water where they attach to the gills of a passing fish. They spend their larval stage as parasites, feeding on the fish for several weeks until they’re ready to drop to the streambed and grow into adult mussels. This strategy is both brilliant and limiting. Brilliant in that it provides baby mussels with food, protection from predators, and transportation to a new home all at once. Limiting in that many Freshwater Mussels use just a single species of host fish. If the host fish becomes less common or can’t reach the Freshwater Mussel beds due to dams or other blockages, the mussels can’t reproduce.

Finally, most Freshwater Mussels prefer streambeds with sand, gravel or cobble rather than finer mud or silt. The same changes in land use that added contaminants to our streams and rivers also added silt, making some areas no longer suitable for these species. The Eastern Floater is more widespread on PEI that our other two species because it is relatively tolerant of poorer water quality and silty streambeds, and uses the very common Three-spine Stickleback (Gasterosteus aculeatus) as its fish host.

Despite their low public profile, Freshwater Mussels provide many important ecological services. As filter feeders, they clean our streams and rivers. Their excretions nourish bacteria, algae and invertebrates that are critical to the aquatic food web. Their shells provide habitat for insect larvae, snails and other invertebrates, which in turn provide food for fish. And they are useful food sources for Mink, Muskrat, Raccoon and Otter. I suspect this pile (Photo 2) was a Mink’s dinner, given the tracks I found nearby. That hole in the stream bank may well be (or have been) a den – I didn’t reach inside to find out!

Photo 2: A pile of Eastern Floater shells, sign of a mink feeding based on the nearby tracks. That could be a den in the bank - I didn't reach in to find out!

The good news is more people are becoming aware of the presence and importance of PEI’s Freshwater Mussels. The great work of our many watershed groups will help these Island species. Another part of PEI - untamed!

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