Freshwater Drum are Zebra Mussel Crushers!
Zebra mussels are a growing scourge in Manitoba waters, first arriving in Lake Winnipeg in 2013. They are now found across the lake, and have spread to Cedar Lake. That range is likely, unfortunately, to expand in coming years. As transport by boats is the primary means of spread, we all need to take special care to wash and clean boats to prevent further spread.
Zebra mussels grow quickly and spread rapidly and change the entire lake community where they are found, usually not for the better. They filter out plankton reducing the food available for fish. Recent work in southern Ontario has found that in lakes infested by zebra mussels, walleye grow slower, and populations are reduced. What, then, can we do to rid these ecologically destructive animals from our waters? The short answer is nothing. They are here to stay. The best we can hope for is to minimize their impact by controlling their numbers.
Natural Predators
Zebra mussels are native to Eurasia but face an array of predators in North American waters. Diving ducks, crayfish, catfish, pumpkinseed, bluegill, carp and freshwater drum all prey upon them. Most of these predators, however, lack the key adaptations to feed on them efficiently. Zebra mussels become a low-quality prey item and are avoided if other food is available.
The key is the ability to crush the mussel shell, which in fish requires pharyngeal teeth. They look like molars attached to the gill arches at the back of the throat. Pumpkinseed have them, but none can compare to those found in freshwater drum. The back of the throat of a drum looks like a rock crusher. Unlike any other fish, large freshwater drum can easily handle the largest zebra mussels and when zebra mussels are abundant, drum will graze on them all day long.
Drum are thus our best bet for a natural control.
Our Most Interesting Fish
But this is just one reason why drum are our most interesting fish. Their name derives from the sound male drum make during the breeding season to attract females. Sonic muscles vibrate against their swim bladder to produce a grunting sound. When drum are breeding in June, they can be easily heard at dusk on quiet lakes.
Drum also have a remarkable life history. They grow quickly for their first decade and a half, reaching a length of 50 to 60 cm. At this point they have outgrown all their natural predators and growth slows down. They make take a half century or longer to grow another quarter meter. Drum over 80 cm in length are 70 to 100 years old, rivaling sturgeon as our oldest fish.
They are unique in being the only exclusively freshwater species in a family of saltwater fish found across the world. Black drum in Texas and Australian mulloway are members of the same family.
The freshwater drum is found from the mouth of the Nelson River on the Hudson Bay coast all the way south to Guatemala. No other freshwater fish ranges as widely in North America.
Anglers know that freshwater drum are powerful fish on rod and reel, but they are not highly prized as a table fish. They should, however, be prized as predators of zebra mussel. Given that, perhaps the next time you catch one consider returning it to the water so it can continue to graze on an unwanted invasive species. It might just pay off down the road in an extra walleye or two.