Freshwater drum

Freshwater drum occupy more of North America than any other freshwater fish on the continent, and the breadth is itself the interesting fact.

THE RANGE RUNS FROM GUATEMALA TO HUDSON BAY — the widest latitudinal distribution of any North American freshwater fish. A species that tolerates that range is a species with very broad environmental tolerances, and drum have them: they handle turbidity, warm water, cold water, hard bottom and soft.

THE HABITAT IS LARGE RIVERS, RESERVOIRS AND LAKES, and within them the fish is a bottom dweller. Drum are found over sand, gravel, rubble and soft sediment, and they concentrate where their food is.

WHICH MEANS MUSSEL AND CRAYFISH GROUND. Drum have heavy pharyngeal grinding plates in the throat and crush hard-shelled prey with them, so a bed of molluscs is a drum feeding station. In the Great Lakes this includes very large quantities of invasive zebra and quagga mussels, which makes drum one of the few native fish exerting meaningful predation on those species.

THEY TOLERATE TURBIDITY WELL and are abundant in the muddy lower reaches of big rivers where clear-water species are not, which is a large part of why they are so widely caught and so widely unappreciated.

THE ONE UNUSUAL LIFE-HISTORY DETAIL SHAPES THE DISTRIBUTION. Drum release buoyant eggs that drift near the surface, which is rare among North American freshwater fish and gives the species enormous dispersal — an egg spawned in a river headwater can end up a very long way downstream. That is part of the explanation for a range spanning thirty degrees of latitude.

AND FOR AN ANGLER THE PRACTICAL POINT IS SIMPLE: drum are found on the bottom, over hard feeding ground, in big water — which is exactly where people fishing for catfish, carp and walleye put their baits, and why the drum keeps turning up.

Freshwater drum is one of the more robust fish in this catalogue and one of the more casually treated, and the gap between those two facts is the reason this section exists.

THE PHYSICAL HANDLING IS STRAIGHTFORWARD. A supporting grip under the belly with the fish held horizontally, wet hands, and no vertical lift by the jaw on a heavy fish — a large drum is a substantial animal and its own weight on its jaw structure does damage. The pharyngeal grinding plates that crush mussels are deep in the throat and are not a hand hazard. The spiny first dorsal and the gill covers are, in the ordinary way.

WHAT ACTUALLY GOES WRONG IS THE ATTITUDE RATHER THAN THE TECHNIQUE. Drum are frequently caught by anglers fishing for something else, they have a reputation as a nuisance fish across much of their range, and they are consequently thrown up the bank, left on stringers, or handled with a carelessness that would be unthinkable applied to a bass or a walleye of the same size. A fish's ability to survive rough treatment is not a reason to give it any.

AND THE ECOLOGICAL ARGUMENT IS WORTH PUTTING TO ANYBODY WHO REGARDS THEM AS RUBBISH. In the Great Lakes and elsewhere, drum consume very large quantities of invasive zebra and quagga mussels — they are one of the few native fish equipped to crush them. A species doing that is doing more for the system than most of what is being fished for over the same ground.

THE OTOLITHS ARE THE OTHER THING PEOPLE KNOW ABOUT THIS FISH. The large, dense, white ear stones — the 'lucky stones' found on lake shores — come from drum, and they are a genuine curiosity. They are also inside a living animal, and the practice of killing a fish to obtain them is a poor trade.

IF THE FISH IS TO BE KEPT, it is perfectly good eating handled properly and promptly, and its reputation for being otherwise is largely a consequence of being left in a warm boat for hours by somebody who did not intend to keep it when they caught it. Decide before the fish is landed, and act accordingly either way.

Freshwater drum reach a size that surprises anglers who know them only as an incidental catch, and the geography of that size is more informative than the numbers alone.

MOST FISH CAUGHT ARE HALF A KILO TO TWO AND A HALF, at thirty to fifty centimetres. That is an ordinary drum and it is what a bottom-fishing angler over a mussel bed encounters repeatedly.

OVER FIVE KILOS AND SIXTY CENTIMETRES IS A LARGE ONE anywhere in the range, and fish over ten kilos are rare wherever they occur.

REPORTED MAXIMA EXCEED TWENTY-FIVE KILOS AND NINETY CENTIMETRES, and the very largest fish come from the big southern river systems rather than from the northern lakes. That is the informative part: the same species across an enormous latitudinal range grows to quite different sizes at different ends of it, because growing season length and water temperature set how many months a year a fish can put on weight.

WHICH IS WHY THIS SPECIES IS A USEFUL ILLUSTRATION OF A GENERAL POINT. Drum has the widest latitudinal range of any freshwater fish in North America, from Guatemala to Hudson Bay. A fish at the northern edge has a short growing season, grows slowly, matures late and lives a long time; a fish in a warm southern river grows fast and reaches a larger size sooner. A size figure quoted without a location is close to meaningless for a species spread over that much latitude.

AGE IS THE OTHER HALF OF IT AND IT IS THE PART THAT MATTERS FOR HANDLING. Drum are long-lived, and the otoliths that make them famous are also what makes their age readable — the ear stones lay down annual increments and can be counted. That work has established that large drum are old drum, in some populations very old indeed. A big fish from a northern lake represents decades of slow accumulation and is not replaced quickly.

SO THE PRACTICAL READING IS THE ORDINARY ONE. The exceptional figures belong to the warm end of the range. A large fish in cold water is old rather than merely big. And the fish that gets thrown up a bank because it is not a walleye may well be the oldest animal anybody caught that day.

Freshwater drum does two things that are unusual for a North American freshwater fish, and both of them are visible in how its year runs.

THE YEAR ITSELF IS CONVENTIONAL ENOUGH. Fish move into shallower water to feed and spawn through spring and summer, and drop into deeper water in winter. Within that, they concentrate over hard-bottom feeding ground — mussel beds above all — which is why an angler fishing for something else over the same ground keeps catching them and why they appear to be everywhere at once.

SPAWNING IS WHERE IT BECOMES UNUSUAL. Drum spawn in open water in late spring and summer, and they release BUOYANT EGGS that float near the surface. Almost every other North American freshwater fish either attaches eggs to something, buries them in gravel, or guards them in a nest. Broadcasting floating eggs into open water is a marine strategy, and it is a reminder that this fish is a drum — a member of a family that is otherwise entirely marine.

WHAT BUOYANT EGGS BUY IS DISPERSAL. Eggs and larvae drift with wind and current rather than staying where they were laid, which spreads a year class across a very large area and puts young fish into habitat the adults never visited. That mechanism is a substantial part of the explanation for the species' enormous range — the widest latitudinal spread of any freshwater fish in North America.

WHAT IT COSTS IS PARENTAL CARE. There is none. The eggs go into the water column and the adults are finished, which means recruitment is entirely at the mercy of conditions in the weeks that follow — wind, temperature, and what is in the water eating drifting eggs.

THE SECOND UNUSUAL THING IS AUDIBLE. The species produces a genuine grunting sound using specialised muscles vibrating against the swim bladder, and it is loud enough to be heard through a hull. Sound production of that kind is a sciaenid family character — the drums and croakers are named for it — and it is associated with spawning in the marine members of the family. It is one of very few freshwater fish in the region that a person can hear.

FEEDING RUNS THROUGH ALL OF IT. Molluscs, crayfish, insect larvae and small fish, with hard-shelled prey crushed by heavy pharyngeal plates in the throat — including, in the Great Lakes, very large quantities of invasive zebra and quagga mussels.