Coaster Brook Trout By Shawn Perich
[TOP LEFT] An Ontario coaster brook trout. | SARAH FERGUSON [ABOVE] A Minnesota coaster taken on a fly. | ANDREW SELVIG
When is a brook trout like an onion? One answer may be when it is fried golden brown. But a better answer is when Lake Superior fish managers and researchers team up to take multiple approaches to learn more about this native fish. The brook trout lives in cold streams running into Lake Superior, as well as in the lake itself. In streams, it is typically a small fish, averaging less than 12 inches in length. In Superior, it is capable of growing much larger, possibly reaching 24 inches or more. In the 1800s, Lake Superior’s giant brook trout, now called coasters, attracted sport anglers from around the world. Unfortunately, during the 20th Century, a combination of factors ranging from overfishing to poor land use practices decimated Superior’s coasters until only remnant populations re-
mained at places like Ontario’s Nipigon Bay and Isle Royale. Now, in the 21st Century, fish managers are trying to restore coasters wherever it is possible to do so. A variety of trout and salmon swim in Lake Superior and its tributaries, but most were introduced from the Pacific coast or Europe. The only natives are brook trout, lake trout and closely related whitefish. After nearly being wiped out by predation from invasive sea lamprey and overfishing, lake trout were successfully rehabilitated during the latter half of the 20th Century. Whitefish remain common in much of the lake and are harvested commercially. Brook trout are abundant in Superior’s tributaries, but remain sparsely populated in most of the lake, including Minnesota, where they frequent shorelines, bays and nearshore waters.
Nick Peterson, Minnesota DNR fishery specialist stationed at French River, makes an analogy to layers of an onion when he describes current efforts in Minnesota and lakewide that use advanced scientific tools and analysis to learn more about brook trout in the Lake Superior basin. They are trying to find answers to some questions. Are there genetic differences between brook trout living in streams and those living in the big lake? Were brook trout native above the waterfalls that create barriers to upstream migration? If there are differences between stream and lake dwellers, is it a function of habitat or something else? “We’re trying to get a holistic picture of brook trout genetics,” Peterson said. On a lakewide basis, the Cooperative Science and Monitoring Initiative is study-
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ing maxillary bones collected from brook trout above and below migration barriers to determine life histories, such as whether an individual fish is a stream resident or migrates to and from the lake. A laser directed at the bone can follow the fish’s life history and determine from elements collected in the bone whether the fish was in the stream or spending time in the lake. Researchers aren’t sure whether coasters are migratory like salmon, leaving the stream at a young age and returning later to spawn, or if they move between the stream and lake depending on stream conditions and water temperature. Researchers know from historic accounts that coaster brook trout were once bigger and more abundant than they are today. But they don’t know how habitat degradation or other factors influence the present population.
