Lake Superior and Michigan Fisheries: A Closer Look
Great Lakes recreational fishing has developed into one of the hottest fisheries in the country, annually contributing over $4 billion to local communities and providing 55 million angler days of recreation.
Lake Michigan, which suffered a nuisance alewife explosion and the decimation of lake trout by sea lamprey, made an unprecedented turnabout in the 1970s through the introduction of Pacific salmon. Lake Ontario has undergone a similar metamorphosis and now has a first-rate trout and salmon fishery. Lake Erie rebounded from its pollution problems and within ten years transformed its reputation. It went from “dead” to one of the top walleye lakes in the country.
Anglers and small business owners living near Lake Superior are asking when this lake's rebirth will occur. Lake Superior is often called a cold, sterile lake. Compared to warm water systems that’s true, but compared to Lake Michigan it's not — at least historically it wasn’t.
Comparing the Lake Superior and Lake Michigan fisheries does not imply that expectations for Lake Superior should be based on the Lake Michigan experience. Rather, Lake Michigan can be a reference point for examining the status of Lake Superior and pointing out its unique qualities.
Fish Production Past and Present
Historically, Lake Superior may have been capable of producing 75 percent of the fish Lake Michigan produced on a whole lake basis or 50 percent on a per unit area basis. Evidence for this comes from commercial harvests and a formula developed by a Canadian biologist.
From 1920 to 1945 the commercial harvest of lake trout from Lake Superior averaged 4.4 million pounds per year compared with 6.0 million pounds per year in Lake Michigan. Assuming each lake was producing a near maximum yield, Lake Superior produced 73 percent of the lake trout that Lake Michigan produced. Lake Superior since it is larger, produced just 51 percent of the lake trout Lake Michigan produced on a per unit area basis.
A similar comparison of potential fish production for the two lakes can be estimated using the lakes’ physical features. A Canadian biologist developed a formula that estimates annual potential fish yield using only the mean depth and total dissolved solids of a lake. His formula (using pre 1960 information) predicted a fish yield for Lake Superior of 0.69 pounds/acre/year compared to Lake Michigan’s predicted 1.31 lbs/acre/year.
In other words the formula predicted that Lake Superior had the potential to produce 53% of what Lake Michigan produced in lbs./acre.
If Lake Superior were now capable of producing 50 percent of what Lake Michigan produces both commercially and recreationally, anglers would be ecstatic and the demand placed on marinas, boat launches, motels, campgrounds, and a whole host of other facilities would be overwhelming. But the Lake Superior fishery is producing only about 10 percent of what Lake Michigan produces annually.
Although current comparative statistics are sketchy at best, it is obvious that either Lake Superior is not producing fish to its potential or that Lake Michigan is producing fish beyond its historic capacity. Both statements may be true to some extent.
Why the Big Difference?
Understanding the disparity between the current production of the two lakes requires going beyond a simple examination of the physical properties of each lake and looking at the biological components.
The species composition of both lakes has changed dramatically since the mid 1940s. Sea lamprey, smelt, alewives, and stocked trout and salmon have been the key players in the change and may explain the unexpected differences in production.
As sea lamprey exterminated the Lake Michigan lake trout during the late 1940s, another invading fish, the alewife, gained a foothold and eventually became dominant. The population increase of Lake Michigan alewives in the early 1960s was explosive. From 1957 to 1967, commercial production of alewives increased from 220,000 pounds to 41.9 million pounds. Alewives became so abundant that they clogged water intakes at steel mills, power plants, and municipal water filtration plants. Die offs of alewives became increasingly severe. The 1967 die off was enormous. The U.S. Fish and Wildlife Service estimated that several billion alewives died that spring. Beautiful public beaches became foul-smelling cesspools.
Even after the 1967 die off, the annual commercial harvest of alewives remained greater than the pre-lamprey commercial harvest of all Lake Michigan species combined. Alewives have had detrimental effects on many of Lake Michigan’s native fish because of their extreme abundance, yet they are responsible for the development of the lake's outstanding trout and salmon fishery.
Ten years after wiping out the lake trout in Lake Michigan, sea lamprey repeated the performance on Lake Superior. Alewives were unable to expand in Lake Superior as they had in Lake Michigan, but smelt, another invader of the Great Lakes, did very well. Smelt increased almost exponentially during the late 1950s.
Unfortunately, as smelt increased in Lake Superior, lake herring (a commercial species and the primary food for lake trout) began a steady decline. Some believe the herring decline was primarily due to smelt, while others feel it was due to overfishing. Whatever the cause, smelt quickly replaced herring as the most important food item of trout and salmon.
Whereas lake herring are able to occupy the surface waters of the entire lake, smelt occupy a more restricted in shore habitat. Thus the increase in smelt did not offset the overall loss of forage that resulted from the herring decline. In addition, the smelt population in Lake Superior declined by over ninety percent between 1978 and 1981.
Therein lies the difference between Lakes Michigan and Superior. During the course of the incredible changes in species composition that took place after the 1940s, Lake Michigan ended up with a prolific forage fish that supported an enormous trout and salmon stocking program, while Lake Superior ended up with only a fraction of the forage base that it had prior to the sea lamprey invasion.
In addition, Lake Michigan annually receives 42,000 more tons of nitrogen and 2,250 more tons of phosphorous than Lake Superior. The larger nutrient loading into the smaller Lake Michigan may make it more productive than it was in the past.
Lake Superior Fishery — The Sunny Side
The Lake Superior fishery is not as insignificant as it may appear in comparison to Lake Michigan’s. Although Lake Superior fish are generally smaller, Lake Superior and Lake Michigan anglers enjoy similar catch rates.
Lake Superior anglers have an advantage in that their fish have lower levels of toxic contaminants. It is uncommon to catch a fish in Lake Superior that exceeds the U.S. Food and Drug Administration tolerance level of two parts per million (ppm) for PCBs. On Lake Michigan, in contrast, PCBs in most of the lake trout and many large salmon and brown trout exceed the two ppm level.
Because Lake Superior has more natural reproduction of lake trout than other Great Lakes, it may be better off in the long run. Native lake trout became extinct in Lake Michigan, but remnant populations in Lake Superior survived the lampreys’ onslaught. Today Lake Superior has many areas with natural reproduction and significant numbers of native lake trout (identified by their lack of clipped fins). The Lake Michigan trout and salmon fishery remains almost totally dependent on stocking. The collapse of the salmon fishery in some areas of Lake Michigan and the recent major losses of hatchery production in Michigan and Wisconsin from a new virus suggest that there are risks in relying so heavily on stocking to support a fishery.
Continued increases in natural reproduction of Lake Superior lake trout could be very important. It is roughly estimated that 22 million lake trout yearlings were produced annually in pre lamprey days. Presently, two million yearlings are stocked each year in the U.S. waters of Lake Superior. That stocking rate has resulted in what many consider to be an excellent fishery. Just imagine how continued improvements in natural reproduction could build on that.
Coho salmon are successfully reproducing in many areas of the lake. Even in the Michigan waters of Lake Superior (the only place in Lake Superior where cohos are stocked), 70 to 90 percent of the cohos caught are naturally produced. If coho stocking stopped, good catches would probably continue. Cohos are second only to lake trout in the number caught.
Chinook salmon, stocked by all three states and Ontario, are adding “big fish” excitement around the lake. Chinooks are also reproducing successfully in some Canadian tributaries and probably in some U.S. tributaries as well. Steelhead and other strains of rainbow trout, brown trout, Atlantic salmon, pink salmon, brook trout, and splake also contribute to the sport fishery.
The future of lake herring, the historic forage fish in Lake Superior, looks promising. There have been good year classes of herring in six of the last ten years, with an extremely large year class produced in 1984. Smelt have not recovered significantly from their 1979 82 low and their future status remains questionable. Nevertheless, if herring continue to recover, there could be more food available for trout and salmon in the near future than there has been for the last 30 years.
Lake Superior Fishery — The Cloudy Side
The biggest biological threat to Lake Superior’s recovery may continue to be exotic species. Some biologists are concerned that large numbers of exotic trout and salmon predators may halt or reverse the recovery of forage species. This same concern appears to have manifest itself in Lake Michigan where alewife numbers have crashed in some areas of the lake, apparently because of intense predation. For Lake Superior to reach its historic potential for trout and salmon production, herring and/or smelt populations must keep pace with the expanding stocking programs and the increasing natural reproduction of trout and salmon.
Lamprey control must keep lamprey abundance at acceptable levels. Although “under control,” lamprey still kill a significant number of trout and salmon (mainly lake trout) in the Great Lakes. Excessive human harvests may also jeopardize trout stocks in some areas of the lake. Management agencies and others are trying to understand the Lake Superior fishery and to deal with these threats to the resource.
Three new exotic species from Europe may also threaten the Lake’s recovery. The ruffe, a small perch; the spiny water flea or B.c., a large predatory zooplankton; and the zebra mussel, a small biofouling clam have all developed reproducing populations in the Lake Superior basin. Of the three new exotics, spiny water flea populations have developed most extensively in the lake and may be capable of inflicting the greatest ecological changes in Lake Superior, but only time will tell.
Lake Superior may not have experienced the overnight recreational fishing bonanza experienced on the other Great Lakes, but it will continue to produce excellent fishing while providing a fishery that is more stable and less dependent on stocking. With only 0.7 million people around Lake Superior compared to 14 million around Lake Michigan, we do not expect to ever see the magnitude of fishing effort that is expended on Lake Michigan. As a consequence, Lake Superior may provide more of a quality fishing experience. Fewer fish will be caught, but because they will be divided among fewer anglers, the Lake Superior catch rate may approach or match Lake Michigan’s.
Anglers should not expect to see Lake Superior develop into a clone of the Lake Michigan fishery. They can expect continued improvements that will ensure an extremely attractive sport fishery and a viable commercial fishery based on the unique qualities that Lake Superior offers as the largest freshwater lake in the world.
By Jeff Gunderson