Two fish important to the double-crested cormorants in the Great Lakes are the alewife and the round goby.
Alewives are a shad-like fish that is native to the east coast, where it lives in seawater but moves into rivers to spawn in fresh water. No one can say with absolute certainty when or how the alewife reached the Great Lakes, but it was first recorded in Lake Ontario in 1837.
Lake Ontario is the lowest and easternmost of the chain of large lakes that constitute the Great Lakes. Upstream is Lake Erie, which is separated from Lake Ontario by Niagara Falls. The falls are an effective fish barrier. Fish can move downstream, over the falls (although presumably most perish in the fall), but not upstream. That barrier was eliminated in the 19th century by the building of the Welland Canal, actually a series of locks that join Lake Ontario to Lake Erie. The surface of Lake Eire is about 100 meters (about 365 feet) higher than the surface of Lake Ontario. The canal system is about 42 kilometers (about 27 miles) long. It was through this series of locks that the alewife reached Lake Erie, and from there was able to reach the rest of the Great Lakes.1
Alewives evolved to live most of their lives in salt water, and in fresh water they seem particularly sensitive to changes, including temperature changes in the water. For much of the year they live in deep water, but when it comes time to spawn they enter shallow water. The spawning corresponds with when cormorants are nesting, when the birds need extra food to provide the extra energy needed to produce eggs and care for young. Since alewives can produce huge numbers of eggs, their presence quite possibly increased the carrying capacity of the Great Lakes for double-crested cormorants at the critical breeding season to levels that are higher than was true at any previous time. We will probably never know for sure because cormorants had been pretty well eliminated from the Great Lakes before anyone made any serious estimate at noting or counting them. Indeed, records of them in the Great Lakes prior to the 20th century are so scarce and fragmented that many of the birds’ detractors insist that they were altogether absent as a breeding species, and ignore what little but actual evidence to the contrary exists.
What we know is that the Great Lakes and other major North American watersheds throughout the continent are greatly and irrevocably different than they were in pre-colonial times, and all indications are that they are, in balance, less supportive of life now than they were prior to industrialization. Dredging and diversion, dams, channelization, wetland drainage , the additions of large numbers of chemicals and toxins and other forms of pollution never known in nature, excessive water use, physical disturbance by shipping and other water use, deforestation, climate change, exterminations and the introduction of non-native species of plants and animals and much else have collectively altered, and often reduced, the ability of our wetlands to sustain life, compared to what would have existed in more primal times. Even that statement has to be qualified with the reminder that if we go far enough back in time, 11,000-plus years, we can find that much of North America was covered with thick sheets of ice, and current water systems such as the Great Lakes did not exist, or great inland seas covered much of what is now dry land.
That said, the non-native species were, of course, absent. The presence of a species such as the alewife, very beneficial to the cormorant, also will have impacts of varying degrees on other species of wildlife sharing their environment. What is important in considering possible pre-Columbian population size of cormorants who eat alewives is knowledge of the volume of the biomass of fish accessible to cormorants in pre-Columbian times, and that is something quite unknown and probably forever unknowable.
What we do know is that inevitably the establishment of new species will at least to some degree displace some native species who share the same habitat.
But alewives are also consumed by predators other than cormorants, and that includes trout and salmon, beloved of sport anglers.
Thus governments on both sides of the international border that runs through the Great Lakes (apart from Lake Michigan, which is entirely in the United States) are not satisfied with the trout and salmon species nature provided. At any rate, the Great Lakes population of the Atlantic salmon, a species greatly favoured by anglers, was totally exterminated. The Great Lakes are now being stocked with oceanic Atlantic salmon. Therefore both American state and Canadian provincial authorities have introduced several non-native species of trout and salmon into the Great Lakes.
Whether these alien trout and salmon species do well does not matter because their numbers are continually augmented by releases of more of their respective kinds from fish hatcheries. This is called a “put and take” fishery.
And whether they can be safely consumed by anglers who catch them seems not to matter either, it being whatever pleasure derives from catching them that is important. In fact, the larger the fish, the older it is, and older ones are so contaminated by toxins that consumption of them is problematical.
And these exotic salmon and trout, including the Coho salmon, a West Coast species with a voracious appetite, also consume alewives.
So we have non-native salmon and trout eating alewives that are also consumed by cormorants. Of this triumvirate — non-native trout and salmon, alewives and cormorants — only one, the cormorant, belongs as a native species, and only it is demonized and subjected to lethal culling, although the salmon are also removed and to the degree they are inedible, those who don’t survive catch and release fishing are wasted — such waste supposedly antithetical to good conservation ethics.
Any negative effect the monstrous Coho and other alien salmon have on native fish or other organisms is acceptable because of the money to be made from the sport fishery. And cormorants eat what salmon eat: alewives.
To be sure, within wildlife management agencies there are enlightened biologists who understand the sham and do not approve of it, but if they are to keep their jobs they must follow policy. To most of the general public, legislators, journalists and “sportsmen,” the presence of alien trout and salmon, as result of them being put there, is considered to be a sign of a healthy environment.
All governments ascribe to the idea of “sustainable use,” but there is nothing sustainable about the take of these alien species. The situation is no more “natural” than putting deer in fenced enclosures and allowing hunters to shoot them, but that’s done as well.
The degree to which both cormorants and alien salmon depend upon alewives was demonstrated when, due to temperature changes in Lake Huron that caused a massive die-off of alewives in 2004, both cormorants and alien salmon also declined. But there was a corresponding increase in native fish species, including a native trout, the lake trout. Lake trout are not as desirable to sport anglers as the alien salmon and trout species, thus the latter are continually dumped into the Great Lakes by various state and provincial wildlife management agencies.
All wildlife agencies argue that alien species of flora and fauna should not be placed in the wild, but they do not really mean it when it comes to “game” species. This hypocrisy is currently creating an illusion that the Great Lakes, by virtue of the fact that monster salmon can be caught in them, are healthier than is truly the case.
NEXT » The Round Goby
The Difference Between Science and Management
The Agricultural Subsidy
The Missing Predator Argument
Semi-Science and Wildlife Management
So ... What Do Real Scientists Say?