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Cormorants: Semi-Science and Wildlife Management

Published 01/25/11
By Barry Kent MacKay, Senior Program Associate

(Photo by Jeff Jones)

Wildlife management responds to political direction that, in turn, responds to public demand. The public and the politicians they influence cannot be expected to know, or care, about the complexities inherent to the natural world. Everything must be simplified before it can be explained to the public. Fish are in decline, cormorants eat fish, ergo, cormorants are responsible for the decline in fish. This scenario is, generally, refuted by the scientific evidence, and cormorant detractors, be they the general public or wildlife managers, can act as though this evidence does not exist (although strides are being made, especially in Canada).

On the other hand, they will refer to wildlife management reports as though they were science. A number of such reports have been published by the not too accurately named New York State Department of Environmental Conservation (NYSDEC). Some from the eastern basin of Lake Ontario, where there has most certainly been a dramatic increase in cormorants in recent decades (although those numbers may now have levelled off), purport to link the increase in cormorants with a decrease in smallmouth bass.

The smallmouth bass, a native species, is of great interest to sport anglers, thus of significant economic importance where it occurs in sufficient numbers. The research done by NYSDEC seemed to indicate that the proportion of smallmouths in the overall diet of cormorants in the eastern basin of Lake Ontario ranged from 0.4 percent of the birds’ total diet in the region to as much as 2.2 percent, the average being approximately 1 percent. As one might anticipate, the bulk of fish eaten by cormorants were small bottom-feeders such as the alewives and sculpins. Round gobies had yet to enter the picture at that time. NYSDEC gave little or no consideration to other possible factor in declines, if any, in the smallmouth bass, or in the declining average size of smallmouths caught be anglers.

Generally speaking, each year produces a new generation, called a “cohort” or “age class,” of fish of any given species. But the highest “elasticity” of a given cohort occurs when they are larval, or very young, before consumption by cormorants occurs. This mortality determines how many fish of that cohort there will be when the fish are large enough to interest anglers — human or avian. As stated, other studies generally show that “game” fish of interest to anglers form only a tiny percentage of the cormorants’ overall diet.

This is not to suggest that cormorants can’t have an impact on such fish on a local level, or temporarily, but even then they are one of a suite of factors. Conditions in which this can happen are exceptional, not the norm, as study after study has indicated.

But facts don’t matter to hard-core cormorant detractors. In 2003 the U.S. Fish and Wildlife Service prepared a “Final Environmental Impact Statement” (FEIS) on the effects double-crested cormorant have on fish of value to anglers, in which it stated that wildlife management agencies don’t need to wait for proof before taking actions against cormorants. This is not “science,” even though FEIS recognizes that that commercial fishing has, at times, “experienced a steady decline for reasons unrelated to fish-eating birds,” and acknowledges that there is a general lack of research showing that cormorants have an effect on economic loss to fisheries. None of that matters; they still supported cormorant culling.

The dynamism of the environment is traditionally downplayed or ignored by wildlife management agencies when they identify “hyperabundant” species and target them for reduction, and such dynamism is very well illustrated in the eastern Lake Ontario basin illustrates by the arrival of a new and powerful factor entering the region: the round goby.

As a general rule when a new species establishes, or re-establishes, itself in an environment that is supportive of its needs, there is a fast increase in its numbers as they expand to fill available habitat. This number will reach a peak, fall back, and then more or less level off at the always changing amount the environment can sustain. This applies to species who are newly arrived, either from natural range expansions (which are particularly likely to happen in highly mobile species, such as flying birds and insects) or are there because they were put there by humans, and the general rule also can apply to species who are recovering from previous serious declines.

And no species illustrates this generality better than the round goby. It has only occurred in Lake Ontario since around the end of the first decade of the 21st century, and already it is enormously abundant in the eastern basin of Lake Ontario. What its long-term effect will be on smallmouth bass or any other species of fish or other aquatic fauna is unknown, but that it will have an effect on many of the lake’s fish is inevitable.

But the current growth rate of the round goby population ultimately is unsustainable. Although it eats zebra mussels, another alien species that experienced explosive population growth, it almost certainly cannot eat enough to significantly control that species, nor can that species provide the means for continued population growth. The round goby also eats small organisms that are essential to the food chains that ultimately sustain the smallmouth bass and other commercially valuable fish species. But inevitably once the peak is reached, there will be a subsequent decline, which could further effect smallmouth bass and other commercially valuable fish species. Meanwhile, it is known that the round goby is an important food fish to double-crested cormorants, presumably edging out other species, including those small percentages that are commercially valued, such as smallmouth bass, negating studies done a decade and more earlier.

Introduction: Why Cormorants Can't Kill All Fish

Wildlife Management North and South of the Border

Energy Transference, Basic Physics and the Technology Prosthesis

Back in the Real World

Cormorants: Food Chains and Basic Ecological Principles

The Alewife, Alien Salmon and Trout, and the Double-Crested Cormorant

The Round Goby

The Difference Between Science and Management

The Agricultural Subsidy

The Missing Predator Argument

Limiting Factors

NEXT » So ... What Do Real Scientists Say?


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