WI - Cormorant Research Group Scientific Literature Double-crested cormorant

Author/s: J.F. Farquhar III

Title: Balancing act: Managing cormorants in upstate New York

Journal: New York State Conservationist, 56(1): 26-28

Full text
One hundred feet away, a flock of five hundred double-crested cormorants takes to the air as the DEC Wildlife team approaches. Upon reaching a dense group of nests, a technician wearing a backpack sprayer filled with vegetable oil begins to coat the eggs in each nest. As she does so, she calls out the numbers 2...2...3...4...0. Another technician records these numerals, referring to the number of eggs treated in each nest.

Coating the eggs with vegetable oil will prevent them from hatching. But because the eggs remain intact, adult cormorants will return to their nests and continue to incubate the eggs for several weeks. Relatively few cormorants chicks will hatch here this year But the unharmed adults will nest again next season.

Where is this scene unfolding, and why would state biologists undertake such an effort to reduce cormorant numbers? The site is Little Galloo Island in Lake Ontario's eastern basin. The reasons involve a complex set of social and biological factors which have led the state to seek a sustainable balance between people and wildlife. Hopeful outcomes include an enjoyable recreational fishery, maintenance of a variety of colonial waterbird species nesting on Little Galloo and a smaller but healthy cormorant population. This represents a difficult and sometimes controversial challenge indeed!

After a decade's absence, double-- crested cormorants returned to Lake Ontario's eastern basin, nesting at Little Galloo Island. As cormorant numbers grew, they became the focus of a hotly debated and intense study. Biologists struggled with a complex situation that is becoming increasingly common: the need to meet competing, and at times quite divergent human interests.

The cormorant is a large, fish-eating colonial-nesting waterbird. It is commonly found on large water bodies, including Lake Ontario, Oneida Lake, and the St. Lawrence River.

Cormorant populations were relatively small through the 1940s and '50s. By the late '60s, populations of cormorants and other large predatory birds dwindled to historically low levels due to human persecution and reproductive failure resulting from human use of pesticides. However, the Migratory Bird Treaty Act and laws restricting the use of harmful pesticides helped many of these same species begin to recover.

An initial colony of 22 pairs in 1974 grew rapidly to 1,500 pairs by 1986 and to more than 5,000 pairs by 1991. Cormorants colonized new sites, including Oneida Lake and islands in the Canadian waters of Lake Ontario. The burgeoning cormorant population delighted some bird enthusiasts but concerned local property owners and those who fished for fun. Could these birds have an adverse impact on the quality of the fishery? Could their dense nesting habits harm the trees and vegetation on newly colonized sites? Were cormorants beginning to overtake nest sites from other local waterbirds? To answer these questions, DEC and other agencies began monitoring cormorants and other colonial nesting birds in the 1980s.

Because of competition for nesting space between cormorants and common terns (a threatened species in New York) Cornell University researchers began removing cormorant nests from Oneida Lake islands in 1992. In 1993, DEC altered stocking practices in Lake Ontario to reduce cormorant predation on lake trout and brown trout. To protect colonies of black-crowned night herons, DEC staff began removing cormorant nests from two Lake Ontario islands in 1994. All of these measures relieved very specific problems, but concerns about growing cormorant numbers and declining recreational fisheries remained on both lakes.

During the rapid expansion of the cormorant population, DEC began an ongoing dialogue with interested individuals and groups. Informational meetings were held as early as 1992, and in 1994, DEC convened a Cormorant Task Force made up of citizens in the Oneida Lake/Lake Ontario communities. Their recommendations provided the basis for much of DEC's current cormorant management program, including nest removal, harassment of adult birds, and improvements to fish-stocking practices.

Cornell's research on Oneida Lake indicated a significant loss in perch and walleye during cormorant "stop overs" in fall migration. In September 1998, USDA's Wildlife Services Unit cooperated with DEC and the Oneida Lake Association to administer an aggressive harassment program to discourage cormorants from stopping over and to reduce the time they spent on the lake.

Meanwhile, studies by DEC and the U.S. Geological Survey established a link between the cormorant population and a reduction in smallmouth bass abundance on Lake Ontario. When these findings were released in 1998, DEC increased their public outreach efforts, including attempts to determine the level of support for a range of potential cormorant management actions. The resulting feedback helped DEC formulate a set of ecosystem management goals and a series of long-term actions to achieve these goals. The public input process demonstrated a need for local cormorant control, a viable fishery, and a diverse ecosystem within the Lake's eastern basin.

A primary management objective is to reduce the population of cormorants nesting on Little Galloo Island to 1,500 pairs, a level comparable to that of the late 1980s. At this level, biologists believe cormorants will have little impact on the fishery. DEC considered several options for cormorant control, from a "no action" alternative, to using harassment, suppressing reproduction, or removing adults by lethal means.

After carefully evaluating the pros and cons of each option and considering public opinion, DEC staff determined that the method most likely to succeed was reproductive suppression by nest removal and egg treatment. In 1999, DEC obtained a depredation permit from the U.S. Fish and Wildlife Service to conduct a field test of the oiling process. After preparing an Environmental Impact Statement for the long-term management of cormorants in the basin, DEC began egg oiling and nest removal.

As a technique, egg oiling has many benefits. It prevents cormorant eggs from hatching without causing the adults to abandon the nest, or attempt to renest elsewhere. While oiling reduces recruitment of young cormorants into the population, it also causes less overall disturbance to other nesting bird species than would different techniques. Because egg oiling does not remove adult cormorants from the population, it takes time to reduce cormorant numbers, but the process can be halted if unplanned consequences arise. DEC's management strategy also seeks to limit cormorant nesting to only Little Galloo Island; nests from other sites in the basin are routinely removed.

To evaluate the success of these efforts, DEC and USDA Wildlife Services staff initiated a satellite radio-tracking study last year. Results have been encouraging. The egg oiling technique used in 1999 and 2000 on Little Galloo Island has reduced annual cormorant reproduction by more than 90 percent. In turn, this has led to a 30 percent reduction in the loss of smallmouth bass; more would have been lost in the absence of control. Management efforts have succeeded in preventing new cormorant colonies from becoming established at sites where they could compete with other nesting species or damage private property. Other bird species have not been adversely affected. Oneida Lake common terns and Lake Ontario night herons have maintained stable populations. Even with the control efforts, cormorants remain an abundant nesting species on the island. Staff counted more than 5,000 nests last year and saw little evidence of movement to other sites.

The harassment program on Oneida Lake has wrought similar benefits. By shortening the duration of stopover and reducing the number of birds using the lake in the fall, overall fish consumption by cormorants has fallen by about 30 percent. As with many wildlife and fisheries management programs, a longterm commitment is necessary. The true measure of success or failure will be determined over several years. Thus far, results have been positive and the program appears to be heading in the desired direction.

Like many natural resource management programs involving competing interests, there is controversy over how to achieve the best results. DEC staff recognize that cormorants are a natural and desirable component of the system. Equally important, however, are populations of other waterbirds, protecting private property interests, and enhancing recreational fisheries. Managing cormorants truly is a "balancing act" in a complex system requiring careful assessment of the needs of fish and wildlife populations and the benefits to people who use our natural resources.

Cormorant management is controversial. A by-product of improving environmental conditions, today's burgeoning cormorant population is problematic at times. But managing an overabundant species is greatly preferable to losing part of our natural heritage.

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S. Volponi