Cormorants take toll on Great Lakes smallmouth bass
Written by BASS Times   
Wednesday, 14 September 2005 09:20
The double-crested cormorant, infamous for raiding Southern catfish farms, now appears to pose a significant threat to the Great Lakes smallmouth fishery. This is the conclusion of several Great Lakes-area state and provincial natural resources agencies, as well as academic researchers who study Great Lakes fish populations.

The Great Lakes have been home to the cormorant for almost 400 years. Since, 1972, the birds have been protected under the Migratory Bird Treaty Act. There are now almost 350,000 cormorants in the Great Lakes region, including 250,000 in Lake Ontario, 80,000 in Lake Huron and 20,000 in New York State. Each of these 4-pound birds can consume about 1 pound of fish per day, so the cormorant's impact on important Great Lakes fisheries is considerable.

Dr. John Casselman, a fisheries biologist with the Ontario Ministry of Natural Resources, has studied cormorant predation on Great Lakes fish for some 20 years. While cormorants feed on several fish species, Casselman says that "predation on smallmouth bass (in the Great Lakes) is significant."

Smallmouth bass only comprise about 3 percent of the cormorant's diet, but the exploding number of cormorants in the Great Lakes is still taking a serious toll on the smallmouth population. Studies conducted in eastern Lake Ontario showed a correlation between increased smallmouth bass mortality and the growing cormorant population. It is estimated that in eastern Lake Ontario alone the birds eat approximately 1.3 million smallmouth bass per year.

While cormorants are able to dive as deep as 100 feet in search of food, they prefer to hunt in much shallower waters. Shallow water happens to be the typical habitat for juvenile smallmouth bass. The cormorants appear to concentrate on smallmouth bass that are 13 inches or less. Fish that are close to 13 inches may be old enough to spawn, so cormorant predation reduces not only the existing smallmouth population but also the potential future population.

Cormorants are aided in their hunting efficiency by the zebra mussels that have infested the Great Lakes. Before the arrival of the exotic mussels, the cormorant's underwater visual range was only about 3 feet. Now that the filter-feeding zebra mussels have dramatically increased water clarity in some areas of the Great Lakes, cormorants are able to see as far as 30 feet while underwater.

Cormorant predation on smallmouth bass in the Great Lakes so alarming that some individuals have taken matters into their own hands. In 1998, nine fishermen killed about 2,000 adult cormorants on Little Galloo Island in Lake Ontario. The men were found guilty of violating the Migratory Bird Treaty Act. They were fined and sentenced to several months of home confinement.

The U.S. Fish and Wildlife Service (USFWS) has overall authority to manage the cormorant population in the U.S. and the Great Lakes. The USFWS may grant exemptions to the Migratory Bird Treaty Act in order to allow experimental reductions of cormorant populations.

Thus far, the U.S. Department of Agriculture, 24 state governments and several Indian tribes have received exemptions.

New York State wildlife officials recently coated 10,000 cormorant eggs with oil. This cormorant reduction method, known as "oiling," suffocates the birds before they hatch. Congress has provided $125,000 to oil 90 percent of the cormorant eggs at five island rookeries in Lake Huron, and to kill 15 percent of the adult birds at these rookeries.

In addition to oiling eggs and killing adult birds, cormorant populations can be reduced by destroying their nests and disrupting their nesting cycle. All of these cormorant reduction options must be approved by the USFWS.

Canadian researchers also found that each of the cormorant reduction methods has its drawbacks. For instance, oiling eggs requires about two years to demonstrate significant results.

Killing adult cormorants has an immediate effect on the bird population, but a disproportionate number of male cormorants are shot because they are less able than the females to escape hunters armed with rifles. The surviving females continue to lay eggs, thus diluting the effectiveness of the adult bird reduction option.

Nest destruction and disruption of the nesting cycle noticeably reduces cormorant populations, but it is so time consuming and labor intensive that it cannot be extensive employed.

The double crested cormorant is not without its defenders. The Fund for Animals, along with other animal rights organizations, have asked a federal court to block any further cormorant reduction activities. The plaintiffs in the case may contend that the USFWS lacks the authority to grant exemptions to the Migratory Bird Treaty Act. It is not known when the court will rule on the case. In the meantime, government and academic researchers plan to continue studying the effects of cormorant populations on Great Lakes fisheries.

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