DOUBLE-CRESTED CORMORANTS AND FISHERIES IN THE GREAT
LAKES BASIN
Fact Sheet
Flying low, in a straight line or ragged-V formation, large dark birds
fly past, feathers rustling as they settle on the water. Swimming with
bodies submerged, head and neck above water, bills pointed upward, they
dive under water to catch fish. Taking flight, they head for another
destination in the Great Lakes basin. Not to be confused with geese or
loons, the birds are double-crested cormorants, called crow-ducks by
European settlers, and Phalacrocorax auritus, by bird scientists.
Adult birds look alike, with dark plumage tinted a greenish gloss on the
head, neck and underparts. They have slender, hooked bills, with webbed
feet set well back on their body, orange facial skin, and an orange throat
pouch, like their relative the pelican. The species is named for the two
small tufts or crests of feathers, that appear for a short period of time
on either side of the head of adult birds in breeding plumage. One to two
year old juvenile cormorants have gray or tan plumage.
Double-crested cormorants reside in many locations throughout North
America. They nest along the Pacific coast from Southwest Alaska to
Mexico, and from lakes in central Alberta to James Bay and Newfoundland,
south along the Gulf of Mexico. Along the Pacific coast and the southern
Atlantic coast, populations are resident year-round. The interior
population, centered in the northern prairies, spread eastward and first
nested on the Great Lakes in 1913. The birds in the Great Lakes population
migrate south, along the Atlantic coast and Mississippi River drainage to
overwinter in the southeastern states and Gulf of Mexico. By May, birds
have returned north to breed and rear their young. They often nest on
islands in the company of terns and gulls, great blue and black-crowned
night herons, and great and snowy egrets. Nests are constructed from
sticks and twigs and located in trees or on the ground. They usually
contain from two to four light blue eggs. Both adult birds incubate the
eggs for about 28 days by wrapping their feet around them, and care for
their young until they become fully independent, about 10 weeks after
hatching.
Cormorants are expert divers, adapted naturally to forage under water
for fish. Fully-webbed feet propel slim, streamlined bodies on dives
usually from 8 to 20 feet. Greater depths are possible. Eye muscles are
specialized to allow acute vision both above and under the water. Feathers
absorb moisture, helping cormorants to stay under water for about 30
seconds. After foraging, cormorants often dry their feathers by perching
in a distinctive wing-spreading posture.
The Great Lakes population of double-crested cormorants was devastated
during the 1960s, primarily by the effects of chemical contamination
especially DDT. Because they are fish-eating birds at the top of the food
chain and long-lived (up to 20 years), adults accumulated pesticides and
other toxins from the bodies of their prey. These chemicals caused
reproductive failure, and chicks that hatched sometimes had crossed bills,
club feet, and eye and skeletal deformities. In addition to contamination,
human disturbance and nest destruction contributed to the decline.
In the early 1970s the Great Lakes population had plummeted, with few
birds remaining or breeding successfully. In Wisconsin, the species was
placed on the list of threatened and endangered wildlife. Nesting
platforms were erected to aid their recovery. In 1972, double-crested
cormorants were added to the list of species protected by the 1918
Migratory Bird Treaty Act. Despite these conservation efforts, the Great
Lakes population continued to decline, with few breeding birds remaining
or breeding successfully. The devastation of the Great Lakes cormorant
population was a grim example of the declining health of the Great Lakes
ecosystem.
Today, the Great Lakes population of double-crested cormorants is at
historic highs. Pollution control has lowered concentrations of toxic
contaminants in their food supply, food is ample throughout their winter
and summer ranges, and they are protected by federal and state laws.
Nesting populations can be found on all the Great Lakes in both United
States and Canadian waters, on inland lakes like Lake Champlain and Oneida
Lake, and on the Niagara River.
Scientists do not expect the population to grow continuously. Instead,
the number of birds should decline eventually, and then stabilize. Nesting
habitat may become an important limiting factor. Disease may also play a
role in this reversal. Although the cormorant population resurgence may
indicate enhanced water quality in the Great Lakes, it has been
accompanied by concern and controversy about the effects the birds may be
having on stocks of recreational and commercial fish species, and island
nesting habitat.
Because cormorants are conspicuous fish-eating birds, anglers in the
Great Lakes basin may consider them a nuisance species and a threat to
populations of recreational and commercial fish species. However, studies
of the feeding habits of cormorants show the birds feed on many fish
species, concentrating on the ones that are easiest to catch. Adult birds
eat about one pound of fish per day. Because the ease with which a fish
can be caught depends on such factors as distribution, relative abundance,
and behavior, a cormorants’s diet can vary considerably from site to
site and throughout the breeding and nesting seasons. All told, small
(three to five inch) fish like alewife, yellow perch or gizzard shad
provide most of their food. The birds find these fish in large schools,
sometimes in shallow water.
Cormorants also feed on steelhead, lake and brown trout when available,
especially when recently-stocked schools of small fish can be found in
shallow near shore waters. Population level effects from cormorant
predation on lake trout, salmon or steelhead are not apparent though, as
diet studies indicate the birds consume very few of these fish in open
waters. Can large colonies of cormorants reduce local populations of
catchable-size pan fish like sunfish and rockbass, or sportfish like
smallmouth bass, walleye pike, or yellow perch sufficiently to compete
with anglers? Recreational and commercial anglers in some locations in the
Great Lakes basin believe they can. Until biologists obtain additional
information, the answer to this question remains unclear.
It is clear, though, that double-crested cormorants can feed heavily on
small fish being raised commercially on minnow farms for bait, or for
human consumption at fish farms or aquacultural sites. Also, in some
locations within the Great Lakes basin, double-crested cormorants are
competing with other colonial nesting water and wading birds for the same
island nesting sites. A special concern exists when this competition
jeopardizes the reproductive success of rare, threatened, or endangered
plant and animal species.
The population resurgence of double-crested cormorants in the Great
Lakes basin has been accompanied by requests for the U.S. Fish and
Wildlife Service, U.S. Department of Agriculture/ Wildlife Services, and
state fish and wildlife management agencies to act. Each agency has a
different role to play. The primary responsibility of the U.S. Fish and
Wildlife Service is regulatory oversight, to ensure that actions taken by
the states will not cumulatively jeopardize cormorant populations. Because
the birds are protected under the Migratory Bird Treaty Act, their nests
and eggs cannot be disturbed, and the birds cannot be captured or shot,
unless a depredation permit is first obtained from the Service. At the
federal level, the Service does not conduct on-the-ground management
activities when cormorants cause damage. This role is the responsibility
of the U.S. Department of Agriculture’s Wildlife Services Program.
Their job is to help states, organizations, and individuals resolve
conflicts between people and wildlife on public and private lands, by
either recommending or implementing wildlife damage management options.
The U.S. Fish and Wildlife Service does not act on a request for a
depredation permit until the U.S. Department of Agriculture recommends
this action.
Federal and state fish and wildlife agencies have responded to public
and private concerns about double-crested cormorants in the Great Lakes
basin. The U.S. Fish and Wildlife Service has funded Great Lakes-wide
population monitoring surveys in coordination with states and the Canadian
Wildlife Service. The agency has issued a regulation permitting the lethal
take of cormorants, without a permit, on catfish and bait fish farms in 12
southeastern states and Minnesota, where economic impacts have been
well-documented and non-lethal control has proven ineffective. The Service
has also funded a variety of studies to assess the impact of cormorants on
fish populations, and has conducted an extensive review of other studies.
The State of New York has altered fish stocking methods in response to
recommendations from a citizen’s task force. It has also requested
and received depredation permits for double-crested cormorant control from
the U.S. Fish and Wildlife Service to prevent nesting colonies from
becoming established on new islands in Lake Ontario, and to prevent the
colony on Oneida Lake from jeopardizing the nesting habitat of common
terns, a state-listed threatened species. The U.S. Department of
Agriculture and the State of New York have conducted a pilot study to
investigate techniques to change migration and roosting patterns of
double-crested cormorants on Oneida Lake. The U.S. Fish and Wildlife
Service has also issued depredation permits to the State of Vermont to
prevent cormorant colonies from spreading to new islands in Lake Champlain
in order to reduce competition with other colonial waterbirds, and to
prevent private property damage. To assist the State, the U.S. Department
of Agriculture has conducted a variety of both lethal and non-lethal
cormorant management activities on the lake.
The U.S. Fish and Wildlife Service will cooperate with state and federal
fish and wildlife management agencies to develop a regional management
plan for double-crested cormorants. While the plan is being developed, the
Service is preparing a comprehensive assessment of the population status
of cormorants, and a review of the impacts of double-crested cormorants on
commercial and sport fish populations in both natural and artificial
settings. Although it is not the current policy of the Service to issue
depredation permits to reduce cormorant predation on sport fish, permit
requests may be considered under unique circumstances. Any significant
policy changes must be based on sound science, and would be implemented
only after coordination with appropriate federal and state resource
agencies and the concerned public.
Additional information on double-crested cormorants is available on the
Internet at the following websites:
McMaster University
http://www.science.mcmaster.ca/Biology/Harbour/SPECIES/CORMRNT/CORMRNT.HTM
U.S. Department of Agriculture/Animal and Plant Health Inspection
Service/Wildlife Services
http://www.aphis.usda.gov/wildlife_damage/nwrc/symposia/cormorant_symposium/index.shtml
U.S. Fish and Wildlife Service/Lake Champlain Fish and Wildlife
Resources Complex
http://www.fws.gov/r5lcfwro/corfct.htm
U.S. Fish and Wildlife Service/Office of Migratory Bird Management:
http://migratorybirds.fws.gov/issues/cormorant/cormorant.html
U.S. Geological Survey/Patuxent Wildlife Research Center
http://www.mbr-pwrc.usgs.gov/id/mlist/h1200.html
http://www.mbr-pwrc.usgs.gov/bbs/htm96/trn626/tr1200.html
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