Audubon Minnesota Position on Cormorant Control in Minnesota

Background

Double-crested Cormorants are a native, fish-eating bird, widely distributed in Minnesota (Figure 1).  Both breeding and migrating individuals are found in the state.  Cormorants breeding in Minnesota winter in the southern United States. 

North American cormorant populations were quite low through most of the 20th century; largely due to persecution by humans before 1950, and environmental contaminants (especially DDT) in the 1950s and ‘60s.  In 1972, use of DDT was restricted and the cormorant was also given protection under the Migratory Bird Treaty Act (MBTA).  Since that time, cormorant populations have been rebounding continent wide.  In Minnesota, cormorants although protected by the MBTA, are not protected by state law.

Currently, the numbers of cormorants in Minnesota are probably lower than pre-settlement.  Pre-1900 reports indicate a very large number of birds with a wider distribution than is seen now.  Minnesota’s populaiton is also lower than in other parts of North America.  Some colonies in North America have up to 15,000 pairs of birds, larger than any colonies in Minnesota.

Little is known about breeding or migratory numbers, population dynamics or other relevant biological factors in state.  In 2004, the only recent statewide survey was conducted by Linda Wires and Francie Cuthbert from the University of Minnesota.  They found 16,206 pairs distributed at 38 sites around the state (see figure 1).  This may mean that there are approximately 42,000 individuals in the state during the summer.  An unknown number of cormorants migrate through Minnesota in spring (late March to mid-May) and fall (mid-September to early December) on their way to and from Canadian breeding grounds.

In Minnesota, cormorants often share colonies with other colonial nesting birds including Great Blue Herons, Great Egrets, Cattle Egrets, Ring-billed Gulls, and Herring Gulls.  The state listed Common Tern, and the  Black-crowned Night Heron, an Audubon Minnesota species of conservation concern, are also found nesting with cormorants.  Piping Plovers and Bald Eagles are found in proximity to some colonies making them susceptible to disturbance from control measures at cormorant rookeries.

Figure 1
Distribution and Colony Size of Double-Crested Cormorants in Minnesota - 2004

L. Wires and  F. Cuthbert, Univ. of Minnesota

Of particular interest are American Pelicans, a state species of Special Concern that is found at 11 shared sites accounting for 10,040 cormorants and 9,763 pelicans (see Figure 2).  These mixed colonies often involve multiple species

Cormorant Control

 Nationally, the growth of cormorant populations has resulted in increased complaints about the birds.  Sport and commercial fishermen in the Great Lakes, operators of fish hatcheries, and aquaculture producers, complained to the U.S. Fish and Wildlife Service and the U.S. Department of Agriculture’s Wildlife Services that cormorant predation on fish was negatively impacting their livelihoods.  

In 1986, the UFWS began issuing “depredation permits” under a provision of the MBTA that allows protected birds to be “taken” (killed) when they are considered a nuisance.  In 1998, the UFWS gave aquaculture producers in 13 states, including Minnesota, much broader authority to kill cormorants. Under this depredation order, aquaculture producers were allowed to shoot cormorants without a permit when they found the birds “committing or about to commit depredations at aquaculture stocks”.  Since 1998 over 1,900 cormorants a year have been taken in Minnesota under this order.  Amended in 2003, the depredation order allows take at roost sites in the vicinity of aquaculture facilities.

Figure 2
Double-Crested Cormorants Colonies with > 4 Colonial Waterbird Species - 2004

L. Wires and  F. Cuthbert, Univ. of Minnesota

A second depredation order issued in 2003 authorizes Federal, State, and Tribal agencies to “take” cormorants by a variety of methods to protect fish, wildlife, plants and their habitats on public and private lands.  In the summer of 2004, cormorants were taken at Leech Lake and the Knife River in order to determine which specific food items those birds were eating.  In March 2005, an Environmental Assessment  “Reducing Double-Crested Cormorant Damage in Minnesota” was released by USDA Wildlife Services.    

Audubon Minnesota's Position

Cormorant control in Minnesota seems to be predicated upon the perception that these birds are responsible for declining fish populations in certain lakes, or pose a threat to commercial fish operations.  A perception that, to date, has not been supported with data or study.  Rather, the simple presence of the birds seems to be enough to trigger the call for control from some quarters.

Audubon Minnesota is not categorically opposed to efforts to control wildlife populations that are out of control and/or having a negative economic impact.  However, we have seen no evidence that cormorants are out of control in Minnesota, or are having a major impact on the fishing success of humans resulting in a significant economic impact.  No studies have been done in Minnesota that show that low or declining fish numbers are due to cormorants, or other fish eating birds.  In fact, there is very little data from anywhere that establishes this link.  Pressure to “manage” cormorant numbers are coming from the sport fishing and aquaculture communities with little to no data.  Rather, there is a repeated refrain, that there are “too many” birds, with no link to how the numbers of birds affects the number of fish.

Audubon Minnesota believes that before any Double-crested Cormorant depredation plans or activities move forward in Minnesota the following conditions must be met:

1. Long-term, ongoing, statewide monitoring of cormorants and other associated colonial nesting species must be in place.  This monitoring must be able to detect significant population declines statewide.  Monies for these studies should come from sources other than current budgets of the MN DNR Eco-Services or Nongame Program.

2. Plans and actions must be based on the best scientific data available for both bird and fish species and be subject to annual review.

3. A proven link between cormorant numbers and economically harmful fish population declines must be established.  Plans should be developed to respond to those declines and goals established that link cormorant population numbers to fish declines

4. Control activities cannot negatively affect non-target species.

5. Population monitoring at each site where activities occur must include both cormorants as well as other colonial nesting species. 

6. Consideration of how control would affect statewide populations of cormorants must be included in any depredation plan or activity..

Audubon Minnesota believes that setting bird population numbers, or management goals, based on fisheries goals is contrary to good bird management and sets a very bad precedent.  The North American Bird Conservation Initiative (NABCI), subscribed to by both the U.S. Fish and Wildlife Service and the MN DNR, has as its philosophy the goal of keeping “common birds common”.  Fish-eating birds will become an exception to this philosophy in the very near future if natural resource agencies manage them to meet fishery objectives.