By Jennifer Kotila
WRIGHT, MEEKER COUNTIES, MN The rise in cormorant population throughout Minnesota, the US, and Canada could be considered a success story in conservation efforts, except for perceived problems cormorants are now creating for area lakes and fisheries.
Local lake associations and sportsmen are up in arms with the Minnesota Department of Natural Resources (DNR) and the US Fish and Wildlife Service (FWS) because they feel their observations are not being taken seriously.
Locally, the rookery at Pigeon Lake on US Highway 15 near Dassel is the largest nesting colony of cormorants in Minnesota at the present time.
It is felt by local lake associations that the significant rise in the cormorant population is creating a significant decrease in game fish populations on local lakes.
Many lake associations would like the birds to be culled (killed as a means of population control) to curb their successful population expansion.
In the last year, the cormorant and pelican impact committee from the Lake Washington Improvement Association has been studying data related to cormorants, and presenting that information to local lake associations and representatives of the DNR and FWS.
It is hoped that all involved can come to an understanding of just how big of an impact the rise in the cormorant population is having on local fisheries.
Legislatively, US representatives John Kline (R) and Colin Peterson (D) introduced legislation to cut through red tape and allow states to manage cormorants.
They testified recently in a House Natural Resources Committee hearing on the “Cormorant Management and Natural Resources Protection Act” (H.R. 3074).
All about cormorants
Double-crested cormorants (DCCO) have been abundant and widespread as a breeding bird and a migrant throughout Minnesota.
Historically, its population in the state was even greater years ago than it is today, according to Erica Hoaglund and Lisa Gelvin-Innvaer, DNR nongame wildlife specialists.
However, cormorants were routinely killed in their nesting colonies in the late 19th and early 20th centuries due to perceived impacts on fish populations, according to the DNR.
By 1925, it is estimated that only 1,000 nesting pairs of cormorants remained in Minnesota, and the population remained low until the 1970s due to continued persecution and the use of the pesticide DDT.
The cormorant has been federally protected since 1972, when it was placed on the Migratory Bird Treaty Act, and, with the banning of DDT, its population throughout Minnesota has been on the rise ever since.
Cormorants breed in colonies, forming rookeries with other water bird species.
A statewide survey in 2004 documented 16,152 nesting pairs at 35 nesting colonies in Minnesota. A 2010 survey documented 15,400 pairs at 40 colonies, according to Gelvin-Innvaer.
Cormorants build small stick nests, with one brood having three to four eggs, according to Hoaglund.
A fairly long-lived bird, wild cormorants live an average of six years, but have been recorded to live up to 20 years.
Their diet, which is of most concern to local lake associations, consists primarily of small fish, aquatic invertebrates, and amphibians, eating about a pound of fish per day, Hoaglund said.
Cormorants are gregarious creatures, spending their time during the day together eating.
In studies on the foraging habits of cormorants, it was discovered that the average range of travel to forage is 1.8 miles from the colony, Hoaglund noted.
However, the study also showed that birds with nests in the colony didn’t travel outside of the area where the colony is located to forage, Hoaglund added.
Most cormorants can be seen foraging on local lakes in the spring and fall, when they are migrating.
Studies have also shown that colonies are density-dependent, meaning that a colony’s population will only reach a point where it is sustainable, Hoaglund said.
Pigeon Lake rookery
At Pigeon Lake, it is believed the colony became established in the mid-1960s, and the DNR has data documenting nesting by cormorants, great blue herons, and great egrets since 1976, according to Gelvin-Innvaer.
Other co-nesters on the island have included American white pelicans, black-crowned night-herons, and ring-billed gulls.
Pelicans, a species of special concern in Minnesota, have been documented at the island since 1999, but may have started nesting there a few years earlier, according to Gelvin-Innvaer.
While the loss of vegetation at Pigeon Lake is startling to see, it’s a natural process, Gelvin-Innvaer said.
“Prior to the vegetation changes, there were no native plant communities of concern. The colony itself is more important from an ecological standpoint,” Gelvin-Innvaer said.
The colony supports species in greatest conservation need, ecosystems, and healthy watersheds, and has been designated by the state as one of 41 important bird areas, Gelvin-Innvaer added.
Not only is the colony at Pigeon Lake important from an ecological standpoint, but wildlife watching has an important impact on the economy.
In 2006, wildlife watchers contributed $45.7 billion to the US economy, with $36 billion related to birdwatching, Gelvin-Innvaer said.
Birdwatching in Minnesota accounts for 33 percent of the $36 billion, according to FWS.
“It’s the goose that laid the golden egg,” Gelvin-Innvaer said.
Impact of cormorants on local fisheries
Fishing creates 43,000 jobs in Minnesota, and $2.8 billion in retail spending each year, generating $640 million per year in taxes to the state and federal governments, said Rick Fernstrom, member of the Lake Washington Improvement Association (LWIA).
The majority of the cormorants’ diet consists of fish, and representatives from local lake associations claim it is ruining their lakes’ fisheries.
“I have been associated with Lake Washington since the 1960s, when my grandparents purchased a cabin,” Fernstrom said.
He and other members of the cormorant and pelican impact committee from LWIA have been avidly researching the scientific data related to cormorants, and using it to argue their position that cormorants are ruining local fisheries.
The objective of the committee was to review the current status of the Pigeon Lake rookery; review cormorant and pelican population data; review data supporting the populations’ impact on wildlife and native vegetation, agriculture, and fishery resources; review recommendations from the DNR and FWS; and, to have a discussion about the Pigeon Lake rookery and local fisheries.
“Currently, we are at an impass with the DNR regarding cormorants,” Fernstrom said, meaning the DNR and FWS do not agree that the cormorant population is affecting area fisheries.
Fernstrom presented the following information at a Wright County Coalition of Lake Associations meeting recently.
Using population data from University of Minnesota studies in 2004 and 2010, the cormorant and pelican population in Minnesota did not change significantly from 2004 to 2010.
However, while nesting pairs decreased in other areas of the state in the last five years, the nesting pairs of cormorants at Pigeon Lake rose by 43 percent, and the nesting pairs of pelicans increased by 52 percent.
As of 2010, there were an estimated 4,290 cormorants at the Pigeon Lake rookery.
If each adult cormorant consumes 1.5 pounds of fish per day, 6,435 pounds of fish per day are required to feed the population.
Assuming the nesting period of cormorants is April through September, cormorants are responsible for eating 1,158,300 pounds of fish per season.
Using the same method for pelicans, which eat about 4 pounds of fish per day individually, 781,920 pounds of fish are eaten seasonally.
The combined fish consumption of cormorants and pelicans is equal to taking 5,390 2-pound fish per day, or 970,110 2-pound fish per season (April - September).
Fernstrom calculated that to be the equivalent of 1,347 fisherman taking four fish every day from April through September.
Not only are cormorants and pelicans consuming enormous amounts of fish from area lakes, but the vegetation at Pigeon Lake has been completely destroyed by their guano, Fernstrom said, adding that it has destroyed habitat for other native birds and wildlife.
He noted that other waterbirds, according to University of Minnesota studies, have been displaced by the rising cormorant and pelican populations, as well.
The black-crowned night heron, which had 22 nests at Pigeon Lake in 2004, had no nests at Pigeon Lake in 2010.
To understand better the impact of cormorants on local fisheries, Fernstrom cited studies for Lake Oneida, NY and Leech Lake in Minnesota, where it was determined that a foraging intensity of greater than 3.4 pounds per acre damages a fishery.
The acreage of lakes surrounding Pigeon Lake is approximately 11,431, meaning the population of cormorants and pelicans forage at an intensity of 94.62 pounds per acre, Fernstrom said.
“That’s 27 times greater than the maximum number for Lake Oneida and Leech Lake,” Fernstrom said.
The recommendations from the cormorant and pelican impact committee are:
• to gain DNR support to request and approve a depredation order for cormorants;
• to reduce the cormorant and pelican population to a nest density comparable to Leech Lake;
• to seek Legacy Funding to assist in gathering more data about area fisheries and the Pigeon Lake rookery;
• to schedule follow-up meetings to track cormorant and pelican reduction efforts;
• to schedule area fishery DNR surveys for 2012, and every two years thereafter;
• to fast-track survey analysis from 2012 for immediate comparison with the most recent surveys; and,
• to conduct a 2014 U of M study to track cormorant and pelican populations.
DNR data regarding local fisheries
Although DNR representatives are generally concerned about the increasing number of cormorants on area lakes, they are not noticing an impact on local fisheries, said Lee Sundmark, area fisheries supervisor from Hutchinson.
Sundmark monitors lakes in Meeker, McLeod, Renville, Redwood, Sibley, Brown, and Nicollet counties, and has met with Lake Washington Improvement Associations’s cormorant and pelican impact committee several times over the course of the last year.
Joe Stewig, assistant area fisheries supervisor from Montrose, presented information regarding lakes in Wright County at the Wright County Coalition of Lakes Association meeting about cormorants.
The Montrose Area Fisheries office monitors lakes in Wright, Stearns, and Sheburne counties.
“No one is more interested in providing quality fishing opportunities than we are,” Sundmark noted.
Admittedly, the DNR does not have enough staff to monitor every lake every year.
In Wright County, lakes are surveyed about every 10 years.
Although lakes in Meeker County are surveyed slightly more frequently, it is still several years between surveys.
However, the Wright County lake survey schedule has not changed to accommodate lake associations’ concerns regarding cormorant feeding habits, but the lake survey schedule for Meeker County lakes has changed.
Lake Washington, Lake Jennie, and Collinwood Lake survey schedules have been moved up from 2014 to 2012, Sundmark said.
While surveys cannot be undertaken every year, the DNR does not see cormorants as having a significant effect on local fisheries.
The surveys which have been done in the past show area lakes to be healthy, with fish populations well within the range expected, according to the DNR.
Locally, walleye do not have a very good reproductive habitat, and they are stocked by the DNR to produce good catch rates, Sundmark said.
It must be remembered that the walleye populations in local lakes consist of stocked fish, and are modest, at best, Stewig said.
Fisheries also have a natural fluctuation to them, and when surveys are looked at historically for all local lakes, they tend to have natural peaks and valleys.
“Radical variations in fish population are not apparent,” Stewig said.
The numbers of small fish seem relatively high in local fisheries, he added.
Perch, bullheads, and sunfish may buffer cormorants effect on the walleye population, and there is a natural variation in fish populations for local lakes.
“When people are coming and asking about cormorants and whether they are problematic enough to shoot, I can’t say that,” Sundmark said. “They may be eating some of the fish, but there are other factors, as well.”
Vegetation shifts, lake levels, the number of people fishing, and the numbers of different fish all affect the health of local fisheries.
For example, Lake Washington had a near-perfect fishery in 2001. “It is unrealistic to expect to maintain a fishery at that level all the time,” Sundmark said.
Since that time, Lake Washington’s habitat has changed, affecting its fishery.
For instance, Eurasian milfoil was found in the lake in the early 2000s. “That’s a game-changer in terms of habitat,” Sundmark said, noting more vegetation will change the composition of fish species.
Milfoil removal then changed the habitat again, which would change the fish species composition again, Sundmark noted.
A large northern pike population also affects walleye populations, which seemed to be affecting Lake Jennie.
“It’s fairly common knowledge that when pike rates are high, walleye rates will be low,” Sundmark added.
In order to try to alleviate the problems caused by a larger northern pike population, the DNR stocked both fingerlings and fry in Lake Jennie in 2008, which seems to have helped, Sundmark said.
Comparing local lakes to Leech Lake
While information from Leech Lake and Lake Oneida, NY is important in understanding the impact of cormorants on local fish population, comparing Leech to local lakes is not comparing apples to apples, Sundmark said.
Many local lakes are rough fish lakes with a larger biomass than northern lakes, he added.
Leech Lake is a mesotrophic lake, and local lakes are eutrophic to hyper-eutrophic, Stewig said.
A lake’s trophic state is defined as the total weight of biomass, and mesotrophic lakes are clearer. Common fish include walleye, perch, smallmouth bass, muskellunge, and northern pike.
Eutrophic lakes are shallow and murky, with a lot of plants and algae. Common fish include largemouth bass, northern pike, perch, and panfish, but as a lake becomes increasingly eutrophic, sport fish dwindle and carp abound.
Although local lakes cannot be compared to northern lakes, a lot of data was gathered regarding cormorants’ foraging habits from Leech Lake during cormorant population control efforts.
In studies done at Leech Lake, it was found that cormorants are opportunistic feeders, and their diet will change depending on what is available, Sundmark said.
The majority of their diet consisted of yellow perch, with 2 to 8 percent of their total diet being walleye.
The cormorant population on Leech Lake has been controlled since 2005, when they were seen as having a negative impact on the walleye population there, and many look to it as being a success story.
However, other factors assisted in the comeback. Walleye was stocked for the first time ever in 2005, and extensive walleye fry stocking has taken place since, Sundmark noted.
Other factors which helped the walleye population re-establish itself are reduced fishing pressure, initiation of a slot limit, and reduced bag limits.