DNR promises to spend more time investigating the issue
By Jennifer Kotila
MEEKER, WRIGHT, MCLEOD, MN The Minnesota Department of Natural Resources (DNR) and representatives from various lake associations are still butting heads over whether the large population of cormorants at the Pigeon Lake rookery, south of Dassel, are affecting the populations of game fish in area lakes specifically walleye.
Local anglers and lake associations want the DNR and US Fish and Wildlife Service (USFWS) to justify allowing the culling of cormorants on Lake Vermilion this year, while refusing to do anything about the population at the Pigeon Lake rookery.
One of the main arguments being used by local lake association members is that Lake Vermilion in northern Minnesota has a larger acreage of open water from which a smaller population of cormorants are able to feed, as compared to the small acreage of open water within the feeding range of a larger population of cormorants at Pigeon Lake.
The DNR and USFWS argue that fish surveys completed at Lake Vermilion indicated that the yellow perch population was decreasing due to an increasing cormorant population, but fish surveys conducted by the Hutchinson Area Fisheries Office of the DNR on area lakes indicate the populations of fish here are well within the normal range.
Minnesota’s DNR commissioner recently set two triggers that would allow population control of cormorants at Lake Washington if the gillnet abundance for walleye is below the 25th percentile for two or more standard DNR fish surveys, and if other rare or sensitive species of waterfowl are at risk due to competition for nesting sites.
The problem is that fish surveys in area lakes are only completed every five years and anglers and area lake associations are concerned data collection is not keeping pace with the rapid population increase of cormorants at the Pigeon Lake rookery.
Lake Vermilion’s fish population is monitored yearly, and a team of research analysts is assigned to the lake year-round.
“They are able to justify a team of specialists for large lakes like Vermilion because of its economic impact,” said Lee Sundmark, Hutchinson Area Fisheries supervisor.
A committee is being formed to establish improved data collection procedures for lakes within 9 kilometers of Pigeon Lake in order to monitor more closely the effects the cormorant population might be having on local fish populations.
“We’re not looking to completely get rid of the cormorants, but just control them,” said Ken Klehr, president of the Lake Washington Improvement Association.
Sundmark shared fish survey data available for local lakes, and Edie Evarts, DNR fisheries supervisor for the Tower management area, shared data regarding Lake Vermilion.
Lisa Galvin-Innvaer provided current numbers for the Pigeon Lake rookery and other rookeries in the surrounding area.
Can Vermilion and area lakes be compared?
The Lake Washington Improvement Association has a cormorant impact committee that has spent countless hours studying the data available to them in order to correlate the population of the Pigeon Lake rookery to perceived fish population decline on area lakes.
It is now using the findings of biologists at Lake Vermilion, who have concluded that Vermilion’s cormorant population and its impact on the fish population warranted the culling of cormorants.
However, comparing area lakes to Lake Vermilion is not a fair comparison, according to the DNR.
“Ninety percent of the walleyes are caught on 10 percent of the lakes, mostly larger lakes like Vermilion,” Sundmark said.
For several years at Lake Vermilion, fish surveys showed a consistent decline in the yellow perch population in the east bay.
Yellow perch are a staple in the diet of the walleye population on Lake Vermilion.
Cormorants established 32 nests on the lake’s Potato Island in 2004, and by 2012, the colony had grown to 424 nests a 30 percent increase from 2011, according to the DNR.
The control of the cormorant population on Potato Island on Lake Vermilion this spring consisted of culling 10 percent of the adult population of cormorants, and oiling the eggs of all nesting pairs. Oiling cormorant eggs prevents them from hatching.
It is the conclusion of the cormorant impact committee of LWIA that the foraging intensity by cormorants on Lake Vermilion, a 39,000-acre lake, is 7.49 pounds of fish per acre.
However, at Lake Washington and the surrounding lakes, which total about 11,400 acres, the foraging intensity of cormorants is 94.62 pounds of fish per acre.
Evarts noted that the most productive areas of any lake are shallow, vegetated areas, and only about 40 percent of Lake Vermilion is considered good for being productive which brings the number of acres cormorants are able to feed on down to 15,600.
The bottom line is, the lakes near Pigeon Lake and Lake Vermilion are so different, it is hard to make a fair comparison, Evarts said.
Vermilion has a rocky bottom, not very many nutrients, and a very simple fish population with walleye, perch, northern pike, and tullibee, Evarts commented.
Area lakes have a wide range of fish species, including bluegill, walleye, black crappie, yellow perch, black bullhead, pumpkinseed, northern pike, carp, and largemouth bass.
While Lake Vermilion is a natural walleye lake, the lakes within the Hutchinson Area Fisheries’ supervision are stocked with walleye hatched from eggs harvested at Lake Vermilion, according to Evarts.
Walleye are produced and harvested in area lakes, according to Sundmark.
“We stock (some area lakes) with fry in the spring, and net fingerlings in the fall. It’s the same as (farm) harvest some years you have good crops, and some not so good,” Sundmark said.
According to his data, 13 of the 33 lakes the DNR uses to produce walleye are within 9 kilometers of Pigeon Lake and have been the highest producers of walleye fingerlings and yearlings eight of the last 16 years.
“In any regard, I don’t see where cormorants are depleting area fisheries, looking at the data I have,” Sundmark said.
When it was decided that cormorants would be allowed to be culled at Lake Vermilion, there was some indication that the lake’s walleye population was being affected but that was not part of the arguments used, Evarts noted.
Instead, researchers were looking at the data for yellow perch, of which the population had declined drastically.
Yellow perch are a primary food source for a number of other species of fish, as well as cormorants, other carnivorous waterfowl, and anglers.
From east to west, Lake Vermilion spans 20 miles, and cormorant population is on the east side of the lake, which is where several years of data indicated the yellow perch population was suffering.
While there were a couple of low population years for yellow perch on the west end of the lake, the population increased to a normal range.
A number of other factors were investigated for the decline in the yellow perch population, but none were as strong as the indication that the increased cormorant population was affecting the yellow perch population, according to Evarts.
According to data collected, fish populations in local lakes, including walleye and yellow perch, are within the normal population range, Sundmark said.
LWIA members admit that may be the case, but used the DNR surveys to argue that while the population of larger walleye is not declining, the population of smaller walleye, which are what cormorants eat, is declining.
They note there are 2.2 million walleye stocked in area lakes each year by the DNR, and it is all going to feed the cormorants.
They argue that between 2004 and 2012, the number of walleye 0 to 8 inches long have decreased in Lake Washington by 88.3 percent, those up to 11 inches long decreased by 73.4 percent, those up to 14 inches in length have decreased 72.6 percent. However, walleye greater than 15 inches in length have increased 6.6 percent.
During that same time period, the cormorant population at Pigeon Lake has increased 43 percent, and the pelican population has increased 52 percent.
“Their statistics are pretty compelling,” admitted Sundmark. “But they are only looking at one lake compared to others. Generally, the fisheries are in good shape.”
In order to allow for the population control of cormorants at Lake Vermilion, researchers had to show enough weight of evidence to justify their request to cull cormorants, Evarts noted.
“Two years ago, there was not enough data to see the trend. It takes a certain amount of time to make sure the trend is there,” Evarts said.
At Lake Vermilion, research over a six-year time period showed the yellow perch population below its normal range.
It could be argued that Lake Vermilion’s large walleye population affected the yellow perch population, Evarts continued, but the trend would have then been evident on both ends of the lake.
At this time, there is simply not enough weight of evidence to justify the culling of cormorants at Pigeon Lake, according to the DNR.
“They care about lakes, and I do too,” Sundmark said. “But, unless I’m convinced something is going on, I’m not going to give into something I just can’t prove.”
Pop. steady at rookery
Despite an outbreak of New Castle disease at the Pigeon Lake rookery the week of Aug. 1, 2012 killing approximately 700 cormorants, 100 pelicans, and a small number of gulls, herons, and egrets the population of cormorants at the rookery has held steady, according to a report produced by the DNR Nongame Wildlife Program this year.
Last spring, a survey of the nesting birds at Pigeon Lake rookery showed 2,334 pairs of cormorants; a survey conducted this spring showed 2,325 pairs.
The population of cormorants at the Pigeon Lake rookery in 2004 was 1,503 nesting pairs; and, in 2010, 2,145 nesting pairs.
Another nearby rookery on privately-owned Swartout Lake, located near Annandale, south of Minnesota Highway 55 on Wright County State Aid Highway 6, had a cormorant population of 86 nesting pairs in 2004; 703 nesting pairs in 2010; and 603 nesting pairs in 2013.
A rookery on a privately-owned island in Lake Waconia, where the culling of cormorants has been permitted since 2008, had a population of 250 nesting pairs in 2004; 467 nesting pairs in 2010 before culling took place, and 425 nesting pairs after culling took place; 324 nesting pairs in 2011; and, virtually no cormorants were present in the spring of 2012.
The survey from this spring showed a cormorant population of about 378 nesting pairs but researchers were only moderately confident in the accuracy of this number due to a large amount of vegetation obscuring nests.
According to an article in the Star Tribune, 187 cormorants were culled from Lake Waconia in 2008; 360 in 2009; 600 in 2010; and, 309 in 2011.
Researchers also surveyed a new rookery in a wetland near Minnetrista, where a cormorant population of 27 nesting pairs was located.