Double-crested cormorants are feasting on round gobies, leaving more sport fish, especially small-mouthed bass and yellow perch, for anglers.
"Cormorants seem to be opportunistic feeders that take whatever is most available," said Russell D. McCullough, senior aquatic biologist for the state Department of Environmental Conservation. By studying the contents of cormorant pellets, regurgitated bones, scales and other undigested particles eaten by the birds, DEC officials reached the conclusion that in 2009, 91.6 percent of the cormorants diet consisted of round gobies from Lake Ontario. Cormorants consume almost 14 million fish during their stay in the north country. Round gobies, an invasive species in the lake, account for 12.7 million of that take.
The gobies are dominating the cormorant diet so the birds are eating a lot less of other species, Mr. McCullough said.
"There may be some competition for goby prey with other predators," he said.
For areas along the St. Lawrence River, gobies are second to yellow perch in cormorant diets.
"Gobies were probably less abundant in the diet of St. Lawrence River cormorant colonies because other types of fish remain relatively more available in the river than they are in Lake Ontario," Mr. McCullough said.
The report states that cormorants consumed 360,000 yellow perch, 160,000 rock bass and 30,000 small-mouth bass during 2009 and fishing charter captains said they have noticed a positive change in the size and number of sport fish.
John A. Delorne, captain for Jon-Boy Charters, Henderson Harbor, said this summer has been the best year for catching yellow perch.
"They're beautiful," he said. "There are a lot of nice yellow perch out there. They're doing fine now because there aren't hundreds of thousands of cormorants around anymore. The perch are nice and big; it's nothing to go out and catch a nice 12 to 14 inch yellow perch."
Mr. Delorne said that although the perch have been plentiful, the gobies are still an issue.
"There are certainly enough gobies around," he said. "Even at my marina there are a couple of thousand here, but we know that the walleye, perch and bass, they're all eating the gobies. At least they are having a positive impact on the food chain."
Mitchell L. Franz, a member of the Lake Ontario Fisheries Coalition and owner of Mit-She Fishing Charters, Henderson Harbor, said cormorant control has been helpful to the recovery of sport fishing in Lake Ontario.
"The numbers seem to be up, and as long as the numbers of sport fish are increasing, that means we are recovering," he said. "You'll still catch gobies depending on where you fish, but the perch and the bass have been excellent for the last two or three years. There is a good number of them, they're a good size and there is a good variety of age class."
Bass are more abundant and larger, yet anglers are still fighting with gobies to keep bait on hooks.
"Bass anglers are still catching a lot of gobies, they're still a nuisance," said Robert W. Dick, owner of Moby Dick Charters, Henderson Harbor.
When DEC started the cormorant control program in 1999, there were about 7,000 nesting pairs of cormorants on Little Galloo Island. Over the years that number has been reduced and Mr. McCullough said they are nearing their goal of 1,468 nesting pairs. As of June 15, there were 1,758.
"Cormorant control efforts in recent years have been somewhat reduced because the cormorant population is near our target level," he said. "In the long term it is very likely that the dominance of gobies in the cormorant diet will decline and other fish species will be consumed in higher numbers. We intend to continue our cormorant population management efforts so that the effect on other species will be moderated."