Lake Huron cormorant monitoring continues:
120 birds harvested for diet study

Jim Moody, Manitoulin Expositor

September 14, 2005

NORTH CHANNEL-The Ministry of Natural Resources (MNR) is wrapping up yet another summer-long study of the cormorant population in Lake Huron, aspects of which this year included the banding of 400 birds to track their movement and the 'collection' of 120 in order to analyze their stomach contents.

The scope of the 2006 research program was downsized from last year, conceded MNR research scientist Ken Abraham, with both egg-oiling and inland-lake analysis being put temporarily on the back burner. But other prongs of the study were extended and new features added, such as the banding program.

"The study was scaled back from previous years, but two elements of the summer's work were initiated in the five-year study," said Mr. Abraham. Colony inventory and nest counts, for instance, first undertaken in 2000, were carried out once more, with a contractor being engaged to visit "all the known colony locations by boat, and count the number of active nests," said the scientist.

Apart from counting nests, "we look for evidence of disease and the stage of hatching," Mr. Abraham noted. "It's a general reconnaissance of each colony, which allows us to estimate how large the population is and how it has grown over a 30-year period."

With the data from this summer yet to be analyzed, it is premature to precisely assess the size of the population compared to previous years, but Mr. Abraham said that, "in general, in visiting the colonies, we found nothing startlingly new in terms of new colonies or the size of them growing." Some population fluctuations may have occurred in certain areas, "but it's safe to say that if there was any great increase, we'd already be aware of it," he noted.

The five-year study that was wrapped up last year-but is still awaiting peer review by scientists outside the ministry before it is published-determined, among other things, that the number of cormorants in the North Channel and Georgian Bay had dwindled appreciably due to a collapse in the alewife population in 2003 and 2004, which the ministry attributes to cold winters.

But that doesn't mean the MNR isn't continuing to gauge the species' impact on local waters, or continue the research done to date. Another element of this past summer's study that built upon previous work was the culling of birds to examine their stomach contents. "Last year on Manitoulin we collected cormorants after they'd been feeding to conduct an analysis of which species they're eating," noted Mr. Abraham, "and we did more of that this year."

MNR staff visited four sites in Lake Huron - two in the North Channel, and two in Georgian Bay - at two different times of the summer, shooting 15 birds each time, at each location, for a total of 120 birds harvested for research purposes.

"The birds were collected in June and July and frozen for later analysis," Mr. Abraham said. "Our biologists are still in the lab studying the stomach contents."

One of the things they will be looking for is whether round gobies-which have moved into Lake Huron as the alewives decline-make up a significant part of the cormorants' diet, said Mr. Abraham. As well, the MNR will make use of an isotope technique to determine whether the fish consumed by the birds originated in Lake Huron or inland lakes.

New this year has been the banding of birds. "We banded about 400 at several colonies," said Mr. Abraham, explaining that a crew of seven or eight volunteers would visit a nesting site early in the season "when the young are flightless," and separate a few from the flock. The unfledged birds are placed in small sacks, and tagged with an aluminum band as well as a coloured plastic band indicating their location, before being released.

"This has been done by other jurisdictions, such as New York State and Michigan ," noted Mr. Abraham. "So we're trying to work with these other jurisdictions to see how 'open,' in scientific terms, the population is-how much they interchange among areas, and where we can expect new recruits to come from."

The mobility of cormorants and their willingness to relocate to new areas are significant factors in determining the effectiveness of culling and egg-oiling initiatives, said Mr. Abraham. If new birds will simply move into an area "where the population has declined, due to natural factors or culling, then that limits the effectiveness (of population control measures). It could mean everybody has to do it on a global Great Lakes scale," he said. "This is partly why we haven't moved ahead with oiling or culling."

The five-year study "revealed that oiling, on its own, is not able to reduce the population of cormorants," Mr. Abraham said. Analysis of that egg-oiling initiative "is still ongoing," the scientist indicated, but some striking observations were made, chiefly that fish rebounded initially at sites where oiling had occurred, only to dwindle again a couple of years later. "The hypothesis is that other birds compensated (for the decline in the number of cormorants at the colonies) by coming in from somewhere else," said Mr. Abraham. "This raised the question regarding the mobility of birds within the system, which led to the banding program."

The MNR plans to expand this tracking system, as well as extend the nest counts and diet studies, next year. Additionally, the ministry will be devoting more resources to studying the birds' impact on mainland lakes across Ontario in the coming year. "We are designing an inland lake monitoring program for very large areas," said Mr. Abraham.

He said it's "not a surprise" that cormorants are moving inland, "given the alewife collapse" in Lake Huron, but "what we want to explore is whether they are establishing colonies on the lakes or if it's just non-breeding birds coming in to feed. We're trying to get ahead of the birds."