Cormorants culprits of contamination

Published February 1, 2000

A private consulting firm hired by a group of concerned citizens has found potentially harmful levels of PCBs, DDE, and mercury on state-owned property, Little Galloo Island, in eastern Lake Ontario. The contamination is due to burgeoning populations of the double-crested cormorant, which has invaded the area in recent years.

Testing performed by Chopra-Lee Inc. of Grand Island, New York, a state-accredited environmental analytical laboratory, found PCB levels of nearly five parts per million in a guano/soil sample, a level exceeding state action levels for cleanup. Two mercury readings also exceeded state levels. The study was conducted during August 1999 and just released.

The concentration of toxic materials found in the soil and bird guano on Little Galloo Island appears to have bioaccumulated. Bioaccumulation occurs when chemically tainted fish are consumed in massive amounts by the gluttonous cormorant, then deposited in the form of excrement, eggshell remnants, and bird carcasses.

Mixing zones

A recent article in The Wall Street Journal called attention to the fact that bioaccumulative chemicals (BCCs), including mercury and PCBs, are still being dumped into areas called “mixing zones” in the Great Lakes and surrounding wetlands. BCCs from these mixing zones eventually permeate all waters of the Great Lakes, and as a result all species in the food chain are exposed.

Mixing zones and the dispersed contamination they cause lead to BCCs being collected by fish and bird species, which themselves become “accumulators.” Unlike fish, the cormorant accumulates toxic chemicals from hundreds of square miles of the lake, brings these chemicals back, and deposits them in the form of guano on a few island acres.

“We are outraged that such a situation exists on state-owned property. It is intolerable that state land contains concentrated BCC which during spring thaw and seasonal rains can leach into local waters, thus exposing area residents,” said the citizens who arranged to have the study conducted, residents of Henderson, New York.

The spread of the cormorant

The double-crested cormorant (DCC) was first reported in the Lake of the Woods area of Ontario, Canada as early as the late eighteenth century. Cormorant nestings were reported in Lake Superior in the 1920s. Breeding was reported on Lakes Erie and Ontario in the late 1930s. By the late 1940s and early 1950s, cormorant nesting pairs were in abundance in the eastern Lake Ontario region. In 1974, 22 pairs of cormorants were reported on Little Galloo Island.

From 1973 to 1991, their numbers increased more than 300-fold in certain areas of the Great Lakes. The dramatic increase in DCC populations was probably augmented by a rise in the numbers of smaller fish, such as rainbow smelt and alewife, along with increases in the stocking of game fish such as salmonoides and bass by the New York State Department of Environmental Conservation (NYSDEC) and the Ontario Ministry of the Environment. In 1996, there were a reported 8,410 pairs of cormorants on Little Galloo island.

Studies recently completed by the NYSDEC have concluded that double-crested cormorants consume significant numbers of smallmouth bass, greatly reducing the overall population. Current estimates of smallmouth bass consumption by cormorants exceed the number taken by anglers by 10- to 30-fold. The expanding cormorant populations have also displaced the black-crowned night heron from Little Galloo Island and destroyed woody vegetation on the island favored by other colonial species.

A health threat

Chopra-Lee Inc. was retained by a group of homeowners in the Henderson Bay area to determine if the population explosion of the double-crested cormorant over the last few decades may pose a health threat to the citizens of the area and/or the environment.

To date, the investigation has shown that birds roosting on Little Galloo Island, especially the double-crested cormorant, have deposited toxic compounds like mercury, PCBs, and DDE on the island. (See sidebar.) The toxic materials have bioaccumulated exponentially on Little Galloo, as compared to other islands in the area, due to the overpopulation of cormorants.

The surface water sampling has shown a potential correlation between Little Galloo Island and the downwind surface water quality. Total bacteria colony-forming units downwind of the island (1,367) were dramatically higher than the upwind sampling location (less than 33). Although no PCBs, DDE, or excessive levels of heavy metals were found downwind of Little Galloo Island, the PCBs and DDE found on the island are a potential leaching source of surface water contamination during heavy rains or spring snow melts.

The study raises concerns for the health of the inhabitants of neighboring Galloo and Stony Islands, where the potable drinking water is provided by Lake Ontario. Those water supplies may be adversely affected by surface runoff from Little Galloo Island. The surface waters of Henderson Bay and other mainland areas are potentially vulnerable to runoff from Little Galloo during periods of excessive rain and/or snowmelt.

The Chopra-Lee Inc. investigation and data from other assessments performed in the area strongly suggest that Little Galloo Island’s overpopulation of the double-crested cormorant has had an adverse effect on the area’s ecosystem. The release and accumulation of bird excrement and dead cormorant carcasses appear to be a direct threat to human health and the surrounding environment.

Dan Thomas is president of the Great Lakes Sports Fishing Council. He can be reached by e-mail at [email protected]. Reprinted with permission from the December 6, 1999 issue of the Great Lakes Basin Report.