Washington, May 15 : A new research has indicated that restoring fish populations such as exotic salmon and trout to the Great Lakes in America might adversely affect the health of Sea Gulls, demonstrating that fishery management actions can sometimes have very unexpected outcomes.
The research, carried out by Craig Hebert and his team from the National Wildlife Research Center in Ottawa, Canada, analyzed 25 years of data on the gulls and found that throughout the Great Lakes region, the birds were in poor health in many areas.
Tests of their fatty acids showed an increase in the type of transfat that mostly comes from food produced by humans.
"It seems that the birds are being forced to make a dietary shift from fish to terrestrial food, including garbage," said Hebert.
Although no one is certain why the birds are eating more garbage, evidence points to fish stocking.
When exotic salmon and trout have been added to the waters, the birds seem to be out competed for their favorite prey of smaller fish, such as alewifes.
Gulls are top predators in this system. When fish are unavailable, the birds turn to land instead for their foraging.
When given a choice between prey fish and garbage, the birds readily chose the fish. Thus, scientists assume that they only eat garbage when the prey fish numbers are low.
Prey fish in the Lake have been declining since 1980.
Although multiple factors may be at play, predation by piscivorous fish appears to be the one factor that was universally important across all five Great Lakes because of massive fish stocking, which was done to create recreational activities, and to reduce populations of exotic prey fish in the hope of restoring populations of native fishes.
"The effects on other species that are more closely tied to the water, such as terns, may be more severe," said Hebert. "Those kinds of birds can only eat fish, so their diet may be affected by this, too. They don't have the option of eating food found on land," he added.