Trout program leaving lake unbalanced

A collapse of Lake Simcoe's herring population may relate to a government program to stock the lake with one of its main predators, the lake trout, says a professor working with the Ministry of Natural Resources.

"One has to wonder if we've got the right balance," David Evans, an adjunct professor at Trent University who has been analyzing data relating to the lake, said recently.

"We have to be concerned about (the herring's) continued existence in the lake," said Evans, who, still in the process of studying data, has yet to publish any findings.

He said rainbow smelt, a species introduced in 1962, is another of the trout's prey that also may have seen its population plummet due to bolstered trout numbers.

"It's possible that lake trout are putting undue predatory pressure on that prey," he said.

Every year, the ministry stocks the lake with about 100,000 lake trout because the fish - as is also the case with lake whitefish - no longer reproduce naturally.

"It has been stocked for many, many decades," Evans said.

Phosphorous loading, identified as a major factor in Lake Simcoe's diminished water quality, has also been connected to the fish's inability to reproduce naturally.

Phosphorous - contained in fertilizer and detergent - causes more plant growth and, consequently, reduced oxygen levels.

Though Evans speculated too many lake trout may have led to fewer herring and smelt, he said there are other factors to consider, including phosphorous, climate change and invading species.

Zebra mussels remove algae, which provide nourishment for the zoo plankton that, in turn, serve as a food source for herring, he noted.

"Nothing is stable in Lake Simcoe because there's so much going on," Evans added.