A marine biologist warns that B.C.'s rebounding humpback whale population may well be threatened if Ottawa approves the Northern Gateway pipeline and the associated oil tanker traffic out of Kitimat.

Part of the proposed tanker route would take those ships through critical feeding grounds for the whales.

Christie McMillan, a marine biologist and president of the Marine Education and Research Society, says scientists already know whales are struck by passing ships, but they don't know how often it happens.

Humpback whale Slash in Queen Charlotte Strait

Parallel wounds indicate were 'Slash,' a humpback whale photographed in B.C. waters in 2006, was hit by a propeller blade. Marine biologists say vessel strikes are becoming a serious concern for humpback whales around Vancouver Island and up B.C.'s coast. (Jared Towers/MERS)

"It's certainly a concern from the point of view that this area has already been identified as very important to humpback whales, so adding vessel traffic will be a concern for sure," she said.

Earlier this week, the federal government announced that it is recommending that the Northern Pacific population of humpback whales be reclassified from "threatened" to "species of special concern" under the Species at Risk Act.

Environmental groups voiced concerns that the move is being made as the government readies for a decision on the approval of the Northern Gateway pipeline, which would feed the oil tanker shipping route that overlaps with the humpback habitat.

McMillan says she isn't passing judgment on the Northern Gateway project, but increasing ship traffic in the areas the whales are known to congregate can only increase the threat of more whales being hit.

An estimated 2,100 humpback whales return to B.C. waters every spring and summer from Hawaii and Mexico.

The Federal government is expected to make a decision on the Northern Gateway pipeline in June.

With files from the CBC's Terry Donnelly