• A humpback whale feeds on herring in the Johnstone Strait on the northeast coast of Vancouver Island

    A humpback whale feeds on herring in Johnstone Strait on the northeast coast of Vancouver Island. Herring are a "forage fish," meaning they are a dietary staple for many large predators and therefore an important indicator of the health of a marine ecosystem. (Photo: Jenny Stevens/Can Geo Photo Club)

A new report from the World Wildlife Fund-Canada warns that "forage fish" — small but abundant fish that are a dietary staple for larger marine predators — are facing increasing pressure from overfishing and environmental changes and that their decline would upset the balance of Canada's marine ecosystems.

The report, released August 2, says that of the 27 fisheries assessed, three forage fish stocks in Atlantic Canada are in critical condition: two herring stocks in the Gulf of St. Lawrence and Atlantic mackerel. Elsewhere in Canada, data on forage fish stocks is either insufficient or nonexistent, including all capelin fisheries and all fisheries in British Columbia. 

Aurelie Cosandey-Godin, a senior oceans specialist with WWF-Canada, says failure to monitor and understand changes in forage fish stocks means a critical link in the marine food chain has been ignored. That could hinder other conservation efforts, such as saving endangered whales and restoring the Atlantic cod fishery.

"These small fish are the ones right in the middle of our ecosystem; they feed on phytoplankton and are fed on by larger predators," Cosandey-Godin explains, adding some marine predators, such as humpback whales, minke whales and harbour seals almost exclusively eat forage fish.

Capelin comprise up to 75 per cent of the diet of large Atlantic cod, meaning the recovery of cod stocks depends on the continued availability of their preferred food. 

Because they aggregate in large shoals, forage fish are easy to harvest even when their overall numbers are declining, making them vulnerable to overfishing. They're also sensitive to changes in their environment, which can cause broad fluctuations in their numbers from year to year. 

The WWF report makes several recommendations it says can help protect forage fish stocks, including ending their use as bait for lobster and implementing fishery management practices that consider all the species in an ecosystem, not just the commercially viable ones. 

"Everything is connected," says Cosandey-Godin. "We need to take into account the full scope of these fish and the foraging needs of their dependent predators."