Fine young cannibal cod

JOHN THOMPSON

The prehistoric cannibal cod that grow to huge sizes inside Ogac Lake, about 100 kilometres south of Iqaluit, are far younger than researchers first imagined.

The cod are an oddity in Nunavut, believed to have lived in isolation in the lake since the end of the last ice age, over 5,000 years ago. In 2003 researchers examined the stomachs of some of the giants, which can grow to weight 70 pounds, and found one-third of them contained other cod – an unusually high rate of cannibalism for the species.

The land-locked cod are so starved for food, one even resorted to swallowing a loon. The bird’s entire neck, skull and feathers were found inside its stomach.

Earlier estimates pegged the giant fish to be around 25 years old. New studies show many of the large fish are about 12, just half the expected age.

This finding goes in hand with another discovery, which helps to answer an unsolved mystery: If food inside Ogac Lake is so scarce, why don’t the cannibal fish eventually eat themselves out of existence?

Last year David Hardie, a researcher from Dalhousie University, dove into the lake and left behind a gadget that would record the water temperature every minute over the course of a year. The temperature records provide a history of how often colder ocean water floods back up the river connected to the lake.

This summer he collected the logs. It turns out seawater sloshes into the lake around 80 to 100 times a year – twice as often as earlier expected. Those waters carry with them a variety of small sealife that the cod snap up the moment it reaches the lake.

“It really goes to show they don’t pass up any free meals. They’ll pretty much eat anything.”

In fact, last year Hardie saw the cod actually line up along the lake’s edge during a high tide in anticipation. Measurements taken that summer showed 250 kilograms of sealife washed into the lake during a single tide.

That amount would decrease during the winter, but it’s possible that algae growing beneath the sea ice washes into the lake. The extra food carried in by the tide helps explain how the fish survive. As Hardie puts it: “There are only so many loons to eat.”

The only thing that washes in that the cod don’t eat are jellyfish. Hardie has seen seven or eight different larval species of fish arrive, but none survived, save the fourline snakeblenny, a small fish with a long, eel-like tail that hides in the cracks of the lake rock.

The tides also help replenish the lake with salt water, which the Atlantic cod, as a marine species, needs to survive.

“It’s possibly very important,” Hardie said.

As for the cod’s age, original estimates were done by researchers 50 years ago. Given the giant proportions of some fish, their numbers seemed reasonable at the time, Hardie said.

The revised ages were found by examining the “ear stone” found inside fish, which have annual growth rings. Even with this, determining the age of fish is tricky business, so experts from Iceland were consulted.

The cannibal cod Hardie examined also had swollen livers five times the usual size. As the main storage for fat, it’s a good indication they’re well fed. In comparison, cod that didn’t eat their own in the lake had red, shriveled livers, a sign of malnutrition.

Hardie fears the novelty of the fish could be their demise. Inuit have traditionally been careful when harvesting from the lake, but modern sport fishers could easily wipe the giant cod out, he said. He guesses the number of monster cod in the lake could be as low as 15 now.

Researchers used a number of safety precautions when catching the fish. They only used a single hook without a barb, and a special harness was used to hold the fish when it was hauling out of the water. Even a sport fisher planning to catch and release a fish could cause serious harm, Hardie said.

“After a long fight, that might be enough to kill them. Even if the fish swims away, it might be lethal.”

Another worry is an air bladder inside the fish, which inflates when it’s pulled from the surface. Researchers deflate this with a syringe before returning the cod to the water, otherwise the fish remains trapped in the fresh water on the lake’s fresh water surface.

On top of all this, the monster cod have a reputation for tasting awful. Hardie said he’d take Arctic char over them any day.

“It’s not so much a taste as a texture. They’re all mushy. They fall apart in the pan. You really need to fry the hell out of them.”