Way up north, the cod are cannibals

Original Source: The London Free Press
Way up north, the cod are cannibals

HALIFAX -- Codfish as big as an eight-year-old child are roaming three Arctic saltwater lakes, eating anything in their path -- including each other. That's what researchers from Dalhousie University in Halifax discovered last summer while doing research on Arctic cod in three landlocked lakes near Baffin Island

"They're voracious," says Dalhousie biology Prof. Jeffrey Hutchings. "If you have one of these on the end of your hook and you haul it up, you see three or four other massive cod going after it."

Hutchings and PhD student David Hardie spent a couple of months in the Far North last summer studying the fish.

They caught some cod that were 1.3 metres long and weighed about 32 kilograms.

Hardie, studying the little-known evolutionary ecology of Arctic fish, has done research in the North for the past five years.

He wanted to visit Ogac Lake -- the name of which is Inuit for cod -- near Baffin Island to follow up on a now-retired Dalhousie professor's work there in the 1950s and '60s.

When he got up there, however, local hunters told him about two other essentially unspoiled lakes with the same kind of cod in them -- the Qasigialiminiq, which is roughly translated as "used to be seals," and the Tariujarusiq, which means "kind of salty," near Cumberland Lake.

"This is beyond the northern range of Atlantic cod in Canadian marine waters," Hardie said.

"They're interesting in their own right because they're in lakes, which is highly unusual for cod. But also because there are no cod that far north in the ocean, so we have certain questions about where they came from and how they've survived in these unusual environments."

These chilly cannibals are stuck year-round with no other source of food except for what washes in on the ocean tides 30 to 40 times a year.

"They get 40 meals a year -- and then they're scavenging for what they can in the lake," Hardie said. "The sooner you can get big and have a year-round supply of small cod to eat, that's the best strategy."

That sometimes means they breed to feed, occasionally eating their own offspring.

The killer cod are usually so hungry, Hardie said, they scoop up everything, even rocks, in their pursuit of smaller fish, sea urchins or seaweed.

"You'll find anything in a cod's stomach and they're also highly cannibalistic as well," said Hutchings. "In fact, the cannibalism rate in this lake is higher than we've ever seen it."

Atlantic cod aren't as cannibalistic, he said, because they have a wider range of dining options.

The northern cod also have been known to set their fishy eyes on a bigger prize. One of the fish that researchers caught was a 75-centimetre specimen that had what appeared to be a red-throated loon in its stomach.

"Most likely it was a loon that was diving down, probably feeding on the small cod and one of the larger cod snuck up behind it and managed to grab it," Hardie said.