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Otter dung reveals secrets of missing sturgeon in B.C. river

UNBC graduate student Cale Babey's search of dozens of river otter latrine sites on the Nechako River turned up more than 1,000 identification tags from hatchery-raised endangered white sturgeon.

2-year study found endangered species a frequent food of river otters

CBC News ·
UNBC graduate student Cale Babey uses an antenna to receive radio signals from tags attached to some hatchery-raised white sturgeon. (Nickolaus Gantner )

A study of the places where river otters poop along the Nechako River is helping conservationists understand how the sleek mammal's appetite for white sturgeon is hampering efforts to save the endangered fish species.

Cale Babey, a UNBC graduate student, became acquainted with dozens of latrine sites frequented by the fish-loving Lontra Canadensis,  as he spent two years searching through their deposits of spraint (otter feces).

Babey was looking for small identification tags from juvenile white sturgeon released by a Vanderhoof hatchery, and he found plenty of them.

"We had had some preliminary evidence that this predation was going on," Babey told Daybreak North host Carolina de Ryk.

 "We now have evidence of over 1,000 sturgeon being eaten by otters in the Nechako," he said.

Cale Babey's trail camera caught this image of river otters on British Columbia's Nechako River. (Cale Babey)

The findings were published in a paper by Cale and co-researchers in the Oct. 5 Journal of Applied Ichthyology.

For his research, Babey passed a handheld device similar to a grocery store scanner over the otter dung. He was looking for tiny one-centimetre passive integrated transponder tags that identify each fish with a unique code.

When an otter eats a fish, it often swallows the tag, then excretes it in its spraint.

In response to the findings on river otter predation of the hatchery sturgeon, Babey said the Nechako White Sturgeon Recovery Initiative is working on strategies to increase post-release survival. One possibility is to grow the juvenile fish in the hatchery for an extra year.

Juvenile white sturgeon in a tank: These fish can live for more than 100 years and grow up to six metres in length but efforts to boost the endangered species through releasing thousands of hatchery fish have been hampered by river otter predation. (Nechako White Sturgeon Conservation Centre)

Although the white sturgeon are a critically endangered species (and the river otters are not), Babey says the carnivorous weasel relatives are not to blame. 

"I think it's not quite fair to look at them as sort of the villain here, but as the predator, and what's an expected predator and prey interaction," Babey said.

"Otters are doing what otters do. Eat fish and eat a lot of fish."


To hear the full interview with Cale Babey on CBC Radio One's Daybreak North with Carolina De Ryk, tap the link below: 

With files from Daybreak North and Deborah Wilson

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