Should Canada cull grey seals to try and save this 'ugly' bottom feeder?
Winter skate are dying in huge numbers, and a new scientific paper points the finger at a big herd of seals
A "striking conservation success" in Atlantic Canada has turned into a "serious conservation problem" as rebounding grey seal herds threaten depleted bottom-feeding fish in the southern Gulf of St. Lawrence, according to a new research paper from Canadian and U.S. scientists.
The focus is on the winter skate, a little-known shark relative with a flat body and a long tail.
"It's quite dire. The skate have declined by 98 per cent since the mid-80s," said Doug Swain, a federal fisheries scientist based in Moncton, N.B.
Swain is lead author of a paper posted in the science journal Ecology Applications, which examines the cause of the winter skate collapse and the risk of extinction.
The paper concludes grey seals are the likely cause of an "unprecedented" winter skate annual adult mortality rate of between 65 and 70 per cent.
'Predator pit' keeping winter skate on thin ice
It argues winter skate are now trapped in a "predator pit." In this cycle, there are so few winter skate to eat that seals switch to other prey, but the winter skate do not recover. Whenever the population increases, seals return to prey on them.
"What this means for winter skate is, instead of driving them to extinction by predation, they are just trapped at very low abundance," said Swain.
The fish are still vulnerable to other events that increase the risk of extinction, such as habitat destruction or warmer temperatures caused by climate change. The paper examines and rejects other scenarios to explain the decline.
Gulf winter skates are not seen in other spots, showing they have not moved from the area studied. There is no directed fishery for them.
The fishing threat has only been accidental capture — known as bycatch — but since the cod collapse, there is only a low level of ground fishing in the gulf. In the scallop fishery, 90 per cent of winter skate survive when discarded.
Meanwhile, the grey seal population has exploded in Atlantic Canada from a low of 8,000 in 1960 to 400,000 today, according to Fisheries and Oceans Canada estimates.
Scientists like Swain contend the recovery threatens other bottom-feeding fish in the gulf. He points to Atlantic cod and white hake. He said up to 90 per cent of adult white hake die every year.
Seal cull could hurt more than it helps
Overfishing is the chief cause of the Atlantic cod collapse, but the species has not recovered, despite a decades-long moratorium. Swain argues cod are in more danger than winter skate, since unlike skate, they winter in one place: around St. Paul's Island off Cape Breton.
While they are now fewer in numbers, cod still gather in dense enough concentrations to attract grey seals.
Swain's paper estimates the downward trend could be reversed, but it would take an enormous seal cull.
Fishermen have long called for a cull, but that option would likely backfire, argues Shannon Arnold of the Ecology Action Centre in Halifax.
"It would destroy exports of Canadian fisheries because it is an animal-welfare issue for so many people. And so if you start to cull seals, there would be a massive outcry and protest to boycott Canadian fishery products," she said.
Like Swain, she sees the plight of winter skate as an example of what happens when an ecosystem gets out of balance. But she blames poor management.
'Ugly' and uncharismatic
"We knew for a long time that these were declining, but these are animals that people don't care about. They didn't have big economic impacts. They're ugly. You know, they're not charismatic," she said.
"So, there was no drive to really go ahead and do something and be precautionary, put the money that you need to figure out what's going on with skate habitat and nurseries, and now it's irreversible."
The Department of Fisheries and Oceans is consulting on whether southern Gulf of St Lawrence winter skate should be formally designated as a species at risk.
That would oblige the federal government to create a recovery strategy and action plan to address known threats.
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