The countdown is on to the cod‘s extinction in certain Atlantic waters — and culling grey seals may be one of the only options to slow the trend.
That’s according to an assessment of cod stocks in the southern Gulf of St. Lawrence, an area that is surrounded by New Brunswick, Nova Scotia and the island of Newfoundland.
The Atlantic cod could be extinct in those waters by mid-century, the study said.
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The cod has a storied history as a cornerstone of Newfoundland and Labrador’s economy.
Catches of Atlantic cod totalled an average of 30,000 tonnes annually between 1917 and 56,000 tonnes annually between 1941 and 1992.
The cod stock collapsed in the late 1980s and early 1990s, forcing a closure of the fishery between 1993 and 1998.
The fishery was reopened in 1998, with a total allowable catch of 3,000 tonnes. This was increased to 6,000 tonnes in 1999 but later reduced again to 3,000 tonnes in 2004.
Ultimately, the directed fishery for Atlantic cod was closed in 2009 and it’s remained so ever since.
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The latest assessment, released by Fisheries and Oceans Canada (DFO) earlier this month, was the first full one to take place since 2015.
Back then, authorities found that the volume of “spawner biomass” — Atlantic cod that can reproduce — totalled 28,700 tonnes in southern Gulf waters, the lowest level in a record dating back 65 years.
The numbers were even more dire in the latest report — which showed the 2018 spawner biomass at 13,947 tonnes — representing 12 per cent of the figure reported in 2000 and four per cent of where it was in 1985.
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Researchers studied numerous factors to explain the decline, such as overfishing, competition for resources and harsh environmental conditions.
Only predation — particularly by grey seals — could illustrate what’s happening with empirical evidence.
The cod stock has seen an “extreme increase” in its natural mortality over the past 40 years, and that trend has coincided with a growing population of grey seals, the study said.
Grey seals used to exist in abundant populations in Gulf waters before they were hunted to low levels in the mid to late 1880s.
Walruses, sharks and orcas also used to prey on them.
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Grey seals fell to a population of about 8,000 animals by 1960.
They have since rebounded to a population of about 400,000 amid restrictions on seal hunting, the wiping out of walruses and declines in orcas and sharks.
“Before the collapse of this cod population in the late 1980s and early 1990s, cod mortality due to predation by grey seals did not appear to be unusually high,” report co-author Douglas Swan, a DFO marine fish ecosystems scientist, told Global News.
“However, following the cod collapse, mortality due to predation by grey seals increased to unusually high levels.”
Research has shown that cod make up as much as 80 per cent of a male grey seal’s diet based on stomach contents, and up to 64 per cent of its diet based on its intestines, with most of them aged five years or older.
Indeed, grey seals could account for all the natural mortality of cod over five years old that had happened over normal levels since 2000, said an article published last year in the Canadian Journal of Fisheries and Aquatic Sciences.
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So what can be done to stem the Atlantic cod’s gradual swim toward extinction in the southern Gulf?
Swain could think of no other action than culling grey seals.
The Canadian Journal article found that if the grey seal population were reduced by 65 per cent, then the decline in cod that can reproduce would be “nearly arrested,” he noted.
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He cautioned, however, that any attempt to remove grey seals would also need to look at the “likelihood of negative indirect effects on cod and other ecosystem components,” such as increases in the populations of other predators that are “also prey of grey seals.”
“Since fishing mortality has already been reduced to negligible levels, I can think of no other action to reduce the probability of extinction,” Swain said.
But is it too late for the Atlantic cod in these waters?
“Nothing is certain,” Swain said.
“But this population has declined to such a low level that I think it is very unlikely that its continued decline can be averted.”
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