Don’t blame the seals; DFO scientists say attachment to pinnipods ignores other ecological factors

[ad_1]

The harp seal population is not “out of control” even though they number in the millions.

With 7.6 million animals, based on 2017 data, they make up the largest seal population in the North Atlantic.

But they are not the “driving factor” affecting the recovery of northern cod.

These are two of the public’s perceptions of seals that were countered during an anti-myth press briefing on Tuesday, June 29 by Fisheries and Oceans (DFO) scientists Dr Gary Stenson and Dr Mariano Koen-Alonso.

They work out of DFO regional headquarters in St. John’s.

Stenson has studied seals for over 40 years.

Koen-Alonso has been a researcher in the department for almost 20 years.

Dr. Mariano Koen-Alonso, Research Scientist at the Department of Fisheries and Oceans in St. John’s. – Barb Dean Simmons

They both say seals aren’t the only driving force affecting northern cod and other species.

However, public perception is a powerful thing and this past year in particular, with fishermen posting videos on social media highlighting the contents of seal stomachs and the great seal migrations, the seal debate and their impact on cod intensified.

But don’t put all the blame on the seals, scientists say.

If you were to consider all of the predators that eat cod, Stenson said, you should consider whales, seabirds, and humans.

Also, Stenson said, harp and gray seals are not as important as some might assume.

On the south coast of Newfoundland, in the area known as 3Ps, harp seals are non-existent, and satellite tracking of gray seals in the Gulf of St.Lawrence and Sable Island shows less five percent of the herd migrates to the region. around the Burin peninsula and the French islands of St-Pierre-Miquelon.

Related stories

Over the years, Stenson said, they have tagged 400 seals on Sable Island and most of those animals have remained on the Scotian Shelf and in the Gulf of St. Lawrence.

“And the gray seals tagged in the summer of 2017 in 3Ps had left the area by the end of October and the majority had not returned by May,” Stenson said.

In addition, he said, gray seals feed on cod primarily in the winter. But the animals are not in the 3Ps zone at this time.

Seal poo also helps tell the story.

Sampling of the feces indicated a low frequency of cod in their diet, Stenson said, and stomach samples indicated sandeel as their main prey.

Consumer Context Regional Headquarters of the Department of Fisheries and Oceans in White Hills, St. John’s. – Barb Dean Simmons

On the northeast coast, in areas known as 2J3KL, research published in 2014 indicated that fishery catches and capelin availability were “important drivers of the cod stock” but not consumption. seals.

Stenson points out that even as the seal population has increased, the northern cod stock has also recovered.

This challenges the public theory that more seals equals less cod.

Meanwhile, the ecosystem is changing, Stenson said.

In 3Ps, the water has warmed since the mid-1990s, causing structural changes, such as an increase in warm-water species like hake.

“There appears to be a correlation between increased water temperatures and increased cod mortality,” Stenson noted.

The environment is changing so rapidly, he added, that scientific fishery data from the past may no longer even be useful.

“We are entering a space where the past history of the ecosystem may not be able to be applied to future predictions.”

In May 2020, this large harp seal showed up at the wharf at Norris Point, Newfoundland. – Contributed

The capelin factor is also part of the calculation, Kone-Alonso added, but not in the way people might think.

Capelin is the food of cod.

And the capelin stocks in Newfoundland are struggling.

So blame the seals?

Wait a minute, science says.

Whales and seabirds also eat capelin.

And commercial fishermen also take some of the fish.

Ultimately, Kone-Alonso said, seals don’t take more than other predators.

In fact, he said, “the amount of capelin alone consumed by fish can be as large as the total amount of all prey species consumed by harp seals.”

Earlier DFO reports, dating back to the 1990s, have offered estimates of how much food seals eat.

According to a 1994 report, when the harp seal herd numbered nearly five million animals, the department estimated that it consumed about one million metric tonnes of capelin and 142,000 metric tonnes of cod.

An adult harp seal. According to the latest data from Fisheries and Oceans, the population is approximately seven million, according to research from 2017. – DFO photo

DFO hasn’t updated the calculation – although it plans to do so – but Stenson says there has been too much fixation on that number.

“When the cod collapsed in the 1990s, we didn’t have estimates of fish consumption or whale consumption, we didn’t have any of those other things. But we had a seal number, and everyone hung on to it and that became the real reason for the collapse. “

And that skewed the context of any conversation about seals, suggested Stenson.

The real answer to what’s going on with fish stocks in Atlantic Canada is a complex combination of predators, prey, and environmental factors, with environmental changes likely being the primary driver.

“This is a major ecological change happening in our waters, so focusing on just one thing will not give you any answer,” he said.

Meanwhile, the seal study continues, Stenson said.

This year and next will be busy, he said, with a survey of harbor seals and gray seals with the goal of obtaining an overall estimate of gray seal and harbor seal populations in Atlantic Canada.

They also plan to do more satellite tagging, track seal migration, and collect more droppings to get more data on seal diets.

“Regarding the harp seal work, we are now analyzing all the diet data and estimating consumption over the next few months. “

They also hope to conduct a harp seal survey next March, the first since 2017, to determine how many pups have been born and how much the seal population has grown – if any – since the last survey.

[ad_2]