Are harp seals responsible for the stalled recovery of At...

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Academic rigour, journalistic flair A seal lying on its belly

Several explanations have been put forward for the stalled cod recovery, including predation by harp seals. THE CANADIAN PRESS/ Paul Daly Are harp seals responsible for the stalled recovery of Atlantic cod? Published: November 30, 2025 1.52pm GMT Tyler Eddy, Memorial University of Newfoundland

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Tyler Eddy
Research Scientist, Fisheries & Marine Institute, Memorial University of Newfoundland

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Tyler Eddy receives funding from the Natural Sciences and Engineering Research Council of Canada, Fisheries and Oceans Canada's Sustainable Fisheries Science Fund, and the Canada First Research Excellence Fund.

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Memorial University of Newfoundland provides funding as a founding partner of The Conversation CA.

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https://doi.org/10.64628/AAM.u5vvwd7we

https://theconversation.com/are-harp-seals-responsible-for-the-stalled-recovery-of-atlantic-cod-269337 https://theconversation.com/are-harp-seals-responsible-for-the-stalled-recovery-of-atlantic-cod-269337 Link copied Share article

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In June 2024, the Canadian government lifted the moratorium on northern cod fishing in Newfoundland and Labrador after 32 years. The decision was controversial because cod numbers had not recovered since they collapsed in the early 1990s.

The collapse of Atlantic cod stocks in Newfoundland and Labrador had a huge impact on the economic and social fabric of the province. The subsequent fishing moratorium in 1992 put nearly 30,000 people in the province out of work.

Several explanations have been put forward for the stalled cod recovery, including environmental conditions, historical overfishing and prey availability.

Another explanation has identified predation by harp seals as the reason cod numbers have remained low. However, given the severity of historical overfishing that occurred, Atlantic cod population growth may be impaired by a number of factors.

The Northwest Atlantic harp seal population was estimated at 4.4 million in 2024, the second-largest seal population in the world. Fishermen have long been concerned about the amount of fish that harp seals consume. However, a 2014 Fisheries and Oceans Canada study concluded that harp seals do not strongly impact the northern cod stock.

The concerns of fishermen about the impact of seals on fish stocks were heard by the Canadian government. In September 2023, the Department of Fisheries and Oceans announced funding for independent seal science. It was through this funding opportunity that I recruited postdoctoral fellow Pablo Vajas and MSc student Hannah West to dive deeper into the issue.

Historical overfishing

Fishing boats are shown in St.John’s, N.L. The collapse of Atlantic cod stocks in Newfoundland and Labrador had a huge impact on the economic and social fabric of the province. THE CANADIAN PRESS/Sarah Smellie

The magnitude and duration of overfishing increase the time fish stocks need to recover. By 1993, northern cod had declined by 99 per cent of its historical biomass, while the other Newfoundland Atlantic cod stocks declined by 77 per cent to 95 per cent. During the fishing moratorium on the offshore fishing fleet, inshore and recreational fisheries continued to operate, but fisheries catches were very low.

Capelin, a small forage fish that is important prey for cod and other predators, is linked to cod population growth and is included in the northern cod stock assessment. Capelin also collapsed in the 1990s and has not recovered to pre-collapse levels, limiting ecosystem productivity. It remains unknown why capelin has not recovered.

Do harp seals eat more than fisheries catch?

Harp seals eat a range of items — their diet varies by prey availability, season, location and time. In our recently published study, we compared diet estimates from stomach content analyses from 7,710 harp seals as well as laboratory analyses of muscle tissue using fatty acids and stable isotopes.

In general, our findings told a consistent story: harp seals are generalists that eat a range of prey, including American plaice, Arctic cod, Atlantic cod, Atlantic herring, capelin, flounder, redfish, sand lance, shrimp, squid and zooplankton. We incorporated these results into a food-web model of predator and prey interactions to calculate the total harp seal consumption of prey and their contribution to mortality. We compared these consumption and mortality rates to those from fisheries.

Our analysis revealed that harp seals consume a higher biomass of shared target species than caught by fisheries. Harp seal consumption rates were 24 times higher than fisheries catch rates for Atlantic cod, Greenland halibut and American plaice from 2018 to 2020.

We also found that harp seals caused 17 times more deaths of shared target species than fishing did. Stock assessments have reported elevated levels of northern cod natural mortality since the collapse. Consistently, our research found that the impact of harp seals on other species in the ecosystem has increased since the fish stocks collapsed.

The harp seal population has declined by 41 per cent since 1998, when it peaked at 7.5 million. This has happened while the number of harp seals harvested for their meat and pelts has also declined. Harp seals have recently been listed as near-threatened by the International Union for Conservation of Nature due to Arctic sea ice loss.

Marine ecosystems in a changing world

By 1993, northern cod had declined by 99 per cent of its historical biomass, while the other Newfoundland Atlantic cod stocks declined by 77 to 95 per cent. (AP Photo/Robert F. Bukaty)

Newfoundland and Labrador’s marine ecosystems are highly dynamic. Since the cod collapse, ecosystems have been less productive, leading to a declining harp seal population and limiting the recovery of collapsed fish stocks.

Despite the decline in harp seal numbers, our findings show that harp seal predation remains an important factor that should be included in Atlantic cod stock assessments.

It should be noted that climate change is an additional factor affecting marine ecosystems and fisheries. More than ever, it is crucial to track the productivity of fish stocks and marine ecosystems to achieve sustainable resource management.