A new paper by a master’s student at Fisheries and Marine Institute of Memorial University examines the diets of North Atlantic harp seals to assess the impact they have on fisheries populations in Newfoundland and Labrador.

The study found that harp seals consume a higher biomass of shared target species than are caught by fisheries and that they have a more significant role than fisheries do on the stalled recovery of groundfish stocks.

Hannah West, a master of science student in fisheries science, is the study’s lead author.

Available in the journal Marine Ecology Progress Series, the paper is titled “Harp Seals Have a Greater Impact Than Fisheries in the Stalled Cod Recovery in Newfoundland and Labrador”.

Fisheries impact

With around 4.4 million individuals, North Atlantic harp seals are the second largest seal population in the world.

The animals’ diet shares many of the same species targeted by fisheries, including Atlantic cod and capelin. Harp seals also consume other groundfish such as Greenland halibut and American plaice.

The study used various methods such as analysis of harp seal stomach contents, fatty acids and stable isotopes to estimate their diets. The data was compared to existing models to analyze consumption at the ecosystem scale to understand predation impact.

The researchers’ analysis revealed that from 2018-2020, harp seals’ consumption rates were 24 times higher than fisheries catch rates for Atlantic cod, Greenland halibut and American plaice.

While comparison of harp seal diet across research methods showed consistency, over time, the frequency of primary prey in their diet fluctuated over time.

“Harp seals are often referred to as indicator species, meaning their diets indicate changes in the ecosystems they prey in,” said Ms. West.

“This data provides insight not only into the impact that harp seals have on fisheries but can also signify when ecosystems and fish populations are shifting.”

Dr. Tyler Eddy, Ms. West’s supervisor and study co-author says Fisheries and Oceans Canada stock assessments have long noted a high northern cod mortality rate that is not due to fishing"

"Our study shows that harp seals are a major component of cod mortality that should be accounted for in future stock assessments,” he said.

Support for stock assessments

Ms. West co-authored the paper with Dr. Eddy, PhD candidate Alannah Wudrick, Dr. Matthew Robertson and post-doctoral fellow Dr. Pablo Vajas from the Marine Institute’s Centre for Fisheries Ecosystem Research.

Their findings provide support for including harp seal predation as an ecosystem factor in future fisheries stock assessments in the province.

Ms. West says the study provides an estimate of harp seal diets in the province through time, location and season.

“Increased understanding of how marine ecosystems work and how populations shift ensures that measures can be put in place to assess and protect the stock of key fisheries species."