Canadian scientists and anglers are tracking the northward movement of swordfish in Newfoundland waters, where the prized fish are being caught in large numbers on Grand Bank and Flemish Cap.
What no one knows is whether this is the result of ocean warming or a cyclical – and temporary – phenomenon.
“It's still unclear if this is becoming the new normal due to climate change, or if biomass will eventually revert back to the way we think it has historically,” said Fisheries and Oceans Canada biologist Kyle Gillespie.
Nine hundred tons of swordfish arrived in Canada last year. Almost a third of the swordfish were taken off Newfoundland, where longline fishing boats from Nova Scotia have been following baited hooks for most of the summer.
Gillespie said that's a rapid change from the previous decade, when the entire Canadian catch was concentrated on the Scotian Shelf and along Georges Bank in southern Nova Scotia.
“What's particularly interesting about analyzing the data from Newfoundland is that for every thousand hooks, we're seeing a lot of fish, and they're larger,” said Gillespie, who is based at the St. Andrews Biological Station. NB
Swordfish are less prone to decay
The shift in distribution coincided with the collapse of the harpoon fishery off southern Nova Scotia over the past three years.
Between 2011 and 2020, harpoon gear accounted for an average of about nine percent of Canada's catch. Harpooners rely on the fact that swordfish usually surface during the day.
One question is whether they become less sluggish due to warmer temperatures below the surface.
Industry veteran Troy Atkinson said the swordfish were caught off Newfoundland 20 years ago and may have been under everyone's noses all that time.
Could swordfish have been here the whole time?
“We suspect the fish have always been in the Grand Banks, but it just didn't make economic sense to make the four-day trip and the extra expense when you could be fishing closer to home,” said Atkinson, president of the Nova Scotia Swordfishers Association.
But he also wonders if it's permanent.
“If we continue to reduce access to George [Bank] And increased landings on the Grand Banks over the next five years and it's not coming back, then we'll know,” he said.
Swordfish follow the Gulf Stream to Canada and feed on squid and other fish in the more productive cold water immediately adjacent to the warmer Gulf Stream.
Kyle Gillespie and fellow Fisheries and Oceans scientist Alex Hanke want to know if the change in their distribution is related to changes in the temperature gradient or changes in the movement of the Gulf Stream.
Pop-up satellite tags
It may also be associated with prey that DFO does not track as much as other species.
“It's likely a combination of water temperature and other environmental and predator factors,” Gillespie said.
To track their movements, Gillespie planned to attach satellite tags to a dozen swordfish during a September 2023 trip to Browns Bank and Georges Bank, off southern Nova Scotia.
But they didn't see any in the areas where the harpoons were hot spots six or seven years ago.
The areas that used to be like clockwork when and where swordfish would come to the surface are gone,” he said.
After the movement of the swordfish
The swordfish tagging operation in Newfoundland will move to 2024.
Satellite tags contain sensors that detect location, dive patterns and water temperature.
When retrieved, they will allow researchers to track movement over a year and compare it to oceanographic conditions.
Information that can be used to develop models of swordfish habitat suitability across ocean basins.
Gillespie is working with the US National Oceanic and Atmospheric Administration and the Portuguese Institute of the Sea and Atmospheric Institute to develop and validate such a model.
Catch rate data
Tags can also help provide answers to spearfishing.
“Have they changed migration routes and are no longer on the Scotian Shelf or further out to sea? To answer these questions we will need tagging patterns, dive patterns, water temperature and catch rate data from different fleets.” Gillespie said.