Swordfish are moving north into Canadian waters

Canadian scientists and fishermen are tracking the northward movement of swordfish in Newfoundland waters, where the prized fish is being caught in large numbers in the Grand Banks and Flemish Cape.

What no one knows is whether this is the result of ocean warming or a periodic, temporary event.

“It is still unclear whether this has become the new normal due to climate change or whether biomass will eventually shift again as we think it has done historically,” said Kyle Gillespie, a biologist with Fisheries and Oceans Canada.

1,900 tons of swordfish were landed in Canada last year. Nearly a third of the swordfish were transported from Newfoundland, where longline fishing boats from Nova Scotia tracked kilometers of baited hooks throughout most of the summer.

This is a rapid turnaround from the previous decade, when the entire Canadian fishery was concentrated along the Scottish Shelf and Georges Bank off southern Nova Scotia, Gillespie said.

“What’s particularly interesting when we analyze the data from Newfoundland is that for every thousand hooks, we encounter a greater number of fish, and they are larger,” said Gillespie, who is based at the Biological Station in St. Andrews. NB:

Swordfish soften to a lesser extent

The shift in distribution has coincided with a collapse in landings in 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 per cent of Canadian catches. Spearfishermen rely on the fact that swordfish usually appear during the day.

One question is whether they soften less due to warmer temperatures below the surface.

Industry veteran Troy Atkinson said the swordfish were caught off the island of Newfoundland 20 years ago and may have been under everyone’s radar the whole time.

Could the swordfish have been here all the time?

“We believe the fish have always been in the Grand Banks, but it didn’t make economic sense to travel four days and incur additional expenses when you can fish close to home,” said Atkinson, president of the Nova Scotia Swordfishermen’s Association.

But he also wonders if this is permanent.

“If we continue to see landings on the Georges (Bank) decline and landings on the Grand Banks increase over the next five years, and it doesn’t go backwards, we’ll know,” he said.

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The swordfish follows the Gulf Stream as far as Canada and feeds on squid and other fish in the colder, more productive waters immediately adjacent to the warm Gulf Stream.

Kyle Gillespie and fellow fisheries and ocean scientist Alex Hankey want to know if the change in their distribution is related to changes in the temperature gradient or shifts in the movement of the Gulf Stream.

Pop-up satellite tags

It may also relate to prey that is not as closely tracked by DFO as other species.

“It’s likely a combination of water temperatures, environmental factors and other prey,” Gillespie said.

To track their movements, Gillespie plans to attach pop-up satellite tags to dozens of swordfish during a trip to Browns Bank and Georges Bank off southern Nova Scotia in September 2023.

But they haven’t seen one in places that were spear hotspots six or seven years ago.

“The areas that used to be like clockwork when swordfish would come to the surface are no longer there,” he said.

Following swordfish movements

The swordfish tagging operation will move to Newfoundland in 2024.

Satellite tags contain sensors that detect location, diving patterns and water temperature.

When retrieved, they will allow researchers to follow movements over the course of one year and compare them to oceanographic conditions.

Information that can be used to build models about habitat suitability for swordfish for entire ocean basins.

Gillespie is working with the US National Oceanic and Atmospheric Administration and the Portuguese Institute of the Sea and Atmosphere to build and validate such a model.

Capture rate data

Signs may also help provide answers to harpoon traps.

“Have they changed their migration routes and are no longer present on the Scottish Shelf or at sea? We will need to combine tagging routes, diving patterns, water temperatures and catch rate data from different fleets to answer these questions.” Gillespie said.

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