Rare Haida Gwaii swordfish puts ocean warming and fisheries in focus

A rare swordfish carcass reported on Haida Gwaii in northern British Columbia is the starting point for an October 9 account by researchers Isabella Morgante and William W. L. Cheung examining how ocean warming affects fisheries. Their account connects the unusual find with broader research on disrupted ecosystems and less predictable catches.

Writing for The Conversation in an article republished by Phys.org, the researchers say filmmaker and outdoorsperson Quinn Barabash found the nearly two-metre-long animal on the islands’ remote shores. Their account does not establish the discovery’s exact date, the fish’s route or its cause of death.

Why a swordfish off Haida Gwaii is unusual

Swordfish are large, highly migratory animals usually found in temperate and warmer tropical waters farther south, the authors explain. They say the species is thought to have been documented in British Columbia only twice previously. That makes the reported discovery unusual, although the sighting count carries the authors’ qualification.

Marine animals can move as they follow favourable ocean conditions, and extreme warming can bring species beyond their usual ranges. Morgante and Cheung suggest warmer waters may make British Columbia more attractive to warm-water visitors. Their explanation offers a possible mechanism, without establishing what brought this individual fish north.

What the fisheries study says about low catches

Morgante and Cheung describe their recent Nature Communications study as an analysis of three decades of data covering 1,246 species across 254 regions. According to their summary, unusually high ocean temperatures and very low primary production increased the likelihood of extremely low fish catches.

The risk was greater when extremes occurred together or persisted across multiple years. The authors report that two consecutive years of extreme temperatures increased the likelihood of extremely low catches by 40% globally. That figure measures a change in likelihood; it does not quantify a reduction in catch volume or predict catches in British Columbia.

The researchers describe consequences extending beyond an unusual species appearing in a new place. Extreme conditions can disrupt food webs and fish-stock productivity, with effects lasting after temperatures fall. As they put it: “A warming ocean changes what species are caught and how predictable the catch is from year to year.”

NOAA research traces changes through the food web

Independent historical research shows how such disruption can spread through an ecosystem. In March 2024, NOAA Fisheries reported on work with Oregon State University examining the Northern California Current, a productive system supporting fisheries and endangered salmon.

Researchers compared two ecosystem models representing periods before and after the onset of marine heatwaves. They examined energy flows and feeding relationships across the food web. NOAA described changes in species abundance and distribution, reduced primary productivity and mass mortality events during anomalously warm periods experienced since 2013.

Responses differed among organisms. Some gelatinous species, including pyrosomes, increased dramatically, while some other jellies and fish declined. The modelling examined those connected changes to assess their implications for the wider ecosystem, including commercially important fisheries and endangered salmon.

Alaska snow crab provides a historical fisheries example

A separate NOAA account published in October 2023 examined the eastern Bering Sea snow-crab collapse. Alaska’s snow crab fishery closed for the first time in 2022 following a sharp decline in adult and juvenile crabs. Using surveys and laboratory studies, scientists identified starvation as the most likely cause of the mortality event associated with the 2018–2019 marine heatwave.

Lead author Cody Szuwalski described a combination of pressures: warmer conditions increased the crabs’ metabolism and food requirements, their foraging habitat contracted, and surveyed animals weighed less than usual. Those findings concern a studied historical mortality event; the cause of the Haida Gwaii swordfish’s arrival and death remains unverified.