Greenland’s sustainable halibut fishery may threaten newfound corals, sponges

Greenland’s sustainable halibut fishery may threaten newfound corals, sponges

  • Industrial trawling for halibut in the Davis Strait off western Greenland is currently done in a certified sustainable manner, but new studies suggest it may be doing long-term harm.
  • The studies describe assemblages of unique marine life on the seafloor both inside and near the halibut fishing zones that could potentially be considered “vulnerable marine ecosystems.”
  • Scientists have called for protection of these potential VMEs, but acknowledge that ending bottom trawling altogether isn’t a viable option when fishing accounts for 93% of Greenland’s exports.
  • Fishing industry stakeholders say they’re confident that existing rules designed to help the halibut fishery meet sustainability requirements will be sufficient to spare these potential VMEs, and point to a new management plan for the entire Greenlandic seabed that is in development as a way to strengthen protections.

In the Davis Strait between Greenland and Canada’s Baffin Island, where only the faintest rays of sunlight penetrate, swim strange-looking flat fish with both eyes on the right side of their heads. These are Greenland halibut (Reinhardtius hippoglossoides), which industrial bottom trawlers have fished here for decades.

To get the halibut in Greenlandic waters, the trawlers operate at least 3 nautical miles (5.6 kilometers) from the coastline and drag cone-shaped nets across the seabed. These nets hauled up approximately 12,400 metric tons of halibut in 2021 alone within Greenland’s waters, but they also overturn rocks and sediment in the process. (Fisheries closer to shore catch more halibut annually, but their method — a fishing line carrying up to 2,500 baited hooks, or longline — is much less destructive to the seabed.) The halibut, along with cod, mackerel, crab and prawn, is the mainspring of the Greenlandic fishing industry.

Bottom trawling takes a toll: it crushes slow-growing deep-sea organisms, some of them millennia old, that are irreplaceable on human timescales. Now, the discovery of potential vulnerable marine ecosystems (VMEs) on the Davis Strait seafloor has shown what, specifically, is at stake off Greenland’s coast. A 2020 paper identified a soft coral garden spanning 486 square kilometers (188 square miles) just outside one of the main halibut fishing grounds. And a paper published in September 2021 describes a field of sea pens, quill-like animals closely related to jellyfish; meadows of cup corals; and mixed assemblages of corals, sponges and sea pens, some located where trawlers fish, that the authors say are possible VMEs as well. The U.N. says countries should protect VMEs, and the discovery is prompting Greenland and its fishers to change their practices. But details are sparse and experts question whether the measures are sufficient.

A mixed assemblage of corals, sponges and sea pens that make up a part of a potential vulnerable marine ecosystem in the Davis Strait. Image courtesy of ZSL and the Greenland Institute of Natural Resources.

A deep study

It took two years for the most recent paper’s authors — scientists from the Zoological Society of London (ZSL), University College London (UCL) and the Greenland Institute of Natural Resources (GINR) — to gather video images of the seabed. As with most deep-sea research, data collection was time-consuming. The ZSL scientists tagged along on two-to-three-week annual cruises led by the GINR, an independent institution that advises the Greenlandic government, to assess the halibut stock. The remote-controlled video sled the ZSL scientists deployed to capture the video took 40 minutes just to sink to the bottom at each of the 76 sites the researchers examined in and around Greenland’s two Davis Strait halibut fishing grounds. In total, the team captured 22 hours of video covering 28,838 square meters (310,410 square feet) of seafloor. Team members scanned the video for species indicative of VMEs, identifying them in notable densities at various sampling sites

“Imagine this homogeneous, muddy sea floor,” said Stephen Long, an expert in fishery management at the ZSL’s Institute of Zoology and lead author of the 2020 and 2021 studies. “Suddenly you’ve got lots of these small novel structures dotted all over the place. And ecologically that’s potentially quite important, because it’s going to change how currents move across the surface, and provide different sorts of habitats for other species.”

The video showed that bottom trawling is likely to have extensively modified the vast area of seafloor surveyed. The authors observed gaping scars and overturned sediment in the trawled area. Marine life was significantly sparser there, too.

Because of the low temperatures in the deep sea, organisms that dwell there often have long life spans — sometimes more than a century — and take decades to reach sexual maturity. “This is the worry. If you trawl an area, then it could be a very, very long time before the habitat looks like it did again,” Long said.

This means that almost without exception, deep-sea fisheries have ended up decimating commercially viable stocks, Long said. He called this a well-documented “boom and bust cycle,” where fisheries exhaust one stock then move on to the next hotspot. This is the reason the European Union banned all trawling in waters of the northeast Atlantic deeper than 800 meters (2,624 feet) in 2016. This rule doesn’t apply to Greenland, however, which left the European Community in 1985 to avoid being subject to common market regulations on fishing.

However, Long called the country’s halibut fishery a “vanishingly rare example of sustainable deep sea fishing from a stock perspective,” because the government has always closely followed the quota suggested by scientists over the past two decades. Referring to GINR stock assessment data, he said “the halibut stock appears to be stable and there have been no precipitous declines, but the caveat to that is that it could always happen tomorrow,” if the fishery expands its operations.

Marks on the sea floor caused by deep-sea fish trawling.
Marks on the sea floor caused by deep-sea fish trawling. Image courtesy of ZSL and the Greenland Institute of Natural Resources.
Stephen Long
Stephen Long aboard the research vessel Paamiut. Image courtesy of Stephen Long and ZSL.

Murray Roberts, a professor at the University of Edinburgh who specializes in the biology and ecology of deep-sea corals, runs iAtlantic, a multidisciplinary research program assessing the health of marine ecosystems across the Atlantic Ocean. He said he’s wary of the serial depletion of any ecosystem, even if a fish stock there is considered at a healthy level. “If you want to know how much we’ve changed an ecosystem, we’ve got to know how it was before we did something to it,” Roberts said. “But often we don’t have a baseline, because scientists rarely have the chance to do research in the deep sea before it’s already been fished.”

Such was the case in the Davis Strait. But in an unusual twist, the fishing industry helped bring to light the destruction it causes there. In 2011, Sustainable Fisheries Greenland (SFG), a consortium of commercial fishers, was seeking a sustainability certification for its prawn fishery from the Marine Stewardship Council (MSC), an independent nonprofit organization that assesses fishery management worldwide. As part of the certification process, SFG needed to remedy a dearth of knowledge about the impact of commercial trawling on the seabed, so it commissioned the ZSL to undertake a study. It soon became evident to ZSL researchers that the seafloor habitats where Greenlandic offshore fisheries were operating had scarcely been mapped. Several research papers, including those identifying the potential VMEs, have been published out of this collaboration.

SFG continues to fund this collaboration, but most of the money now comes from a grant from the IUCN, the global wildlife conservation authority. A member of the ZSL team also receives funding for the project from the MSC’s Ocean Stewardship Fund.

The prawn fishery that started it all acquired MSC certification in 2013, and the halibut fishery followed in 2017, associating their products with a supply chain that is accredited for sustainable fishing practices.

The video sled used by ZSL to capture images
The video sled used by ZSL to capture images of the deep sea coming back on deck. Image courtesy of Stephen Long and ZSL.

Government and fishers respond

Greenland is an example of the political conundrum that arises from attempts to safeguard the abundant biodiversity of the deep sea while securing continued financial stability for fishers. According to government statistics, fishing is Greenland’s most important industry, accounting for 93% of the country’s total exports, and a third of revenue generated by all companies operating there. The fishing of halibut, both inshore and offshore, brings in sizeable revenue: the island’s largest company, a state-owned fishing enterprise called Royal Greenland, reported that in 2021 Greenland halibut accounted for 25% of its total sales of $808 million, which is just over a quarter of Greenland’s total GDP of $2.98 billion. The dearth of alternative industries and of infrastructure across the island to connect communities has deepened the country’s dependence on fishing, of which bottom trawling is a significant part.

As a result, simply prohibiting bottom trawling isn’t under discussion in Greenland. “Socioeconomically… it’s completely not a viable management option to say… we’ve had a look at this in London, and it’s really bad news for the sea floor to do deep sea fishing,” Long said, adding that the way forward is to mitigate high impact.

Policymakers are looking for ways to protect both the fisheries and the marine environment — a tricky balance to strike. In September 2021, soon after the latest paper was published, the government began the process of creating a management plan for the entire Greenlandic seabed. The new plan will take a methodical approach to the treatment of known deep-sea species found in Greenland’s exclusive economic zone (EEZ) — the band of water up to 200 nautical miles (370 kilometers) off the island’s coast — with a view to developing a protocol on what to do where the seabed hasn’t yet been explored.

Katrine Kaergaard, head of the Fisheries Division at the Greenland Ministry of Fisheries, Hunting and Agriculture, said the government will revise all trawling areas once the management plan is concluded, by the end of 2022. But she said she could not yet say when the plan will take effect or what it includes, as discussions are underway.

Other measures by the Greenlandic government to mitigate damage from bottom trawling are already in place. Over the past decade, the government has closed several areas in southwest Greenland to trawling in order to protect sea sponges and corals found there over the years, Kaergaard said. Satellite-tracking systems ensure that any vessels that fish where they’re not supposed to can be prosecuted and fined, Mads Rossing Lund, a senior adviser at the Fisheries License Control Authority, said in an email.

Halibut drying
Halibut drying in Oqaatsut, Greenland. Image by kaet44 via Flickr (CC BY 2.0).

On Jan. 1, 2021, the government set limits surrounding each of the two areas where halibut trawlers have been active over the past 25 years. According to Kaergaard, it did so as a condition for the halibut fishery to continue receiving MSC certification, and “to ensure that potential VMEs were not harmed” until more was known about the seabed there and the management plan could be implemented.

However, when the ZSL paper came out the following September, it pointed out that the new limits permit “a considerable expansion of fishing effort into previously unimpacted areas” and that the large potential soft coral VME extends precariously into the southern area available for trawling.

The paper also expressed concern for the newly identified sea pen field, which is well within the current fishing footprint. And it suggested that so-called move-on rules that Greenland has in place — requiring vessels to stop fishing and move at least 2 nautical miles (3.7 km) away if the amount of sponges or corals in their nets exceed certain thresholds — are inadequate to protect this and other potential VMEs. “There is therefore scope for serious or irreversible harm in the future. Indeed, the observations made here may represent an already partially degraded VME and/or one in recovery having not been trawled for over a decade,” the paper says.

But Kristina Guldbaek, a project manager at SFG, expressed confidence in existing regulations to protect any sensitive ecosystems within the trawled area. “The vessels will always try to avoid fishing in areas with corals and/or sponges because they risk damaging the gear or having to move if the limits are exceeded,” she said. “The offshore fishery for Greenland halibut is well managed and monitored — hence the MSC-certification.”

Guldbaek also played down concerns that the large potential VME that hosts soft coral could now be subject to trawling. It’s located in an area known as Tovqussaq Bank that has “very steep slopes which makes it impossible to trawl there,” she said. Moreover, she said the GINR has requested the government close this area to trawling — a decision that now rests with the environment ministry.

Asked whether the discovery of potential VMEs in areas subject to trawling would affect the Greenland halibut fishery’s MSC certification, Elvar Lund, stakeholder and engagement manager at MSC North Atlantic, said MSC-certified fisheries must avoid impacting VMEs through the application of “precautionary management measures” that the MSC reviews every five years. The halibut fishery’s certification expires in November, and Lund said that unless further research identifying an impact on VMEs comes to light, the fishery’s staying within its historic footprint meets the MSC’s criteria for its certification to be renewed.

Grenadier fish among cup coral field and brittle stars
Grenadier fish among cup coral field and brittle stars on the deep-sea floor. Image courtesy of ZSL and the Greenland Institute of Natural Resources.

Is it enough?

Some scientists expressed skepticism that the current measures are sufficient to protect both fishers’ livelihoods and vulnerable seabed species over the long haul.

“The West Greenland area is vast, so freezing the current trawling footprint should work,” said Les Watling, a professor at the University of Hawai‘i at Mānoa who has extensively studied deep-sea organisms and seamounts in the North Atlantic Ocean. “But in the long run it probably won’t, because the habitat will be so ruined that the fishery will have to move elsewhere.”

Alluding to his 2008 paper that compared the seabed devastation trawling causes to the clear-cutting of a forest, Watling added that merely recognizing these seabed species as vulnerable won’t be enough. They are, he said, “the analogs of trees on land, but the forest is more than just trees, it has lots of other species. You cut the trees, you lose those other species too.”

The Davis Strait seabed is home not only to the corals, sponges and sea pens highlighted by the ZSL, but also to numerous species that grow into the mud but are “too small to see with cameras,” Watling said. This suggests that the destruction of wildlife is far more extensive than what the ZSL documented. Affected animals could include urchins, clawed lobsters and terebellid worms, the latter of which live in the top 4 centimeters (1.6 inches) of the seabed.

“When you see the massive trawl marks, some of which are 10 to 20 cm [4 to 8 inches] in depth you know that many species will have had their burrows collapsed,” Watling said. The terebellid worms, in particular, are also likely to get kicked up into the water from their mud-lined homes, leaving them easy prey for other creatures. Fortunately for the halibut fishery, this potentially means an increase in numbers of animals that feed on the worms, and these in turn are food for the halibut.

Watling said he favors restricting trawled areas as much as possible.

For his part, Roberts of iAtlantic said the government and the fishery could consider shifting to longline fishing as a less destructive way of catching halibut. Even so, he cautions, the hooks could snag on corals and sponges on the seafloor.

Beyond Greenland, Roberts said that in Norway, another country heavily reliant on the fishing industry, it took years of hard work by scientists and large amounts of research funding to finally establish that deep-sea corals were important fish nurseries, and that these corals were being severely damaged by fishing. He said such cases show that, often, people do too little too late to protect the deep sea.

This has led him toward a more radical question. “Although I try to be pragmatic, and I run projects where it’s all about trying to balance and manage human activities, I do struggle with sustainability in the deep sea,” he said. “It’s interesting to put a philosophical view on it and ask: why is it right that any one sector has the right to remove any component of an ecosystem for commercial benefit and walk away? I think we should find value in diversity for its own wonder and for its existence, even as the pressures are growing.”

Banner image: A soft coral garden in west Greenland. This structurally complex habitat includes cauliflower corals, feather stars, gorgonians, sponges, anemones, brittle stars, hydrozoans, and calcified bryozoans. Image © Long, Sparrow-Scinocca, Blicher, Hammeken Arboe, Fuhrmann, Kemp, Nygaard, Zinglersen and Yesson.


Long, S., Sparrow-Scinocca, B., Blicher, M. E., Hammeken Arboe, N., Fuhrmann, M., Kemp, K. M., … Yesson, C. (2020). Identification of a soft coral garden candidate vulnerable marine ecosystem (VME) using video imagery, Davis Strait, west Greenland. Frontiers in Marine Science7. doi:10.3389/fmars.2020.00460

Long, S., Blicher, M. E., Hammeken Arboe, N., Fuhrmann, M., Darling, M., Kemp, K. M., … Yesson, C. (2021). Deep-sea benthic habitats and the impacts of trawling on them in the offshore Greenland halibut fishery, Davis strait, west Greenland. ICES Journal of Marine Science78(8), 2724-2744. doi:10.1093/icesjms/fsab148

Long, S., & Jones, P. J. (2021). Greenland’s offshore Greenland halibut fishery and role of the Marine Stewardship Council certification: A governance case study. Marine Policy127, 104095. doi:10.1016/j.marpol.2020.104095

Morrison, K. M., Meyer, H. K., Roberts, E. M., Rapp, H. T., Colaço, A., & Pham, C. K. (2020). The first cut is the deepest: Trawl effects on a deep-sea sponge ground are pronounced four years on. Frontiers in Marine Science7. doi:10.3389/fmars.2020.605281

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