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Sharks are caught incidentally in Arctic fisheries when they take baited hooks, become wrapped in longline gear, are trapped in gillnets, or enter bottom trawls. Greenland shark (Somniosus microcephalus) is the main shark documented in the Canadian Arctic bycatch material discussed here, including in fisheries targeting Greenland halibut. Some gear changes and release practices have evidence behind them, but each applies to particular fishing methods; no single fix works across every fishery. The scale of the problem is also uncertain because observer coverage and reporting are incomplete.
What shark bycatch means in Arctic fisheries
Bycatch is the unintentional capture of animals that a fishery is not targeting. In the Canadian Arctic, Greenland shark is documented as incidental catch in bottom trawls, demersal longlines and gillnets. These gears are used in deep-water fisheries, including fisheries for Greenland halibut. The fishery’s target is not the shark, but the gear can still catch it while operating for other species.
“Arctic bycatch” is not one uniform rate or event. The likelihood of capture depends on the gear, location, depth, season and fishing effort, among other factors. A hook-based rate from a particular longline fishery cannot be treated as a rate for trawls or gillnets, or as representative of the whole Arctic. The available estimates also come from different periods and methods, and some fisheries have limited observer coverage or reporting.
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The Canadian assessment published by Environment and Climate Change Canada in 2025 describes current reported bycatch as coming largely from offshore Greenland halibut demersal trawl, longline and gillnet fisheries, as well as other deep-water fisheries. That describes documented Canadian activity; it should not be read as a complete inventory of all Arctic fishing or shark capture.
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How different fishing gears catch sharks
Bottom-set longlines: baited hooks and entanglement
A demersal, or bottom-set, longline consists of a mainline laid on or near the seabed, with baited hooks attached by shorter lines called gangions. Greenland sharks may take the bait and be hooked in the mouth. They can also become wrapped in the mainline or trailing gear, including around the body or tail. A shark may therefore be caught by a hook, entangled without being hooked, or both.
Entanglement complicates retrieval and release. A length of mainline wrapped around a shark can take time to remove and can damage or cost fishing gear. In a Cumberland Sound study published in 2020, the mean length of mainline entangled around the body and/or tail region was 28.7 metres. The study also reported that 15% of captured sharks had been cannibalized. Those are observations from that study, not general estimates for Arctic sharks or all longline fisheries.
All of the remaining sharks in that study were alive and survived disentanglement under the study conditions. That result does not establish survival rates elsewhere: gear configuration, entanglement severity, handling and other conditions can differ. It does show why release procedures matter, and why the condition of a shark when it is brought alongside is not the only consideration.
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Gillnets: entrapment and potential mortality
Gillnets are panels of netting that catch fish when they become entangled or trapped in the mesh. Greenland sharks can be caught in them as non-target catch. The 2025 Canadian assessment reports that adding bait to gillnets in Canadian Arctic and Atlantic Canadian fisheries increased Greenland shark bycatch catch per unit effort compared with non-baited gillnets. This finding concerns the settings assessed; it is not a universal estimate of the effect of bait in every gillnet fishery.
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Mortality in gillnets is a particular concern, but its scale for Greenland sharks is uncertain. Greenland sharks are ram ventilators, meaning they rely on swimming to move water over their gills. The Canadian assessment considers gillnet mortality potentially high for that reason. Mortality observations for other ram-ventilating species caught in fixed gillnets are relevant context, but they are not a measured Greenland-shark mortality rate. The assessment says both accurate bycatch levels and post-release survival remain poorly known.
Bottom trawls: incidental capture in the net
Bottom trawls are towed along or near the seabed to catch target species. Greenland sharks can enter the trawl as non-target catch. In Canadian demersal shrimp trawls, a historical decline in reported Greenland shark bycatch followed the introduction of a Nordmøre grate, an excluder fitted in the trawl. The assessment also notes a possible reduction in the area being trawled. Because both factors may have contributed, the decline cannot be attributed to the grate alone as though it were a controlled test of that device.
A separate 2025 study of northern shrimp trawls found promise in a large escape opening for reducing megafauna bycatch, including Greenland shark, while having minimal effects on shrimp catch. This is evidence for a particular design and fishery context, not proof that the same opening will work in every trawl or can be adopted without testing its effect on target catch.
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What the reported numbers do—and do not—show
Published figures illustrate that capture occurs, but they are not directly interchangeable. The longline figures below use hooks as the effort denominator and come from Cumberland Sound fisheries in different periods. Other estimates refer to tonnes or annual numbers across broader areas and methods. They should not be compared as if they were standardized counts of the same population or a complete Arctic-wide total.
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| Reported figure | What it describes | Source and qualification |
|---|---|---|
| 1.1 sharks per 1,000 hooks | Winter Cumberland Sound Greenland halibut longline fishery; mean for 1987–2006 | Fisheries and Oceans Canada, 2008, as cited by the NAFO research summary and the 2025 COSEWIC assessment |
| 6.3 sharks per 1,000 hooks | Open-water Cumberland Sound Greenland halibut longline fishery in 2009; 570 sharks in total | Young, 2010, as cited by NAFO and the 2025 COSEWIC assessment |
| At least 420 tonnes | Greenland shark bycatch cited in a Greenland halibut stock assessment | NAFO, 2023, as cited in the 2025 COSEWIC assessment; not a comprehensive Arctic-wide total |
| More than 1,700 individuals annually in Canadian waters | Canadian estimate based on observer data | COSEWIC, 2025; the assessment warns that current rates are poorly estimated because coverage and reporting are limited |
| At least 3,500 individuals annually globally | Global estimate cited for Greenland shark bycatch | Kulka et al., 2020, as cited in COSEWIC, 2025; the assessment cautions that this may be a gross underestimate because data, observer coverage and reporting are incomplete |
The two Cumberland Sound rates differ in season and period: one is a winter average over 1987–2006, while the other describes the open-water fishery in 2009. They are not a controlled comparison of seasons, and the difference alone does not establish why the rates changed. Both are specific to longline effort. A rate per 1,000 hooks cannot be compared directly with a trawl bycatch figure expressed in tonnes or a broader annual estimate in individuals.
Counts are also only as complete as the systems that record them. The 2025 assessment notes limited observer coverage and incomplete reporting, including fisheries with little or no observer coverage. Historical records may give estimated catch weight rather than the number of sharks. As a result, recorded catch is not necessarily total catch, and annual estimates should not be mistaken for precise, complete mortality totals.
Which measures can reduce capture or its effects?
Use monofilament nylon gangions in the studied longline setup
The clearest longline gear evidence in the material comes from the 2020 Cumberland Sound study. It found that monofilament nylon gangions reduced disentangling time and gear damage compared with braided multifilament nylon gangions, without reducing Greenland halibut catch. The authors recommended replacing multifilament gangions in longline fisheries where Greenland shark bycatch occurs.
This is a practical, gear-specific result: it supports monofilament gangions as a way to make disentangling less time-consuming and reduce gear loss in the studied setup while maintaining target catch. It does not establish that every line, material specification or fishery will have the same outcome. The study does not validate a particular consumer fishing line, product, diameter or breaking strength.
Remove trailing gear and handle longline-caught sharks carefully
The Cumberland Sound study recommends removing trailing fishing gear before releasing a shark, since gear left attached may compromise survival. The Canadian assessment also says discard mortality is thought to be lower in longlines when sharks are hooked by the mouth and handled carefully, with jaw damage and time at the surface minimized. This is guidance about reducing release impacts, not a quantified survival guarantee.
Entangled sharks can require a different release response from sharks hooked only in the mouth. Where the mainline is wrapped around the body or tail, disentangling may take longer and can increase injury risk. The 2020 study’s survival observations apply to its own conditions; they do not resolve post-release survival across other fisheries, gears or handling situations.
Evaluate trawl escape designs in the fishery where they would be used
The large escape opening studied in northern shrimp trawls is promising because the reported reduction in megafauna bycatch, including Greenland shark, came with minimal effects on shrimp catch. Fishery managers and operators still need to consider the particular trawl, target catch and fishing conditions. A result from a northern shrimp trawl should not be presented as a universal solution for bottom trawls.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsThe Nordmøre grate is another relevant example in Canadian demersal shrimp trawls, but the historical decline associated with its introduction occurred alongside a possible change in trawled area. The available account therefore supports considering the grate as part of the explanation, not assigning it the whole effect.
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Do not rely on the tested SMART hook treatment
A 2018 test of magnetic/electropositive SMART hook treatment did not deter Greenland shark capture in the tested fishery: all sharks in that test were caught on SMART hooks, and some had more than one hook in the jaw. The study also found that Greenland sharks could draw bait into the mouth from 25–35 centimetres using suction feeding. On this evidence, the tested SMART treatment should not be recommended as established Greenland shark bycatch mitigation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why location, season and better monitoring matter
Spatial-temporal modelling cited by the 2025 Canadian assessment found that bycatch probability varied with depth, NAFO area and season. That variation can help identify where and when capture risk differs, but correlation in a model is not proof that a particular closure or effort restriction will reliably reduce bycatch. Any such management measure would need to be assessed against the fishery and the quality of its catch data.
Monitoring is essential both to estimate the scale of bycatch and to test whether a mitigation measure works. A useful comparison needs to keep track of the fishing method and target fishery, location and depth, season, effort denominator, soak duration, observer coverage and reporting quality. For the captured sharks, size, entanglement severity, release condition and whether trailing gear was removed also matter. Without that context, a local rate or outcome can be misleading when applied elsewhere.
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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →The unresolved questions are substantial: total mortality, post-release survival across gear types and standardized Arctic-wide bycatch remain uncertain. Better observer coverage, reliable reporting and survival data are needed to distinguish real changes in capture from changes in where or how fishing is monitored. For now, the strongest practical options are those supported in their specific settings: monofilament gangions and careful release in the studied longline context, and tested trawl designs evaluated for the fishery in which they would operate.
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