What is Bycatch?
Bycatch refers to the incidental capture of non-target species in fishing operations. It is one of the most significant and underappreciated animal welfare issues in the world, affecting hundreds of billions of individual animals annually across a vast range of species.
Commercial fishing gear is not species-selective. Trawl nets, longlines, purse seines, gillnets, and other methods catch far more than their target species. The non-target animals — fish, seabirds, marine mammals, sea turtles, sharks, rays, and invertebrates — are typically killed or severely injured and discarded overboard.
38M+
Tonnes of bycatch annually (est.)
~40%
Of global fish catch is bycatch
300,000+
Cetaceans (dolphins, whales) killed/yr
250,000+
Sea turtles caught annually
The Welfare Dimensions of Bycatch
Bycatch is typically treated as a conservation and sustainability issue — about species population impacts. But it is also a profound animal welfare issue. Each bycatch animal is an individual sentient being who experiences the process of capture, handling, and death.
The Experience of Capture
- Trawl nets: Fish and other animals are dragged through water for hours, experiencing extreme pressure, crowding, and exhaustion. Many die of suffocation or injury within the net.
- Longlines: Hooks cause penetrating injury. Animals may be suspended on hooks for hours or days before lines are hauled.
- Gillnets: Animals become entangled, often unable to breathe (especially air-breathing mammals and turtles), and drown over minutes to hours.
- Purse seines: Large nets encircle entire schools; enormous numbers of non-target fish are crushed and suffocated.
Death by asphyxiation: Most bycatch fish die through asphyxiation — a process that causes significant suffering. Fish removed from water experience the equivalent of drowning in reverse. Rapid decompression from depth also causes severe internal injuries (barotrauma).
Species Most Affected
| Species Group | Annual Bycatch Estimate | Primary Fishery |
|---|
| Non-target fish species | Hundreds of billions | All trawl and net fisheries |
| Dolphins and porpoises | ~300,000+ (cetaceans total) | Tuna purse seines, gillnets |
| Sea turtles | ~250,000 | Shrimp trawls, longlines |
| Seabirds | ~320,000+ (esp. albatross) | Longlines |
| Sharks and rays | Tens of millions | Longlines, trawls, gillnets |
| Seals and sea lions | Hundreds of thousands | Gillnets, trawls |
| Invertebrates (crabs, corals) | Enormous but poorly quantified | Bottom trawling |
Dolphins and Tuna Fishing
The Eastern Tropical Pacific tuna fishery historically set nets on dolphins (tuna school beneath them), killing hundreds of thousands annually before the "dolphin-safe" campaign of the late 1980s forced reform. While dolphin bycatch in this fishery declined significantly, "dolphin-safe" certification has been criticised for not accounting for other bycatch species (juvenile bigeye tuna, sharks) and for being poorly enforced globally.
Shrimp Trawling: Among the Worst Bycatch Ratios
For every kilogram of shrimp landed from tropical shrimp trawling, historically 5–20 kilograms of other animals were caught and discarded dead. These include juvenile fish of dozens of species, sea turtles, seahorses, and countless invertebrates. Modern bycatch reduction devices have improved ratios somewhat but the fundamental problem remains.
Solutions and Progress
Technological Solutions
- Turtle Excluder Devices (TEDs): Trapdoor mechanisms in shrimp trawl nets that allow sea turtles to escape. Required in US waters; significant mortality reduction demonstrated.
- Acoustic pingers: Devices attached to gillnets that emit sounds deterring cetaceans. Shown to reduce porpoise bycatch by up to 90% in some fisheries.
- Circle hooks: Replace J-hooks on longlines; reduce sea turtle bycatch by 80–90% while maintaining target catch.
- Bird-scaring lines: "Tori lines" keep seabirds away from baited hooks on longlines. Dramatically reduce albatross bycatch.
- Selective trawl gear: Modified net designs with sorting grids or escape panels allow non-target species to exit.
Regulatory Solutions
- Time-area closures: Closing fishing areas seasonally when vulnerable species concentrate
- Gear restrictions: Banning gillnets in protected areas or near-shore cetacean habitats
- Observer programmes: Independent monitoring of bycatch rates (currently covering only a tiny fraction of fishing effort globally)
- Bycatch caps: Setting legal limits on non-target catches within fisheries management plans
Vaquita porpoise: The world's most endangered marine mammal — fewer than 10 individuals remain — is on the brink of extinction entirely due to gillnet bycatch in the Gulf of California. This is the ultimate demonstration of the conservation and welfare costs of unmanaged bycatch.
Consumer Action
- Use the Monterey Bay Aquarium Seafood Watch guide to choose low-bycatch seafood options
- Reduce or eliminate seafood consumption — no fishing method is bycatch-free
- Support organisations campaigning for stronger bycatch regulations (Oceana, Sea Shepherd, WWF ocean programmes)
- Avoid "dolphin-safe" certification without scrutiny — look for more comprehensive sustainability ratings
- Advocate for mandatory bycatch observer programmes and transparent reporting
Bycatch
Commercial Fishing
Dolphins
Sea Turtles
Albatross
Shrimp Trawling
Ocean Welfare
Turtle Excluder Devices