Bycatch & Fisheries Bycatch | Animal Welfare Hub

What Is Bycatch?

Bycatch refers to the non-target species caught unintentionally during commercial fishing operations. When a trawl net, longline, or gillnet is deployed to catch a target species, it cannot distinguish between that species and others. Dolphins, sea turtles, seabirds, sharks, juvenile fish of all species, and countless other animals are caught, injured, and often killed as an unintended consequence.

The scale of bycatch is staggering: estimates by the Food and Agriculture Organization (FAO) suggest that 38–40% of all marine catch globally is bycatch — representing perhaps 63 million tonnes of non-target species per year. Much of this is discarded back into the ocean, dead or dying. Bycatch is one of the least visible but most numerically significant sources of marine animal suffering.

Major Bycatch Victims

🐬 Dolphins and Porpoises

An estimated 300,000 cetaceans (dolphins, porpoises, and small whales) are killed as bycatch annually worldwide. Common dolphins in the Bay of Biscay, Māui dolphins in New Zealand (fewer than 60 individuals remain), and vaquita porpoises in Mexico (fewer than 10 exist) face existential threats from bycatch.

🐢 Sea Turtles

All seven sea turtle species are threatened or endangered. An estimated 250,000 sea turtles are killed or seriously injured annually by fishing operations. Longlines, trawls, and gillnets are all significant sources of turtle mortality. Sea turtles that become entangled often drown, as they must breathe air.

🦅 Seabirds

Longline fishing — using lines stretching up to 130 km with thousands of baited hooks — kills approximately 300,000 seabirds annually, including albatrosses, petrels, and shearwaters. Albatrosses are particularly vulnerable: 15 of 22 species are threatened with extinction, largely due to longline bycatch. Birds dive for the bait, become hooked, and drown.

🦈 Sharks and Rays

Sharks and rays are caught as bycatch in enormous numbers — estimated at tens of millions annually. Many are killed for their fins (shark finning) or discarded. Oceanic whitetip, hammerhead, and other shark populations have declined 80–99% since the mid-20th century, with bycatch being a primary driver.

Fishing Methods and Their Bycatch Profiles

Different fishing methods have very different bycatch rates and victim species:

Bottom trawling: Highest bycatch rates of any method. Nets dragged across the sea floor catch everything — juvenile fish, invertebrates, sponges, non-target species. Bycatch can exceed 90% of total catch in some shrimp trawl fisheries.
Longlines: Thousands of baited hooks catch target fish (tuna, swordfish, halibut) but also sea turtles, seabirds, sharks, and non-target fish species. The hook-and-line interaction causes injury and drowning.
Gillnets: Walls of netting suspended in the water trap fish by their gills. Entangle dolphins, sea turtles, sharks, and diving birds. Drift gillnets are particularly destructive and are banned in some jurisdictions.
Purse seines: Large nets that encircle schools of fish. In Eastern Pacific tuna fishing, dolphins historically swam above tuna schools and were encircled along with the fish — leading to hundreds of thousands of dolphin deaths before conservation measures were enacted.
Pole and line / trolling: The most selective fishing methods. Target fish are caught one at a time, dramatically reducing bycatch. Used by MSC-certified "pole and line" tuna fisheries.

Ghost Gear: The Persistent Killer

Lost and abandoned fishing gear — "ghost gear" — continues killing long after it is discarded:

An estimated 640,000 tonnes of fishing gear is lost or abandoned in the ocean each year
Ghost nets continue to fish for years, catching and killing fish, dolphins, sea turtles, and seabirds in a process called "ghost fishing"
Marine mammals, turtles, and seabirds become entangled in ghost gear, drown, or suffer injuries from monofilament line cutting into flesh
Ghost gear is the deadliest form of marine debris — far more damaging to marine life than plastic pollution by number of animals killed
Ghost Gear Initiative and similar programs work to retrieve abandoned gear from the ocean floor

The Dolphin-Safe Tuna Story

The history of dolphin-safe tuna is one of the most instructive in animal welfare advocacy — a case study in both what campaigns can achieve and the limitations of simple solutions:

The Dolphin-Safe Certification

In the 1980s, public outcry over footage of dolphins drowning in purse seine nets targeting Eastern Pacific tuna led to the "dolphin-safe" campaign. The result was significant: the US Dolphin Consumer Protection Act (1990) and the "dolphin-safe" label drove industry to change practices. Eastern Pacific dolphin deaths in tuna fishing fell from hundreds of thousands per year to approximately 1,000 per year — a genuine conservation and welfare success.

However, the story has a complication: dolphin-safe tuna is often caught by methods (FAD fishing — using floating devices that aggregate fish) that have very high bycatch of juvenile tuna, sharks, sea turtles, and other species. In avoiding dolphin bycatch, the certification may have shifted mortality to other less charismatic species. This illustrates the challenge of addressing bycatch species-by-species rather than systemically.

Solutions and Mitigation Measures

A range of technological and policy solutions reduce bycatch:

🔊 Acoustic Deterrents ("Pingers")

Acoustic deterrent devices attached to nets warn dolphins and porpoises to avoid them. Pingers have been shown to reduce cetacean bycatch by 70–95% in some fisheries. The EU mandates pinger use in some fisheries, but compliance remains inconsistent.

🪝 Circle Hooks

Replacing J-hooks with circle hooks on longlines reduces sea turtle bycatch by up to 90% in some fisheries, as turtles are less likely to be fatally hooked. Circle hooks also reduce some seabird bycatch. Widely recommended but not universally mandated.

🦅 Bird-Scaring Lines

Brightly colored streamers ("tori lines") deployed above longlines scare seabirds from diving for bait. Combined with line-weighting (sinking hooks quickly below diving depth), seabird bycatch can be reduced by over 80%. The Agreement on the Conservation of Albatrosses and Petrels (ACAP) promotes these measures.

📋 Bycatch Limits and Discards Ban

The EU's Landing Obligation (2015) requires all catch to be landed — eliminating "highgrading" (keeping only highest-value fish and discarding the rest). The aim is to reduce incentives for wasteful fishing, though implementation has faced challenges.

Seafood Certification: What Labels Tell You About Bycatch

Seafood sustainability certifications vary in how well they address bycatch:

Marine Stewardship Council (MSC): The most widely recognized seafood certification. MSC requires that bycatch be assessed and managed, but critics have pointed out that some MSC-certified fisheries have significant bycatch issues. The MSC standard has been revised to strengthen bycatch requirements.
Dolphin Safe: Specifically addresses dolphin bycatch in tuna fishing; does not address other bycatch species. A useful but narrow certification.
Friend of the Sea: Covers bycatch requirements including shark finning prohibition and bycatch reduction measures.
Pole and Line Foundation: Specifically certifies pole-and-line tuna fishing, the lowest-bycatch method for tuna.

What You Can Do

🐟 Choose Low-Bycatch Seafood

Pole-and-line caught tuna, farmed bivalves (oysters, mussels, clams — with near-zero bycatch), and MSC-certified fisheries with strong bycatch management. See our Ocean Fishing page for more.

🌊 Reduce Seafood Consumption

Every reduction in seafood demand reduces pressure on fisheries. Plant-based seafood alternatives (seaweed, jackfruit, plant-based "fish") are increasingly available and good. See our Plant-Based Guide.

📢 Support Policy Reform

Advocate for mandatory pinger use, circle hook requirements, and time-area closures to protect critical habitats. Contact representatives about strengthening international fishing agreements.

💰 Support Marine Conservation

Ocean Conservancy, Pew Trusts Ocean, and ACAP work on bycatch reduction and marine conservation policy.

Bycatch