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Bycatch — The Hidden Cost of Commercial Fishing
For every kilogram of target species landed, commercial fishing gear can capture several kilograms of non-target animals — from juvenile fish and sharks to turtles, seabirds, and marine mammals.
38M
Tonnes bycatch / year
40%
of global catch is bycatch
300,000
Cetaceans killed / year
250,000
Sea turtles caught / year
What Is Bycatch?
Bycatch refers to any marine life caught unintentionally during fishing operations targeting a different species. It is one of the most significant threats to global ocean biodiversity and a major driver of fish population decline, sea turtle endangerment, and cetacean mortality.
Bycatch includes both discarded bycatch — animals thrown back, usually dead — and retained bycatch, where fishers keep non-target species of commercial value even if they were not the intended catch. Global estimates suggest approximately 38 million tonnes of bycatch are generated annually, representing roughly 40% of all marine life caught commercially.
These figures are conservative estimates. Because discarded bycatch is often unreported, the true scale is widely believed to be significantly higher. The FAO estimates that historically around 27 million tonnes per year has been discarded at sea — animals that were caught and killed but returned to the ocean.
Bycatch Impacts by Taxonomic Group
Juvenile FishNon-commercial juveniles of commercial species are among the most common bycatch. Catching juveniles before they reproduce shortens stock recovery timelines dramatically.
Sharks & RaysAn estimated 50 million sharks are caught as bycatch annually. Long-liners targeting tuna have had severe impacts on oceanic shark species, many of which are now IUCN-listed as Threatened.
Sea TurtlesAll seven sea turtle species are affected by bycatch, particularly from shrimp trawls and longlines. An estimated 250,000 sea turtles are incidentally captured per year, with many drowning in trawls.
Dolphins & PorpoisesGillnets are the primary bycatch threat to small cetaceans. The vaquita porpoise — with fewer than 10 individuals remaining — is facing extinction almost entirely due to gillnet bycatch in the Gulf of California.
SeabirdsLongline fishing kills an estimated 300,000 seabirds annually, including albatross. Birds dive for baited hooks and drown. 15 of 22 albatross species are now threatened due largely to longline bycatch.
Non-target FishShrimp trawls are among the most destructive gear types for bycatch ratio — for every 1kg of shrimp landed, up to 10kg of non-target fish, crustaceans, and other organisms may be discarded.
Fishing Gear and Bycatch Risk
| Gear Type | Target Species | Bycatch Risk | Main Bycatch Concern |
|---|---|---|---|
| Bottom trawls | Groundfish, shrimp | Very High | Juveniles, benthic invertebrates, habitat destruction |
| Drift gillnets | Tuna, swordfish, salmon | Very High | Dolphins, porpoises, sharks, sea turtles |
| Longlines | Tuna, swordfish, halibut | High | Seabirds (albatross), sea turtles, sharks |
| Purse seines | Tuna, anchovies | Moderate | Dolphins (tuna-associated sets), juvenile tuna |
| Pots & traps | Crab, lobster | Low | Ghost fishing in abandoned gear; non-target crustaceans |
| Pole & line | Tuna, mackerel | Very Low | Minimal — species-selective by design |
| Hand-gathering | Shellfish, urchin | Negligible | Highly selective |
Solutions and Progress
Bycatch is not inevitable. Technology, regulation, and consumer pressure have achieved significant reductions where applied consistently:
- Turtle Excluder Devices (TEDs) — Required on US shrimp trawlers since 1989; reduced sea turtle bycatch by an estimated 97% in affected fisheries
- Acoustic pingers — Small sonar devices attached to gillnets that alert dolphins and porpoises; shown to reduce cetacean bycatch by 50–90%
- Bird-scaring lines (Tori lines) — Streamer devices above longlines prevent seabirds from reaching baited hooks; mandatory in several longline fisheries
- Circle hooks — Replacing J-hooks on longlines reduces sea turtle bycatch by up to 90% with little impact on target catch rates
- Real-time monitoring — Camera systems (EM) on fishing vessels provide accurate bycatch reporting and deter under-reporting
- Selective gear designs — Square-mesh trawl panels, larger mesh sizes, and fish escape windows allow juveniles to escape while retaining adults
- Time and area closures — Seasonal closures of high-bycatch aggregation areas protect vulnerable species during sensitive periods
What You Can Do
As a consumer, choosing seafood certified by the Marine Stewardship Council (MSC) or rated "Best Choice" by Monterey Bay Seafood Watch is the most direct action you can take to reduce bycatch pressure.
- Look for MSC certification (blue tick logo) on seafood packaging — MSC-certified fisheries must meet strict bycatch limits to maintain certification
- Choose pole-and-line caught tuna over net-caught when available
- Avoid shrimp from uncertified trawl fisheries, which typically have the highest bycatch ratios
- Use Aquareap's Sustainable Seafood Guide and Endangered Species pages to identify high-bycatch-risk species
- Support organisations campaigning for stronger bycatch reporting and vessel monitoring requirements