Chapter 02 · Nature, land & waterBiodiversity & Nature
Bycatch
Definition
Per FAO usage, the part of a catch taken incidentally in addition to the target species — comprising retained incidental catch plus discards (the portion returned to sea, dead or alive). Broader scientific usage covers incidental capture of non-target species including seabirds, sea turtles, sharks, rays and marine mammals, and may extend to discarded target species, cryptic (unobserved) mortality and ghost fishing by lost gear.
References
Definition (incidental catch + discards); discards absent from international statistics.
Non-target species groups (seabirds, turtles, sharks/rays, marine mammals); broader-term variants; definitional variability by fishery.
Overview
What it means
Bycatch is where fishing meets biodiversity loss: it is the principal driver of decline for many albatross, turtle, shark and cetacean populations, and discarded catch represents a vast waste of biomass — historically excluded from international catch statistics, understating fishing's true footprint.
Mitigation is well-evidenced: circle hooks, turtle excluder devices, bird-scaring lines, time-area closures and gear modifications can cut bycatch dramatically where adopted and enforced. Definition variability across fisheries and jurisdictions complicates measurement and comparison.
How it is used
Fisheries management sets bycatch limits and mitigation requirements; tuna RFMOs impose measures on longline and purse-seine fleets; seafood certification (MSC) and buyer policies screen for bycatch performance; observer and electronic-monitoring programmes estimate rates.
Why it matters
Bycatch converts food production into an unmanaged mortality tax on ocean wildlife; reducing it is among the most tractable, technology-ready conservation wins available in fisheries.