Tuna longline fisheries discard 28.5% of their catch as bycatch, killing 50,000-100,000 seabirds annually while only 6 of 60 MSC-certified tuna fisheries have resolved ETP conditions

Pelagic longline fisheries targeting tuna and tuna-like species deploy billions of hooks annually and produce bycatch rates exceeding 20-25% of total catch. A decade-long study of a Pacific tuna longline fishery found a target-to-bycatch ratio of 1:1 across 104.8 million hooks, catching over 2 million individuals from 117 taxa with a retention rate of only 62%. Average discard rates for tuna longlines are 28.5%, second only to shrimp trawls at 62.3%. Why it matters: Longline bycatch kills an estimated 50,000-100,000 seabirds, thousands of sea turtles, and millions of sharks annually, so populations of slow-reproducing apex predators and endangered species are depleted faster than they can recover, so marine ecosystem trophic structures destabilize as top predators are removed, so cascading effects like jellyfish blooms and mesopredator release alter fisheries productivity for other commercially valuable species, so the entire certification and sustainability labeling system loses credibility when as of December 2024 only 6 of 60 MSC-certified tuna fisheries had closed out all conditions related to endangered, threatened, and protected species impacts. The structural root cause is that longline gear is inherently non-selective -- a baited hook on a 100km mainline cannot distinguish between a target yellowfin tuna and a non-target albatross -- and while proven mitigation measures exist (bird-scaring lines, weighted branch lines, circle hooks, night setting), compliance is essentially unmonitored because fewer than 5% of longline fishing effort carries independent human observers, and electronic monitoring systems are not yet mandated by any tuna Regional Fisheries Management Organization.