The ocean’s invisible catch: wildlife killed without being targeted

The animals a fishery did not intend to catch

Bycatch is the capture of animals that were not the target. A seabird dives for bait on a longline; a turtle encounters a gillnet; a small cetacean cannot detect or escape mesh; a shark is landed with the intended fish. Some animals drown, some are injured during release, and some die later from wounds or exhaustion.

The total is difficult to see because fisheries use different gear, operate across jurisdictions and vary enormously in monitoring. Yet NOAA identifies bycatch as a serious conservation problem for marine mammals, sea turtles and seabirds. For a species with slow reproduction, the accidental loss of a few adults every year can outweigh successful breeding.

One mechanism, many threatened profiles

The wandering albatross is vulnerable to baited longlines. The loggerhead turtle can be hooked or entangled. The whale shark and the Critically Endangered vaquita demonstrate how fishing pressure reaches animals with radically different biology.

“Fishing” is therefore not a single threat. Risk depends on gear, depth, season, bait, location and the ability to release an animal alive. A seafood species may be abundant while a rare non-target animal in the same operation continues to decline.

Solutions already exist—but must reach the water

Circle hooks and suitable bait can reduce turtle capture in some longline fisheries. Weighted lines, night setting and bird-scaring streamers reduce seabird interactions. Turtle-excluder devices create escape openings in trawls. Acoustic or ropeless approaches can lower particular mammal risks. Observers and electronic monitoring reveal whether measures work.

No modification is universal, and poorly designed rules can move risk from one species or fleet to another. The effective approach is measurable: identify where mortality occurs, test gear with fishers, require proven practices and publish results. Rebuilding target fish stocks can also reduce pressure to fish harder and longer.

Explore the affected species in the Species Explorer, then compare their life histories. The slower an animal matures and reproduces, the less “accidental” mortality its population can absorb.

Sources and further reading

• NOAA Fisheries: Bycatch
• NOAA Fisheries: fishing gear and risks to protected species
• NOAA Fisheries: pelagic longlines