What Happens to the Fish Nobody Wanted? Most of It Goes Back Dead

The word covers everything caught that was not the target of the fishing operation, which includes other commercial species, undersized individuals of the target species, fish above a quota that cannot legally be landed, and animals of no commercial value at all. A distinction matters between catch that is landed and sold, which causes no waste even though it was unintended, and catch that is returned to the sea, which is where the problem lies. Survival on return varies enormously by species and gear, being reasonable for some hardy bottom-dwellers and close to zero for species whose swim bladders expand fatally as they are hauled up.

The difficulty is inherent in how fishing works:

• •A net encloses a volume of water and everything in it
• •Mesh size sorts by body dimension only, not by species
• •Baited hooks attract anything that eats that bait
• •Long lines soak for hours with nobody watching them
• •Bottom trawls sweep the seabed and take whatever lives there
• •Fish of different species frequently shoal together

Estimates of how much is discarded vary widely and the disagreement is about method rather than about the facts being disputed. Discarding happens at sea, unobserved, so figures come from placing independent observers on a sample of vessels and scaling up, from logbooks that fishers complete themselves, or from cameras. Each has known problems, since observed vessels behave differently, logbooks under-report what is thrown back, and camera coverage is patchy. Global estimates have been published ranging from under ten per cent to over forty per cent of the total catch, and the range reflects which sources were used and how gaps were filled. Better measurement has generally lowered the headline figures while confirming that particular fisheries are very bad.

The consequences extend past the immediate loss of the animals returned, and the indirect effects are the ones that matter for populations. Species that mature slowly and reproduce rarely, including sharks, rays, turtles and albatrosses, cannot replace losses quickly, so even a modest rate of incidental capture can drive a decline that is invisible in catch figures because the animals were never the target. Removing large quantities of small fish that nothing wanted alters what is left for other predators. Discarding also feeds seabird populations artificially, inflating numbers that then crash when discarding is reduced, which has been observed following policy changes and complicates judging whether a reform worked.

Several approaches work and the effective ones are usually specific pieces of gear rather than general exhortation. Escape grids in shrimp trawls let turtles and large fish push out through an opening while shrimp pass through the bars, and are mandatory in several countries. Larger or square mesh panels let undersized fish swim out. Circle hooks reduce turtle and seabird catches on long lines. Weighted lines that sink quickly and streamers that scare birds away from the stern have cut albatross deaths dramatically in some fisheries. Landing obligations that require everything caught to be counted against quota change the incentive directly, and are difficult to enforce. Closing areas and seasons where the wrong species congregate is blunt and effective.

Gear encloses a volume or offers a baited hook and cannot distinguish species, so unwanted catch is inherent rather than careless, and much of what is returned does not survive. Estimates range from under ten to over forty per cent of the total catch because discarding is unobserved and every measurement method has known faults. Escape grids, square mesh panels, circle hooks and bird-scaring streamers all work.