Fishing equipment lost at sea does not stop working when it stops being tended. It continues to trap animals, and the reason is a straightforward property of the material it is made from.
The gear is designed to keep catching
Nets, pots and traps are built to hold animals without supervision between visits, which is exactly what they continue doing once the connection to a vessel is lost.
A trap on the seabed keeps its shape and its entrance, and animals enter it for shelter or bait as they would any structure.
Trapped animals eventually die and become bait themselves, which draws further animals into the same gear in a self-sustaining cycle.
Synthetic materials do not rot
Older gear was made from natural fibers that weakened and failed within a season or two of immersion, which limited how long a lost net remained dangerous.
Modern nets and lines are synthetic polymers that retain strength for years in seawater, so the same accident now produces a far longer-lived hazard.
Gear that eventually breaks down does so by fragmenting into smaller pieces rather than disappearing, adding to the material suspended in the water column.
Loss usually is not carelessness
Storms move gear, vessels sever buoy lines with propellers, and equipment snags on rock and wreckage and parts under tension.
Conflicts between mobile and fixed gear in the same grounds account for a share as well, since a trawl passing over set traps can carry them away.
Because loss is largely accidental, prevention focuses on marking, mapping and gear design rather than on enforcement against fishers.
Escape mechanisms limit the damage
Many fisheries now require traps to include a panel secured with material that corrodes or degrades within a defined period, opening the trap if it is left down.
Escape vents sized to release undersized animals serve the same purpose during normal use and continue functioning after a loss.
These provisions do not recover the gear, but they substantially shorten the period during which it keeps killing.
Recovery work is slow and specific
Locating lost gear requires side-scan sonar, diver surveys or reports from fishers who know where snags occur, since the seabed is large and the targets are small.
Removal is done by divers or by grappling from a vessel, and it has to be careful because a net grown into a reef can take the reef with it.
Programs that pay fishers to report and retrieve gear tend to work best, because the people who fish a ground already know where the losses happened.