Mitigation Techniques

Fish aggregating devices, or ‘FADs’, are floating objects, either natural or artificial, that attract and aggregate fish, including tuna schools. Silky and oceanic whitetip sharks are the main bycatch species in purse seine fisheries, incidentally caught when vessels fish on drifting FADs or entangled in the netting beneath FADs. Sea turtles are occasionally caught in seines and may be snared in the netting on, or under, FADs. Bycatch can be significantly reduced through effective FAD design (non-entangling, biodegradable) and management (e.g., limit FAD numbers & fishing seasons, shift a percentage of fishing effort to free schools, fish sharks from the net with handlines and release, target tuna schools greater than 10 tonnes, release sharks from deck using safe handling and release techniques).

Safe handling and release refers to using best practice methods for dealing with bycatch species, to maximise their chances of survival after interacting with fishing gear. It can also include vessel manoeuvring to avoid taking bycatch species, for example, avoiding setting purse seines on whale sharks. Illustrated Guides and more general literature have been collected in the BMIS.

Small cetaceans may become trapped when purse seiners fish on free-swimming schools of tunas. The backdown procedure and Medina panel are used in combination with skiffs and rafts to create an escape route and shepherd the cetaceans to safety.

'Gear configuration - other' is a catch-all for changes in the deployment of fishing gear (aimed at reducing bycatch) that are not covered by other mitigation methods listed in this database. Examples include gear-switching and gear modification.

Using sound to discourage or distract bycatch species from interacting with fishing gear. Auditory deterrents are not generally considered useful in reducing bycatch of seabirds, turtles and sharks, except in limited circumstances. In the main, this is because the feasibility and long-term effectiveness of an acoustic deterrent is affected by habituation. Acoustic deterrents (e.g., pingers) are used with some success for marine mammals, in particular, cetaceans.

The use of chemical attractants or deterrents in longline and purse seine fisheries aims to exploit differences in sensory biology between target and non-target species, improving the specificity of fishing and thus reducing bycatch.

Bycatch rates can vary among fishing vessels operating in the same fishery, even after accounting for factors such as vessel size and fishing effort, and these differences can persist from year to year.

High energy lasers have been used to deter seabirds from interacting with bait, catch or discards. However, they have been shown to be ineffective at deterring seabirds from danger areas around fishing vessels and likely damage seabird visual systems, with negative effects on foraging behaviour (ACAP 2023).