BYCATCH

Overview

Bycatch is the term used to describe animals that are caught unintentionally in a fishery. It can include other fish species that weren’t specifically targeted by also sharks, manta rays, dolphins, turtles, and seabirds. It is estimated that around 10% of the world’s global catch is discarded at sea each year. Many marine species are threaten with extinction because of high levels of bycatch from commercial fisheries.

Definitions

Target Species - The species that fishers aim to catch for commercial purposes.

Non-Target Species - Any species caught incidentally during fishing operations that were not the intended catch.

Bycatch - the term used to describe animals that are caught unintentionally in a fishery.

Discard - the name given to the portion of each catch that is thrown back into the ocean, because it lacks commercial value or fishing regulations prohibit keeping them.

Deep Dive

Unfortunately, few fishing techniques are selective. Though fisheries may be targeting only a single species, most fishing gear still traps and kills many other animals in the process. Bycatch is either of a different species, the wrong sex, or is undersized or juvenile individuals of the target species. These unwanted animals caught by fisheries may sometimes be kept and sold if they have commercial value, but often they are thrown back to the ocean dead or dying as discard. Bycatch is a widespread problem that happens in most fisheries and in all seas. It affects thousands of species, from delicate corals to gigantic whales.

Sharks, for example, are a significant bycatch species, particularly in high seas fisheries. Longline vessels primarily targeting tuna or billfish set out hundreds of kilometers of baited hooks. It doesn’t matter what protective status a shark has, it will still be interested in bait on the end of a hook. The number of sharks (or any bycatch species) caught incidentally is difficult to quantify because of the under or lack of reporting from different nations. It is estimated that tens of millions of sharks are caught as bycatch each year, and a recent study found that the global abundance of oceanic sharks and rays has declined by 71% since 1970 due to increased fishing pressure. Oceanic shark species are most at risk as they converge on ocean hotspots where there are high concentrations of prey, which are of course also targeted by large-scale commercial fishing fleets. These incredible survivors have lived through five mass extinctions, yet now their future hangs in the balance as shark populations around the world are being wiped out by overfishing.

Fisheries bycatch is also considered a primary driver of sea turtle population declines, killing hundreds of thousands of these gentle marine reptiles each year[1]. Sea turtles need to breathe air, so getting caught in fishing nets or line can lead them to drown before they can be released by fishers. Six out of seven species of sea turtle are now listed as Vulnerable through to Critically Endangered by the IUCN Red List of Threatened Species (with the seventh Data Deficient) due in part to by-catch in fisheries.

Cetaceans are another frequent victim of bycatch, with hundreds of thousands of whales, dolphins, and porpoises dying in fishing nets each year[2]. These gentle ocean giants and famously intelligent and social creatures often tear muscles, break teeth and slice off their fins in their desperation to escape fishing nets and avoid suffocation, becoming more entangled as they struggle[3]. Those individuals that are fortunate enough to break free are usually still wrapped in fishing ropes which saw into their flesh, leaving them with painful injuries and often killing them slowly through infection or starvation.

Which fishing methods have the most bycatch?

Levels of bycatch vary massively between different fishing methods, with trawl, longline and gillnet fisheries considered some of the worst offenders.

Trawling involves pulling a fishing net through the water behind one or more boats, either high in the water column (pelagic trawling) or along the seabed (bottom trawling). These walls of death are dragged through the ocean, indiscriminately catching everything in their path that is too big to fit . The biggest trawlers are floating factories that can process, package, and freeze thousands of tonnes of fish and keep trawling for weeks at a time. As reported by Greenpeace, the largest of these supertrawlers are over 140m metres in length and have nets up to a mile long.

Longlines are lines baited with hooks attached at intervals by shorter branch lines. Depending on the target species, these lines are either anchored to the sea floor to catch sable, cod, or halibut (demersal longlining) or left to drift (pelagic longlining) to catch swordfish or tuna. The average U.S. longline set is 28 miles (45 km) long with thousands of hooks, meaning every night enough longline is deployed to wrap around the world 500 times. Longline and trawl fisheries are estimated to kill over 300,000 seabirds each year, the majority of which are albatrosses and petrels.

Gillnets are walls of netting that hang in the water column with mesh sizes designed to allow fish to get only their head through the netting but not their body. The fish’s gills get caught in the mesh as they try to back out of the net, making them even more entangled. Set gillnets are attached to poles or an anchor system to hold the net in place whilst drift gillnets are kept afloat at the desired depth using a system of weights and buoys. They are typically used to target large species such as salmon, tuna, and cod, but they also catch large numbers of sharks, turtles, and marine mammals. It is estimated that gillnets kill at least 400,000 birds each year.

What other things influence the amount of bycatch?

Consumers favouring a small number of species. High-grading is described by the FAO as the discarding of a portion of a vessel’s legal catch that could have been sold to have a higher or larger grade of fish that bring higher prices. Consumers frequently opt for the same few popular species such as tuna, salmon, cod, and shrimp, putting great pressure on their populations and encouraging discard.

Poor fisheries management. Lack of enforcement or political will means that devices or gear designed to reduce bycatch are not used as often as they should be. Small-scale and artisanal fisheries are increasingly recognized as having an equal or greater impact on marine resources than larger-scale industrial fisheries; effective enforcement of regulations for these fisheries is challenging and they are frequently unmonitored and unregulated. A recent study found that the total annual captures of manta and devil rays by the Sri Lankan artisanal fishing fleet exceeds the estimated annual captures of mobulids in all global, industrial purse seine fisheries combined.

Hope

Despite the challenges posed by bycatch, there have been some positive developments in recent years. Increased awareness and concern about the impacts of bycatch on marine ecosystems have driven significant efforts to address the issue. There are some fishing methods that are more selective and therefore have low levels of bycatch. For example, pole and line fishing, in which fishers hook individual fish using hand-held wooden poles with short lines, spearfishing, in which a fisher throws or fires a spear at a single target fish at a time, is another example. Spearfishing can still be problematic however when, for example, too many female fish are targeted due to their large size, affecting the spawning output of their local population.

a) Innovative Fishing Gear: Several initiatives and research projects are exploring innovative fishing gear designs to reduce bycatch. For instance, the development of "TEDs" (Turtle Excluder Devices) for shrimp trawlers has significantly decreased sea turtle bycatch in some regions. The leader lines of some longline fishing fleets have been changed from wire to monofilament to reduce the bycatch of sharks. Using bird-scaring lines, dyed bait, setting lines at night or with weights, all help reduce the bycatch of seabirds by longline fishing.

b) Fisheries Improvement Projects (FIPs): FIPs are collaborative efforts involving fishermen, conservation organizations, and governments to improve fishing practices and reduce bycatch. These projects aim to achieve sustainable fishing practices while protecting non-target species.

c) International Cooperation: Various international agreements and conventions, such as the Agreement on the Conservation of Albatrosses and Petrels (ACAP) and the Agreement on Port State Measures (PSMA), are encouraging countries to work together to combat illegal, unreported, and unregulated (IUU) fishing, which can contribute to bycatch.