Most fisheries are unselective to some degree in that they incidentally catch other species along with their target catch during the process of fishing. This non-target catch is known as "bycatch".
Bycatch species tend to be associated with certain fisheries (for example sea turtles with tropical shrimp trawl fisheries). Nevertheless bycatch, in terms of diversity of species caught and ratios of bycatch to target catch, can vary significantly over the geographic region and over time.
Bycatch reflects variations in marine communities, types of fishing methods used, and changes in the target catch of fisheries. For example, in some parts of Asia, former shrimp trawl fisheries have become "multi-species" fisheries where a much greater proportion of the catch is used. In contrast bycatch in West Africa is often the result of illegal, unreported and unregulated (IUU) fishing by foreign industrial bottom trawlers, who specifically target high-value species and discard anything consider to have little market value. Bycatch also varies according to its impacts, which are not always immediately evident. For example, even a low rate of bycatch can have an ecological impact if fishing effort is high and bycatch species are vulnerable to over-fishing, for example those that are long-lived and slow to reproduce such as sharks and marine turtles. In some cases bycatch is predictable and straightforward to control, and is therefore easier to avoid. In other cases, bycatch is unpredictable and very difficult for fishermen to control. In the latter is the case, bycatch reduction should be achieved by switching fishing methods to a type with little or no impact. A significant proportion of the world's bycatch is discarded back into the ocean. | ||||
Why bycatch occurs
The existence of high levels of bycatch in today's fisheries is in part a reflection of how the oceans' resources are harvested. Fisheries typically target one single species.
Some fishing methods, such as driftnets, target species towards the top end of the marine food chain, such as tuna and swordfish. Aside from the ecological impacts of removing these generally large "piscivorous" (fish-eating) target species, the fishing methods employed often lead to the incidental capture of other large species such as cetaceans, sea turtles and seabirds. In contrast, bottom trawlers are used to target species lower down marine food webs, such as shrimp or prawns. However, due to their fine-meshed nets and the way they are dragged along the seabed, bottom trawlers can capture high levels of non-target species. | ||||
""A key part of resolving the bycatch problem depends on rethinking our approach to
fishing, and modifying this approach to be more in line with ecological, rather than economic, principles." (Hall et al., 2000) | ||||
Focusing fishing effort on a narrow range of species using methodologies that have severe impacts on marine ecology is not the most efficient way to harvest marine resources. From an ecological perspective, it seems a very unlikely way to preserve ecosystem structure and function, while from a social and economic position it is unsustainable and short-sighted. A more common sense approach would be to spread fishing pressure across the food web, thereby utilising the biomass (protein) found at a range of trophic levels. Obviously, care would still have to be taken to avoid the bycatch of juvenile fish and vulnerable or endangered species. Equally, overall fishing pressure should not be allowed to exceed recommended scientific limits. However learning to process and market a diverse range of species will be a more ecologically sustainable approach in the long term. |
What is bycatch? |
