Bycatch is defined as "the unwanted marine species caught while fishing for another species." Species that are caught and considered "bycatch" are discarded and usually do not survive. This not only harms marine communities but also wastes valuable oceanic resources.
- According to NOAA (National Oceanic & Atmospheric Administration), "approximately 30 million tons of bycatch are discarded each year in the world's commercial fisheries, compared to a total of about 85 million tons of landed catch" (Approximately 35% of everything caught commercially is bycatch, and subsequently discarded).
- According to the U.N. FAO (Food & Agriculture Organization), approximately 685,949 metric tons of bycatch are discarded each year in NW Atlantic fisheries
- The true totals of bycatch are unknown due to the lack of oversight and the ease in which fishing fleets can secretly discard species without having to record the data
- Marketable species that are too small and do not meet size requirements or are prohibited from being landed in a region are caught in the fishing gear and need to be discarded
- Species with no market value are simultaneously caught with intended catch and are discarded
- Due to the increased specialization of fisheries and fishing techniques focusing on the catch of one particular species; inadvertent, marketable fish are caught by fleets that are trying to land a different catch that happens to interact with the other species and are subsequently discarded
- The catch of protected, non-fishery marine species (such as marine mammals, turtles, and bird species). Due to the strong bond between certain non-fishery species and the preferred fish species (such as the relationship between dolphins and blue-fin tuna) the unintended species are often targeted, rounded up and caught to ensure the desired catch is landed. This leads to the discarding of those species who most often do not survive. Example: The "porpoise fishing" technique when purse seine fishing for blue-fin tuna
- A fifth major issue with bycatch is through fishing gear that has been abandoned at sea (due to intentional release, breaking away, or becoming lost). This leads to significant death totals of all marine species, none of which will ever become landed. Because there is no way to accurately quantify the number of these occurrences, there is no reliable data pertaining to the continual loss of marine species in this manner.