Definition of By-catch: species caught in a fishery while it is intended to catch another species; or reproductively-immature juveniles of the target species. Basically, when you are fishing on a large scale, and you catch a species not intended for harvest, or young individuals of the species being harvested that are not suitable for whatever the intended use may be.

Amount of by-catch is changed depending on the technique used by the fishery as well as other variables.

By-catch, on a global level, appears to be most evident in shrimp trawling. The Food and Agriculture Organization (FAO) reports as much as 20 pounds of by-catch per every pound of shrimp being caught at some fisheries. They also report a global level of 5
Shrimp by-catch
.7 pounds of discarded by-catch per pound of shrimp.external image moz-screenshot.jpg

Cetaceans, like dolphins, whales, and porpoises, are severely affected by fishing, and are therefore victims of by-catch. With the ever-increasing scale of the fishing industry, more cetaceans are being caught in nets and hooks as a result of by-catch. Specifically, dolphins have been by-caught in driftnet fisheries, and this has caused great controversy. Cetacean by-catch has resulted in processed tuna containers saying that they are 'dolphin free'.

Fisheries have taken steps to avoid by-catch including dying bait, and using acoustic deterrents, both are forms of by-catch reduction devices (BRDs).