7.0 Additional background on acoustic deterrents for marine mammals
Large increases in fishing during the latter half of the 20th century brought total world fisheries production from 20 million mt in 1950 to over 100 million mt in the 1990s (Hilborn 1990, FAO 1993, FAO 1995, Safina 1995). Wild caught marine fish account for approximately 85% of this production (Mace 1997). These impressive increases were possible because of growth in world population, more fishing vessels, and the development of technologies that enabled more fish to be caught per unit of effort. Many of these technologies grew out of developments from WWII such as electronic navigation which enabled boats to return to good fishing locations time after time, hydraulic winches for hauling nets and traps with fewer people, sonar for finding fish schools underwater, and new types of nets and hooks that proved more efficient and durable.
A deleterious aspect of this massive global fishing industry is bycatch: the unintentional catching and killing of birds, non-target fish species, marine turtles, and marine mammals during the course of normal fishing operations (Mooney-Seus 1999). The problem lies in the fact that ocean ecosystems are composed of multi-species complexes. Most fishing operations are non-discriminatory, and usually catch other animals in the course of harvesting the target species. These incidentally caught animals are the bycatch. While there is variation in bycatch rates between fisheries world wide, it is estimated that on average the total bycatch or discard is approximately 20%; that is for every five kilograms of a target species caught there is one kilogram of bycatch thrown overboard, usually dead (Alverson et al. 1994).
All major stakeholders (scientists, environmentalists, and the fishing industry) are concerned about this problem. There are now world-wide efforts to try and reduce bycatch. In many cases, the fishing industry is leading in the development of technologies to mitigate bycatch (Mooney-Seus 1999).