Globally, marine fisheries are now reaching the limits of exploitation. In many marine ecosystems, 20% or more of primary production is required to support fisheries, and biological processes as opposed to the power of the fishing fleets now limit fish production (Pauly and Christiansen, 1995). As a result, few potentially productive sea areas remain unfished. According to the Food and Agriculture Organization (FAO) of the UN (Food & Agriculture Organization, 1991), 70% of the world's 80 most important commercial fish stocks are now either fully exploited, over-exploited, depleted or rebuilding as a result of over-fishing.
Currently, 90% of the world's fish catch comes from the coastal ocean. With catches in coastal seas coming under increasing pressure, fisheries have expanded into deeper waters in recent years in order to target new resources (such as the orange roughy, a species congregating at sea mounts for spawning; see Probert et al., 1997); this is an undesirable move into boom-and-bust exploitation of K-selected species lacking the population resilience to sustain intensive exploitation. Target species are under increasing pressure globally from a rapidly expanding internationally competitive fleet. The global cost of fishing is reckoned to be some US$124 million, generating a revenue of US$70 million, which is indicative of a huge fleet over-capacity (costing some US$54 million) sustained by subsidy (Food & Agriculture Organization, 1993). The number of fishing boats in the world has doubled since 1970. In addition, the secondary effects of such intensive fishing activities -such as environmental impacts and the effects of discarding practices-that have largely been overlooked by fisheries managers until recently are now assuming increasing prominence (Jennings and Kaiser, 1998; Moore and Jennings, 1999). Thus, in a recent controversial paper on the destruction of benthic communities caused by mobile fishing gear, Watling and Norse (1998) speculated that half of the global continental shelf area is subjected to destructive forces on a scale dwarfing reprehensible forest clear-cutting practices on land. Such speculation, however, may overstate the case. It fails to highlight the fact that average conditions are derived from a mosaic of heavily repeat-trawled areas along preferred tows often adjacent to gear-damaging, or otherwise less profitable, grounds that represent untouched havens even in the most heavily fished regions, e.g. the southern North Sea. In addition, different, but still functional and hugely productive, benthic ecosystems may remain that have become adjusted to fishing pressure.
Certainly, if fisheries are to be sustainable in the long-term then harvesting practices need to be managed in an environmentally sympathetic (and hopefully ethical) manner. The notion of sustainable