As stated in Chapter 14, most of the world’s wild fish stock harvest is stagnant or declining. The global harvest captured in the oceans and inland waters has peaked in 2000 at 96 million tons and subsequently fallen to 90 million tons in 2003, remaining at that level until 2009.
Fisheries, like rangelands discussed in Chapter 10, can be conceptualised in terms of a range of possible carrying capacities and sustainable yields, depending on the objectives. If preservation is desired, for example of the world’s whale stocks, an ecological carrying capacity can be sought; it is also possible to maximise the production of high quality sport fish, or of small ‘industrial’ fish. The recent history of the world’s marine fisheries has been an accelerating trend towards industrial fishing, harvesting smaller and smaller fish, not for direct human consumption but for feed. 20 per cent of world production now consists of small pelagic species used for making fishmeal which, in turn, is used in pig and poultry production and in salmon and shrimp aquaculture.
Despite the apparent stability of the oceans, their fish and other populations are as much subject to fluctuation as are rangeland cattle. One of the most productive fisheries in the world, providing 20 per cent of the world’s fish landings in the 1960s and 1970s, is generated by upwellings of cold, nutrient rich waters off the coast of Chile and Peru.
The upwellings off the western coast of South America support rich populations of plankton on which pelagic anchovies and pilchards feed. Peru’s catch of anchovies grew in the 1960s to a total of over 12 million tons, but in 1972 it suddenly collapsed to a mere 2.5 million tons. The fishery shifted to sardine from 1977 to 1985, and expanded farther south off Chile. Anchoveta off Peru became dominant again in 1986 as waters cooled and sardine declined, but anchovetta started to decline after 1994 and dropped sharply during 1998.
The immediate cause of the collapses appeared to be the arrival of El Niño, a phenomenon of the Pacific Ocean which produces persistent warm surface waters, so greatly reducing plankton growth. However, El Niño was not the only factor. The shifts from an anchovy regime to a sardine regime are synchronous in Peru, Chile, California and across the Pacific in Japan. They are characterized by a switch from a warm water (sardine) regime in the Pacific to a colder (anchovy) regime every 25 years or so. But the reasons for the shift are not understood.
Managing fisheries subject to such great instability is, like managing rangelands and forests, a difficult task requiring continuous adaptation and flexible responses to changing circumstances. While it is possible to define clear objectives and identify precise, sustainable targets, they are rarely achievable and it is easy to get into an incremental situation in which steadily increasing returns are suddenly replaced by collapse.
Part of the answer relies in creating appropriate policies and regulations, often at international level. A beginning was made in the 1970s with the creation of 200 mile off-shore Exclusive Economic Zones, but effective sustainable management has only arisen where governments have got together to agree on targets, and been ready and able to police them.Once targets have been set, it is possible to find effective technical means to achieve them, whether through quotas, size of fishing fleet or types of net. But most important, is the need to be flexible and to be cautious, and to learn rapidly. In general it pays, in the long run, to fish at somewhat less than the maximum sustainable yield, so providing a cushion in the face of unexpected events and extreme variability.
Hilborn, R. and Walters, C.J. 1992 Quantitative Fisheries Stock Assessment Chapman and Hall, New York (Figure)
Chavez, F.P. et al, 2003. From Anchovies to Sardines and Back: Multidecadal Change in the Pacific Ocean. Science,299, 217-221
Ludwig, D., Hilborn, R. and Walters, C. 1993 Uncertainty, resource exploitation, and conservation: Lessons from history. Science, 260: 17 and 36