Maximum Sustainable Yield

Maximum sustainable yield is a term population ecologists and economists use to define the theoretical top catch or yield of a species that can be taken indefinitely without depleting the population. The maximum sustainable yield is assumed to be half of the carrying capacity of a species. Commonly, the maximum sustainable yield is more than the optimum sustainable yield, which ends when yield is no longer economical.

Maximum sustainable yield is a long-term management approach, not a crisis recovery method. The European Union (EU), for instance, uses it for all stocks, not just those that are approaching unsustainability. According to the logistic model of growth, population in a new habitat or one that is depleted will initially experience a slow growth rate, but will grow rapidly once it reaches a foothold level. Rapid growth will slow when the population nears the carrying capacity of the habitat. The goal of maximum sustainable yield is to raise or lower the population to the level where the highest growth rate is most likely. The new population level should be capable of indefinite maintenance. Maximum sustainable yield is highly variable, depending heavily on weatherinfluenced factors. Global warming affects maximum sustainable yield by altering the weather.

A sixth of the Earth’s population depends on the sea for over a third of its animal protein; 1.5 billion use fish for 20 percent, while 3 billion use fish for 15 percent (the 2007 world average is 15.7 percent). Approximately 1 billion people use fish as their primary source of animal protein. Average consumption worldwide in 2008 was 37 lbs. (17 kg.) per person, an all-time record. Fishing, processing, and related services provide a livelihood for 8 percent of the world’s population. When the number including families, it adds up to 500 million people relying on an industry that employs 200 million people worldwide. Directly employed in 2010 were 35 million people on 20 million boats. That was 13 million boats and over 20 million fishermen too many for sustainability, according to the United Nations (UN).

Total fish consumption from capture and aquaculture in 2008 was 142 million metric tons, with capture accounting for 54 percent in 2008, down from 57 percent in 2006. The 2008 annual catch was about 85 million U.S. tons, or 77 million metric tons. The total is down from 1989, the peak year, with 86 million metric tons. The 1989 catch culminated a 50-year process in which the catch rose by a factor of four. However, the world total conceals the disparities in different parts of the world—the Indian Ocean catch continues to rise, while 13 of the 15 major areas have shown declines (the Atlantic cod catch is down by a factor of almost three since 1970.)