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Introduction What Is Overexploitation? Overfishing Scale of the Problem Mechanisms of Overfishing Consequences of Overfishing Destructive Fishing Methods Hunting and Poaching Historical Extinctions from Hunting Current Poaching Crisis Bushmeat Trade Overexploitation of Plants Maximum Sustainable Yield Solutions to OverexploitationThe passenger pigeon was once the most abundant bird in North America. Flocks of billions darkened the sky for hours as they passed overhead. By 1914, the last individual, a female named Martha, died in the Cincinnati Zoo. The species went from billions to zero in less than a century, hunted for meat and sport until there was nothing left.
The passenger pigeon is the most dramatic example of a pattern that has repeated throughout human history and continues today. When humans exploit a species faster than it can reproduce, the population collapses. When the collapse is severe enough, the species disappears entirely. Understanding overexploitation, its causes, its consequences, and how to prevent it, is one of the most urgent challenges in conservation biology.
Overexploitation is the harvesting of a species at a rate that exceeds its capacity to reproduce and maintain its population size.
All exploited species can sustain some level of harvesting. A fish population can sustain fishing that removes individuals at the same rate the population produces new ones. A forest can sustain timber harvesting at the rate at which trees grow. The problem arises when harvesting exceeds the biological productivity of the species, leading to population decline.
Overexploitation is not limited to deliberate hunting or fishing. It includes any extraction of living organisms from natural populations at unsustainable rates, including the collection of wild plants, shells, coral, and other natural products.
Overfishing is the removal of fish from a population faster than the population can reproduce and replenish itself.
The Food and Agriculture Organization of the United Nations estimates that approximately 34 percent of the world's fish stocks are now overfished, meaning they are being harvested faster than they can reproduce. A further 60 percent are being fished at maximum sustainable levels, leaving virtually no buffer. Only 6 percent are underfished.
Global fish catches peaked in the late 1980s and have declined since, despite increasing fishing effort, a clear signal of overexploitation.
The historical record documents numerous species driven to extinction by hunting.
Poaching is the illegal killing or capture of wildlife. It continues to threaten numerous species.
Bushmeat hunting is the killing of wild animals for food, particularly in tropical Africa, Southeast Asia, and South America.
At subsistence levels, bushmeat hunting represents a traditional, sustainable food source for forest communities. The problem arises when commercial hunting scales up dramatically.
Commercial bushmeat hunting driven by demand from urban populations is emptying forests of wildlife even where forest cover remains intact. This phenomenon has been described as the empty forest syndrome: forests that appear intact but have been stripped of their larger animals through unsustainable hunting.
Great apes, forest antelopes, and forest elephants are among the most heavily affected species.
Plant overexploitation receives less attention than animal poaching but is equally significant.
Maximum sustainable yield (MSY) is the largest catch that can be taken from a population indefinitely without causing it to decline.
It is calculated from the population's growth rate and carrying capacity. At intermediate population sizes, a population grows fastest and can sustain the highest harvest. Fishing at MSY should theoretically maintain populations indefinitely.
In practice, MSY is difficult to calculate accurately because: