For any animal species that we harvest, whether by hunting or fishing, there is a maximum number of individual animals that can be taken from any particular ecosystem before we damage the population's ability to sustain itself. If a particular species rapidly declines in number, then other species dependent on it as a food source may also decline. The loss of some species, known as keystone species, can have a drastic impact on the ecosystem as a whole.
Globally, there are many species at risk from hunting to fill the growing demand for illegal trade in exotic pets and bushmeat, as well as bones, organs, and other tissues for traditional medicines. The IUCN lists 48% of all primates in its red list of endangered species, many of which are threatened by illegal hunting. The 25 most endangered primates feature some species with less than 100 individuals remaining, such as the golden headed langur in Vietnam, which has been hunted to near extinction for use in traditional medicines.
Chronic overfishing is putting marine biodiversity at serious risk. The oceans are home to a large percentage of the Earth's biodiversity as they occupy 70% of its surface, but the International Programme on the State of the Ocean (IPSO) estimate that 10,000 tonnes of fish are harvested from the ocean every hour, causing major depletion of fish stocks as well as reducing the populations of virtually all other marine creatures, from seabirds to coral. As a result of unsustainable fishing practices, previously abundant fisheries can now produce only a fraction of the food yielded in the past. Years of overfishing in the Canadian seas off Newfoundland, particularly the use of huge nets to drag the ocean floor, caused devastation to the local marine ecosystem and destroyed the ability of the cod population to sustain itself. This led to rapidly declining numbers, eventually resulting in the Canadian government closing the area to fishing in 1992. The consequences of the cod stock collapse were not only damaging to the marine environment but also resulted in the loss of approximately 40,000 jobs in the local fishing industry. Today there is evidence that cod numbers are increasing, but they remain at only one third of the level they need to reach before they are considered fully recovered.
In Europe, fishermen are subject to a quota system to try to limit the numbers taken from particular species, in an effort to preserve dwindling stocks. Despite these measures, estimates put overexploitation of all EU fish stocks at 70%, with over 20% being fished beyond safe biological limits. The unintended consequence of the quota system is the discard of as much as 70% of all fish caught, which cannot be landed once a ship's quota is used. Currently the EU is working on proposals to reform the Common Fisheries Policy to try to end the practice of discard and further protect fish species under threat, while maintaining the economic viability of the fishing industry.
Without strict limits on fishing, we risk the mass extinction of species and loss of a vital food source for many of the world's people.