Threats Facing the Marine Environment: Overfishing


Most of the commercially viable fish stocks in the world are over-fished. Some are being driven to almost certain extinction, including the Blue-fin Tuna and several species of shark. However, it is not just the big predatory fish that are over-harvested; Anchovy and Sand Eels in European waters are among many species whose populations are in a poor state due to overfishing. These are important food sources for species further up the food chain, including seabirds and cetaceans, which are therefore put at risk.

Overfishing not only threatens the marine ecosystem, but it threatens the human population as well. Fishing communities' livelihoods are threatened and in several parts of the developing world, fish is an important component of the diet.

Examples of overfishing:

  • Sand Eels (Hyperoplus sp) in the North Sea - not important for human consumption but taken in vast numbers to convert to animal feed and fertiliser. Up to 1m tonnes were taken per year until 2002 when the population crashed and the annual take fell by 2/3. The decline in sand eel stocks are implicated in declines and failures in breeding seabirds including Arctic Tern, Kittiwake and Puffin.
  • Anchovy stocks collapsed in the Bay of Biscay in the early 2000s, and the fishery was closed by the EC in 2005, and after 5 years was reopened in 2009. The EC quota for the 2010/11 season was set at 15,600 tonnes, which equates to 30% of estimated biomass![1] so is unlikely to be sustainable. Anchovy are a major food of seabirds and cetaceans, including the Balearic Shearwater which is a critically endangered seabird that used to visit Biscay in large numbers.
  • Herring were once hugely abundant in the North Sea, but stocks collapsed in the second half of the 20thC. The former abundance of the herring attracted a large number of Blue-fin Tuna, and up to 3,000 of them were caught on the Dogger Bank a year, but when the herring collapsed the Tuna disappeared.
  • Blue-fin Tuna have a worldwide distribution, but virtually all stocks are overfished, most with seine nets and long-lines that are unselective and very efficient. Some are fished with more sustainably with single hooks. The Mediterranean Bluefin Tuna is at risk of extinction due to scale of fishing for the Japanese market. The small Killer Whale population resident in the Straits of Gibraltar is considered critically endangered as it is dependent on these migrating Tuna for its food.

Although over-fishing is recognised by authorities and governments worldwide, there is little political will to develop scientifically based recovery plans and implement them. The Mediterranean EU states set quotas for Blue-fin Tuna at rates 47% higher than recommended by scientists[2].