Overfishing can be defined in a number of ways. However, everything comes down to one simple point: Catching too much fish for the system to support leads to an overall degradation to the system. Overfishing is a non-sustainable use of the oceans.
Below are a few definitions in use by organisations and governments. See the the glossary of marine and fisheries terminology for more definitions of terminology used on this website.
The practice of commercial and non-commercial fishing which depletes a fishery by catching so many adult fish that not enough remain to breed and replenish the population. Overfishing exceeds the carrying capacity of a fishery. http://www.lehigh.edu/~kaf3/books/reporting/glossary.html
Catching too many fish; fishing so much that the fish cannot sustain their population. The fish get fewer and fewer, until finally there are none to catch. http://www.reefed.edu.au/home/glossary/o
Fishing with a sufficiently high intensity to reduce the breeding stock levels to such an extent that they will no longer suppport a sufficient quantity of fish for sport or commercial harvest. http://www.fishonline.org/information/glossary/
Worldwide, fishing fleets are two to three times as large as needed to take present day catches of fish and other marine species and as what our oceans can sustainably support. On a global scale we have enough fishing capacity Fishing capacity: A concept which has not yet been rigorously defined, and there are substantial differences of opinion as to how it should be defined and estimated. However, a working definition is the quantity of fish that can be taken by a fishing unit, for example an individual, community, vessel or fleet, assuming that there is no limitation on the yield from the stock. to cover at least four Earth like planets.
On top of the overcapacity many fishing methods are unsustainable in their own way. These methods have a large impact on the basic functioning of our marine ecosystems. These unselective fishing practices and gear cause tremendous destruction on non target species. Bycatch Bycatch: Unwanted marine species caught while fishing for another species / discards Discards: Marine species thrown back after capture. Normally, most of the discards can be assumed not to survive and bottom trawling destruction are two examples of this.
Continue to chapter two: Why is overfishing a problem.
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