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Marine fisheries: A brief overview

8 Jul 2014

Humans have been engaged in fishing for centuries. In Europe, the earliest record of fishing dates back to 8000 BC when both freshwater and sea fish were targeted. However, the 11th century was a turning point as fossil records show a dramatic shift to sea-fishing, possibly due to the depletion of freshwater species. A second wave of change occurred in the 19th century, when steam powered boats could drag heavy fishing nets either within the water column (pelagic trawler) or on the sea bed (bottom trawler) to harvest seemingly vast stocks of sardines, tuna and herring. During the two World Wars industrial fishing activities were largely reduced which allowed heavily fished stocks to recover. However, in the last 60 years as fishing power, technological developments and demand increased, fisheries greatly expanded worldwide.


Today, one of the biggest problems of industrial fisheries that it is aimed to capture a single fish species, but fishing gears are not designed to distinguish targeted from non-targeted species. Subsequently, large amount of bycatch is generated, and those species that have no market value are often discarded (see earlier blog entry on bycatch). It is estimated that annually 27 million tonnes of fish are discarded by industrial fishing vessels. Specifically, shrimp trawlers are one of the most wasteful fisheries, while the highest quantities of discard are generated in the Northwest Pacific.


Industrial fisheries are also heavily subsidised. Subsidies allow fishing fleets to have cheap fuel, funds to build more efficient boats and to have advanced technological equipment to find marketable fish. While this allows fisheries to be economically viable, it leads to overfishing and environmental degradation. As a consequence, today three out of four fish stocks are either overexploited or depleted.


In order to manage commercial fisheries and fish stocks, the concept of maximum sustainable yield (MSY) was implemented during the second half of the 20th century. MSY is the maximum amount of fish that can be fished without causing population collapse. However, the problem of MSY is that its calculation is based on fish landings, which are often not accounted for bycatch and discards.


To take the pressure off the marine environment and allow depleted fish stocks to recover, aquaculture activities have been on the rise in recent decades. But aquaculture activities are also a source of many problems. In order to feed large-sized predatory fish, large amount of small fish needs to be caught by fisheries, and for example by converting 5 kg of small fish only 1 kg of marketable fish is generated. Also, aquaculture is a source of diseases, parasites, invasive species, and the use of chemicals and antibiotics can have a lasting effect on wild migratory fish species.


A more beneficial management tool is the creation of marine protected areas (MPAs) and no-take zones, which could allow fishing stocks to rebuild and to secure a long-term and economically viable fishing industry. But the majority of MPAs suffer from inexistent management measures. One possible solution could be shifting fisheries subsidies to the creation and maintenance of MPAs. This could conserve marine habitats and biodiversity, and provide employment for millions of people. But most importantly, MPAs could be a source of harvestable fish (spillover effect) for marine fisheries without habitat degradation and overexploitation.



Wanda Bodnar



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