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Impacts on commercial species


Catch with flatfish and cod. Photo: T. Otto (BfN)
Catch with flatfish and cod. Photo: T. Otto (BfN)

Some three million tonnes of fish, shellfish and crustaceans are caught each year in the North Sea alone, making this one of the highest-yield marine regions anywhere in the world.

As in other marine areas, many stocks in the North Sea and Baltic Sea are fished above maximum sustainable yield (MSY). MSY is the catch quantity that does not endanger stock replenishment while securing high yields for the longer term. This is an express objective of the recently reformed EU Common Fisheries Policy (CFP).

Poor state of fish stocks

Fish stocks have long been in a very poor state in the Baltic Sea and most of all in the North Sea, despite the availability of a solution in the form of fisheries management based on the ecosystem approach. Besides the large proportion of species that are overfished or beyond safe biological limits, a further problem is that the situation of many stocks cannot be assessed due to a lack of data. Looking at the status of commercially exploited fish stocks in the German North Sea EEZ that are fully assessed by the International Council for the Exploration of the Sea (ICES), a negative picture emerges with four out of seven stocks overfished and only the plaice population within safe biological limits (see figure).


Status of commercially fished stocks in the German North and Baltic Sea EEZ that are fully assessed by ICES (data: ICES 2013).

Status of commercially fished stocks in the German North and Baltic Sea EEZ that are fully assessed by ICES (data: ICES 2013).

In the German Baltic Sea EEZ, of the commercially exploited fish stocks fully assessed by ICES, three out of four species are outside of safe biological limits. The eastern sprat population is the only stock to show a positive trend, with fishing mortality (the proportion of the stock removed by fishing) consistent with maximum sustainable yield (FMSY) and a spawning stock biomass (SSB) that is at least above the precautionary reference point (Figure 3).

Severe negative impacts on the ecosystem

Fisheries are among the human activities with the most severe negative impacts on the marine ecosystem. Those impacts include:

  • Depletion of numerous commercially exploited fish stocks;
  • Changes in ecological communities – bycatch of juvenile fish and non-target species alters the composition of fish communities;
  • Destruction of benthic communities – most of all, fishing with mobile, bot-tom-contact fishing gear (such as otter trawls, beam trawls and dredges) of the kind widely used in the North Sea has major adverse impacts on benthic habitats such as sandbanks and reefs with their characteristic eco-logical communities. The extent of harm done depends on the fishing gear, its weight, the tow speed, the habitat type and the species involved. Slow-growing species and older organisms such as sea urchins and sea anemo-nes around reefs can be irretrievably destroyed. Species that do not reach maturity until several years of age and that only have few offspring are especially sensitive to the impacts of fishing and can be wiped out com-pletely if fishing intensity is too excessive.

 
 

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