Threats to Marine Wildlife

The North Sea’s marine wildlife is subject to a wide range of threats, including:

Damage and destruction of fragile habitats and wildlife (e.g. by certain fishing activities, dredging of sand and gravel, and coastal and offshore construction).
Disturbance of wildlife, especially feeding and breeding grounds (e.g. by recreational or commercial boat traffic, or noise from offshore construction).
Over-fishing of commercial fish and shellfish stocks
The introduction of non-native 'alien' species
Pollution (from industry and coastal agriculture)
Climate change (eg. sea level rise, rises in sea temperature, changes in the acidity of the water)

Damage and Destruction of Habitats

The seabed of the North Sea has in many places been damaged beyond recognition as a result of human activities. Over time we have taken more and more resources from the sea. These effects have not only altered the size and amount of fish available to catch but have also changed the appearance of the North Sea seabed from what it once was. During the mid 19th century the southern area of the North Sea was once a productive oyster fishery, covered in a mosaic of invertebrates (including corals and seafans). The invention of steam trawlers during the 1880s was to change this. As trawlers repeatedly dragged their nets back and forth over the seabed they began depleting the waters of everything and anything living within it. Trawlers are not limited to taking only the intended species. Over time creatures not only attached to the seabed within the southern North Sea but also living within the water also began to disappear. As result of this unsustainable fishing practice the last commercial oyster catches were made in 1930s.

Wildlife Disturbance

The North Sea is home to a wide range of marine mammals, such as grey and common seals, harbour porpoise, minke and fin whales all of which are subject to activities occurring within the waters in which they swim. Research throughout the world has been studying whale and dolphin behaviour in response to boats. Potential effects of disturbance have been summarised as being those which are 'immediate effects' (e.g. direct harm caused to the animal by collisions), 'short-term effects' (e.g. including interruption or changes of essential behaviours such as respiration, feeding, resting,socialising,communicating and group spacing) and 'long-term effects' (e.g. changes in distribution, reduced fitness and reduced breeding potential).

Overfishing

Over the decades, dramatic declines have been recorded in populations of fish within the North Sea. Species which were once common (e.g. blue-fin tuna, European sea sturgeon, angel shark) are on the verge of extinction in the North Sea, while the most valuable and important stocks – the ‘bread and butter’ for North Sea fishermen - (e.g. herring, cod) have been reduced to a tiny fraction of their former abundance. It is estimated that 99% of fish mass has now been removed from the North Sea.

Alien Species

Every year marine species are transported from their native area to places where they have not previously been found. These non-native, 'alien species' may arrive by accident (for example, attached to the hull of a ship, or in sea water taken onboard a ship from the Pacific, say, and pumped out into the North Sea ) or they may be introduced intentionally (e.g. to set up a shell-fish farm). An example of an introduced species now found in the North Sea is the slipper limpet. This snail hitched a ride in a consignment of American oysters, arriving in Essex in the late 19th century. It has now spread throughout the southern North Sea and as far north as Yorkshire.

Pollution

This may occur as a result of marine or land based activity. In the past, dumping of sewage and industrial waste has posed a problem in the southern region of the North Sea. The coastal countries of the North Sea have in place international agreements to minimise dumping of hazardous waste at sea and discharge from land of some toxic materials. However, enforcement of dumping and pollution restrictions is difficult.

Climate Change

Climate change poses a major threat to the North Sea’s marine life. All marine organisms live within a specific 'niche', requiring specific conditions (e.g. water depth, temperature) in order to survive. Changes in sea temperature can result in some species being unable to survive. As the North Sea warms, species that prefer colder water (e.g. cod) are steadily shifting north to remain in cooler water, while warm water species such as spider crabs (maja brachydactyla) and sea bass are moving into the North Sea from the south. Another impact of climate change, sea level rise, may result in the direct loss of habitats such as saltmarsh and mudflats. Finally, another global change is an increase in the acidity of sea water. In the North Sea, this could have an serious negative effect on animals that produce calcium carbonate shells, such as molluscs and crustaceans.