Porpoise

Weißflankenschweinswal ( Phocoenoides dalli )

The harbor porpoise ( Phocoenidae ) are a family of small toothed whales with six species in three genera. They are related with the dolphins, but differ in a number of anatomical features. Especially characteristic is the shape of the head and teeth. Best known in Europe is the Common porpoise ( Phocoena phocoena ) with reserves in North Sea and Baltic Sea.

Anatomy

With body lengths up to 2.5 m, these animals are among the small cetaceans, the California harbor porpoise is a maximum 1.5 m one of the smallest. The animals can weigh between 30 and 200 kg, depending on body size. Porpoises have a stocky body with a round head and blunt snout with no beak. The jaws contain up to 120 spatulate teeth. The fin is often triangular in shape and is located behind the center back, only Glattschweinswal has no dorsal fin.

Dissemination

The six types live in all oceans, mostly near the coast. Preferably, they are found in the seas of the Northern Hemisphere, only two of the six species live in the southern hemisphere. The Glattschweinswal is also found in some rivers, such as the Yangtze River.

In the same porpoises are observed since 2013 increasingly form the partially schools with up to six animals. The stock in the Baltic Sea in 2013 was about 300 individuals.

Behavior

Porpoise hunt mainly fish, many also eat cephalopods and crustaceans. They usually live in small groups of up to ten individuals, which in some species can but unite to gatherings of hundreds of animals. Among themselves they communicate with different clicks and whistling. Like all toothed whales, they are able to use ultrasound for echolocation. Porpoises are fast swimmers - the Weißflankenschweinswal should count at 55 km / h the fastest whales. Your jumps at the surface, however, are little acrobatic.

Classification

• Genus Phocoena Brillenschweinswal ( Phocoena dioptrica )
• Porpoise ( Phocoena phocoena )
• California porpoise ( Phocoena sinus )
• Burmeister 's Porpoise ( Phocoena spinipinnis )

• Glattschweinswal ( Neophocaena phocaenoides )

• Weißflankenschweinswal ( Phocoenoides dalli )

Human impact

Not only unexpected natural events, such as adverse weather conditions such as hurricanes, storm surges or rapid ice formation can lead to disasters and thus affect the population stock of harbor porpoises. It is mostly anthropogenic influences the long-term impact on the populations and mitigate these or lead to exhaustion. While natural disasters lead to a short-term slump in the stock figures and subsequent recovery, human influences are usually characterized by a gradual loss. " The number of carcasses of harbor porpoises on the German Baltic coast from 25 to 152 animals has about six-fold between 2000 and 2009."

Human impact is varied and not only the Baltic Sea is affected. " Threats to the survival of harbor porpoises in the North Sea go by a variety of anthropogenic activities, changes in the marine ecosystem, diseases and also of climate change from ". Human activities in many areas, such as lead in tourism, in shipping, in fisheries ( bycatch ) by whaling, poaching and especially about pollution to diverse disorders in populations of harbor porpoises. In addition, seismic exploration or submarines cause further acoustic damage. This noise has a large stress for the animals. If some or a variety of these factors together on this leads to a total load, which leads to an unstoppable individuals shrinkage and a loss of biodiversity.

Bycatch

" Bycatch is the part of the catch that is either thrown back or not managed ." Many porpoises die in this way the undesired fishing. The thin plastic nets of fishing boats with diagonal mesh sizes 10-27 cm equipped. Above all, plaice and turbot are caught with these nets. However, they also allow that other fish and mammals are beige do with it. Since the networks are mainly designed to catch as many fish, they offer little protection and consideration to the great marine life.

The many captive wriggling fish lure the porpoises to by the silvery flash of scales and arouse the curiosity of marine mammals. This porpoises accidentally fall into the for them not visible and audible imperceptible fishing nets. This leads to the fact that the marine mammals entangled in the nets, can not be detached and then drown.

On the basis of analyzes could be categorized as by-catch in 2008 on the entire German Baltic coast eighteen porpoises. 2010, only six animals were diagnosed as " suspicion of by-catch ", but you can not clearly identify this often because of the advanced state of decay. Comparing the catch data of the North and Baltic Seas with the data world, the bycatch rate outside the German coast is considerably larger. The population in the Baltic Sea has become so small that every little bycatch shows dramatic effects. Especially where the global ban of by-catch is not so heavily controlled and turn out the penalties only slightly, many marine mammals are intentionally not caught and never again exposed to the freedom.

Chemical influences

Chemical influences in the oceans act primarily on the end links of the food chain, such as on fish, birds, whales and seals. The summation of toxins leads to a decline in the population stock of harbor porpoises in the North Sea and Baltic Sea. Above all, a high toxic concentration of mercury in the brain, liver, and fat of the animal, in conjunction with a poor diet and / or diseases that marine mammals weigh very much.

Due to globalization and increased number of imports and exports, shipping is gaining an increasingly important role on the seas. "By operation of the ship substantial amounts of oily and other chemical residues ", which contribute significantly to the pollution of the Baltic and North Sea. Waste tarry residues and oil films can also lead to skin necrosis and parasites infesting the animals. Emissions from shipping, such as nitrogen dioxide (NO2 ), sulfur ( S), particulate matter and carbon dioxide (CO2 ) contribute to pollution of the ecosystem.

DDT and PCBs have high concentrations of reproductive disorders on at any marine mammals. PCB with a content of about 70 mg / kg leads to sterility. Other chemical pollutants, such as chlorinated hydrocarbon compounds and heavy metals lead to changes in morphology with respect to the decrease in length. It has been proven a fatal course of PCB concentrations in 1980 at the coast of Mecklenburg-Western Pomerania between a porpoise, which 260 mg / kg PCB had stored in fat.