Porpoises

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Porpoises
Two common porpoises (Phocoena phocoena)

Two common porpoises ( Phocoena phocoena )

Systematics
Subclass : Higher mammals (Eutheria)
Superordinate : Laurasiatheria
Order : Whales (cetacea)
Subordination : Toothed whales (Odontoceti)
Superfamily : Dolphin-like (Delphinoidea)
Family : Porpoises
Scientific name
Phocoenidae
Gray , 1825

The porpoises (Phocoenidae) are a family of small toothed whales with seven species in three genera. They are related to the dolphins , but differ in a number of anatomical features. The shape of the head and teeth is particularly characteristic. The most famous in Europe is the common porpoise ( Phocoena phocoena ) with occurrences in the North and Baltic Seas .

anatomy

With a body length of up to 2.5 m, these animals belong to the small group of whales , the California porpoise is one of the smallest with a maximum of 1.5 m. The animals can weigh between 30 and 200 kilograms, depending on their height. Porpoises have a stocky body with a round head and blunt snout with no beak. The jaws contain up to 120 spatula-shaped teeth. The fin is often triangular and sits behind the middle of the back, only the porpoise has no fin.

distribution

The seven species live in all oceans, mostly near the coast. They are preferably found in the seas of the northern hemisphere, only two of the seven species live in the southern hemisphere. The porpoise is also found in some rivers, such as the Yangtze River .

Porpoises have been observed increasingly in the Elbe since 2013, some of which form schools with up to six animals. According to Karsten Brensing , the population in the Baltic Sea was around 300 individuals in 2013 .

The porpoise is Germany's only whale species and is threatened with extinction. For the small population, drowning in safety nets is the greatest danger.

behavior

Harbor porpoises mainly hunt fish , with many also eating cephalopods and crustaceans . They usually live in small groups of up to ten individuals, which in some species can join together to form hundreds of animals. They communicate with each other with different clicks and whistles. Like all toothed whales , they are able to use ultrasound for echolocation . Porpoises are fast swimmers - the white-flanked porpoise is said to be one of the fastest whales at 55 km / h. Their jumps on the surface, on the other hand, are not very acrobatic.

classification

Influence of man

Not only unexpected natural events such as B. unfavorable weather conditions such as hurricanes, storm surges or rapid ice formation can lead to catastrophes and thus affect the population of harbor porpoises. Mostly it is anthropogenic influences that have a long-term effect on the populations and reduce them or lead to complete exhaustion. While natural disasters lead to a brief collapse in the population and subsequent recovery, human influences are usually characterized by a gradual decline. "Between the years 2000 and 2009, the number of dead porpoises found on the German Baltic coast increased about six-fold from 25 to 152 animals".

Human influence is diverse, and it is not just the Baltic Sea that is affected. "Threats to the population of harbor porpoises in the North Sea come from a large number of anthropogenic activities, changes in the marine ecosystem, diseases and also climate changes". Human activities in many areas, such as B. in tourism, in shipping, in fishing (bycatch), through whale hunting, poaching and especially through pollution lead to manifold disturbances of the populations of porpoises. In addition, seismic explorations or submarines cause further acoustic damage. This noise is a major stress factor for the animals. If some or a large number of these factors occur together, this leads to an overall burden that leads to an unstoppable loss of individuals and a loss of biodiversity.

Bycatch

“Bycatch is that part of the catch that is either thrown back or not managed”. Many porpoises die from this type of unwanted fishing. The thin plastic nets of the fishing boats are equipped with diagonal mesh sizes of 10–27 cm. Especially plaice and turbot are caught with these nets. However, they also allow other fish and mammals to be caught. Since the nets are primarily designed to catch as many fish as possible, they offer little protection and consideration for the large marine animals.

The many wriggling fish caught attract the porpoises with the silvery flash of the scales and arouse the curiosity of the marine mammals. As a result, the harbor porpoises unintentionally get caught in the fishing nets that are not visible to them and cannot be heard acoustically. This leads to the fact that the marine mammals get entangled in the nets, cannot free themselves and then drown.

Chemical influences

Chemical influences in the seas mainly affect the end links of the food chain, such as B. fish, birds, whales and seals. The summation of the toxins leads to a decline in the population of harbor porpoises in the North and Baltic Seas. Above all, a high toxic concentration of mercury in the brain, liver and fat of the animal, in connection with a poor diet and / or diseases, are very stressful for marine mammals.

Due to globalization and the increased number of imports and exports, shipping on the seas is gaining an increasingly important role. "The operation of the ship creates considerable amounts of oily and other chemical residues," which contribute significantly to the pollution of the North and Baltic Seas. Tar residues and oil films can also lead to skin necrosis and parasite infestations in the animals. Emissions from shipping, such as nitrogen dioxide (NO 2 ), sulfur (S), fine dust and carbon dioxide (CO 2 ), contribute to the burden on the ecosystem.

The pesticide dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCB) show reproductive disorders in all marine mammals in high concentrations. PCB with a content of more than 70 mg / kg leads to sterility. Other chemical pollutants, such as chlorinated hydrocarbon compounds and heavy metals, lead to changes in the morphology with regard to the decrease in length. A fatal course of PCB concentrations was proven in 1980 on the Mecklenburg-Western Pomerania coast in a harbor porpoise, which had stored 260 mg / kg PCB in fat.

literature

  • Gerhard Schulze: The porpoises: Family Phocoenidae. (= Die Neue Brehm-Bücherei. Volume 583). 2nd Edition. Westarp Sciences, Magdeburg 1996, ISBN 3-89432-379-5 .
  • H.-W. Louis, J. Schumacher: Manual of the marine nature protection law in the North and Baltic Sea. National law including international and European requirements. Springer, Berlin / Heidelberg 2012, ISBN 978-3-642-25416-1 .

Web links

Commons : Porpoises  - Collection of images, videos and audio files
Wiktionary: porpoise  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ The marine biologist Karsten Brensing. In: Deutschlandfunk , nuances. in conversation with Michael Langer. November 24, 2013.
  2. ↑ Environmentalists see the Baltic and North Seas in poor condition. In: Greenpeace report. Die Zeit, July 9, 2020, accessed on July 9, 2020 .
  3. ↑ a b G. Schulze: The porpoises: Family Phocoenidae. 1996, p. 111.
  4. ↑ Koschinski: 7
  5. ^ C. Dahlke: Bundesfachplan Offshore. 2013, p. 64.
  6. ↑ RWD Davies et al.: Definition and assessment of worldwide bycatch. 2009, p. 1.
  7. ↑ See Federal Agency for Nature Conservation
  8. ↑ a b G. Schulze: The porpoises: Family Phocoenidae. 1996, p. 110.
  9. ↑ H.-W. Louis, J. Schumacher: Handbuch des Meeresnaturschutzrechts. 2012, p. 12.