The Harbour porpoise or the Common porpoise (scientific name: Phocoena phocoena) is one of six species of marine mammal in the family Phocoenidae. The other five are the Finless porpoise, the Spectacled porpoise, the Gulf of California harbor porpoise, Burmeister's porpoise, and Dall's porpoise.
|Harbor Porpoise (Phocoena phocoena) Photo by Ari Friedlaender|
|Size comparison of an average human against the Harbour porpoise. Source: Chris Huh|
The harbour porpoise is the most commonly seen porpoise, and is the most widely distributed of all cetaceans (whales and dolphins) in northern Europe. It is easily recognised as it has a low triangular dorsal fin and lacks a beak. It is small in comparison to other porpoises, has a plump body with a dark grey to bluish coloured back, a pale belly and a rounded head. At birth, young Harbour porpoises are dull in colour and typically have birth lines, which look like folds in the skin, and persist for the first few hours after birth.
There are four recognised subspecies:
- Phocoena phocoena phocoena in the North Atlantic - of which the Baltic Sea subpopulation is Critically Endangered
- Phocoena phocoena vomerina, in the eastern North Pacific,
- an un-named subspecies in the western North Pacific (Rice 1998)
- Black Sea harbour porpoise (Phocoena phocoena relicta) which is Endangerd
The Harbour porpoise is a small cetacean with a blunt short beaked head. It exhibits counter-shading with the animal being generally dark grey on the back and white on the belly. A short, wide-based, triangular dorsal fin, with small bumps on the leading edge is situated midway along the back. The flippers are dark, small and rounded at the tips. The straight mouth line is dark and slopes upwards towards the eye. Phocoenids appear to live in smaller groups and have a simpler social structure than most delphinids. Most Harbour porpoise are found in small groups consisting of fewer than eight individuals, but occasionally form large, loose groups of 50 to several hundred for feeding and migration.
Harbour porpoises live either solitarily or in groups, normally of three to five individuals, although sometimes more. Individual porpoises or mother and calf pairs are observed, and high numbers can be seen during migrations. Like dolphins, the harbour porpoise orientates itself by means of echolocation. It has a particular way of swimming with a rolling movement (imagine a turning wheel); part of the back, including the dorsal fin surfaces briefly before re-entering the water giving the appearance of a rotating motion. This movement will normally be repeated three to four times, prior to a long dive.
A social species, the Harbour porpoise travels in groups numbering between two to five individuals, but larger groups may form during migration. It feeds on a variety of fish, including herring, mackerel and anchovy, a variety of invertebrates are also taken. It is known that echolocation is used in the detection and capture of prey, but this is not yet fully understood. Sight and passive listening (for the sounds made by prey) are also important during hunting. Mating occurs in summer, and gestation (pregnancy) takes 11 months. The calf is suckled for up to eight months and sexual maturity is reached at about four years of age. The Harbour porpoise has possibly the shortest life-span of any cetacean; they rarely live for more than 12 years.
Large numbers of harbour porpoises are caught in fishing nets, because the porpoises feed on schooling fish such as herring and mackerel, in relatively shallow coastal waters. They are also affected by increasing pollution in coastal waters, and are considered vulnerable or threatened in many parts of their range. They are social, and feed in groups, working their way northward to spend the summer in cooler waters and back south as far as Los Angeles, in the Pacific, and the Carolinas or even Florida, in the Atlantic, for the winter. These small, stocky animals breed when they are three to five years old. Females nurse their calves for about nine months. The stomachs of 4-5 month old juveniles killed in gill-nets contained both milk and solid food, which indicates that they were beginning to feed themselves.
Overview charactersitics of the species include endothermic metabolism and bilateral symmetry. Phocoena phocoena is a small cetacean that is 1.5 to 2.0 metres (m) long, but averages 1.6 m. Body mass ranges from 45 to 90 kilograms (kg), but most characteristically averages about 50 kg. The female of the species is usually about ten to twenty percent larger than the male.
The colour of this species varies from individual to individual, but the most common coloration pattern is a dark dorsal surface that shifts to a lighter coloured hue ventrally. Although the dark color is usually black or deep gray, albinos have been reported in which the dark segments are completely or partially white. The flippers, dorsal fin, and tail are all dark in colour, and there is a black stripe that runs from the edge of the mouth or eye to the flipper on either side. There is no noticeable forehead or beak on this species, and the blunt snout is short, giving the head a somewhat cone-like shape.
Phocoena phocoena has two pectoral flippers, a single dorsal fin, and a tail with two partially separated flukes. All of these appendages are short and not very sharp, with the dorsal fin being triangular shaped and usually around 15 to 20 centimetres (cm) high. There is a noticeable keel located near the all dark tail flukes, with the tail itself spanning anywhere from 30 to 65 cm.
Inside the slightly upturned mouth there are rows of 16-28 spade-shaped teeth. There is no variance in the shape or type of teeth in Phocoena phocoena. (Dollinger (editor), 1988; Nowak, 1999; The Porpoise Page, 1998)
Key species behaviours: natatorial; motile; migratory; territorial; and social. The Harbour porpoise usually swims near the surface, rising to the surface to breathe about every 25 seconds; moreover, the blow is not readily visible at sea. It does not present a particularly playful attitude, ignoring boats and rarely leaping out of the water. Harbour Porpoises do not move rapidly, but when pursued can reach speeds of around 23 kilometres per hour. When diving for food this porpoise remains submerged for an average of four minutes, and is considered capable of attaining divng depth of up to 200 metres. This cetacean dives without lifting its tail.
Although schools of up to 100 individuals may sometimes be observed, Phocoena phocoena is more typically seen in pairs or in groups of up to ten. When the largest groups do occur, it is usually because a number of smaller groups have joined together while following a rich food source.
Mothers characteristically bring newborn calves to secluded coves to nurse. Some populations are known to migrate, but when they return to their regular waters they are territorial, patrolling certain areas. (Johnston.1999), (Nowak. 1999)
These animals rarely live more than 13 years in the wild (Ronald Nowak 1999). One captive specimen was still alive at 20.4 years of age (Richard Weigl 2005).
Key Reproductive Features are: Iteroparous; Seasonal breeding; Gonochoric/gonochoristic/dioecious (sexes separate); Viviparous. It is not clear how protracted the mating season is for Phocoena phocoena, but it appears that mating chieflyly occurs from June to September with births occurring from May to August. It is commonly noted that gestation lasts 11 months with nursing following for another seven or eight months.
A female will give birth to one calf per year, with the birth size of the calf being six to eight kilograms and length of 0.7 to 1.0 metres. Sexual maturity is reached by the fifth year. (Johnston. 1999), (Nowak.1999)
Distribution and Movements
The IUCN Red List notes:
Harbour porpoises are found in cold temperate to sub-polar waters of the Northern Hemisphere (Gaskin 1992, Read 1999). They are usually found in continental shelf waters, although they occasionally travel over deeper offshore waters.
In the North Atlantic, they are found from the southeastern United States to southern Baffin Island (they apparently do not enter Hudson Bay) in the west, and from Senegal to Novaya Zemlya in the east. They also occur around southeast and western Greenland, Iceland, and the Faroe Islands, and this is the only cetacean species that currently regularly occupies the Baltic Sea.
This species can be found in cool temperate and sub-polar waters. Usually found in near shore waters, but occasionally over deeper waters. Found in both salt and freshwater areas, harbour porpoises require a shallow coastal natural environment, and are often found in estuaries; in fact, not only can the Common porpoise tolerate brackish estuaring waters, but is not infrequently found further up in coastal rivers and streams. In the Western Atlantic, they also move far out to sea near the end of summer and reappear in spring. Other regional populations move south or farther away from shore to avoid ice buildups. (Nowak, 1999)
Diet consists mainly of smooth, non-spiny fish, and cephalopods. Herring, pollack, hake, sardines, and cod are also common prey. Other marine organisms such as mollusks, squid and shrimp are consumed by P. phocoena. Daily dietary intake would normally consist of about five kilograms of fish biomass (around ten percent of this porpoise's body mass).
The harbour porpoise produces click-like sounds similar to those used by other cetaceans as a means of echolocation in order to locate food. (Johnston. 1999), (Nowak. 1999)
Economic Importance for Humans
Taken heavily in various areas, the meat is used for human and animal consumption, and its oil is used in lamps and as a lubricant.
Threats and Conservation Status
The IUCN Red List estimates that the global abundance of the Harbour porpoise is at least 700,000 individuals. Further:
The harbour porpoise has been hunted in many areas of its range, e.g. in Puget Sound, the Bay of Fundy, Gulf of St. Lawrence, Labrador, Newfoundland, Greenland, Iceland, Black Sea, and the Danish Belt Seas. Many of these fisheries are now closed, but hunting of Harbour porpoises still occurs in Greenland. In Greenland more than 700 per year were taken in 1990-1993 (Teilmann and Dietz 1995). In 2003 the reported catch had increased to 2320 (NAMMCO 2005). Assessments of population impacts of these takes are not available.
In the Black Sea, large directed takes occurred during 1976-1983. Within that period, the total number of harbour porpoises killed was at least 163,000-211,000. Commercial hunting of Black Sea cetaceans, including Harbour porpoises, was banned in 1966 in the former USSR (present Georgia, Russia and Ukraine), Bulgaria and Romania, and in 1983 in Turkey. Illegal direct killing of unknown numbers continued in some parts of the Black Sea until 1991 (Reeves and Notarbartolo di Sciara 2006).
Today, the most significant threat in most areas is incidental catches in fishing gear, primarily gill nets. Incidental mortality in fishing gear is likely to occur throughout the range of the species, but substantial incidental takes have been documented (summarized in Donovan and Bjørge 1995) for the Gulf of Maine (1200-2900/year), Bay of Fundy (80-400/year), West Greenland (1400/year), North Sea (4600/year), Celtic Shelf (1500/year), and also off central California during the 1980s and 1990s (tens to hundreds per year; Barlow and Hanan 1995). More recent monitoring programs of Danish set-net fisheries in the North Sea revealed an average of 5,591 porpoises taken annually in the period 1987-2001 (Vinther and Larsen 2002). However, most North Sea gill-net fisheries were not monitored for marine mammal bycatch (ICES 2002).
In the Black Sea incidental mortality in bottom-set gillnets is estimated to have been in the thousands annually through the 1980s (e.g., Birkun 2002a). Almost all (>99%) of the porpoises are caught in bottom-set gillnets. The scale of this mortality almost certainly increased in recent times owing to the rapid expansion of illegal, unreported and unregulated fishing in the Black Sea.
Other types of threats include chemical pollution, vessel traffic, anthropogenic noise, and depletion of prey by overfishing. Due to its near shore distribution, Harbour porpoises are exposed to coastal sources of pollution throughout most of the species range. Chemical pollution (PCBs) has been described as having adverse effects.
An explosion at a gas-drilling platform in the Azov Sea in August 1982 resulted in the deaths of over 2000 porpoises (Birkun 2002b). Severe habitat degradation and prey depletion caused by intensive fishing in the Black Sea, together with explosive growth of populations of invasive species are considered important threats for local Harbour porpoises (Reeves and Notarbartolo di Sciara 2006). Reduced prey availability coincided with two mass mortality events (in 1989 and 1990) that affected all three Black Sea cetacean species, but primarily harbour porpoises (Birkun 2002c). Severe pulmonary nematodosis, caused by Halocercus spp. and complicated by bacterial super-infection, was recognized as a primary cause of the deaths, which were mainly of young animals.
Although taking of Phocoena phocoena is now illegal in most areas, the species remains at risk. Deliberate and accidental deaths continue because modern fishing nets are almost undetectable to porpoises. Since these nets are commonly used in nearshore areas, in the natural range of Phocoena phocoena, they cause a high mortality to this cetacean. Various measures are being taken in the USA and other nations to limit deaths. In addition to mortality related to fishing, porpoises also suffer from chemical and noise pollution. (Dollinger. 1988), (Johnston. 1999), McWilliam. 1999), (Nowak. 1999)
IUCN Red List: Least Concern
CITES: Appendix II
Since the 1940s, there is evidence of a decline in the numbers of this species in United Kingdom (UK) waters. The main threats are thought to include entanglement in fishing nets, chemical and noise pollution, hunting, boat traffic, and lack of food.
A UK Biodiversity Action Plan priority species, the harbour porpoise is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders, 1985; it is illegal to intentionally kill, injure, or harass any cetacean (whale or dolphin) species in UK waters. The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS) has been signed by seven European countries, including the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness. Increased awareness of this species may help to secure its future.
Black Sea Harbor Porpoise
The IUCN Red List reports:
The subspecies’ range includes the Black Sea proper, Azov Sea, Kerch Strait (e.g., Tzalkin 1938), Marmara Sea, Bosphorus Strait (Öztürk and Öztürk 1997), northern Aegean Sea (Frantzis et al. 2001) and also, very likely, the Dardanelles Straits (Harun Guclusoy 2006, pers. comm. to Frantzis) connecting the Marmara and northern Aegean Seas (see Figure 1 in attached PDF). The Black Sea population is completely isolated from the nearest P. phocoena population in the northeastern Atlantic by a wide range hiatus in the Mediterranean Sea (Frantzis et al. 2001). Although there is no agreement on when it happened (Kleinenberg 1956, Frantzis et al. 2001), it is clear that Harbour Porpoises came to the Black Sea via the Mediterranean which, therefore, must have had its own population in the past.
In the 20th century, the number of Black Sea Harbour Porpoises was dramatically reduced by massive direct killing for the cetacean-processing industry that continued until 1983 (e.g. Smith 1982, IWC 2004). The numbers of animals taken were not recorded accurately; much of the catch data was recorded as numbers of animals undifferentiated to species (all three Black Sea small cetacean species were targeted) and by wet weight aggregates (e.g. pounds or tons of dolphin/porpoise landed). However, it can be inferred that the population size of P. p. relicta was reduced due to the direct kills (totalling some hundreds of thousands) by the time the total ban on dolphin hunting was enforced in the Black Sea region. It is strongly suspected that during the subsequent period from 1983-2006, not only did the population not recover but it declined markedly, primarily due to large-scale mortality in bottom-set gillnets (Birkun 2002a). In addition, there are other ongoing threats including human-induced habitat degradation. These threats are poorly managed in most Black Sea countries and therefore further decline of the population seems likely. It is also important to consider the effect on population trends of the mass-mortality events mentioned elsewhere in this assessment (gas platform explosion in 1982, die-off from ice conditions in 1993 and the two events in 1989 and 1990 possibly related to parasitic and bacterial infections).
Until 1983, unregulated hunting was the primary threat (IWC 1992, 2004). Very large numbers of harbour porpoises, as well as other cetaceans, were taken during the 20th century by all Black Sea countries for a variety of industrial uses (Kleinenberg 1956, Tomilin 1957). Although the total number killed is unknown, it may have been as many as four or five million for all species combined (e.g. see review in Smith 1982). It is widely accepted that all Black Sea cetacean populations, including Harbour Porpoises, were badly reduced by the directed fishery (IWC 1983, 1992, 2004). Catches of Harbour Porpoises were numerically fewer than those of Common Dolphins until 1964 when Harbour Porpoises became predominant (Danilevsky and Tyutyunnikov 1968, Smith 1982). Berkes (1977) reported that in Turkey, approximately 4,400 tons (4,400,000 kg) of cetaceans (all three species combined) were processed annually from 1971-73. He assumed an average weight per carcass of 50 kg (unspecified to species). Importantly, Berkes noted that shooting (the predominant method of dolphin killing in Turkey) could result in about half of the killed animals being lost due to sinking. If, following Berkes, one supposes that in the early 1970s the annual total of removals by the Turkish fishery amounted to 8,800,000 kg (including both processed and lost carcasses), or up to 176,000 animals of which >50% were Harbour Porpoises, this would imply at least 88,000 killed per year (of which 44,000 were landed). These very crude calculations suggest that Turkish catches of Harbour Porpoises in the early 1970s were at least as high as, and possibly much higher than, those estimated for 1976-1981 (34,000-44,000 per year according to IWC, 1983, assuming that harbour porpoises accounted for 80% of the total). At least since 1991, there has been no evidence of illegal directed takes although such takes had been reported before that time (IWC 1992).
At present, incidental mortality in fishing nets is the most serious threat (e.g., Birkun 2002a). Although all three Black Sea cetacean species are 'bycaught', the majority (95%) of recorded cetacean entanglements are of porpoises. Unfortunately, absolute numbers of removals cannot be estimated from the available data. However, there are indications that the annual level of Harbour Porpoise bycatch may be in the thousands. Almost all (>99%) of the porpoises are caught in bottom-set gillnets for Turbot (Psetta maeotica), Spiny Dogfish (Squalus acanthias) and sturgeon (Acipenser spp.). The peak occurs from April–June during the Turbot season in the Azov Sea and Kerch Strait and throughout the shelf area of the Black Sea, including territorial waters of all six riparian countries. Almost all (99.9%) recorded bycatches are lethal (BLASDOL 1999). Illegal, unreported or unregulated fishing is widespread in the Black and Azov Seas and a significant proportion of the bycatch may occur in such operations.
An explosion at a gas-drilling platform in the Azov Sea in August 1982 resulted in the deaths of over 2000 porpoises (Birkun 2002b).
Large-scale pelagic and small-scale coastal fisheries may affect Black Sea harbour porpoises indirectly by reducing their prey populations and degrading their habitat. Primarily, this relates to anchovies and sprats in the Black Sea and gobies in the Azov Sea. In particular, overfishing, eutrophication and the population explosion of an introduced predator, the ctenophore Mnemiopsis leidyi, led to a dramatic (8 to 12-fold) decline of sprat and anchovy abundance in the early 1990s (Prodanov et al. 1997). This reduced prey availability coincided with two mass mortality events (in 1989 and 1990) that, although they affected all three cetacean species, primarily affected porpoises (Birkun 2002c). Severe pulmonary nematodosis, caused by Halocercus spp. and complicated by bacterial super-infection, was recognized as a primary cause of the deaths, which were mainly of young animals. For other species, it has been hypothesised that malnutrition along with immuno-suppression associated with PCB contamination provokes or intensifies the effects of epizootics (e.g. Mediterranean Striped Dolphins; Aguilar and Borrell, 1994). Reported levels of DDTs and HCHs in Black Sea Harbour Porpoises are higher than those in conspecifics elsewhere in the world (Tanabe et al. 1997). Chemical pollution is thus also a potential threat, particularly in the context of epizootics.
Commercial hunting of Black Sea cetaceans, including Harbour Porpoises, was banned in 1966 in the former USSR (present Georgia, Russia and Ukraine), Bulgaria and Romania, and in 1983 in Turkey. The riparian states assumed international obligations to protect Black Sea cetaceans as contracting parties of the Convention on Biological Diversity (CBD), Convention on the Conservation of Migratory Species of Wild Animals (CMS), Convention on the Conservation of European Wildlife and Natural Habitats (Berne Convention), Convention on the Protection of the Black Sea Against Pollution (Bucharest Convention), Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, Appendix II), and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). The Harbour Porpoise, P. phocoena, is mentioned in Annex II of the EC Directive No.92/43/EEC on the conservation of natural habitats of wild fauna and flora. In 1996, the Ministers of Environment of Black Sea countries adopted cetacean conservation and research measures within the framework of the Strategic Action Plan for the Rehabilitation and Protection of the Black Sea (paragraph 62). The Harbour Porpoise is included as Data Deficient in the regional Black Sea Red Data Book (1999). However, in 2002 it was listed as Endangered in the Provisional List of Species of the Black Sea Importance, an annex to the Black Sea Biodiversity and Landscape Conservation Protocol of the Bucharest Convention.
On a national level, Black Sea cetaceans, including Harbour porpoises, are protected by environmental laws, governmental decrees and national Red Data Book listings. The harbour porpoise is listed in the Red Data Books of Bulgaria, Russia and Ukraine, which do not use the IUCN categories and criteria. In Russia and Ukraine, inscription in national Red Data Books means that the species should be monitored and managed by appropriate state/national programmes. Such a programme has existed in Ukraine since 1999 (the Delfin-programme adopted by the Ministry of Environment). Action plans for the conservation of Black Sea cetaceans were produced in Ukraine (2001) and Romania (2003) but they have no legal effect. In 2003-05 nine coastal protected areas were joined to form the Ukrainian National Network for Cetacean Conservation, an informal network consisting of 19 institutions (operational units) situated in 17 localities along the seaboard of Ukraine. Those protected areas are (from west to east): the Dunaisky [Danube] Biosphere Reserve, Chernomorsky (Black Sea) Biosphere Reserve, Swan Islands Branch of the Crimean Nature Reserve, Cape Martyan Nature Reserve, Karadag Nature Reserve, Opuk Nature Reserve, Kazantip Nature Reserve, Azov and Sivash National Park, and Meotida Landscape Park. The inventory of cetacean habitats has been completed and a common methodology for cetacean monitoring has been introduced in these protected areas. The ACCOBAMS Implementation Priorities for 2002-06 (Notarbartolo di Sciara 2002) envisage the development of a pilot conservation and management project in the well-defined area between Cape Sarych and Cape Khersones, southern Crimea (Ukraine).
Baltic Sea Harbor Porpoise (Baltic Sea Subpopulation of the North Atlantic Harbour Porpoise)
The IUCN Red List notes that "several genetic and morphometric studies have concluded that the Baltic porpoises are a separate subpopulation distinct from those living in Kattegat, Skagerrak and North Sea (e.g., Tiedeman et al. 1996, Huggenberger et al. 2002). [However, a] recent genetic study found no differences that would justify a separate Baltic subspecies (Palme et al. 2004).
The current information on abundance provides evidence for a population size of fewer than 250 mature animals in the Baltic Sea subpopulation. A continued decline in mature animals can be inferred based on the current information on bycatches. All individuals in the Baltic Sea population belong to one subpopulation.
In the Baltic Sea area the historic range apparently included all of the Kattegat/Skagerrak area, the Gulfs of Riga, Finland, and Bothnia, and much of the Baltic Sea proper. However, in the latter half of the 1900s, the range was reduced considerably, and currently porpoises are considered to be virtually absent in the north-eastern Baltic (Koschinski 2002).
The abundance of the Baltic Sea stock has been estimated at 599..., of which about 50% or 300 would likely be mature (Taylor et al. 2007)... There is evidence that porpoises in the Kattegat –Skagerrak area migrate to the North Sea (Teilmann et al. 2004).
Although there are no reliable estimates of pre-exploitation subpopulation size, harbour porpoises were once numerous in the Baltic proper (Kinze 1995).
Historically, large commercial catches occurred when porpoises migrated through the Danish Straits, mainly during winter and spring months. Annual catch levels averaged about 1,000 porpoises during most of the nineteenth century, increasing to 2,000 at the end of the century with a subsequent declining trend during the twentieth century until catches increased again in the 1940s. According to Kinze (1995), historical directed catches in the Baltic proper might have been higher than the catches in the Danish Straits.
Today, the most significant threat is incidental catches in fishing nets, primarily various types of gillnets (including both set gillnets and driftnets; Berggren 1994, Koschinski 2002). In addition to gillnets, harbor porpoises are also taken in smaller numbers in trawls (Berggren 1994). The current bycatch, known to be at least seven porpoises per year, is thought to be unsustainable, and Baltic porpoises may become extinct in the near future unless actions are taken to prevent future anthropogenic mortality (ASCOBANS 2000). Skóra and Kuklik (2003) recorded information on 62 observations of harbour porpoises in Polish waters during 1990-1999. Of these, 45 (75.6%) were reported bycaught in fishing gear, 10 observed at sea and 7 found dead on the shore. The bycatches occurred mostly in driftnets set for salmonids and bottom-set gillnets set for cod.
The annual bycatch in German Baltic fisheries is assumed to be between 3-5 porpoises (ICES 2005). Eight porpoises in Poland and two in Latvia were reported bycaught in 2003-2004 (ICES 2005). In Finland two porpoises were reported bycaught in the period 1986-1999. No bycatches were reported from Finland after 1999 (ICES 2003).v Pollution is of particular concern in the Baltic Sea where toxic compounds (in particular PCBs) have been described as the likely source for reduced fertility and population decline in Baltic Sea pinnipeds (Helle et al. 1976, Helle 1980, Bergman and Olsson 1986, Bergman 1999). Porpoises from the Baltic Sea have up to 254% higher mean levels of PCBs than corresponding samples from the Kattegat and Skagerrak (Berggren et al. 1999, Bruhn et al. 1999), and currently, a number of lesions and pathological changes are reported from the Baltic Sea porpoises (Siebert et al. 1999, Clausen and Andersen 1988), including pneumonia, liver fibrosis, arthrosis, abscesses in muscles, lungs and other organs, skin lesions and heavy attacks from parasites (Siebert et al. 1999, Clausen and Andersen 1988). Therefore, pollution cannot be excluded as a contributing factor in the past decline in abundance in the Baltic Sea. However, a recent decline of PCB concentration in Baltic Sea biota has been observed (Bignert et al. 2003).
In the North Sea incidental takes have been determined to be above the advised maximum level of removals. The European Union adopted a regulation aimed at reducing the incidental catch of small cetaceans in fisheries in European Union waters. The regulation includes measures restricting Baltic Sea drift net fisheries, providing for mandatory use of acoustic deterrent devices (pingers) in some EU gillnet fisheries in the North and Baltic Seas, and the use of onboard observers on vessels of over 15 m in length. A review of the progress of implementing resolution is scheduled for 2007.
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