Phocoena phocoena (Linnaeus,
English: Harbour porpoise
Spanish: Marsopa común
French: Marsouin commun
Phocoena phocoena © Wurtz-Artescienza
Harbour porpoises have a short, stocky body resulting in a rotund
shape, which enables them to limit heat loss in cold northern climes.
Adult females reach a mean body length of 160cm and males only 145cm.
Mean mass is 60 kg and 50 kg, respectively (Bjorge and Tolley, 2009).
In some parts of the range, however, animals are much smaller: in
the Black Sea mean body length of adult females and males is only
133 and 123 cm, respectively, making these the smallest representatives
of the species (Gol'din, 2004).
The dorsal side is dark grey, while the belly is a contrasting
light grey to white which sweeps up to the midflanks in a mottled
pattern. There is a dark stripe from the mouth to the flippers.
The small triangular dorsal fin and the characteristic swimming
pattern of several short, rapid surfacings followed by an extended
dive of several minutes are characteristic for this species. Whereas
early morphological studies suggested a close relationship of the
harbour porpoise with P.
sinus and P.
spinipinnis, recent genetic information suggests that the
closest relative of the harbour porpoise is in fact Dall's porpoise,
dalli (Bjorge and Tolley, 2009). There is molecular and
morphological evidence of frequent hybridization between free-ranging
Dall's and harbour porpoises (Willis et al. 2004).
Harbour porpoises are found in cool temperate and subpolar waters
of the Northern Hemisphere (Jefferson et al. 1993). Significant
differences in the skulls of P. phocoena from the North Atlantic,
the western North Pacific, and the eastern North Pacific have been
found and two subspecies are recognised, one in the Atlantic and
one in the Pacific. However, western Pacific animals differ sufficiently
from those in the eastern Pacific to warrant subspecific separation,
although no species-group name has been based on a western Pacific
specimen (Rice, 1998 and refs. therein).
Distribution of the four subspecies of Phocoena
phocoena: cold temperate and subarctic
waters of the Northern Hemisphere (Hammond et al. 2008a; IUCN; enlarge
P. p. phocoena is distributed in the North Atlantic Ocean and
ranges on the western side from Cumberland Sound on the east coast
of Baffin Island, south-east along the eastern coast of Labrador
to Newfoundland and the Gulf of St. Lawrence, thence south-west
to about 34°N on the coast of North Carolina; it is also found
in southern Greenland, north to Upernavik on the west coast and
Angmagssalik on the east coast. In the eastern Atlantic, its range
includes the coasts around Iceland; the Faroes; and the coasts of
Europe from Mys Kanin and the White Sea in northern Russia, west
and south as far as Cabo de Espichel, Portugal (38°24'N), including
parts of the Baltic Sea and the British Isles. An apparently isolated
population ranges along the coast of West Africa from Agadir (30°30'N),
Morocco, south to Joal-Fadiouth (14°09'N), Senegal (Van Waerebeek
et al., 2000); its members appear to attain a greater body length
than European individuals. (Rice, 1998 and refs. therein). In the
Gulf of Bothnia and the Gulf of Finland, both in the Baltic Sea,
the species is no longer observed (Koschinski, 2002). P. p. phocoena
is vagrant along the arctic coast east to Novaya Zemlya and Mys
Bolvanskiy (Rice, 1998). It has also been observed in Svalbard (Joergensen,
2007). The species is mostly absent from the Mediterranean, except
for former, or sporadic, occurrences in the western part (Strait
of Gibraltar, Islas Baleares, Barcelona, and Tunisia; Rice, 1998).
Genetic analysis shows that movements of harbour porpoises across
the Atlantic appear to occur at a low level (Rosel et al. 1999)
and harbour porpoises from West Greenland, the Norwegian West coast,
Ireland, the British North Sea, the Danish North Sea and the inland
waters of Denmark (IDW) are all genetically distinguishable from
each other (Andersen et al. 2001). In a more recent review, Evans
et al (2009) suggest subdivision of the North Atlantic into the
following stocks or subpopulations: 1) Gulf of Maine & Bay of
Fundy; 2) Gulf of St Lawrence; 3) Newfoundland; 4) West Greenland;
5) Iceland; 6) Faroe Islands; 7) Northwest/Centralwest Norway &
Barents Sea; 8) Northeastern North Sea & Skagerrak; 9) Southwestern
North Sea & Eastern Channel; 10) Inner Danish Waters; 11) Baltic
Sea; 12) Celtic Sea (plus South-west Ireland, Irish Sea & Western
Channel); 13) North-west Ireland & West Scotland; 14) Bay of
Biscay (West France); 15) IBNA (NW Spain, Portugal & NW Africa).
P. p. relicta is another geographically disjunct population
which inhabits the Black Sea, the Sea of Azov, the Bosporus, and
the Sea of Marmara (Rice, 1998), with at least four individuals
reported in the northern Aegean Sea (Rosel et al. 2003). Analyses
of geographic variation in mitochondrial DNA (mtDNA) support the
existence of this subspecies (Read, 1999). Viaud-Martinez et al.(2007)
found that the morphologically different Black Sea population has
been genetically separated from eastern Atlantic populations for
thousands of years, warranting its classification as a subspecies.
P. p. subsp. occurs in the Western North Pacific Ocean.
It ranges from Olyutorskiy Zaliv south along the east coast of Kamchatka,
including Komandorskiye Ostrova and the Near Islands in the western
Aleutian Islands, throughout the Ostrova Kuril'skiye, and all around
the shores of the Sea of Okhotsk, including Zaliv Shelikhova, Hokkaido,
and Honshu as far as Nishiyama on the west coast and Taiji on the
east. A distributional gap in the Aleutian Islands between Shemya
and Unimak separates this race from the next. P. p. subsp. is vagrant
north through Bering Strait as far as Ostrov Vrangelya (Rice, 1998).
P. p. vomerina Gill, 1865 is distributed in the Eastern North
Pacific Ocean and ranges from the Pribilof Islands, Unimak Island,
and the south-eastern shore of Bristol Bay south to San Luis Obispo
Bay, California. P. p. vomerina is vagrant north to Point Barrow
in Alaska, and the mouth of the Mackenzie River in the Northwest
Territories of Canada, and south to San Pedro in Southern California.
3. Population size
There are no synoptic surveys covering the entire range within
ocean basins, but abundance has been estimated for selected portions
of the range. Taken together, these numbers indicate that the global
abundance of the harbour porpoise is at least about 700,000 individuals
(Hammond et al. 2008).
Note that all abundance estimates have to be taken with a grain
of salt: According to Read (1999) there was an 80% discrepancy between
abundance estimates for the Gulf of Maine in 1991 and 1992 (37,500
as opposed to 67,500, respectively). Similarly, aerial surveys conducted
in 1995 and 1996 in the German North Sea revealed a mean abundance
of 4,288 in 1995 and 7,356 harbour porpoises in 1996 (Siebert et
al. 2006). In the south-western Baltic Sea, abundance estimates
varied between 457 (CV 0.97, March 2003) and 1,726 (CV=0.39, June
2003) (Scheidat et al. 2008).
The factors responsible for this variation may be related to migratory
behaviour in response to changes in water temperature or prey availability
on a regional scale, but are not fully understood. Methodology also
plays a role: Carretta et al. (2001) estimated the abundance of
harbour porpoises in northern California at 5,686 from a November
1995 ship survey. However, this abundance estimate was significantly
different from an aerial survey estimate obtained 1 to 2 months
earlier in the same region, where abundance was estimated at 13,145.
A possible explanation was insufficient transect effort during the
ship survey, or underestimates of the fraction of porpoise groups
missed on the trackline due to large swells.
From North to South: The estimated corrected abundance estimate
for the Bering Sea harbor porpoise stock from a 1999 aerial survey
is 48,215 (CV = 0.223). No fishery-related harbour porpoise mortalities
were observed during the 2002-2006 period (Angliss and Allen 2008a).
For the Gulf of Alaska the estimated corrected abundance estimate
from a 1998 aerial survey is 31,046 (CV = 0.214) (Angliss and Allen
2008b). Fishery related mortalities extrapolate to an estimated
mortality level of 35.8 animals per year (Manly 2007).
The Southeast Alaska estimated corrected abundance based on a 1997
aerial survey is 11,146 (CV = 0.242). No incidental fishery-related
mortalities were reported (Angliss and Allen, 2008c).
Between the British Columbia (BC)-Washington and the BC-Alaska
borders, surveys conducted in 2004 and 2005 yield an abundance estimate
of 9,120 (95% CI = 4,210-19,760) (Williams and Thomas, 2007).
For the inside waters of Washington and southern British Columbia,
aerial surveys conducted during August of 2002 and 2003 led to an
estimate of 10,682 (CV=0.38) animals. For coastal Oregon (north
of Cape Blanco) and Washington waters the corrected estimate of
abundance, based on a 2002 aerial survey from shore to 200 m depth
is 37,745 (CV=0.38). The mean estimated mortality for the gillnet
fishery in 1999-2003 is 0.6 harbour porpoise per year.(Carretta
et al. 2009).
The northern California/southern Oregon stock was estimated from
pooled 1997-99 aerial survey data including data from both inshore
and offshore areas, yielding an abundance estimate of 17,763 (CV=0.39).
The Monterey Bay and the Morro Bay stock were estimated from 1999
and 2002 aerial surveys at 1,613 (CV = 0.42)and 1,656 (CV = 0,39)
animals, respectively (Carretta and Forney, 2004).
Based on pooled 1995-99 aerial survey data, an updated estimate
of abundance for the central
California harbour porpoise stock is 7,579 harbour porpoises (CV=0.38;
NMFS, K. Forney, unpublished data; Carretta et al. 2009).
Abundance estimates are lacking for the western Pacific Ocean (Hammond
et al. 2008).
The best current abundance estimate of the Gulf of Maine/Bay of
Fundy harbour porpoise stock is 89,054 (CV=0.47), based on the 2006
survey results (Waring et al. 2009).
In Greenlandic waters the harbour porpoise has been observed around
in the south from Ammassalik on the east coast to Avanersuaq in
northwest Greenland. The main distribution lies between Sisimiut
and Paamiut in central west Greenland (Teilmann and Dietz, 1998).
There are no available abundance estimates for the Greenland harbour
porpoise stock (NAMMCO, 2009).
A survey conducted in the eastern North Atlantic in July 2005 (SCANS
II), covering continental shelf seas from SW Norway, south to Atlantic
Portugal, gave an estimate of 385,600 (CV = 0.20) (Hammond et al.,
2008), with regional estimates: North Sea (c. 231,000), Baltic (23,000
in Kattegat/Skagerrak/Belt Seas/Western Baltic Sea), Channel (40,900),
and Celtic Shelf (58,400). From line transect surveys in July 1994
(Hammond et al., 2002), with a somewhat different coverage, population
was estimated at 341,000 porpoises (CV=0.14; 95% CI: 260,000-449,000):
North Sea (c. 250,000), Baltic region (36,600 in Kattegat/Skagerrak/Belt
Seas/Western Baltic Sea), Channel (0), and Celtic Shelf (36,300).
Comparing the two surveys, although the overall number estimated
for the North Sea, Channel and Celtic Sea was comparable (341,000
in 1994, and 335,000 in 2005), numbers in the northern North Sea
and Danish waters had declined from 239,000 to 120,000, whereas
in the central and southern North Sea, Channel and Celtic Shelf,
they had increased from 102,000 to 215,000. This is thought to represent
a southwards range shift rather than actual changes in population
size (Winship, 2009), at least for the month of July. This is consistent
with recent studies using stranding data and observations from seabird
surveys indicating a comeback of the species along the Dutch and
Belgian coast (Laczny and Piper, 2006; Haelters and Camphuysen,
In the Skagerrak / Kattegat region between the Baltic and the North
Seas, 36,046 (CV = 0,34); 5,262 (CV = 0,25) were estimated (Hammond
et al. 2002). Teilmann et al. (2003) used satellite transmitters
on animals in Skagerrak/North Sea and in Inner Danish Waters. Throughout
the year there was no overlap in the home range of adult porpoises
tagged in the two areas, respectively. The authors suggest a population
boundary in the northern Kattegat across the Danish island of Læsø.
This population structure is confirmed by genetic studies of all
ages during the summer season (Teilmann et al., 2003; 2008).
Harbour porpoises were also once numerous in the Baltic Sea south
and east of the Belt region but today the population is estimated
in the low thousands. Scheidat et al. (2008) give combined estimates
for the German EEZ south in Kiel Bight, Mecklenburg Bight and the
German waters of the Baltic proper ranging between 457 (March 2003;
CV = 0.97) and 4610 (May 2005; CV = 0.35). The abundance in Kiel
Bight was estimated at 588 (CV= 0,48) from 1994 data, with a density
of 0.101 ind/km² (Hammond et al. 2002), of which about 50%
or 300 would likely be mature (Taylor et al. 2007). Recent density
estimates are somewhat higher, with 0.13 ind/km² in July 2004
(Scheidat et al. 2008).
Between Kiel and Mecklenburg Bights the relative abundance of porpoises
decreases continuously (Gillespie et al. 2003), from 16.2 acoustic
detections/100-km in the northern Kiel Bight, 9.2/100km in the southern
Kiel Bight, and 2.8/100km in the Mecklenburg Bight to only 0.1/100km
in the Baltic proper. During visual surveys, porpoises were only
sighted in Kiel Bight. These results are consistent with Scheidat
et al. (2008) who found similar densities in Kiel Bight: 0.13 ind/km²
(95% CI = 0.02 - 0.38) and Mecklenburg Bight: 0.178 ind/km²
(95% CI = 0.007 - 0.41) in July 2004, but only 0.008 ind/km²
(95% CI = 0-0.03) in the Pomeranian Bight further east. The latter
confirms earlier estimates of 599 individuals for an area around
the Island of Bornholm determined in 1995 by L. Hiby and P. Lovell
(pers. comm. to Scheidat et al. 2008), corresponding also to a density
of roughly 0.09 ind/km². A survey of Polish coastal waters
conducted in 2001 using the same acoustic equipment, which found
0.05 detections/100km (Gillespie et al. 2003).
Kilian et al. (2003) support these findings using autonomous click
detectors (PODs): Around the island of Fehmarn, harbour porpoise
click trains were recorded almost every day, whereas along the east
coast of the island of Rügen, only few porpoise encounters
were collected. Nevertheless, for most areas investigated, porpoises
were present regularly. Verfuss et al. (2007) also noted a significant
decrease from west to east in the percentage of days with POD porpoise
detections. There were more days of porpoise detections in summer
than in winter, suggesting that the German Baltic Sea is an important
breeding and mating area for these animals. Scheidat et al. (2003)
report that on the Oderbank east of Rügen, Baltic harbour porpoise
concentrations between May and August 2002 were very high with 0.086
animals per km aerial transect, as opposed to 0.014 and 0.024 in
nearby Mecklenburg and Kiel Bights, respectively. The reason for
this high density in the area of the Oderbank could be foraging
behaviour (S. Koschinski, 2010, pers. comm.).
The results of several surveys conducted between 2001 and 2005 in
the Black Sea suggest that present total population size is at least
several thousands and possibly in the low tens of thousands (Hammond
et al. 2008): 2,922 (95% CI = 1,333 - 6,403) in the Azov Sea (Birkun
et al. 2002); 1,215 (95% CI = 492-3,002) in the northern, north-eastern
and north-western Black Sea (Birkun et al. 2004), 3,565 (95% CI
= 2,071-6,137) in the south-eastern Black sea (Birkun et al. 2006)
and 8,240 (95% CI = 1,714 - 39,605) in the central Black Sea (Krivokhizhin
et al. 2007).
4. Biology and Behaviour
Habitat: Throughout its range, P. phocoena is limited
to the waters of the continental shelf by its demersal foraging
behaviour and diving capacity (see below). In northern California
significantly more porpoises than expected occurred at depths of
20 to 60m as opposed to depths beyond 60 m (Carretta et al. 2001).
Harbour porpoises are seldom found in waters with an annual average
temperature above 17°C, preferring cool waters, where aggregations
of prey are concentrated (Read, 1999 and refs. therein).
In the Horns Reef area, eastern North Sea, small-scale changes in
local currents reflecting upwelling driven by the interaction of
the semi- diurnal tidal currents with the steep slopes of the bank
are the main habitat driver of harbour porpoises. The distribution
of harbour porpoises alternates between 2 upwelling cells less than
10 km large, depending on the direction of tidal currents (Skov
and Thomsen, 2008). Similarly, at Morte Point in North Devon, UK
porpoises are found to aggregate in an area of high tidal flow,
where prey items are likely to be abundant (Goodwin, 2008).
Fine-scale distribution in the Bay of Fundy was influenced by tides
and prey availability. Whereas over the course of a month individuals
ranged across large areas (7,738 to 11,289 km²), they also
concentrated their movements in small focal regions (August-September
mean = 250 - 300 km² ) close to islands, headlands, or restricted
channels, where density was significantly larger during flood than
ebb tide and associated to prey aggregations along localized fronts
(Johnston et al. 2005).
Behaviour: The harbour porpoise is difficult to observe.
It shows little of itself at the surface, so a brief glimpse is
the most common sighting. On calm days it may be possible to approach
a basking animal, but it is generally wary of boats and rarely bow-rides.
It can sometimes be detected by the blow which, although rarely
seen, makes a sharp, puffing sound rather like a sneeze (Carwardine,
1995). Observations from cliffs above calm fjords yield the best
results (Culik et al. 2001).
Harbour porpoise Photo © Boris Culik
Schooling: Most harbour porpoise groups are small, consisting
of fewer than 8 individuals (pers. obs.). They do, at times, aggregate
into large, loose groups of 50 to several hundred animals, mostly
for feeding or migration (Jefferson et al. 1993). Harbour porpoises
are not generally found in close association with other species
of cetaceans and instead are observed to avoid bottlenose dolphins
truncatus) due to aggressive and lethal interactions (Read,
Reproduction: Most calves are born from spring through mid-summer
(Jefferson et al. 1993). The majority of female harbour porpoises
in Denmark and the Bay of Fundy become pregnant each year and are
simultaneously lactating and pregnant for much of their adult lives.
In contrast, female porpoises in California do not appear to reproduce
each year (Read, 1999 and refs. therein). In Aberdeenshire, North
Sea, Scotland most porpoise calves and juveniles were recorded between
June and September, when 35% of harbour porpoise groups contained
immature animals. The proportion of calves amongst porpoise sightings
was higher during June than any other month (Weir et al. 2007).
Sexual maturity is reached at the age of 3 years and gestation lasts
approximately 10.5 months. The life span is on average 8 to 10 years,
the oldest documented individual was 23 years old (Bjorge and Tolley,
Food: Harbour porpoises eat a wide variety of fish and cephalopods,
and the main prey items appear to vary on regional and seasonal
scales (Jefferson et al. 1993). In the North Atlantic, harbour porpoises
feed primarily on clupeoids and gadoids, while in the North Pacific
they prey largely on engraulids and scorpaenids. Squids and benthic
invertebrates have also been recorded, the latter considered as
secondarily introduced (Reyes, 1991 and refs. therein). Individual
prey are generally less than 40cm in length and typically range
from 10cm to 30cm in length (Read, 1999).
Many prey items are probably taken on, or very close to, the sea
bed. Even though a wide range of species has been recorded in the
diet, porpoises in any one area tend to feed primarily on two to
four main species (e.g. whiting Merlangius merlangus and
sandeels (Ammodytidae) in Scottish waters). The literature on porpoise
diets in the northeast Atlantic suggests that there has been a longterm
shift from predation on clupeid fish (mainly herring Clupea harengus)
to predation on sandeels and gadoid fish, possibly related to the
decline in herring stocks since the mid-1960s. Evidence from studies
on seals suggest that such a shift could have adverse health consequences.
Food consumption brings porpoises into contact with two important
threats - persistent organic contaminants and fishing nets, both
of which have potentially serious impacts (Santos et al. 2003; Santos
et al. 2004).
In the Kattegat and Skagerrak stomach contents of juvenile and
adult harbour porpoises contained mostly Atlantic herring (Clupea
harengus) while Atlantic hagfish (Myxine glutinosa) was
also important for adults (Boerjesson et al., 2003). In another
study on animals stranded and by-caught in Denmark, cod (Gadidae),
viviparous blenny (Zoarcidae) and whiting (Gadidae) made up most
of the stomach contents while in the Netherlands whiting was the
main prey, making up around 34 % of the total reconstructed prey
weight (Santos et al. 2005).
In Danish waters, maximum dive depth generally does not exceed
50m, corresponding to the depth of the Belt seas and Kattegat. Maximum
dive depth recorded was 132 m from animals moving north into Skagerrak.
Dives were frequently recorded in the category 10-15 min, and harbour
porpoises dive continuously both day and night, with peak activity
during daylight hours (Teilmann et al. 2007). Dives to at least
226 m have been recorded via telemetry in other areas (Westgate
et al. 1995).
According to Read (1999) porpoises in each of the Bay of Fundy-Gulf
of Maine, Gulf of St. Lawrence, Newfoundland and Labrador, and Greenland
populations move into coastal waters during summer. In some areas,
harbour porpoises move offshore to avoid advancing ice cover during
winter. According to Gaskin et al. (1993) seasonal harbour porpoise
migrations, especially in and out of the Sea of Okhotsk, must occur
because of extensive ice coverage in winter, but in Japanese waters
there are confirmed records of porpoises as far north as the northern
tip of Hokkaido Island in January.
In the western North Atlantic, harbour porpoises arrive in the Bay
of Fundy area in July, staying there until approximately late September.
There is little evidence that the region may be significant either
as a mating area or a calving ground. The arrival of females with
calves coinciding with the arrival of juvenile herring is more suggestive
of a feeding ground (Reyes, 1991 and refs. therein). Trippel et
al. (1999) noted in a by-catch study in the lower Bay of Fundy that
during years of low herring abundance, low harbour porpoise entanglement
rates are observed. This suggests harbour porpoise movements matched
the migratory behaviour of one of their preferred prey species.
Long-term studies using satellite-linked radio telemetry indicate
that porpoises are extremely mobile and are capable of covering
large distances in relatively short periods, with mean daily distance
travelled varying between 14 - 58 km. Animals move throughout the
Bay of Fundy and Gulf of Maine, utilising home ranges that encompass
tens of thousands of km² and suggesting that they form a single
population at risk of entanglement in both Canadian and US fisheries
(Read and Westgate, 1997).
Observations gathered from surveys off New Hampshire suggest this
may be part of the wintering areas for the Bay of Fundy population,
which may have a north-south (and inshore-offshore) seasonal migration
limited to the continental shelf in the eastern seaboard (Reyes,
1991 and refs. therein). Stranding data from the North Carolina
coast confirm that harbour porpoises typically strand during the
winter and spring months during migrations (Webster et al. 1995).
For the Baltic Sea, Koschinski (2002) summarised that 1) there might
be a tendency of animals from the Kattegat to migrate into the North
Sea during winter months; 2) a proportion of animals may stay in
the western Baltic during the winter or even in the Baltic proper;
3) there might be a difference in migratory tendency between putative
subpopulations; and finally 4) migration patterns might depend on
winter severity. Verfuss et al. (2007) identified the Kadet Trench
and Fehmarn Belt as important migration corridors.
Satellite telemetry revealed that in a few cases subadult porpoises
tagged in the inner Danish waters moved into the Skaggerak/North
Sea while only one of the tagged porpoises moved into the Baltic
proper for a short visit (Teilmann et al. 2003). Teilmann et al.
(2008) satellite-tagged 24 porpoises on the border between Skagerrak
and Kattegat on the northern tip of Denmark (Skagen, Jylland) and
39 in Kattegat, Little Belt, Great Belt or Western Baltic (Inner
Danish Waters, IDW) from 1997 to 2007. All animals from the northern
group stayed in the northern Kattegat or in the Skagerrak and North
Sea (including the EEZ of Norway and Sweden). Porpoises tagged in
IDW stayed south of this area (including the EEZ of Germany, Sweden
and Poland) except for five animals. Three of these stayed the majority
of time in IDW and the other two animals moved immediately after
tagging into the Skagerrak and North Sea and stayed there for the
entire contact period. Based on these data, Teilmann et al. (2008)
propose that the Danish waters be divided into four management areas
for harbour porpoises 1) southern North Sea, 2) northern North Sea
and Skagerrak, 3) Inner Danish Waters and Kattegat and 4) The Baltic
The Black Sea population is isolated, but there are a few records
of P. p. relicta from the Aegaean Sea, showing that at least
some parts of the population may migrate (Rosel et al. 2003).
Direct catch: Directed fisheries have occurred in Puget
Sound, the Bay of Fundy, Gulf of St. Lawrence, Labrador, Newfoundland,
Greenland, Iceland, Black Sea, and the Baltic Sea. Many of these
fisheries are now closed, but hunting of harbour porpoises still
occurs in a few areas. Greenland and the Black Sea are the only
areas where large direct catches have been reported within the last
20 years (Jefferson et al. 1993). According to Reyes (1991) around
1,000 porpoises were taken annually in West Greenland using rifles
and hand-thrown harpoons. Harbour porpoises are mainly caught between
April and November, with a peak during June to October (Teilmann
and Dietz, 1998). In 2003 the reported catch had increased to 2,320
(NAMMCO 2005); reported takes were 3,100 in 2005 and 2,563 in 2006;
without any abundance estimates on population size or potential
biological removal levels, these numbers are a matter of concern
(NAMMCO 2009). Hunting on a small scale also still occurs in Japan,
Canada and the Faroe Islands.
In the Baltic Sea, historical catch levels averaged about 1,000
porpoises per year 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. Historical directed catches in the Baltic proper might have
been higher than the catches in the Danish Straits (Kinze, 1995).
Due to the resulting low abundance, the current bycatch, known to
be at least 7 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
In the Black Sea, unregulated hunting was the primary threat until
1983, (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. 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
(Birkun and Frantzis, 2008).
Incidental catch: Due to their habitat in productive coastal
waters, harbour porpoises are captured incidentally in commercial
fisheries throughout their range. Porpoises are taken in a variety
of gear types including weirs, pound nets, cod traps, purse seine
nets and surface gill nets, but the vast majority of this mortality
occurs in bottom-set gill nets.
In Newfoundland gillnet fisheries, incidental catches of small cetaceans
were estimated to be 862 in 2001, 1,428 in 2002 and 2,228 in 2003,
virtually all of which were harbour porpoises. Most by-catches were
reported in the nearshore cod fishery, although there were also
numerous reports of catches in fisheries for lumpfish, herring and
Greenland halibut and in offshore fisheries for monkfish, white
hake and Greenland halibut. Most incidental catch events occurred
during July-September along the south coast (Benjamins et al. 2007).
In the gillnet fishery of the Estuary and Gulf of St. Lawrence,
Canada, a questionnaire survey provided bycatch estimates of 2,215
(95% CI 1,151-3.662) and 2,394 (95% CI 1,440-3,348) porpoises in
2000 and 2001, respectively. Although these numbers are very high,
they indicate a 24-63% reduction in bycatch since the late 1980s
(Lesage et al. 2006).
Bycatches in herring weirs in the Bay of Fundy, Canada varied between
eight in 1996 to 312 in 2001 (Neimans et al. 2004).
In Icelandic waters, harbour porpoise by-catches numbered 120 in
2006 and 147 in 2007 (NAMMCO, 2009).
The annual bycatch of harbour porpoise in the Danish North Sea
bottom-set gillnet fisheries was estimated to have been in the range
of 2,867-7,566 between 1987-2001, with a significant reduction in
the most recent years due to a decrease in both effort and landings
(Vinther and Larsen, 2004).
A distinct increase in the numbers of strandings of porpoises showing
lesions indicative of bycatch along the Dutch and Belgian coastline
has occurred in recent years, in parallel to the increasing number
of porpoises sighted in the southern North Sea (Haelters and Camphuysen,
2008). By-catch and drowning were noted most frequent in winter
and spring. By-catch and drowning rate was responsible for 7 - 19
% of deaths similar to the statistics in neighbouring countries
(Osinga et al. 2008).
Kuklik and Skóra (2003) report that in Polish waters of the
Baltic Sea, by-catch occurred mostly in so-called salmon "semi-driftnets"
and cod bottom-set nets, amounting to 62 by-catch reports between
1990 and 1999. Berggren et al. (2002) estimated potential limits
to anthropogenic mortality for harbour porpoises in the Baltic region
and concluded that immediate management action is necessary to reduce
the magnitude of by-catches to meet the conservation objectives
of ASCOBANS, the Agreement on the Conservation of Small Cetaceans
in the Baltic and North Seas. In German Baltic Sea waters low by-catch
numbers are reported (8 individuals reported in 2008, IWC 2009).
However, between the years 2000 and 2007, strandings have increased
dramatically from 25 to 173. A large proportion of these animals
has net marks or cuts indicating a vast majority of unreported cases
(Herr et al. 2009; Koschinski and Pfander, 2009).
In northern Portuguese waters (Ferreira et al. 2003) confirmed
bycatch was responsible for 34% of all strandings and up to 18%
of the deaths were suspected to have been caused by interactions
with artisanal fishing gear. This coastal area is used by harbour
porpoises as an important feeding and breeding site, thus making
bycatch a serious threat to the species. Up to 53% of all harbour
porpoise strandings recorded involved animals caught in beach purse-seine
nets. Despite limited monitoring effort, by-catches of harbour porpoises
have also been documented in artisanal gillnet fisheries in Senegal
(Van Waerebeek et al., 2000).
Baker et al. (2006) report on detecting by-caught harbour porpoises
through molecular monitoring of 'whalemeat' markets in the Republic
of (South) Korea, based on nine systematic surveys from February
2003 to February 2005.
There is some hope that acoustic deterrents may help to reduce
by-catch rates in gillnets in certain fisheries, provided foraging
harbour porpoises can find prey in pinger- as well as net-free areas
(Culik et al. 2001). These devices are now mandatory in Danish gillnet-fisheries
around wrecks (Finn Larsen, pers. comm.) as well as in the North
and Celtic Seas, the German Baltic Sea between Warnemünde and
the Polish border and in 2 areas in Swedish Baltic for gillnet vessels
over 12 m length (EU Regulation 812/2004). Another solution may
lie in using enticing sounds, i.e. of alerting porpoises to nets
rather than attempting to deter them. Koschinski et al. (2003) and
Eskesen et al. (2003) report that certain sounds trigger investigative
behaviour, echolocation activity increasing by 70-130% to investigate
the sound source. This may help in alerting them to otherwise "invisible"
nets. However, a field study by Kindt-Larsen (2008) concluded that
a pinger producing porpoise-alerting-sounds based on porpoise clicks
did not reduce bycatch. The author does not exclude, however, the
possibility that an alerting pinger which succeeds in stimulating
porpoises to a higher click rate may achieve this.
Another possibility for the reduction of by-catch is the use of
acoustically reflective nets. High-density iron-oxide (IO) gillnets
proved to be effective in reducing by-catch while catches of target
species (cod) were reduced by as much as 30%. However, both effects
were attributed to the mechanical properties of the net material
rather than to acoustic reflectivity (Larsen et al. 2007). However,
Mooney et al (2004) and Koschinski et al. (2006) found that in an
acoustically enhanced Barium-Sulfate net, acoustic target strength
was higher at 150 kHz than in a standard nylon net. Koschinski et
al. (2006) conclude that harbour porpoises can detect the enhanced
net 4.4 m in advance of standard nylon nets. However, because porpoises
were found to often swim without echolocating, the authors suggest
using a combination of reflective nets and warning sounds.
The most promising means for elimination of by-catch is the closure
of important areas for certain fisheries and a shift to porpoise
friendly gear such as baited pots and jigging reels, in some cases
Overfishing: Large scale fisheries operating in the North
Sea take are targeted at species which are important prey items
for harbour porpoises. A similar situation occurs with the commercial
fisheries for horse mackerel and anchovy in the Black Sea (Reyes,
1991 and refs. therein). Independent of fishery-related data, stable
isotope analysis from harbour porpoises tissue collected prior to
and after the 1960's in the North Sea indicates that lately they
have been feeding at a lower trophic level than during the preceding
century (Christensen et al. 2008) and this may also be reflected
in the available recent stomach content analyses.
Climate change: One of the prey items of harbour porpoises
in the Scottish North Sea, sandeels, are known to be negatively
affected by climate change in a number of ways. When porpoise diet
from spring 2002 and 2003 was compared to baseline data of 1993-2001,
the diet was found to be substantially different, with a significant
and substantially smaller proportion of sandeels being consumed
in March and May. Whereas 33% of stranded (?) porpoises died of
starvation in spring 2002 and 2003, only 5% did so during the baseline
period, suggesting that the negative effects of climate change on
sandeel availability may have serious negative effects on harbour
porpoise populations (MacLeod et al. 2007).
Pollution: A considerable body of literature exists describing
the levels of various pollutants in tissues of the harbour porpoise.
Contaminant levels in harbour porpoises often vary geographically
and may serve as useful markers in studies of population structure
(Read, 1999 and ref. therein, Koschinski, 2002).
Pesticides, plasticisers, flame retardants (such as PBDEs BPA and
HBCD) and trace metals are of special concern due to their bioaccumulative
or endocrine disrupting potential.
In 48% of all samples, concentrations of polychlorinated biphenyls
(PCBs) in blubber of female harbour porpoises from the Atlantic
coast of Europe were above the threshold at which effects on reproduction
could be expected. This rose to 74% for porpoises from the southern
North Sea. The average pregnancy rate recorded in porpoises (42%)
in the study area was lower than in the western Atlantic. Porpoises
that died from disease or parasitic infection had higher concentrations
of persistent organic pollutants (POPs) than animals dying from
other causes (Pierce et al. 2008). Perfluorooctane sulfonate (PFOS)
contamination in samples from the German Baltic Sea and from coastal
areas near Denmark are comparable to levels found in Black Sea harbour
porpoises and might pose a threat to these populations (Van de Vijver
et al. 2007).
Furthermore, as opposed to a series of other local top-predators,
harbour porpoises in Danish coastal waters contained the highest
hepatic concentrations of butyltin, an antifouling agent in ship
paint, with (134-2283 ng/g ww), indicating a strong degree of bio-magnification
in the food chain (Strand et al. 2005).
Noise pollution: Harbour porpoises react very sensitively
to anthropogenic noise. Consequently, shipping, marine exploration,
construction and operation of noisy equipment such as sonar are
likely to affect the behaviour and distribution of the species.
Dense maritime traffic e.g. was correlated with reduced harbour
porpoise density in the North Sea (Herr et al. 2005). Furthermore,
there are many areas where ammunition was dumped at sea. Underwater
detonations, e.g. from ammunition removal, mine diver training,
ship shock trials, closure of drill holes and other military or
civil applications can seriously harm harbour porpoises due to extremely
strong pressure changes created by the shock wave (S. Koschinski,
2010, pers. comm..)
The planned construction of offshore wind turbines in the North
and Baltic Seas involves the emission of high numbers of intense
impulsive sounds when turbine foundations are driven into the ground
by impact pile driving, evoking at least a temporary threshold shift
(TTS) in the auditory system of harbour porpoises (Lucke et al.
2008). Cumulative effects of multiple pulses must be considered
(Southall et al. 2007). During operation of the offshore turbines,
available data indicate that the potential masking effect would
be limited to short ranges in the open sea (Koschinski et al. 2003).
Range states (Hammond et al. 2008) :
Belgium; Bulgaria; Canada; Cape Verde; China; Denmark; Estonia;
Faroe Islands; Finland; France; Georgia; Germany; Gibraltar; Greenland;
Iceland; Ireland; Japan; Latvia; Lithuania; Mauritania; Morocco;
Netherlands; Norway; Poland; Portugal; Romania; Russian Federation;
Senegal; Spain; Sweden; Tunisia; Turkey; Ukraine; United Kingdom;
USA; Western Sahara.
The species is listed in Appendix II of CITES. The Baltic Sea and
Black Sea, the western North Atlantic and the North West African
populations are listed in Appendix II of CMS.
The IUCN considers the species as "Least Concern" with
the exception of the Baltic Sea (Critically endangered) and Black
Sea (Endangered) populations (Hammond et al. 2008a). This is justified
by all individuals in the Baltic Sea population belonging to one
subpopulation, which numbers fewer than 250 mature animals. A continued
decline can be inferred based on the current information on bycatches
(Hammond et al. 2008b).
In the Black Sea, large directed takes between 1976 and 1983, intensive
mortality as by-catch in fisheries, large numbers of casualties
attributed to the petrochemical industry, epidemics, and ice entrapments,
and a general degradation of the environment have led to a reduction
in population size of 70% over the past 30 years (Birkun and Frantzis,
There have been several reports of decline of harbour porpoise
populations in various parts of the range. The low abundance of
porpoises observed around Japan may be the result of overhunting
or incidental catches in the past (Reyes, 1991 and refs. therein).
Acknowledgement: We are grateful to Sven Koschinski for kindly
reviewing this species summary.
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© Maps by IUCN.