BSEP116B Biodiversity in the Baltic Sea - Helcom

Number of stranded porpoises
180
160
140
120
100
80
60
40
20
0
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Figure 4.1.2. Number of stranded (including by-caught) harbour porpoises
recorded at the German Baltic Sea coast for the years 1990 to 2007.
Sources: Siebert et al., unpublished report to the Ministry for Agriculture,
the Environment and Rural Areas (2008); as well as the database of the
German Oceanographic Museum, Stralsund.
ings and strandings of harbour porpoises in the
Baltic Sea (Box 4.1.1).
Carlén (2005) reported 146 live sightings of
harbour porpoises in Swedish waters between May
2003 and September 2004, with three of these
observations located along the Swedish coast of
the Baltic Proper. In Finnish waters, a total of 23
harbour porpoise observations were reported
during 2001–2007 (Finnish Environmental Administration
2008). In Polish waters, a total of 10 sightings
was reported for 1990–1999 (Skóra & Kuklik
2003). Sighting rates in Danish and German waters
are higher in summer than in winter (Kinze et al.
2003, Siebert et al. 2006).
Annual totals of 110, 139, and 107 strandings
were reported for the Danish coasts (mostly in
the HELCOM area) for the years 2000, 2001, and
2002, respectively (Kinze et al. 2003). Along the
German Baltic coast, 11 to 158 stranded (including
by-caught) individuals were reported annually for
the years 1990–2007 (Figure 4.1.2). Skóra & Kuklik
(2003) recorded seven strandings on the Polish coast
during the years 1990–1999. Such information constitutes
minimum numbers as not all sightings and
strandings are reported. For the years 1950–2005,
the non-governmental organization Coalition Clean
Baltic for the Protection of the Baltic Sea (CCB) collated
the numbers of dead porpoises reported per
country (Table 4.1.2).
4.1.2 Factors influencing the status of
the harbour porpoise
Several types of human activities negatively influence
the status of the harbour porpoise. In recent
decades, the most important anthropogenic
threats to harbour porpoises are incidental bycatch,
prey depletion, noise pollution and chemical
toxins. Harbour porpoises have previously been
severely hunted in the Baltic region (Lockyer &
Kinze 2003).
Incidental by-catch in fishing gear is the most serious
and lethal threat to harbour porpoises (for which
reason driftnets have already been prohibited).
In general, by-catch rates depend on the fishing
methods and the fishing effort employed, whereas
the reported number of by-caught porpoises
depends largely on the awareness and cooperation
of fishermen. Currently, the minimum estimates of
by-catches (see Table 4.1.2 and Chapter 6, Fisheries)
far exceed the mortality limits for the population of
the Baltic Proper, indicating that such by-catches will
prevent recovery (Berggren et al. 2002).
Prey depletion owing to overfishing and habitat
destruction is known to lead to starvation and the
deterioration of health (e.g., MacLeod et al. 2007).
Table 4.1.2. Numbers of dead porpoises reported from the Baltic Sea by member countries to ASCOBANS in
1950–2005. Out of this, reported by-catch is given in brackets (Coalition Clean Baltic 2006).
64
Years Sweden Germany Poland Russia Lithuania Latvia Estonia Finland
1950–1959 7 (2) 8 (5) 5 (?)
1960–1969 50 (50) 14 (?) 8 (2) 1 (1) 6 (?) 25 (?)
1970–1979 7 (6) 13 (2) 6 (3) 1 (1) 10 (6)
1980–1989 35 (27) 36 (2) 7 (6) 1 (1) 1 (0) 3 (3) 1 (?)
1990–1999 17 (14) 49 (2) 62 (45) 1 (1)
2000–2005 16 (0) 40 (5) 25 (18) 2 (2) 1 (1) 17 (0)
Total 125 (97) 159 (139) 116 (79) 1 (1) 3 (2) 4 (4) 14 (?) 53 (?)