BSEP116B Biodiversity in the Baltic Sea - Helcom

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Number of individuals 12000 10000 8000 6000 4000 2000 Ground Air Expon. (Ground) y = 3E-64e 0,0773x 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 Figure 4.2.2. Numbers of grey seals counted from ground level along the Swedish coast. The annual rate of increase was 8% up to 2005. Surveys from air, started in 2006, give higher point estimates. Equation given for exponential (Expon.) curve fit. the 1750s. Harbour seals reproduce in June, mate in July, and moult in July–August. Harbour seals in the Kalmarsund region were close to extinction in the 1970s. Hunting, possibly in combination with effects of contaminants, resulted in a severe population bottle-neck and only some tens of pups were observed in the beginning of the 1970s (Härkönen et al. 2005). After protective measures were taken and seal sanctuaries were established in the 1980s and 1990s, the population increased by 7% per year up to 2007, when 630 seals were counted during moult. The pup production also showed a similar positive trend and close to 100 pups were born in 2007. Because harbour seals in this area spend about 65% of their time on land, the true population size is close to 1 000 seals. There is virtually no information on the health status of this population. 68 ible data is for the Swedish coastal waters. The mean annual rate of increase in the period 1990– 2005 was about 8% (Figure 4.2.2), which is somewhat less than the theoretical maximum growth rate of 10% for the species (Harding et al. 2007). Surveys from air carried out in 2006 and 2007 in Sweden give higher estimates of abundance, but it will take at least six years until such data can provide useful information for trend analyses (Harding et al. 2007). The recovery of grey seals south of 59º N, where they had been regularly present before they were hunted to extinction in the beginning of the 20th century, is very slow (Herrmann et al. 2007). Although grey seals are observed more often than 10 years ago, no resident colonies have been reported on the southern Baltic coast (from Germany to Latvia). Harbour seals (Phoca vitulina) Harbour seals occur only in the southern part of the Baltic and there are no historical records of harbour seals north of a line from Västervik (Sweden) to Hiiumaa in Estonia. The harbour seals in the Kalmarsund region are genetically distinct from adjacent populations, with gene sequences present in only this population. The current harbour seal population in the southwestern Baltic (Scania and Denmark) seems to have colonized the area after the grey seals were severely depleted in Harbour seals in the southern Baltic, the Kattegat, and the Skagerrak also declined steeply in the beginning of the 20th century as a consequence of the coordinated Nordic extermination effort. Bounty statistics suggest that more than 17 000 harbour seals were present in the area in 1890, but only about 2 000 seals remained at the end of the 1930s (Heide-Jørgensen & Härkönen 1988). Heavy hunting pressure kept the population at this level until the beginning of the 1970s, when hunting was prohibited and seal conservation areas were established. Annual surveys of the population started in 1979 and the population increased at 12% per year until 1988 when it was hit by a phocine distemper virus (PDV) epidemic that killed about half the population. Subsequently, the population increased exponentially at 13% per year until a new PDV epidemic in 2002 killed 66% of the seals in the Skagerrak and 30% in the Kattegat (Härkönen et al. 2006). A third epidemic caused by an unknown pathogen appeared in 2007 and killed some thousands of seals, but the total impact cannot be evaluated until survey results from 2008 become available. The total ‘true’ population size was about 10 100 in 2007, but this number should be regarded as uncertain because seals may have died in great numbers after the surveys in 2007 were conducted. The reproductive status of this population appears to be normal because 95% of mature
Table 4.2.1. Population estimates and threats to the conservation of seals in the Baltic Sea. Population beginning 20th century Estimated hauled-out population/trend International protection Conflict seal/ fishery Major threats Harbour seal 5 000 (Baltic Proper) Baltic Proper: Currently: 630 1970s: 100 Trend +7.9% per yr Bern/Bonn Conventions Minor Contaminants/diseases Entanglement in fishing nets Human disturbances Food limitation Kattegat and S. Baltic: Currently:10 100 1976: 2 200 Trend:+3% per yr 90 000 North of latitude 59°: Currently: 22 000 1970s: 2 500 Trend: +8.5% per yr Habitats Directive Moderate Grey seal Bern Convention, Habitats Directive Severe Entanglement in fishing nets Contaminants/diseases Human disturbances South of latitude: 59° Currently: 640 Trend: slightly increasing 180 000 Gulf of Bothnia: Currently: 4 800 Trend: +4.3% per yr Gulf of Riga: Currently: 1 500 Trend: Zero Gulf of Finland: Currently: 300 Trend: Zero Archipelago Sea: Currently: 150 Ringed seal Bern Convention Increasing Global warming Contaminants/diseases By-catches Minor Minor females reproduce, and the population growth rate is close to maximum levels for the species. However, the material collected in 1988 showed high prevalences of bone lesions (parodontitis and alveolar exostosis) (Mortensen et al. 1992). Alveolar exostosis is not present in material collected before 1950. Furthermore, experimental studies have shown that harbour seals carrying PCB loads comparable to levels observed in the Kattegat exhibit impaired immune functions (DeSwart 1995). 4.2.2 Factors that influence the status of seals in the Baltic Sea The current and future status of Baltic seals can be expected to be affected by a number of anthropogenic factors (Table 4.2.1). Xenobiotic substances have had a severe impact on the health and abundance of ringed and grey seals, and also affect hormonal processes in harbour seals. The multitude of chemical substances produced poses a potential threat to the health of all top consumers in the Baltic biota (Bergman & Olsson 1986, Bergman et al. 1992, Bergman 1999, Bäcklin et al. 2003, Bredhult et al. 2008). Unsustainable management of fish stocks can lead to the depletion of important food organisms for marine mammals in the Baltic. The currently decreasing blubber thickness in grey seals (Figure 4.2.3) and ringed seals (Britt-Marie Bäcklin pers. comm.) may be linked to such effects. Similar effects are suspected in the Kattegat, where the population growth rate declined during the years before the 2002 PDV epidemic. By-catches in fisheries reduce the growth rate in populations of marine mammals, which increases the risk for rapid declines in most scenarios in ecological risk analyses (Hansson et al. in prep.). No systematic information is available on by-catches of marine mammals in the Baltic. History shows that Baltic seals are very vulnerable to hunting especially during warmer periods with 69
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Baltic Sea Environment Proceedings
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Published by: Helsinki Commission K
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TABLE OF CONTENTS PREFACE . . . . .
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6.6 Hazardous substances . . . . .
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1 INTRODUCTION 8 1.1 An integrated
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Box 1.1. Biodiversity The term biod
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of saline water from the North Sea
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14 On a global scale, marine ecosys
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Box 1.2. Regime shifts in the Balti
Page 20 and 21: 2 MARINE LANDSCAPES AND HABITATS 18
Page 22 and 23: From an ecological point of view, a
Page 24 and 25: Box 2.1.2. The Baltic marine landsc
Page 26 and 27: • A coherent data set on benthic
Page 28 and 29: Denmark Estonia Finland Germany Lat
Page 30 and 31: Mud-sandflat, Greifswald Lagoon, Ge
Page 32 and 33: 3 COMMUNITIES Communities are assem
Page 34 and 35: 32 Spring bloom index 1200 1000 800
Page 36 and 37: 34 Unusual events and new species i
Page 38 and 39: 36 Depth limit (m) the Gulf of Both
Page 40 and 41: Number of species 16 14 12 10 8 6 4
Page 42 and 43: Figure 3.2.7. Left panel shows pred
Page 44 and 45: Implications for the Baltic Sea Act
Page 46 and 47: Biomass (wet weight, mg per m 2 ) B
Page 48 and 49: the other hand, is not selected by
Page 50 and 51: iomass can be used to assess enviro
Page 52 and 53: Average number of species 20 15 10
Page 54 and 55: 52 Macoma baltica where the influen
Page 56 and 57: the total BT identified for each ma
Page 58 and 59: Recruitment (thousands) 8000000 700
Page 60 and 61: Alien species Several alien fish sp
Page 62 and 63: 4 SPECIES The number of species in
Page 64 and 65: Table 4.1.1. Results of dedicated a
Page 66 and 67: Number of stranded porpoises 180 16
Page 68 and 69: is recommended to survey harbour po
Page 72 and 73: Mean blubber thickness (mm) 40 35 3
Page 74 and 75: Breeding pairs 60000 50000 40000 30
Page 76 and 77: predation on nests and nesting adul
Page 78 and 79: sites outside the Baltic, decreased
Page 80 and 81: Table 4.3.1. Development of the pop
Page 82 and 83: 80 Number of breeding pairs 3000 25
Page 84 and 85: The strategic goal of the BSAP to h
Page 86 and 87: for a given site or area. The secon
Page 88 and 89: Mussel bed reef community, Jasmund,
Page 90 and 91: Table 5.3. Assessment results of th
Page 92 and 93: Aerial photo of harbours seals (Pho
Page 94 and 95: 6 HUMAN PRESSURES ON BIODIVERSITY A
Page 96 and 97: Table 6.1.1. Catch range during the
Page 98 and 99: Baltic herring trawling, Bothnian B
Page 100 and 101: 6.1.3 Major international framework
Page 102 and 103: 100 Oil turnover (millions of tonne
Page 104 and 105: NOx emissions and sewage Macrophyte
Page 106 and 107: Communication links There are a num
Page 108 and 109: Figure 6.3.3. Left: concrete-stone
Page 110 and 111: ecommendations would contribute to
Page 112 and 113: Tourist fishing 110 cial fishery fo
Page 114 and 115: 112 Figure 6.5.1. Integrated classi
Page 116 and 117: can be considered as having been a
Page 118 and 119: Although no direct, dramatic mass m
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Bearing in mind the complex hydrogr
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Box 6.7.1. Invasion status of the B
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Table 6.7.1. Examples of ecological
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munities that formerly consisted of
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6.8.2 Activities generating noise i
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128 and fish in the Baltic Sea area
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800 700 600 bag of the two German B
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Fish swarm on kelp (Laminaria sp.)
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tion of ice cover, either through r
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7 STATUS OF THE NETWORK OF MARINE A
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Box 7.1. Natura 2000 network of pro
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25 20 on how the criteria on ecolog
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estrial, nearshore marine, and offs
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144 >30 psu 18-30 psu 11-18 psu 7.5
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Permission needed Restricted Forbid
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Figure 7.8.a. MARXAN ’best portfo
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The BSPA network is relatively well
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Mammals. Among the mammals, the pop
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154 taxonomic groups and communitie
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156 provided by an ecosystem. Use o
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158 Reduction of human pressures Wh
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160 fishing on fish population dyna
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162 Baden, S., Boström, C. (2001).
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164 Season 2001-2002. Acta Zoologic
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166 Gasiūnaitė, Z.R., Cardoso, A.
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168 HELCOM & OSPAR (2003): Joint HE
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170 ICES (2008c). Report of the Bal
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172 area: density-dependent effects
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174 Noer, H., Clausager, I., Asferg
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176 Scheffer M., Carpenter S.R., Fo
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178 by passive acoustic monitoring.
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180 Warzaw, Poland Vilhunen, Jarmo,
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182 6.7 Alien speices Authors: Lepp
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ANNEX III: CONSERVATION STATUS OF T
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ANNEX IV: HABITAT OR SPECIES DISTRI
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ANNEX V: STATUS OF BREEDING AND WIN
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BSEP116B Biodiversity in the Baltic Sea - Helcom

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