BSEP116B Biodiversity in the Baltic Sea - Helcom

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Baltic herring trawling, Bothnian Bay. 96 bottom trawling may cause heavy damage to several species of thin-shelled bivalves and starfish, whereas thick-shelled bivalves seem to be more resistant. An increased proportion of damage with increasing body size was found for the mussels Macoma calcarea, M. balthica, Arctica islandica and Musculus niger owing to an unfavourable shell surface/thickness relationship amongst larger specimens (Rumohr & Krost 1991). The same study indicates a considerable impact on benthic communities, specifically for A. islandica. Trawling activities do not necessarily lead to a total destruction of benthic communities, but rather to the resuspension of sediments and dislocation of living organisms, mainly epibenthic organisms. This leads to an increase in predatory and scavenging species (Krost 1990, Rumohr & Krost 1991 and references therein). However, the effect is relatively regional, being confined to the southern Baltic Sea. Marine mammals The adverse effects of fisheries on seal populations can be summarized as: (i) the direct killing of seals as competitors to the fishery; (ii) accidental drowning of seals in fishing gear; (iii) entanglement of seals in discarded netting; and (iv) a decrease in food resources for seals (Pilats 1989). As seals are generalists in terms of feeding and their main prey is therefore the most abundant fish in the system (Lunneryd 2001), open-sea fisheries can affect seal populations via a reduction in their food resource. In contrast, coastal fisheries directly impact the survival of seals as they can become entangled in the static gears (such as trapnets and gillnets) employed by the coastal fishery. It has been estimated that at least 300 grey seals, 80 ringed seals and 7–8 harbour seals are captured as by-catch annually in the Baltic Sea (ICES 1995). More recent estimates are available for the Swedish Baltic Sea coastal fisheries, where in total over 400 grey seals and 50 ringed seals were by-caught in 2001 (Lunneryd et al. 2004, 2005). In 2001, a survey estimated the annual by-catch rate of harbour porpoises to be 25 porpoises caught in bottom trawls and 89 porpoises in gillnets, trammel nets and pelagic trawls in the Swedish part of the Skagerrak and Kattegat (ASCOBANS 2008). In the German part of the
Baltic Sea, most of the 105 recorded by-caught porpoises in the years 1990 to 2001 were reported from bottom-set gillnet fisheries or were stranded with characteristic net-marks (Siebert et al. 2006). While these numbers are considered to be minimum figures, Rubsch & Kock (2004) estimated the annual by-catch in the German set-net fishery to be 57 individuals in the western Baltic Sea and 25 in the German part of the Baltic Proper. A total of 45 by-caught animals were reported from Polish waters between 1990 and 1999 (Skóra & Kuklik 2003). In Latvia, two porpoises were found entangled in fishing nets in the Gulf of Riga in October 2003 and in January 2004, respectively (ASCOBANS 2004). A modelling study by Berggren et al. (2002) estimated the potential limits to anthropogenic mortality for harbour porpoises. To achieve the goal of a population recovery to more than 80% of carrying capacity, by-catch limits of two individuals per year in the Baltic Proper and three individuals per year in the Kiel Bight–Mecklenburg Bight area should not be exceeded. Seabirds Several studies from different parts of the Baltic Sea have shown that set-net (gillnet) fisheries in the Baltic Sea cause the death of tens of thousands of birds every year. The by-catch problem is of special relevance where gillnet fisheries are practiced in areas with high concentrations of resting, moulting or wintering seabirds. The conflicts are usually seasonal. Finland, especially eider, black guillemot (Cepphus grylle), razorbill (Alca torda) and red-throated and black-throated divers (G. stellata and G. arctica) are the species most affected (Hario 1998). The most recent Swedish by-catch study covering the Swedish fishery as a whole (Lunneryd et al. 2004) showed that the cormorant was the species predominantly affected, followed by eider, guillemot, merganser, and long-tailed duck. The threat of drowning in fishing gear is larger for piscivorous species than for benthophagic ducks, although in most areas the total number of piscivorous birds drowned is lower owing to their smaller populations. The studies available mainly investigated bird by-catches in near-coastal waters. Information about the by-catch on fishing grounds further offshore is scarce, although it is known that high densities of birds and high fishing intensity may overlap seasonally in these areas also. Another effect of fisheries on birds is related to the discarding of unwanted catch and offal at sea. Gulls especially benefit from this food source. Furthermore, the increase in sprat stocks as a consequence of cod overfishing is expected to have a positive effect on piscivorous birds, especially auks. Abiotic environment In general, the effects of bottom-towed gears on abiotic habitats are primarily (i) removal of physical features, (ii) reduction in complexity, and (iii) alteration of the physical structure of the seafloor (ICES 2005b). Piscivorous birds (divers, grebes, mergansers, auks, cormorants) and benthophagic ducks may become entangled and die in fishing gear. At the southern coast of the Baltic Sea, the longtailed duck (Clangula hyemalis) is the most numerous species caught in gillnets, followed by black scoter (Melanitta nigra), common scoter (Melanitta fusca) and red-throated diver (Gavia stellata), while in some areas, eider (Somateria mollissima), greater scaup (Aythya marila), guillemot (Uria alge) and cormorant (Phalacrocorax carbo) are also found in large numbers (I.L.N. & IfAÖ 2005, Schirmeister 2003, Stempniewicz 1994, Kirchoff 1982, Kowalski & Manikowski 1982). In the coastal waters of Lithuania, losses of Steller’s eiders are of concern owing to the rareness of this species (Dagys & Žydelis 2002). In Towed demersal fishing gear can also substantially affect the abiotic environment in the Baltic Sea area, where this fishing practice is applied. For example, in the intensely fished Kiel Bight, the total area disturbed was estimated at 630 km 2 per year causing a mobilization of nutrients estimated to be 0.6–2.5 tonnes silicate, 0.3–1.3 tonnes nitrogen and 0.1–0.5 tonnes phosphorus per km 2 and year (Krost 1990). The increase in nutrient concentrations was followed by an increase in oxygen consumption of 1.5–7.8 tonnes per km 2 and year. This points to a considerable impact of fishing activities on the marine environment (Krost 1990). There is no documented evidence that traditional coastal fisheries (e.g., by means of trapnets and gillnets) have affected the abiotic environment. 97
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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
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2 MARINE LANDSCAPES AND HABITATS 18
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From an ecological point of view, a
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Box 2.1.2. The Baltic marine landsc
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• A coherent data set on benthic
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Denmark Estonia Finland Germany Lat
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Mud-sandflat, Greifswald Lagoon, Ge
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3 COMMUNITIES Communities are assem
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32 Spring bloom index 1200 1000 800
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34 Unusual events and new species i
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36 Depth limit (m) the Gulf of Both
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Number of species 16 14 12 10 8 6 4
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Figure 3.2.7. Left panel shows pred
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Implications for the Baltic Sea Act
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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 70 and 71: Number of individuals 12000 10000 8
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 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
Page 120 and 121: Bearing in mind the complex hydrogr
Page 122 and 123: Box 6.7.1. Invasion status of the B
Page 124 and 125: Table 6.7.1. Examples of ecological
Page 126 and 127: munities that formerly consisted of
Page 128 and 129: 6.8.2 Activities generating noise i
Page 130 and 131: 128 and fish in the Baltic Sea area
Page 132 and 133: 800 700 600 bag of the two German B
Page 134 and 135: Fish swarm on kelp (Laminaria sp.)
Page 136 and 137: tion of ice cover, either through r
Page 138 and 139: 7 STATUS OF THE NETWORK OF MARINE A
Page 140 and 141: Box 7.1. Natura 2000 network of pro
Page 142 and 143: 25 20 on how the criteria on ecolog
Page 144 and 145: estrial, nearshore marine, and offs
Page 146 and 147: 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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