BSEP116B Biodiversity in the Baltic Sea - Helcom

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Table 6.1.1. Catch range during the past five years and the current state of selected major Baltic commercial fish stocks (ICES 2008b,d). SSB: Spawning stock biomass; F: Fishing mortality. Stock Catch range in past 5 years (2003–2007, 10 3 tonnes) SSB in relation to precautionary limits F in relation to precautionary limits F in relation to high long-term yield Western cod 20–24 Increased risk Undefined Overfished Eastern cod 50–71 Undefined Harvested sustainably Overfished Herring in SD 91–116 Undefined Harvested sustainably Underfished 25–29 (excl. GoR) and 32 Gulf of Riga 31–40 Undefined Harvested sustainably Overfished herring Sprat 308–405 Unknown Increased risk Overfished Flounder 15–19 Unknown Unknown Unknown 94 to about 100 000 tonnes recently. In contrast, the stock of Gulf of Riga herring has more than doubled during the past two decades. Flounder catches have increased since the early 1990s and are currently over 15 000 tonnes annually. The dynamics in the landings of eleven marine fish species over time are shown in Figure 6.1.2 (ICES 2008b). Landings of the major Baltic fish stocks are shown in Table 6.1.1. 6.1.2 Ecosystem effects of fishing activities The major impact of fishing is undoubtedly on exploited fish stocks, but there are also impacts on benthic invertebrate and fish communities, marine mammals, seabirds and the abiotic environment. The effect of fishing on various ecosystem components other than fish is different in the open sea from that in coastal areas mainly owing to the different fishing gears employed, which depends on the species composition of exploitable resources and the different habitat characteristics. Fish stocks The main ecological impact of fisheries is the removal of large quantities of fish, in particular target species. The major effects include, amongst others, a decrease in fish abundance and/or spawning stock biomass, a decrease in the size of individual fish at sea, and changed predator-prey interactions. A dramatic reduction in a piscivorous marine fish population may initiate a multi-level trophic cascade and indirectly also affect zooplankton and phytoplankton populations (Casini et al. 2008). Although the effect of fisheries on nontarget species is of great importance from an ecosystem perspective, there is only very little known on this topic. Effects of fishing on fish stocks and fish communities are also discussed in Chapter 3 of this report. An important impact on the ecosystem is also caused by by-catches and discards. Except in the cod fishery, the extent of fish by-catch is unknown in the Baltic Sea. Discard estimates for the two Baltic cod stocks are available since 1996 when sampling began. The western and eastern cod discards have fluctuated during the period of data availability (i.e., 1996–2007) from 5.0–26.6 million and 3.7–23.3 million individuals, respectively. However, the discard estimates are relatively uncertain (ICES 2008b). Calculations show that the amount of cod offal discarded in the entire Baltic Sea (i.e., sub-divisions 22–32) reached a peak in the early 1980s (average ca. 58 000 tonnes annually) and was relatively low in the 1990s, with an annual mean of about 19 000 tonnes (ICES 1997). Demersal communities In general, bottom trawls have an impact on marine biota in several ways including (i) a reduction in structural biota; (ii) a reduction in the geographic range of species; (iii) a decrease in populations that have low rates of turnover; (iv) fragmentation of populations; (v) alteration of the relative abundance of species; (vi) sub-lethal effects on individuals; (vii) an increase in populations that have high rates of turnover; and (viii) favouring populations of scavenging species (ICES 2000). There are only a few studies available in the Baltic region on bottom trawling impacts on the marine ecosystem. It has been documented that
Landings of herring (tonnes) 350000 300000 250000 200000 150000 100000 50000 600000 500000 400000 300000 200000 100000 Landings of sprat (tonnes) 0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Herring Gulf of Riga Herring SD 30 Herring SD 25-29, 32 excl. Gulf of Riga Sprat SD 22-32 Landings of cod in Kattegat and SD 22-24 (tonnes) 60000 50000 40000 30000 20000 10000 0 0 1960 1970 1980 1990 2000 2010 450000 400000 350000 300000 250000 200000 150000 100000 50000 Landings of cod in SD 25-32 (tonnes) Cod SD 22-24 Cod Kattegat Cod SD 25-32 25000 1600 Landings of flounder and plaice (tonnes) 20000 15000 10000 5000 1400 1200 1000 800 600 400 200 Landings of sole and turbot (tonnes) 0 0 1950 1960 1970 1980 1990 2000 2010 Flounder Plaice SD 22-29 Sole (Kattegat & Skagerrak) Turbot SD 22-29 Figure 6.1.2. Dynamics of landings of eleven major fish stocks/species in the Baltic Sea from 1952–2006 (ICES 2008b). 95
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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
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 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 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
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
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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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