SHARKS IN THE BALTIC Distribution, use and conservation of cartilaginous fishes in the Baltic Sea S HARK ALLI A NCE Contents and authors TH O 1. Introduction 1 R NY SKA TE, AN EGG-C 2. Geographic and oceanographic description 2 as 3. Shark, ray, and chimaera species (cartilaginous fishes) of the Baltic Sea 4 E OF T H E S 4. Fishing pressure on Baltic cartilaginous fishes 15 T ARR Y SKA TE, SPU 5. Conservation 18 RD OG 6. Conclusion 21 A T FISH M 7. Recommendations 22 ARK ET © HE ET 8. Appendices 23 IK E Z Appendix 1: List of threatened and declining species of Baltic ID OW cartilaginous fishes 23 I T Z Appendix 2: Multi-lingual species list of Baltic cartilaginous fishes 24 9. References 26 Authors and acknowledgments Heike Zidowitz is a marine biologist and chair of the German Elasmobranch Society. She coordinates Shark Alliance activities in Germany. Dr. Michael George is a marine biologist and ichthyologist based in Hamburg, Germany. He serves as the secretary of the German Elasmobranch Society. Sonja Fordham is the Policy Director for the Shark Alliance and a citizen of Finland; she focused on the conservation aspects of this report. Dr. Sven O. Kullander is senior curator of ichthyology and associate professor at the Swedish Museum of Natural History in Stockholm, Sweden. Dr. Wojciech Pelczarski is senior scientist at the Sea Fisheries Institute, Gdynia, Poland where he conducts fishery research on sharks and tunas. Thanks go to the following: Marc Dando, Heino Fock, Boris Frentzel-Beyme, Claudine Gibson, Eugenijus Leonavicius, Andy Murch, Christian Pusch, Matthias Stehmann, Charlott Stenberg, Susanne Stolpe and Dietmar Weber. IntroductionBaltic Sea A matter of survival Whereas the brackish waters of the Baltic Sea are known to be limiting in terms of the distribution and diversity of all marine life, the region is home to sharks, rays (including skates) and chimaeras, collectively known as cartilaginous fishes. More than 30 such species have been recorded in the Baltic, although many are considered rare or vagrants. This report reviews and analyses the available information on the presence, use and conservation of Baltic cartilaginous fishes. The aim is to fill existing knowledge gaps and inform management so as to ensure the survival of these especially vulnerable species. Bothnian Bay FINLAND Bothnian Sea NORwaY SWEDEN nd Archipelago nla f Fi Sea lf o Gu estoNIA k RUssIA rra ge Gulf of ka S Kattegat Riga LatVIA Baltic Proper DENMARK The Sound North Sea The Belts LITHUANIA Western Kaliningrad Baltic W E S BELARUS LEY F E POLAND R N A GERMANY N D E S THE SHARK ALLIANCE – Sharks in the Baltic – May 2008 PAGE 1 SECTION 1 regionGeographic and hydrographic description The region (ICES) refers to the Kattegat and Skagerrak together as a “transitional area”. The Helsinki Commission (HELCOM) The Baltic Sea is the largest semi-enclosed brackish includes the Kattegat as part of the Baltic Sea, but body of water in the world 48. Surrounded almost excludes the Skagerrak. For the purposes of this report, entirely by land, it is connected to the North Sea so as to better reflect the bio-geographic background of (and hence the North Atlantic) by narrow straits: the species distribution, the Kattegat is considered part of the Kattegat and Skagerrak, which are located between Baltic Sea and the Skagerrak with its deep-water trench Denmark and the southern part of the Scandinavian (the Norwegian Deep) is a transitional area to the region peninsula. It is bordered by Denmark, Sweden, Finland, under review. Russia, Estonia, Latvia, Lithuania, Poland and Germany, while Norway is situated on the transitional waters of The Baltic Sea has a water volume of 21,600km³ 50 and the Skagerrak, at the mouth of the North Sea. covers an area of 413,000km² 50, with an average depth of 52 metres (m) 50. Its deepest part (459m) lies at Landssort, The area under review can be sub-divided into the between the Swedish islands of Gotland and Gotska following geographic areas: Skagerrak, Kattegat, the Sound, Sandön, in the Baltic Proper 74. The Sea spans from the Belts, Western Baltic, Baltic Proper, Gulf of Riga, Gulf of Germany’s Flensburg Fjord eastward through the Gulf Finland, Archipelago Sea, Bothnian Sea, and Bothnian Bay of Finland to St Petersburg, Russia. Its southernmost (see Table 1). extension is the Pomeranian in the Polish town of Swinoujscie, while the northernmost point is found in the There is some controversy with regard to the borders Bothnian Bay on the Swedish-Finnish border 75. During of the Baltic Sea. Some authors include the Kattegat as normal winters, ice covers about 45% of the Baltic’s surface part of the Baltic Sea, while others exclude it and set the area (approximately 200,000km²) 34, including Bothnian border at the Belts and Sound areas (Danish Straits). Bay, the Gulf of Finland, the Bothnian Sea, the Archipelgo The International Council for the Exploration of the Sea Sea, and the Gulf of Riga. The Skagerrak is roughly triangular in shape, measuring 240km long 76 IIId31 and between 80 and 140km wide . IIa It deepens towards the Norwegian coast to more than 700m at the Norwegian Deep. IIId30 Hydrography and topography of the Baltic Sea IId32 IVa It takes 25 to 35 years to fully IIId29 exchange the waters of the Baltic Sea 50. Exchange from the North IIIan IIId27 Sea through the Skagerrak, Kattegat IIId28 and Danish Straits (the Sound IIIas IVb IIIb IIId25 IIId26 IIIc22 IIId24 Figure 1: Map of the Baltic Sea and IIIc24 adjacent waters, showing the ICES Area names and sub-divisions (IIIb is also IVc called sub-division 23). Data source: Map ICES 2004 Advisory Committee on Ecosystems 36. SECTION 2 PAGE 2 THE SHARK ALLIANCE – Sharks in the Baltic – May 2008 TABLE 1: Geographic sub-divisions of the Baltic Sea with their ICES Area names and salinity value of near-surface waters in practical salinity units (PSU). Geographic name ICES Area Salinity (PSU) Skagerrak IIIan 30–28 Kattegat IIIas 28–18 The Sound IIIb (sub-area 23) 18–9 The Belts IIIc 22 18–9 Western Baltic Partly IIIc 22, IIIc and llld24 18–7 Baltic Proper IIId 25, 26, 27, 28, partly 29 9–6 oxygenated water. During periods of stagnation, Gulf of Riga Partly IIId 28 6–4 decomposition of organic material trapped in deep water Gulf of Finland IIId 32 6–3 can cause local oxygen depletion, resulting in mass Archipelago Sea Partly IIId 29 6–5 mortality of aquatic life. As a result, most Baltic fishes live Bothnian Sea IIId 30 6–4 Bothnian Bay IIId 31 4–1 near the surface or in shallower, coastal waters. Human- Data source: Salinity taken from Schramm 1996 65 induced eutrophication (nutrient enrichment resulting in the proliferation of oxygen-depleting plant life) can further stress the fishes in this challenging environment. and Belts area between the Danish islands) and into the Eutrophication has been blamed for cases of decline in central Baltic Sea, and vice versa, is slowed by a narrow bony fish populations and biodiversity41 and very likely mixing zone. The high-density seawater of the North Sea affects cartilaginous fishes as well. flows in towards the bottom layers of the Baltic Sea, while lower density, low-salinity water leaves the Baltic Sea near The mixing of Baltic water layers is mainly forced by the surface 50. meteorological influences such as wind and heat exchange. Baltic currents are highly variable and primarily driven by Inflow from rivers and precipitation creates a freshwater wind, horizontal density gradients, and differences in sea surplus in the Baltic, leading to greater freshwater exit level 20. Tidal forces in the Baltic Sea are minimal. (950km³ per year) than seawater entry (470km³ per year) 50. As a result, the Baltic Sea is brackish with a horizontal In addition to regular water exchanges, strong influx events gradient of salinity, declining from western to eastern parts occasionally occur in the Baltic. These irregular phenomena and southern to northern parts. The vertical circulation, usually take place in the late autumn and winter and however, is restricted by layering caused by the density depend on atmospheric circulation and a particular differences in sea and freshwater that create a distinct sequence of wind and resulting sea level changes. Until border between waters of different salinity and density50 . the 1980s, these events occurred on average every four to Deep water can only be exchanged by horizontal water five years51 , but have since happened only once every 10 influx, which is impeded by topographic barriers. For years (1983, 1993, 2003) 61. These special hydrographical example, the Darss Sill (with a water depth of only 18m) conditions limit the distribution of Baltic flora and fauna, inhibits rapid eastward transport of highly saline and particularly around the Danish Straits. Only euryhaline organisms (those capable of tolerating a wide range of salinity) 35 and other well-adapted species wind 7.8m/s 33 survive under such highly variable ➞ 31 environmental conditions. 29 27 The range of species favouring high-salinity water, including 25 most cartilaginous fishes, depends 23 both on the intensity of eastward 21 currents and the strength of the last 19 inflow event. 17 15 13 11 Figure 2: Salinity and current direction of 9 current the bottom layers of water in the western 100cm/s 7 Baltic Sea area on 10 November 1996. ➞ 5 Data source: SALPRO research project. See: www.io-warnemuende.de THE SHARK ALLIANCE – Sharks in the Baltic – May 2008 PAGE 3 SECTION 2 Shark, ray and chimaera species (cartilaginous fishes) of the Baltic Sea Species descriptions Habitat: Benthic, mainly on sandy and muddy bottoms; down to 1,000m, but mainly at 50-100m 71.