Survey of River and Sea Lampreys in German Waters of the Baltic Sea – Basis of Successful Rebuilding Programmes. ICES CM 2005
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Not to be cited without prior reference to the authors ICES Annual Science Conference 2005 CM 2005/W:06 Rebuilding Programmes for Threatened Fish Populations Survey of river and sea lampreys in German waters of the Baltic Sea – basis of successful rebuilding programmes R. Thiel, H. M. Winkler, P. Riel and R. Neumann ABSTRACT In order to prepeare population rebuilding programmes, the status of river lamprey and sea lamprey was investigated within the German waters of the Baltic Sea. From August 2003 until August 2005 the following sources of data were analysed: (i) research fisheries with otter and shrimp trawls, (ii) records from commercial and recreational fisheries, (iii) records from ichthyological museum collections, (iv) commercial catch statistics and relevant publications. 317 records of river lampreys with 19,977,622 individuals and 89 records of sea lampreys with 129 individuals were obtained for the period from 1649 - 2005. The number of recorded individuals of river lampreys per year was two times higher from 1649 - 1939 than in the following period 1940 - 1989. Only 1 % of the yearly records of river lampreys from this time period was estimated from 1990 - 2005. No distinct trend of the temporal population development of sea lamprey was found. From 1829 - 1989 the highest number of records of sea lamprey (70 %) was estimated for subdivisions 22 and 24. From 1990 - 2005 all records of sea lamprey in German Baltic waters were distributed within the coastal waters and estuaries. Areas with distinct higher densities of sea lamprey records were not estimated. Most of the records of river lamprey (88 %) originated from subdivisions 24 and 26 from 1649-1989. The species was mainly distributed within the Szczecin Lagoon and adjacent waters, the lower Vistula River, the Vistula Lagoon, the Bay of Gdańsk and the Curonian Lagoon. From 1990 - 2005 most of the records (83 %) and recorded individuals (98 %) of river lamprey from German Baltic waters originated from the Szczecin Lagoon and its adjacent waters. 9 Spawning sites of river lamprey were found in the river systems of Peene, Warnow and Stepenitz. Regular annual spawning of river lamprey occurs not at all spawning sites. Actual reproduction of sea lamprey is not known from rivers of the German Baltic Sea area. From 1887-1999 about 14,377 kilogram of river lampreys were caught annually in the southern Baltic Sea. 82 % of the total lamprey catches of the southern Baltic Sea originated from subdivision 26. Highest lamprey catches were obtained during the decades from 1890 - 1919. The contribution of the lower Vistula River, Vistula Lagoon and Bay of Gdańsk increased remarkable from 1887-1939, whereas the importance of the Szczecin Lagoon and adjacent waters for the lamprey fishery decreased during the same period of time. A remarkable proportion of lamprey catches is contributed from the region of the Curonian Lagoon since 1950. However, the critical situation for the populations of river lamprey in both marine and freshwater habitats of the German Baltic Sea area requires a rebuilding programme for the still existing but threatened populations. Keywords: river lamprey, sea lamprey, Baltic Sea, past distribution, commercial catch, recent records, rebuilding programme Ralf Thiel, Philip Riel, Renate Neumann: German Oceanographic Museum, Katharinenberg 14-20, D- 18439 Stralsund, Germany [tel: +49 3831 2650 300, fax: +49 3831 2650 209, e-mail: [email protected]]. Helmut M. Winkler: University of Rostock, Department Biological Sciences, Universitätsplatz 2, D-18055 Rostock, Germany [tel: +49 381 498 6272, fax: +49 381 498 6262, e-mail: [email protected]] 1 INTRODUCTION Lampreys belong to the Agnatha – the most primitive and oldest group of all living vertebrates. Their fossils are available from the late Silurian and Devonian periods, 450 million years ago (Maitland 2003). Most recent lamprey species have an antitropical distribution and occur in the temperate and arctic regions of both the northern and southern hemispheres (Kelly & King 2001). Exceptionally, the genus Tetrapleurodon occurs in subtropical Mexico, but lives here at high altitude (Salewski 2003). In Eurasia and North America lampreys are represented by the genus Lampetra, Petromyzon, Ichthyomyzon, Lethenteron, Eudontomyzon, Entosphenus and Caspiomyzon. There are 39 recognised lamprey species worldwide (Potter 1980), of which there are 34 present in the northern hemisphere (Krappe 2004). Four species represent the Petromyzontiformes in Germany (Freyhof 2002). These are sea lamprey (Petromyzon marinus Linnaeus, 1758), river lamprey (Lampetra fluviatilis (Linnaeus, 1758)), brook lamprey (Lampetra planeri (Bloch, 1784)) and Vladykov´s lamprey (Eudontomyzon vladykovi Oliva & Zanandrea, 1959). River lamprey and sea lamprey are the only two anadromous lamprey species living in German waters of the Baltic Sea, its estuaries and rivers (Spratte & Hartmann 1998, Winkler et al. 2002). However, the river lamprey is found from southern Norway to the western Mediterranean. The species inhabits the coastal waters of the whole Baltic Sea. It has also been reported from Turkey (Erguven 1989). Anadromous sea lampreys occur over much of the Atlantic coastal area of western and northern Europe, from northern Norway to the western Mediterranean, and eastern North America. In Europe it is distributed as far north as Varanger Fjord in Norway (70° N) and as far south as the western Mediterranean (Beamish 1980, Hubbs & Potter 1971). It has recently been documented from the Aegean Sea by Economidis et al. (1999) and from the Kola Bay (Reshetnikov 2003). According to Kelly & King (2001) there exist also several landlocked populations of sea lamprey, but not in the Baltic Sea region, where the species occurs in very low densities. It is known that populations of anadromous lampreys have declined dramatically in European inland waters, including Germany, since the mid of the 20th century (e.g. Kelly & King 2001). Due to their decrease in stocks and numbers in inland waters, both lamprey species are listed in Annex II of the European Union Habitats Directive as species of community interest, whose conservation requires the designation of Special Areas of Conservation; in Appendix III of the Bern Convention, which permits some exploitation of their populations; and in many Red Data Books throughout Europe, which list these species often as threatened. However, there is a great lack of information with regard to the status of anadromous lamprey species in marine waters, e.g. in the Baltic Sea. In order to check, if rebuilding programmes for anadromous lampreys are necessary and how they should be performed in that case, we analysed the status of diadromous lamprey species within the German waters of the Baltic Sea area. In addition, this paper provides useful information for biodiversity considerations with regard to river and sea lamprey and 2 outlines requirements for their conservation in Germany. Furthermore, to provide such information is particularly relevant to fulfill the requirements of the European Habitats Directive, the EU Water Framework Directive, and of coastal zone management and conservation. In detail, this study was performed to describe, analyse and discuss: (1) the past distribution of lampreys in subdivisions 20-26 of the Baltic Sea, (2) the spatial and temporal characteristics of the commercial catch of lampreys in the southern Baltic Sea, (3) the recent records of lampreys in German Baltic waters, and (4) the location of spawning sites of lampreys in German tributaries of the Baltic Sea region. MATERIAL AND METHODS During a 25 months period from August 2003 until August 2005 the status of anadromous lampreys in German waters of the Baltic Sea area was investigated based on the analysis of the following sources of data: (i) research fisheries with otter and shrimp trawls, (ii) records from commercial and recreational fisheries, (iii) records from ichthyological museum collections, (iv) commercial catch statistics and relevant publications. Evaluation of hauls from research fishery The research fisheries were carried out with different bottom trawls (otter and shrimp trawls) in the Exclusive Economic Zone and in the coastal waters of Germany in the Baltic Sea region between the Islands of Ruegen, Usedom and Bornholm during autumn 2003, in spring, summer and autumn 2004, and in spring and summer 2005. Fish sampling was performed at 22 stations. Overall, 165 hauls were carried out. Trawls were towed during daylight and lasted for 30-60 min. After collection, adult and larger juvenile individuals were identified to species, counted, weighted, measured and released back into the water immediately. Fish larvae and small juveniles were investigated in the laboratory. More details of the construction of the trawls, the sampling procedures and catch efficiencies of the gears are given in Thiel et al. (2004, 2005). Additionally, the Federal Research Centre for Fisheries contributed catch records of lampreys from the German Baltic waters since 1991 based on data resulting from more than 3,000 hauls, taken with otter trawls. Some additional data originating from studies in the Pomeranian Bay and from hydro-acoustic surveys were available from 1978. More details regarding the sampling regime used by the Federal Research Centre for Fisheries are presented in the paper by Kloppmann et al. (2003). Compilation of recent catch records from commercial and recreational fishery In order to ensure that commercial