Working Group on Seabird Ecology (WGSE). ICES CM 2004/C:05 ...

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Our 2004 meeting attracted twelve <strong>Working</strong> <strong>Group</strong> members. The considerable efforts have been rewarded by a sense of achievement and new understandings from the data brought together, and also of the great benefits and synergies of group working to clear objectives. Following the new ‘sandwich’ arrangement, WGSE offered stakeholders the possibility to join us before and after the <strong>Working</strong> <strong>Group</strong> meeting. We were joined by Dr Euan Dunn, of the Royal Society for the Protection of Birds (RSPB)/ Birdlife International, on Friday afternoon and we discussed the contents of the nearly completed <strong>Working</strong> <strong>Group</strong> Report and the proposed Terms of Reference for WGSE 2005. We note the relative impracticality for representatives of organisations located at distance from the meeting venue to be able to discuss issues both before and after meetings. Also the ‘sandwich’ approach was announced only shortly before our meeting so that interested parties would have had little time to arrange to attend. However, WGSE welcomes participation in this form and is pleased to receive scientific information from any source. 1.4 Note on bird names Throughout the text we provide the common English names of bird species. A full list of species names together with their scientific binomial appears in Annex 3. 1.5 Acknowledgements The <strong>Working</strong> <strong>Group</strong> wishes to thank the Fishery Research Service, Aberdeen, for providing a room for our meeting, and keeping the coffee machine topped up. We particularly thank Simon Greenstreet, Ray Johnstone and Dick Ferro for providing facilities, Tony Fox, Simon Greenstreet, Ommo Hüppop, Bill Montevecchi and Dick Veit for providing information and reviewing content of sections of the report, and Bill Turrell for joining us for a very useful discussion of the approach being developed in REGNS. 2 FACTORS INFLUENCING TRENDS IN ABUNDANCE OF SEABIRDS IN THE BALTIC SEA Term of Reference: Review the factors influencing trends in abundance of seabirds in the Baltic Sea. 2.1 Introduction The status and trends of seabirds in the Baltic Sea have been reviewed at the 2003 meeting of WGSE (ICES, 2003). Given that there have been major declines in numbers of certain populations and species and increases in numbers in a few species, it is important to review likely causes for these trends. Because of a bulk of local literature in different languages in all countries bordering the Baltic Sea and also a substantial amount of unpublished information it is quite difficult to get a good country-wide coverage of these factors. The presence at WGSE of representatives from countries bordering the Baltic Sea needs to be higher to fill these apparent gaps in detail. This section is thus to specify some of the main factors known to influence seabird population trends in the Baltic Sea without being necessarily comprehensive. Also, many more details will be summarised later by others in a report to be produced for HELCOM. 2.2 Factors known or assumed to be responsible for the trends observed 2.2.1 Climate Winters of different strength have a substantial influence on distributions and numbers of waterbirds along the coast but also in offshore areas (e.g., Kube 1996; Vaitkus 2001; Garthe et al. 2003). Species with relatively restricted habitat selection, especially those living in shallow waters (e.g., common goldeneye and Steller's eider), respond to cold winters and thus ice formation much more quickly than species exhibiting a more flexible habitat selection such as velvet scoter and long-tailed ducks (Zydelis, 2001). The climatic trend is thus of major importance for explaining trends in birds spending their winter in the Baltic Sea, with many species and substantial proportions leaving the eastern Baltic already in normal winters and many more leaving even the generally warmer southern and western parts in cold winters. Unfortunately, hardly any large-scale surveys have been conducted in offshore areas in cold winters so far so that the extent of changes outside the coastal areas remains partly speculative. 2.2.2 Bycatch in fishing gear The scale of additional mortality imposed upon different seabird populations from the use of different passive fishing gears throughout the Baltic Sea is currently unknown. It is known that bycatch of many species occurs throughout the 6 ICES WGSE Report 2004
egion, but its size and importance has not been assessed. A number of national or regional investigations has been undertaken, focusing on gill-net fisheries, e.g., in Finland (Hario 1998), Latvia (Urtans and Priednieks 2000), Lithuania (Dagys and Zydelis 2002), Poland (Stempniewicz, 1994), and Germany (Kirchhoff, 1982; Schirmeister, 2003). The numerical effects of such activities vary with the type of gears used and the temporal and spatial overlap between fishery activities and seabird distribution and abundance. The impacts at the population level will vary according to the demographic patterns and the populations concerned: long-lived species with low reproductive rates suffer greater effects on overall abundance than short-lived species with high reproductive potential. A well-documented example is the study of common guillemots ringed in Sweden. Bycatches of this species appear to be the single most serious threat to the population, and the proportion of recoveries of ringed birds in fishing gear, compared with other finding circumstances, has significantly increased during a 28-year period (Österblom et al., 2002). 50% of guillemots found dead were caught in fishing nets, most notably in drift gillnets for salmon and set gillnets for cod. Österblom et al. (2002) concluded that the observed increased use of cod gillnets in the Baltic Sea may have contributed to the observed decrease in guillemot adult survival rate. 2.2.3 Fishery discards and offal Scavenging on discards and offal is a widespread phenomenon in the Baltic Sea as it is in other shelf areas of Europe, but the number of bird species involved is generally lower and strongly biased towards gulls, especially herring gulls (Garthe and Scherp, 2003). Herring gulls were clearly the most numerous scavenging species in all areas and all seasons studied, followed by great black-backed gulls, lesser black-backed gulls and mew gulls. High percentages of discarded gadids (cod, whiting), clupeids (herring, sprat), scad, rockling and offal were consumed by seabirds during experimental discarding on fishing boats, whereas percentages of flatfish consumed were extremely low. By combining official discard and offal statistics and experimental discarding, Garthe and Scherp (2003) estimated that 6,500 t of fish discards and 16,000 t of offal were consumed annually by seabirds in the Baltic Sea. The proportion of discards in herring gull pellets was on average 1.6% (range: 0–4.5%) and 17.5% (range: 9.4–25.5%), respectively, at two study sites in the southwestern Baltic Sea. Even if these percentages are not extremely high it seems likely that herring gulls in particular but also great black-backed gulls in winter and lesser black-backed gulls in summer should have benefited from this surplus food. 2.2.4 Oil pollution Zydelis and Dagys (1997) consider oil pollution due to ship traffic as the most important threat to wintering seabirds and waterbirds in the coastal zone of Lithuania. Oil rates of beached birds were up to 34% in years without any major accidents and up to 90% in years with such accidents. As oil exploration is assumed to increase in the eastern Baltic Sea chronic oil pollution is thought to be a major factor for the forthcoming years. Particular emphasis is put to strongly increasing traffic of oil tankers transporting oil from the eastern Baltic Sea coast into the North Sea and NE Atlantic. Major accidents occur from time to time. In March 2001, 1,750 birds were found dead after the 'Baltic Carrier' oil spill with estimates up to ten times higher: (www.europa.eu.int/comm/environment/civil/marin/reports_publications/final_reports/baltic_carrier.pdf). In June 2003, an oil spill from the “Fu Shan Hai” hit Christiansø, where 164 birds were found dead; total mortality was estimated as up to ten times higher, with about 50% being common guillemots (www.danbbs.dk/~lynx/chroe_obs/). 2.2.5 Predation by native and introduced predators Predation by mammalian ground predators is one of the main reasons for declines in breeding gulls and terns (as well as shorebirds) along the Baltic Sea coasts. Different predators are involved, native (e.g., red fox Vulpes vulpes) as well as introduced (e.g., American mink Mustela vison) species. In addition to other local factors, predation and disturbance by American minks has been one the main factors responsible for the decline of black-headed gulls in Latvia (e.g., Viksne and Janaus, 1993; Viksne et al., 1996). Mew gulls in Schleswig-Holstein (northern Germany) suffer from repeated breeding failure due to intense predation above all from red foxes (Kubetzki, 2001). Further east along the German Baltic Sea coast, foxes and some other mammals caused severe reduction in breeding success and breeding populations of many coastal species (Dierschke et al., 1995; Hartmann and Stier, 2003). Large-scale losses of breeding habitats such as small islands which are hardly accessible to predators have strongly enhanced the predation pressure on the remaining breeding colonies. These colonies are usually easily accessible for predators (Kubetzki, 2001). After the experimental removal of minks from islands in SW Finland some species returned to their former breeding sites (Nordström et al., 2003). However, removal of native species is a much bigger issue at least for most of the southern Baltic Sea coast (Garthe et al., 2003). ICES WGSE Report 2004 7
Page 1 and 2: ICES Oceanography Committee ICES CM
Page 3 and 4: Contents 1 Introduction............
Page 5: 1 INTRODUCTION 1.1 Participation Th
Page 9 and 10: addition, mass mortality events on
Page 11 and 12: During autumn migration surprisingl
Page 13 and 14: Table 3.4.1. Score of the nine vuln
Page 15 and 16: It might be considered useful to di
Page 17 and 18: performance and climatic variables,
Page 19 and 20: Calculation of numbers of birds in
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Page 35 and 36: Kittiwake breeding success at Foula
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Page 51 and 52: Relation to strategic plan: Resourc
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