We analysed ~310 records of river lampreys Lampetra fluviatilis (Linnaeus, 1758) (~19 977 663 specimens) and 54 records of sea lampreys Petromyzon marinus Linnaeus, 1758 (~86 specimens) for the southern parts of ICES Subdivisions 22 and 24 to 26 in the Baltic Sea covering the period 1649 to 2005. Most sea lamprey records came from Subdivisions 22 and 24. The majority of river lamprey records stem from Subdivisions 24 and 26. We found no distinct temporal trend for sea lamprey stock development. However, a long-term trend showing decreasing catches of river lamprey was detected, indicating a stock decrease of this species from 1887 to 1999. The largest numbers of lamprey (largely river lamprey but may include some sea lamprey as species were not distinguished in the past) were caught in the period 1890 to 1919. Approximately 82% of the total lamprey catch in our study area was made in Subdivision 26. Roughly 65.3% of the mean annual yield of lampreys came from the lower Vistula River, the Vistula Lagoon and the Bay of Gdań sk. The river lamprey was mainly distributed in estuarine and coastal marine areas. Offshore records of sea lamprey were also rare. From 1990 to 2005, most river lamprey records and recorded individuals originated from the Szczecin Lagoon and its adjacent waters, demonstrating the present importance of these waters for their spawning migrations. Of 9 known river lamprey spawning sites, 5 were found in the Peene River system which flows into the Szczecin Lagoon. At present, no sea lamprey reproduction site is known from rivers of the German Baltic Sea area. A rebuilding programme is required for the river lamprey; this should definitely contain measures to restore lost spawning sites and the connectivities within the river systems where spawning populations still occur. Protected areas in estuarine waters with important lamprey migration routes may be an additional measure for the conservation of these anadromous species.

The zebra mussel (Dreissena polymorpha), a sessile suspension feeder, has been known to enhance the benthos in the sediment around mussel beds and druses. The enhancement is mainly due to biodepositing activity of the mussel and the resultant organic enrichment of the sediment. In addition, mussel beds increase habitat complexity. In June 2007, we studied the distribution of D. polymorpha beds and their effects on the benthos in Kleines Haff, the western part of the Szczecin Lagoon, a Southern Baltic coastal water body. We expected that: (i) the sediment near a Dreissena bed will support meio-and macrobenthic assemblages more abundant than those living away from the bed, and (ii) the meioand macrobenthic assemblages close to the Dreissena bed will show a stronger dominance of the taxa relying on the organic enrichment (nematodes among the meiofauna; oligochaetes and chironomids among the macrobenthos). Meiobenthos was sampled at two localities, one (MB4) featuring D. polymorpha druses and the other (MB5) supporting a distinct zebra mussel bed. The two localities differed in their meiobenthic communities: whereas no difference in abundance and composition was observed between the sets of samples collected at MB4, MB5 showed a distinctly more abundant meiobenthos in the uppermost sediment layer near the zebra mussel bed, but the overall abundance was lower than that away from the bed. We conclude that the meiobenthic response to the presence of D. polymorpha was, at least in part, mediated by site-specificity of sediment characteristics. Macrozoobenthos was sampled at four stations in the vicinity of MB5 and around another Dreissena locality (MB10), and was also identified in the sediment samples collected for the meiobenthos. The macrobenthic abundance was higher by a factor of 2.4 (sandy sediment) to 4.9 (silty bottom) near the Dreissena beds than away from them. Irrespective of their situation relative to Dreissena aggregations, both meio-and macrobenthos were dominated by the taxa associated with organic enrichment. The macrobenthos associated with Dreissena beds included Gammarus tigrinus, a non-indigenous amphipod, whereas another non-native species, the polychaete Marenzelleria neglecta, was present in the macrobenthos of sandy sediments of the area.

The status of twaite shad was investigated within the Southern Baltic Sea and transitional area between the Baltic and North Seas (division IIIa). The following sources of data were analysed: (i) commercial catch statistics and relevant publications, (ii) records from ichthyological museum collections, (iii) records from recent commercial and recreational fisheries, (iv) research fisheries with trawls. A total of 476 records of twaite shad including more than 16 million individuals were obtained for the time between the years 1836 and 2005. About 72.9% of all records originated from commercial catch statistics and publications, whereas 18.9% were received from ichthyological collections. Research fisheries provided 6.3%, and 1.9% of the records were obtained from recent commercial and recreational fisheries. Most records of twaite shad were estimated for subdivisions 24 (45.2%) and 26 (35.5%). From 1836 to 1959, 29.

Between spring 2001 and autumn 2004, the habitat use, vertical migration, and density of Mysis relicta in the lakes "Breiter Luzin" and "Schmaler Luzin" in northeastern Germany were investigated by horizontal net hauls, epibenthic sledge hauls, and SCUBA diving. On 3-4 July 2001 we estimated a density of 466.03 ind./m 2 in the water column of lake "Breiter Luzin", but in April of 2002 population density was only 5.26 ind./m 2 . In October 2004 the observed densities increased with depth, starting at the lower sublittoral down to the upper profundal on about 1000 ind./m 2 . Downward from 22 m, densities fluctuated around this value up to 30 m depth. During daytime, mysids were never observed above 9 m. Below this limit all suitable parts of both lakes were occupied. We found no evidence for a preference of different sediment types as mud or sand. During daytime mysids showed a strong affinity for the lake bottom, and adults tend to live in deeper areas than juveniles. At night this distribution seems to be inverted. In July 2001 the proportion of adults (especially females) was highest in the metalimnion and the upper hypolimnion, whereas the proportion of juveniles increased with depth.

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