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Summary The study analyses for the first time the diet composition of grey seals inhabiting the Polish Baltic Sea coast. Samples of seal scat were collected in the Mewia Łacha Nature Reserve at the mouth of the Vistula River. Using genetic and osteological methods, the remains of organisms included in the grey seals diet were analysed for their taxonomy (families and species). Based on the analysis of 49 scat samples from grey seals, 761 hard parts that could be identified by taxon were isolated. The predominant species in the samples were perch, Perca fluviatilis (almost 78% of samples); pikeperch, Sander lucioperca (67%); lamprey, Lampetra fluviatilis (almost 35% of samples); Baltic cod, Gadus morhua callarias (almost 31% of samples) and sea trout, Salmo trutta trutta (26.5%). Genetic analysis confirmed the presence of Atlantic cod DNA in 69% and sea trout in 63% of samples. The genetic material of the Atlantic herring, Clupea harengus has not been identified in the analysed scat samples. Information on grey seals feeding on river lampreys seems to be valuable in the context of lack of knowledge on the occurrence of lampreys in the Vistula River. The methodology used showed that seals fed on species that were the most abundant in the area which is directly associated with the migration cycle of fish. The results of our study allowed the conclusion that the grey seal is an opportunistic predator and its diet reflects and exploits the variations in its habitat.

Catch and consumption of torpedo scad (Megalaspis cordyla) over the western Indian Ocean, but also the western Pacific from Japan to Australia is constantly increasing. Taking into account the degree of exploitation and missing information on the population structure of torpedo scad stocks it is crucial to provide population data. The analysis included individuals obtained in 2012 and 2013 from local markets in Madagascar, Tanzania, Vietnam and Cambodia and after successful DNA extraction fragment of the nuclear rhodopsin gene (RH1) and 9 microsatellite regions (SSRs) were amplified and analysed. Based on the obtained results it was found that there was no 100% overlap between the compared RH1 sequences and those from GenBank. In the case of the studied SSRs, the results allowed the initial characterisation and assessment of the genetic diversity of populations. Moreover, population assignment test distinguished the studied populations into two geographically distant subpopulations.

The first occurrence of striped red mullet Mullus surmuletus in the Pomeranian Bay (in 2007) and the occurrence of three very rarely noted species (tub gurnard Chelidonichthys lucerna , Atlantic horse mackerel Trachurus trachurus , thicklip grey mullet Chelon labrosus ) collected in 2007–2008 in the Pomeranian Bay, Szczecin Lagoon and Lake Dąbie are reported. Their expansion is probably due to increased sea temperatures resulting from climate change, as well as the inflow of saline water. The ‘visitors’ hosted eight pathogens from four taxonomic groups: Protozoa, Nematoda, Acanthocephala and Mollusca. Nematodes, the most numerous ones, were found in three host species. All the parasite species were new for the hosts examined; only the larvae of the acanthocephalan Corynosoma strumosum had already been recorded in one of the hosts ( Chelidonichthys lucerna ). The stomachs of almost all the fish examined were empty, but the species composition of the parasite fauna found showed that the fish must have ingested some food in the Pomeranian Bay.