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In the past the European otter Lutra lutra was distributed throughout most of Europe but since the 1980s its distributional range has been reduced. Currently, the otter population is increasing. Conservation efforts have been implemented, however due to the natural elusiveness of the species it is difficult to monitor. Non-invasive sampling has proven to be the most effective method to derive population parameters such as presence/absence, genetic variability and population structure in European otters. The method to collect non-invasive samples is robust and provides reliable data. This study investigates the validity of the present state-of-The-Art method of identifying otter feces, and suggests modifications and improvements of the method. Results from the comparison of field collected data and data derived from a blind test show that the method is applicable in areas abundant with otters, however the method loses its power in the periphery of the distributional range. In these areas, it would be relevant to supplement traditional sampling with DNA analysis to verify the identification of the sample.

The Danish part of theWadden Sea comprises 1,500 km2, and makes up about one tenth of the wholeWadden Sea area. In contrast to the other parts of theWadden Sea the water quality in the Danish section is not influenced by large rivers, but mostly inputs from the North Sea. During the period 1990-2010 nitrogen in the water body has been nearly halved. The increase in the number of houting, an endemic fish species, indicates it may now be secure due to intensive river restoration. Breeding birds are numerous, but the populations of many species have decreased recently. Millions of water birds stay during spring and autumn, and the site is of international importance to 20 species. The harbour seal is the most numerous of the sea mammals, and the small population of grey seal is increasing in number. The Danish part of the Wadden Sea is well protected, but still under pressure from changes in land use and recreational activities.

Hunting of eiders Somateria mollissima from motorboats is common in Danish marine waters, and to reduce hunting pressure on eiders and other diving duck species in Denmark, motorboat hunting was banned within 42 marine sites covering an area of 2,934 km2, although the effects of this regulation have to date not been examined. Our case study analyses the effects of excluding motorboat hunting from an area of 682 km2 of the Danish Wadden Sea (hereafter the ‘Study Area’) which also supported a large area of blue mussel beds, the preferred food for eiders. Our study covered the entire Danish Wadden Sea (total area 1,225 km2) during the hunting seasons (October-February) of 1980–2003 using 85 aerial surveys of eiders and motorboats used by hunters. Eider numbers increased by 56% in the Study Area following the ban on motorboat hunting despite a 50% reduction in the eider flyway population over the same period. There was a significant negative relationship between the density of hunter motorboats and t...

Escape distances (EDs) have been used to study sensitivity of waterbirds to different sources of disturbance, to design reserves for waterbirds, and to define eco-targets for the Wadden Sea management plan. However, the use of ED as an index of sensitivity has been criticised because it can be highly variable. Although some factors affecting variation in the EDs of species have been studied, there is still a need for further analysis of factors that may affect it. In this study, we analysed the EDs of 19 waterbird species (geese, ducks, waders and gulls) exposed to a walking person (N = 1,371) during autumn and spring 1980–1984 under controlled conditions in the Danish Wadden Sea. We analysed how EDs varied between species in relation to body mass and hunting and within species in relation to flock size and weather conditions. EDs increased significantly with species body mass, and quarry species (dabbling ducks, curlew Numenius arquata, golden plover Pluvialis apricaria, common gull Larus canus ...

Although the Danish Wadden Sea is of international importance for several bird species, large-scale blue mussel Mytilus edulis fishing took place from 1984–1987, ceasing thereafter due to low mussel stocks. Mussel fishing removes much of the blue mussel biomass, especially larger individuals. Hence we predict that intensive mussel fishing will affect their predators, such as the Eider Somateria mollissima , which is predominantly a blue mussel feeder by, 1) reducing the amount of blue mussels in their diet relative to alternative prey items, 2) exploitation of smaller blue mussel shell classes, 3) loss of body condition, 4) changing feeding distribution to aggregate to the remaining mussel stocks, and 5) decreasing numbers. Before winter 1986/87 blue mussel biomass was estimated at 40,600 tons, decreasing to 15,400 tons in 1987/88 due to mussel fishery. We collected Eiders in both periods to monitor their diet and body mass and used aerial surveys to determine changes in numbers and distribution. Between the two periods, blue mussels declined in the Eiders diet, numbers of Eiders with empty stomachs increased and the mean length of blue mussel taken by Eiders decreased. Eider body condition declined from 1986/87 to 1987/88, mostly the result of the reduction in numbers of individuals with blue mussel remains in their gizzards and in better body condition compared to those taking alternative food items or having empty gizzards. Eiders shifted their distribution from the southern part of the Danish Wadden Sea to the northern part, where the remaining blue mussel stocks were situated. Eider numbers were lowest in 1987/88, the year of lowest blue mussel stocks. We conclude that intensive mussel fishery affected the Eider's diet, reduced their body condition and affected distribution and abundance. The results also showed that availability of blue mussels may have a key role in building up and maintaining body condition in Eiders during winter.

Estimating ‘total counts’ of waterbirds from aircraft is a widely used survey method, and we assessed the effectiveness of this method for geese, ducks, waders and gulls by comparing the results of counts from aircraft with ground counts in the Danish Wadden Sea during 1984–1998. In total, 47 counts were carried out in 12 counting sites and the results were compared for 18 waterbird species, which varied in abundance, flock size and degree of aggregation. Significantly greater numbers of waterbird species were identified from the ground than from aircraft (mean number: 16.1 vs 10.6 species). Depending on the accuracy of aerial counts compared to ground counts, the species were divided into three categories: a) brent goose Branta bernicla, shelduck Tadorna tadorna, mallard Anas platyrhynuchos, eider Somateria mollissima and oystercatcher Haematopus ostralegus had a high level of correspondence between densities obtained from ground and aerial counts (detection rate of >80% with no statistical diff...

Tusenøyane in southeast Svalbard is the main nesting area of the Svalbard population of light-bellied brent goose. Field studies in Tusenøyane in 1987, 1989 and 1991 show that nesting geese are subject to heavy nest predation pressure by polar bears Ursus maritimus, and in some years arctic foxes Alopex lagopus prevent geese from attempting to nest. Polar bears are most abundant when there is dense pack ice in the surrounding Barents Sea. Geese nesting in territories with high snow cover during early incubation suffer the heaviest predation pressure. Sea-ice cover in the Tusenøyane area, as shown by satellite imagery, at the time of incubation explained 58% of the variance in breeding output of the population as a whole (n = 17 years). Nest predation pressure appears to be a major factor in limiting the ability of the Svalbard population of light-bellied brent geese to recover to its former size. Geese arrive at Tusenøyane during the first week of June, but wait 7-10 days before laying eggs. Eggs hatch at a time when the quality of the preferred food plant, Cochlearia officinalis, has started to deteriorate and when most of plants of highest quality and size have already been depleted by the adult birds. It is suggested that the timing of nesting is a compromise between optimal food quality and avoidance of nest predation by polar bears.

Regime shifts are likely to have strong impacts on all trophic levels and their interactions. In addition, weather conditions and sea level rise together with tidal currents may change sediment morphology in coastal areas and estuaries. Here, we studied the effects of these drivers of ecosystems on abundance of seven wader species feeding on macrozoobenthos in the German sector of the Wadden Sea. We hypothesized that regime shift caused decreases in wader abundance and that changes in sediment morphology driven by sea level rise and tidal amplitude affected these changes. We analyzed numbers of waders on a short term, 1998–2016, that matched a large-scale geographical study of sediment morphology in the German sector, and at a long term, 1987–2019. Changes in numbers of waders were estimated as slope of coefficients of the trends of wader species numbers in the two periods. The average (se) year of decreases in numbers of waders was initiated for most species and tidal basins in the year 1992 (± 0.4) that followed a regime shift in the Southern North Sea and in the Wadden Sea in 1988–1989. There were no statistical differences between the years when numbers of waders started to decrease between the northern and the southwestern tidal basins of the German sector, indicating that the drives affected both coastal sections simultaneously. Significant relationships were found between slopes of coefficients of wader species and sediment morphology and physical features as sea level rise and tidal amplitude. Relationships were most pronounced for the long term, 1987–2019 compared to the short term, 1998–2016. We conclude that regime shift and changes in sediment morphology driven by sea level rise and sediment change can affect abundance of migratory wader species in large estuaries and shallow coastal waters.

During the summer of 1982 waders, Charadriidae, were recorded regularly by FM in the station area of Ny-Alesund (78"55'N, ll"56'E). From 6 to 18 July waders were censused by HM and JF in a 6.32 kmz area around Ny-Alesund (Fig. 1). Parts of the area were covered each day and all birds seen were mapped. All suitable habitats were covered within a distance of 25-50111 at least once, and early snow-free ridges were surveyed especially.