101,085 research outputs found
Radio-telemetry observations of the first 650 km of the migration of Bar-tailed Godwits Limosa lapponica from the Wadden Sea to the Russian Arctic
No full textIn 1999 and 2000, 45 Bar-tailed Godwits Limosa lapponica were supplied with radio-transmitters during spring staging on the island Texel in the western Wadden Sea. With the use of Automatic Radio Tracking Stations (ARTS) on Texel and in south Sweden, and hand-held receivers on Texel, it was possible to follow the later part of the stopover period on Texel for 34 birds (76%) and the passage over south Sweden for 26 birds (58%). Thus, the method of automatic tracking of overflying migrating shorebirds works successfully where the migration corridor is narrow and predictable, as in the case with late spring shorebird migration from the Wadden Sea towards arctic Russia. The timing of departure from Texel and passage over south Sweden of radio-marked birds, with median dates of 30 May and 2 June respectively, were in agreement with published data on the spring migration of Siberian-breeding Bar-tailed Godwits L. l. taymyrensis. The individual variation in migration dates was larger than expected, with birds passing south Sweden between 25 May and 10 June, indicating that the time-window for departure might be broader than previously thought. There was no clear difference between males and females in timing of migration. The time difference between departure from Texel and passage over south Sweden (average 3.3 days) indicates that most Bar-tailed Godwits do not embark on the long flight towards Siberia directly from the western Wadden Sea, but are more likely to stop in the more easterly portion of the Wadden Sea before the final take-off. This pattern is similar to what has been found in other shorebirds and geese (e.g. Red Knots Calidris canutus and Dark-bellied Brent Geese Branta bernicla) migrating along the same route.
User limits or natural limits: can we set limits to human use, based on a natural functioning of the Wadden Sea?
No full textMytilus galloprovincialis-type foot-protein-1 alleles occur at low frequency among mussels in the Dutch Wadden Sea
No full textThe presence of M. galloprovincialis-type genes among the population of mussels in the Dutch Wadden Sea, historically described as M. edulis, was assessed. We applied the molecular technique in which a fragment of the gene coding for an adhesive protein of the byssus of mussels is amplified by PCR and assayed for length using electrophoresis. Among 321 individual mussels collected in August–October 2001 at 14 sites (5 intertidal, 9 subtidal) widely dispersed over the Dutch Wadden Sea, 6 specimens (collected at 5 sites) were found that showed a heterozygote genotype with both the M. edulis- and the M. galloprovincialis-type alleles being amplified; all others were identified as homozygotes for the M. edulis-type allele. Differentiation in frequencies of heterozygotes among sites was not detected. The ofact that the M. galloprovincialis-type allele was present at low frequency (0.0093) may be attributed to one of three possible, and not mutually exclusive, causes: incomplete diagnosticity of this marker, an historically stable introgression zone in the Wadden Sea, or a recent invasion.
Scale and intensity of intertidal habitat use by knots Calidris canutus in the Western Wadden Sea in relation to food, friends and foes
No full textIn August-October 1988-1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10000 to 25000 birds. Over 100000 knots were recorded on three occasions. Knots feed in large flocks, individual birds usually experiencing 4000 to 15000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964-1992 there were no clear trends in the number of knots, but canutus-knots were particularly abundant in July-August 1991, whereas in 1992 both subspecies were absent.
Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distribution of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m2) and Cerastoderma, and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km2, much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10-15 km2), a difference that is correlated with prey spectrum, prey availability and predictability.
Méthodologie d'étude des pics de mortalité dans les populations d'oiseaux sauvages. Application aux spatules blanches Platalea Leucorodia du Banc d'Arguin (Mauritanie) et aux eiders à duvet Somateria Mollissima de la mer des Wadden (Pays-Bas) entre 1997 et 2002
No full textLes oiseaux sauvages sont très sensibles aux fluctuations de leur environnement, Plusieurs facteurs sont susceptibles de causer dans leurs populations des pics de mortalité. La recherche de ces causes passe toujours par une phase de définition précise du problème, suivie d'une phase d'élaboration d'hypothèses et de contrôle de celles-ci pour enfin donner des éléments de réponse aux questions posées. Cette méthode est appliquée à deux exemples d'actualité, celui des Spatules Blanches Platalea leucorodia du Parc National du Banc d'Arguin en Mauritanie et celui des Eiders à Duvet Somateria mollissima dans la Mer des Wadden aux Pays-Bas. Les réponses proposées laissent encore de la place à de futures recherches. Grâce à de telles études, des mesures pertinentes peuvent être prises dans les cas où une intervention humaine est envisagée pour contrôler les mortalités
Valuation of functions of the Wadden Area
No full textThe rationale of this position paper is to explore ways to employ valuation methods to assess the impacts of alternative policy decisions on the functions of the Wadden Area. Based on this rationale, this paper aims to bring an ecological-economic perspective on the benefits of the Wadden Area. It highlights key issues involved in the notion and application of monetary valuation methods for valuing the (ecological) functions of the area. It also pays attention to the development of policy handles on the basis of the outcome of the valuation of ecological functions. Particularly, the paper discuss Payment for Environmental Services (PES), which aims at preservation and protection by purchasing conservation. The use of a valuation instrument within a Payment for Environmental Services Scheme is new. Valuation is of course an established technique within a Cost-Benefit framework. However, Payment for Environmental Services is an innovative way of designing policy instruments in the collaboration between ecologists and economist
Spatially structured genetic variation in a broadcast spawning bivalve: quantitative vs. molecular traits
No full textUnderstanding the origin, maintenance and significance of phenotypic variation is one of the central issues in evolutionary biology. An ongoing discussion focuses on the relative roles of isolation and selection as being at the heart of genetically based spatial variation. We address this issue in a representative of a taxon group in which isolation is unlikely: a marine broadcast spawning invertebrate. During the free-swimming larval phase, dispersal is potentially very large. For such taxa, small-scale population genetic structuring in neutral molecular markers tends to be limited, conform expectations. Small-scale differentiation of selective traits is expected to be hindered by the putatively high gene flow. We determined the geographical distribution of molecular markers and of variation in a shell shape measure, globosity, for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea and adjacent North Sea in three subsequent years, and found that shells of this clam are more globose in the Wadden Sea. By rearing clams in a common garden in the laboratory starting from the gamete phase, we show that the ecotypes are genetically different; heritability is estimated at 23%. The proportion of total genetic variation that is between sites is much larger for the morphological additive genetic variation (QST = 0.416) than for allozyme (FST = 0.000–0.022) and mitochondrial DNA cytochrome-c-oxidase-1 sequence variation (ΦST = 0.017). Divergent selection must be involved and intraspecific spatial genetic differentiation in marine broadcast spawners is apparently not constrained by low levels of isolation.
Trends in Wadden Sea Fish Fauna, Part II: Dutch Demersal Fish Survey (DFS)
No full textShallow waters along the North Sea coast provide nursery areas for juveniles of several fish species, including commercially exploited species, and natural habitat for resident species and seasonal visitors. These areas have gone through major changes in the last decades due to climate change and human activities, which will likely result in changes in the abundance and species composition of the fish fauna in coastal waters
wasn't/wadden
No full textbe vThere wasplenty o' fish,but you couldn't _ couldn't fish among _ ....at them times down there;you wadden allowed to fish....YesJ. D. A. WIDDOWSON AUG 1974Used I and SupUsed SupUsed SupSource appears in DNE Sup as T 409-6
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