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Validatie fysische parameters: optimalisatie methodologie voor het bepalen van sedimentaanvoer naar het Schelde-estuarium
No full textMonitoring van kustbroedvogels in de SBZ-V ‘Kustbroedvogels te Zeebrugge-Heist’ en de westelijke voorhaven van Zeebrugge tijdens het broedseizoen 2018
Get PDFThis report describes the fluctuations in the numbers of breeding pairs in the Special Protected Area under the Bird Directive ‘Kustbroedvogels te Zeebrugge-Heist’ and in the adjacent western port of Zeebrugge during the period 1985-2017. Until recently, this was by far the most important breeding site for coastal breeders in Belgium and of high importance (> 1% of the biogeographic population) for the European tern populations as a whole. The conservation targets that were set in 2004 (being 22 ha of suitable nesting habitat without significant impact by land predators) for terns breeding in the Special Protected Area were never met since. The populations of the 3 tern species (Sandwich, Common and Little Tern) and of Black-headed Gulls breeding in the Special Protected Area have strongly declined after 2008 and the reproductive output has been extremely poor ever since. The decline is due to the presence of land predators, initially cats and rats, and from 2009 onwards also fox. The maximum number of breeding pairs amounted to respectively 4,067, 3,052 and 425 for Sandwich, Common and Little Tern,, but in 2016 these species no longer bred in the SPA. In 2017, fox was not present and the area again attracted Common Terns, although in lower numbers than before. In 2018, the SPA hosted 560 pairs of Common Tern, 23 pairs of Little Tern, 52 pairs of Black-headed Gull and 2 pairs of Mediterranean Gull, next to 60 pairs of Herring Gull and 354 pairs of Lesser Black-backed Gull. Considering the SPA conservation targets, the nests of the latter two species were systematically cleared. About 60% of the tern population chose to breed in the areas that were electrically fenced to prevent fox predation and disturbance. Eventually almost all tern chicks outside the fence were predated by fox, leading to a poor breeding success of Common Terns of 0.2 fledglings per pair. Inside the electric fence breeding success was not measured, but seemed somewhat higher. Also, in the non-protected western part of the Zeebrugge port, breeding numbers are in strong decline due to fox disturbance and predation and deterioration of the habitat. This area used to host large numbers of Herring Gulls (max 2,433 pairs in 2010) and Lesser Black-backed Gulls (max 4,760 pairs in 2011), but after 2013 both species strongly decreased in numbers as foxes frequented the breeding site. In 2018, 375 pairs of Herring Gull and 852 pairs of Lesser Black-backed Gull bred in the western part of the port, all on fox-free rooftops or in electrically fenced areas. The total population in Zeebrugge (SBZ-V included) amounted to 472 and 1,390 pairs, respectively. After 2013 the numbers of Herring and Lesser Black-backed Gull have increased elsewhere in Flanders and especially along the coast the number of breeding sites is rapidly growing. This suggests that part of the Zeebrugge colony has moved to both new and existing breeding sites. Indeed, recoveries of colour-ringed individuals revealed that there is a strong connection between Zeebrugge and other breeding sites along the Flemish coast. Other ringed gulls moved to existing colonies in the north of France, the south of the Netherlands and the south-east of the UK. Colour ring sightings further suggest that the gulls that colonised the SBZ-V most likely originate from the western part of the Zeebrugge port
First results from WATERHYPERNET - a Network of Hyperspectral Radiometers for Multi-satellite Water Reflectance Validation adapted to Sentinel-2ABCD
Get PDFInsights into the short-term tidal variability of multibeam backscatter from field experiments on different seafloor types
Get PDFThree experiments were conducted in the Belgian part of the North Sea to investigate short-term variation in seafloor backscatter strength (BS) obtained with multibeam echosounders (MBES). Measurements were acquired on predominantly gravelly (offshore) and sandy and muddy (nearshore) areas. Kongsberg EM3002 and EM2040 dual MBES were used to carry out repeated 300-kHz backscatter measurements over tidal cycles (~13 h). Measurements were analysed in complement to an array of ground-truth variables on sediment and current nature and dynamics. Seafloor and water-column sampling was used, as well as benthic landers equipped with different oceanographic sensors. Both angular response (AR) and mosaicked BS were derived. Results point at the high stability of the seafloor BS in the gravelly area (2 dB and 4 dB at 45° respectively. The high-frequency backscatter sensitivity and short-term variability are interpreted and discussed in the light of the available ground-truth data for the three experiments. The envelopes of variability differed considerably between areas and were driven either by external sources (not related to the seafloor sediment), or by intrinsic seafloor properties (typically for dynamic nearshore areas) or by a combination of both. More specifically, within the gravelly areas with a clear water mass, seafloor BS measurements where unambiguous and related directly to the water-sediment interface. Within the sandy nearshore area, the BS was shown to be strongly affected by roughness polarization processes, particularly due to along- and cross-shore current dynamics, which were responsible for the geometric reorganization of the morpho-sedimentary features. In the muddy nearshore area, the BS fluctuation was jointly driven by high-concentrated mud suspension dynamics, together with surficial substrate changes, as well as by water turbidity, increasing the transmission losses. Altogether, this shows that end-users and surveyors need to consider the complexity of the environment since its dynamics may have severe repercussions on the interpretation of BS maps and change-detection applications. Furthermore, the experimental observations revealed the sensitivity of high-frequency BS values to an array of specific configurations of the natural water-sediment interface which are of interest for monitoring applications elsewhere. This encourages the routine acquisition of different and concurrent environmental data together with MBES survey data. In view of promising advances in MBES absolute calibration allowing more straightforward data comparison, further investigations of the drivers of BS variability and sensitivity are required
Discards in the common fisheries policy: the evolution of the policy
Get PDFThis chapter deals with the development of the European Union (EU) discard policy over time. It describes the process from 1992, when the issue of discards was first recognised in the Common Fisheries Policy (CFP) reform process, to the Landing Obligation (LO) adopted in 2013. It analyses the context to which policy choices were made that shaped the present format of the EU LO, how it is being implemented and the impact it is having on associated fisheries management measures. Finally, future possible policy developments are examined
Advies over de potenties voor natuurontwikkeling op de voormalige campings te Raversijde - Oostende
Get PDFMetabarcoding free-living marine nematodes using curated 18S and CO1 reference sequence databases for species-level taxonomic assignments
Get PDFHigh‐throughput sequencing has the potential to describe biological communities with high efficiency yet comprehensive assessment of diversity with species‐level resolution remains one of the most challenging aspects of metabarcoding studies. We investigated the utility of curated ribosomal and mitochondrial nematode reference sequence databases for determining phylum‐specific species‐level clustering thresholds. We compiled 438 ribosomal and 290 mitochondrial sequences which identified 99% and 94% as the species delineation clustering threshold, respectively. These thresholds were evaluated in HTS data from mock communities containing 39 nematode species as well as environmental samples from Vietnam. We compared the taxonomic description of the mocks generated by two read‐merging and two clustering algorithms and the cluster‐free Dada2 pipeline. Taxonomic assignment with the RDP classifier was assessed under different training sets. Our results showed that 36/39 mock nematode species were identified across the molecular markers (18S: 32, JB2: 19, JB3: 21) in UClust_ref OTUs at their respective clustering thresholds, outperforming UParse_denovo and the commonly used 97% similarity. Dada2 generated the most realistic number of ASVs (18S: 83, JB2: 75, JB3: 82), collectively identifying 30/39 mock species. The ribosomal marker outperformed the mitochondrial markers in terms of species and genus‐level detections for both OTUs and ASVs. The number of taxonomic assignments of OTUs/ASVs was highest when the smallest reference database containing only nematode sequences was used and when sequences were truncated to the respective amplicon length. Overall, OTUs generated more species‐level detections, which were, however, associated with higher error rates compared to ASVs. Genus‐level assignments using ASVs exhibited higher accuracy and lower error rates compared to species‐level assignments, suggesting that this is the most reliable pipeline for rapid assessment of alpha diversity from environmental samples
