M.J. Baptist

Bird radar validation in the field by time-referencing line-transect surveys

Track-while-scan bird radars are widely used in ornithological studies, but often the precise detection capabilities of these systems are unknown. Quantification of radar performance is essential to avoid observational biases, which requires practical methods for validating a radar’s detection capability in specific field settings. In this study a method to quantify the detection capability of a bird radar is presented, as well a demonstration of this method in a case study. By time-referencing line-transect surveys, visually identified birds were automatically linked to individual tracks using their transect crossing time. Detection probabilities were determined as the fraction of the total set of visual observations that could be linked to radar tracks. To avoid ambiguities in assigning radar tracks to visual observations, the observer’s accuracy in determining a bird’s transect crossing time was taken into account. The accuracy was determined by examining the effect of a time lag applied to the visual observations on the number of matches found with radar tracks. Effects of flight altitude, distance, surface substrate and species size on the detection probability by the radar were quantified in a marine intertidal study area. Detection probability varied strongly with all these factors, as well as species-specific flight behaviour. The effective detection range for single birds flying at low altitude for an X-band marine radar based system was estimated at ∼1.5 km. Within this range the fraction of individual flying birds that were detected by the radar was 0.50±0.06 with a detection bias towards higher flight altitudes, larger birds and high tide situations. Besides radar validation, which we consider essential when quantification of bird numbers is important, our method of linking radar tracks to ground-truthed field observations can facilitate species-specific studies using surveillance radars. The methodology may prove equally useful for optimising tracking algorithms.

Short-term impact of deep sand extraction and ecosystem-based landscaping on macrozoobenthos and sediment characteristics.

We studied short-term changes in macrozoobenthos in a 20m deep borrow pit. A boxcorer was used to sample macrobenthic infauna and a bottom sledge was used to sample macrobenthic epifauna. Sediment characteristics were determined from the boxcore samples, bed shear stress and near-bed salinity were estimated with a hydrodynamic model. Two years after the cessation of sand extraction, macrozoobenthic biomass increased fivefold in the deepest areas. Species composition changed significantly and white furrow shell (Abra alba) became abundant. Several sediment characteristics also changed significantly in the deepest parts. Macrozoobenthic species composition and biomass significantly correlated with time after cessation of sand extraction, sediment and hydrographical characteristics. Ecosystem-based landscaped sand bars were found to be effective in influencing sediment characteristics and macrozoobenthic assemblage. Significant changes in epifauna occurred in deepest parts in 2012 which coincided with the highest sedimentation rate. We recommend continuing monitoring to investigate medium and long-term impacts.

The Wadden Sea in the Netherlands: Ecotopes in a World Heritage Barrier Island System

Publisher Summary The Wadden Sea forms the coastal strip bordering the North Sea in NW Europe. Along most of its length it is separated from the North Sea by a string of barrier islands. The system consists of many recognizable geomorphic units (here called ecotopes), such as islands, high sandbanks, sand dunes, salt marshes, subtidal and intertidal sand and mudflats, and channels of different depths and widths. The Wadden Sea intertidal flats are characterized by their location within tidal basins behind barrier islands. They contain a sequence of large to small ebb and flood gullies. The flats near the inlet are predominantly sandy and those near the coast are muddy. The Wadden Sea is a mesotidal barrier island system that only has minor river influences, fringing the flat and low-lying NW European coastal plain. In contrast to most mudflat systems in the world, the Wadden Sea area has not been formed as a river delta, nor is part of an estuary or bay, although there are some estuaries and bays within the Wadden Sea itself. The Wadden Sea consists of a number of very different habitats, ranging from islands to intertidal flats, salt marshes, and gullies and channels. Depending on the mapping scale, these can be further subdivided into smaller recognizable units. For management purposes, it is essential that the proper scale is adhered to when discussing specific issues. For mapping, it is important that elements can be distinguished based on discernable characteristics. When a single organism uses different habitats for different purposes, simple correlations between habitats and the occurrence of species are confounded.

Ecologisch Gericht Suppleren: meetplan geïntegreerde ecosysteem survey 2017

Suppleties van zand op vooroever of strand worden in opdracht van Rijkswaterstaat uitgevoerd om de Nederlandse kust tegen erosie te beschermen en om voldoende zand in het kustfundament te houden. Een groot deel van de suppleties vindt plaats in of nabij de kuststrook die binnen de Natura2000 regelgeving wordt beschermd, de Noordzeekustzone. Het is dus van belang de eventuele effecten van deze praktijk op de natuur zorgvuldig te bestuderen, zodat dit effect kan worden afgezet tegenover het algemene nut voor de maatschappij. Betere kennis van de effecten kan leiden tot beperking van eventuele schade aan- en mogelijk zelfs tot versterking van- gewenste natuurwaarden en ecosysteemdiensten. Tot nog toe is er relatief weinig aandacht geweest voor de gevolgen van suppleren op vispopulaties in vergelijking met benthos, terwijl de kinderkamerfunctie van de ondiepe kustzone een zeer belangrijke economische ecosysteemdienst levert. Kennis van de habitatfactoren die het voorkomen van juveniele vis in kinderkamers bepalen leidt tot een verbeterd inzicht van de gevolgen van suppleties op vispopulaties en van de voedselketen van viseters in de ondiepe kustzone. In overleg met natuurorganisaties en de kennisinstituten Deltares en Wageningen Marine Research is in 2016 het document `Ecologische effecten van zandsuppleties’ (Herman et al., 2016) geschreven met als doel onderzoek te formuleren naar ecologische effecten van zandsuppleties. In het onderdeel ‘uitvoeringsplan’ (deel C in Herman et al. 2016) zijn 3 onderzoekslijnen (ook wel Krachtlijnen genoemd) gedefinieerd, te weten: Vooroever, Duinen en Waddenzee. Het hier beschreven meetplan voor een survey in 2017 valt onder de onderzoekslijn Vooroever. De onderzoeksvraag die in dit meetplan wordt behandeld volgt uit de prioritering van de krachtlijn Vooroever: (Cumulatieve) gevolgen van reguliere suppleties op samenstelling en functioneren van het ecosysteem van de vooroever. Deze onderzoeksvraag luidt: “Wat zijn de cumulatieve gevolgen van reguliere suppleties op samenstelling en functioneren van het ecosysteem van de ondiepe vooroever van de Nederlandse kust?” Conform het plan van aanpak voor dit programma (Herman et al., 2016) wordt voorgesteld om een survey uit te voeren in de vooroever (0 tot 10-12 m diepte), waarbij benthos, vis en habitatkarakteristieken worden bemonsterd. Deze geintegreerde ecosysteem survey is daarmee een onderdeel van een groter pakket van geplande dataverzameling in het kader van Ecologisch Gericht Suppleren II. Het hoofddoel van de survey is om data te verzamelen over het voorkomen van (juveniele) vis in relatie tot relevante omgevingsvariabelen, zowel abiotisch als biotisch. De survey zal inzicht verschaffen in het functioneren van het kustecosysteem en kennis opdoen over de wisselwerking met biotische en abiotische omgevingsvariabelen. De resultaten van de survey zullen dienen voor het opstellen van habitatmodellen voor juveniele vis om hiermee effecten van suppleties te kwantificeren. Dit rapport beschrijft de meetstrategie, de meetmethoden, de te meten variabelen (vis, benthos en omgevingsvariabelen) en de bemonsteringslocaties voor de ondiepe geintegreerde ecosysteem survey 2017.

11 – The Wadden Sea in the Netherlands: Ecotopes in a World Heritage Barrier Island System

Publisher Summary The Wadden Sea forms the coastal strip bordering the North Sea in NW Europe. Along most of its length it is separated from the North Sea by a string of barrier islands. The system consists of many recognizable geomorphic units (here called ecotopes), such as islands, high sandbanks, sand dunes, salt marshes, subtidal and intertidal sand and mudflats, and channels of different depths and widths. The Wadden Sea intertidal flats are characterized by their location within tidal basins behind barrier islands. They contain a sequence of large to small ebb and flood gullies. The flats near the inlet are predominantly sandy and those near the coast are muddy. The Wadden Sea is a mesotidal barrier island system that only has minor river influences, fringing the flat and low-lying NW European coastal plain. In contrast to most mudflat systems in the world, the Wadden Sea area has not been formed as a river delta, nor is part of an estuary or bay, although there are some estuaries and bays within the Wadden Sea itself. The Wadden Sea consists of a number of very different habitats, ranging from islands to intertidal flats, salt marshes, and gullies and channels. Depending on the mapping scale, these can be further subdivided into smaller recognizable units. For management purposes, it is essential that the proper scale is adhered to when discussing specific issues. For mapping, it is important that elements can be distinguished based on discernable characteristics. When a single organism uses different habitats for different purposes, simple correlations between habitats and the occurrence of species are confounded.

The Wadden Sea in the Netherlands

Publisher Summary The Wadden Sea forms the coastal strip bordering the North Sea in NW Europe. Along most of its length it is separated from the North Sea by a string of barrier islands. The system consists of many recognizable geomorphic units (here called ecotopes), such as islands, high sandbanks, sand dunes, salt marshes, subtidal and intertidal sand and mudflats, and channels of different depths and widths. The Wadden Sea intertidal flats are characterized by their location within tidal basins behind barrier islands. They contain a sequence of large to small ebb and flood gullies. The flats near the inlet are predominantly sandy and those near the coast are muddy. The Wadden Sea is a mesotidal barrier island system that only has minor river influences, fringing the flat and low-lying NW European coastal plain. In contrast to most mudflat systems in the world, the Wadden Sea area has not been formed as a river delta, nor is part of an estuary or bay, although there are some estuaries and bays within the Wadden Sea itself. The Wadden Sea consists of a number of very different habitats, ranging from islands to intertidal flats, salt marshes, and gullies and channels. Depending on the mapping scale, these can be further subdivided into smaller recognizable units. For management purposes, it is essential that the proper scale is adhered to when discussing specific issues. For mapping, it is important that elements can be distinguished based on discernable characteristics. When a single organism uses different habitats for different purposes, simple correlations between habitats and the occurrence of species are confounded.