Bureau Waardenburg (Netherlands)

Abstract Recently, highly pathogenic avian influenza (HPAI) A (H5N1) clade 2.3.4.4b viruses have caused mass mortality events in seabirds worldwide, raising concern for long-lived species with low reproductive rates. Using individual-level data from the 2022 mass mortality event in northwestern European Sandwich terns ( Thalasseus sandvicensis ), we show that older individuals were disproportionately more affected, while no sex bias was observed. This age-specific mortality likely removed the most experienced individuals from the population. Our findings highlight a previously underappreciated mechanism through which HPAI outbreaks may impair the resilience of long-lived avian populations.

ABSTRACTAimTo identify the broad‐scale oceanic migration routes (‘marine flyways’) used by multiple pelagic, long‐distance migratory seabirds based on a global compilation of tracking data.LocationGlobal.Time Period1989–2023.Major Taxa StudiedSeabirds (Families: Phaethontidae, Hydrobatidae, Diomedeidae, Procellariidae, Laridae and Stercorariidae).MethodsWe collated a comprehensive global tracking dataset that included the migratory routes of 48 pelagic and long‐distance migrating seabird species across the Atlantic, Indian, Pacific and Southern Oceans. We grouped individuals that followed similar routes, independent of species or timings of migration, using a dynamic time warping clustering approach. We visualised the routes of each cluster using a line density analysis and used knowledge of seabird spatial ecology to combine the clusters to identify the broad‐scale flyways followed by most pelagic migratory seabirds tracked to‐date at an ocean‐basin scale.ResultsSix marine flyways were identified across the world's oceans: the Atlantic Ocean Flyway, North Indian Ocean Flyway, East Indian Ocean Flyway, West Pacific Ocean Flyway, Pacific Ocean Flyway and Southern Ocean Flyway. Generally, the flyways were used bidirectionally, and individuals either followed sections of a flyway, a complete flyway, or their movements linked two or more flyways. Transhemispheric figure‐of‐eight routes in the Atlantic and Pacific oceans, and a circumnavigation flyway in the Southern Ocean correspond with major wind‐driven ocean currents.Main ConclusionsThe marine flyways identified demonstrate that pelagic seabirds have similar and repeatable migration routes across ocean‐basin scales. Our study highlights the need to account for connectivity in seabird conservation and provides a framework for international cooperation.

Human-driven change is impacting ecosystems globally, with consequential declines in biodiversity. Long-distance migrants are particularly susceptible as they depend on conditions over large geographical scales and are more likely to experience a greater range of pressures. One long-distance migrant that has experienced substantial declines across the North-East Atlantic is the Arctic Skua Stercorarius parasiticus however, little is known about their migratory behaviour or the routes they undertake. We used geolocators with salt-water switches to track Arctic Skuas from four breeding populations. To investigate migration strategies, we developed a Hidden Markov Model approach that used saltwater immersion data to classify stopovers and transit flights. We found that the skuas used several discrete staging areas during their south and northbound migrations with an area of apparent high marine productivity in the mid-North Atlantic being of high importance. Extensive overlap of individuals from different breeding populations occurred in staging areas, resulting in weak spatial connectivity between breeding and staging areas, further emphasizing their importance. At the population-level, variation in migration strategies was driven by individuals from Svalbard, which is declining less than the other populations tracked. Relative location of wintering areas also influenced migration strategies, with individuals migrating further spending a smaller proportion of their migration at stopovers compared to those wintering closer, and instead employed a fly-and-forage strategy. Identifying the complex non-breeding distribution, weak migratory connectivity and highly conserved migration strategies of Arctic Skuas is a vital step to link how conditions experienced during migration influences population dynamics and to prioritise future research and conservation actions.

Abstract In 2022, highly pathogenic avian influenza (HPAI) A(H5N1) virus clade 2.3.4.4b became enzootic and caused mass mortality in Sandwich terns and other seabird species across northwestern Europe. We present data on characteristics of the spread of the virus between breeding colonies and the number of dead adult Sandwich terns recorded at breeding sites throughout northwestern Europe. Within two months after the first mortalities were reported, in total 20,531 adult Sandwich terns were found dead, which is >17% of the total northwestern European breeding population. Losses are likely higher, as we expect that many victims were not found (mortality rate might be up to 74% of the breeding population). Inside the colonies almost all chicks died. After the peak of the outbreak, in a colony established by late breeders, 25.7% of adults showed immunity against HPAI subtype H5. Removal of carcasses helped in reducing the spread of the disease and consequently total mortality. More research on the sources and modes of transmission, incubation times, effective containment and immunity is urgently needed to combat this major threat for colonial seabirds.

We collected data on mass mortality in Sandwich terns (Thalasseus sandvicensis) during the 2022 breeding season in the Netherlands. Mortality was associated with at least 2 variants of highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b. We report on carcass removal efforts relative to survival in colonies. Mitigation strategies urgently require structured research.

Avian migration is recorded over long distances, but some species winter much closer to their breeding sites or do not migrate at all. Specifically, the family of gulls Laridae shows great within and among species variation in migration. However, the migration ecology of many gull species is still unknown, even for abundant and widespread species such as the Black-headed Gull Chroicocephalus ridibundus. Here, we aimed to map the migration of Black-headed Gulls using GPS-tracking data from eight birds from a declining colony at Griend in the Dutch Wadden Sea to study migration routes and timing as well as wintering habitat of these birds. Furthermore, we used this GPS-data and 199 colour-ring resightings of adult birds from the same colony to study their wintering locations and habitat. The GPS-tagged birds migrated away from the Dutch Wadden Sea between mid-September and late November. All migrated in western to south-western directions to wintering areas at 130 to 560 km from the breeding colony. The GPS-tagged individuals wintered in The Netherlands, France and the United Kingdom and migrated towards these wintering sites both diurnally and nocturnally. The data indicate that most movements over the North Sea were nocturnal, whereas most migratory movements over land were during the day. Colour-ring data showed that females wintered significantly further away than males. We found no indications for differences in timing of migration between males and females and also no sex-specific preference for nocturnal or diurnal migration. We argue that the hitherto undocumented prevalence of nocturnal sea crossings calls for a better assessment of the potential risks of offshore wind energy developments in the North Sea. As such, this and new GPS-tracking data of Black-headed Gulls can aid in the conservation of this common and widespread species by providing novel insights in migration behaviour and the connectivity between breeding and wintering grounds.

In the North Sea agreement an area 100 km2 at the Frisian Front will be designated for European flatoyster (Ostrea edulis) restoration. This report presents results from a field survey in two search areas, of 100 km2 each, concerning the suitability for restoration of European flat oysters. Sediment was sampled for grain size determination. High silt or very coarse sediment is considered unsuitable. In addition, pictures of the sea bed were taken to determine the presence of shells as potential settlement substrate for larvae. Based on the results of the field survey and subsequent laboratory analysis, both search areas at the Frisian Front are considered suitable for European flat oyster restoration, although the presence of shells was low. Within each location there were no clear gradients observed in presence of shells, which is considered suitable for the development of European flat oyster reefs, or low silt content, which is also considered suitable for the reef development. On average, the northern half of both locations seems to be more suitable than the southern half. Large-scale active restoration of European flat oyster beds is not without risks and presently unknown factors may influence the process. To enhance the success rate and spread the risk it is therefore advised to designate the northern half of both locations to reach the agreed total of 100 km2.

<p>Like other countries The Netherlands are facing several societal challenges. As space is very scarce in the Netherlands it is vital to find chances for synergy in solutions to the challenges. It is investigated whether an upgrade of natural values in a large Dutch freshwater lake could go together with installing solar panels on water and thus generate sustainable energy. Our first exploration shows that this kind of synergy has potential for both biodiversity and renewable energy. The presentation will show the design, requirements, uncertainties, chances and risks.</p><p>The area of interest is Lake IJssel, a freshwater lake covering an area of 1,100 km<sup>2</sup> with an average depth of 5.5 m. Lake IJssel was constructed by the completion of a dam in 1932, transforming the former brackish water of the Zuiderzee into a lake. The water levels are precisely controlled, and the lake provides several ecosystem services. The present ecosystem is imbalanced with low productivity and low biodiversity.</p><p>To strengthen the delta nature in the Dutch waters a national Program for nature restoration has been launched. Goal for Lake IJssel is creating more natural transitions: from wet to dry and from fresh to salt. This is done by creating the missing habitats necessary for a healthy ecosystem like shallows with submerged vegetation and wetlands with a natural fluctuation of water levels. At the same time, the region surrounding Lake IJssel is trying to find opportunities for generation of renewable energy. Solar panels on the open water of the lake is one of the options. We have developed a design consisting of a cluster of artificial island modules.</p><p>The entire design consists of seven modules of which four modules provide space for solar panels. Each solar module consists of a constructed ring dike with an open connection to the lake providing a water surface where wave action is greatly reduced so thatsolar panels can be installed safely. In this exploration, we opted for a panel coverage percentage of 50% of the surface. If we decrease the water depth by one or two meters under the solar panels with local sediment, the light can penetrate to the lake floor. This creates a favorable environment for aquatic plants. Under the panels, a relatively open, structure-rich vegetation of mainly pondweeds is expected, which is interesting for growing young fish in the summer due to a combination of food supply and shelter. In winter, when the vegetation has disappeared, these waters are expected to be attractive for the wintering of (larger) fish. In addition, the mounting structures of the panels also contribute, providing a substrate for mussels and other invertebrates.</p><p>The idea has not yet been tested in practice. The possibility of multiple use of space for ecology and energy is so far based on the judgement of the best available experts and experiences. A pilot study and monitoring are required to gain more insights in the ecological impacts of solar panels in this ecosystem.</p>

Abstract Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of δ13C and δ15N from bulk baleen has been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here we apply analysis of δ15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state, and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.4-3.5 versus 2.7-2.9, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. δ15N values from phenylalanine confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine δ15N values revealed physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.