Consumption of discards by herring gulls Larus argentatus and lesser black-backed gulls Larus fuscus off the Belgian coast in the breeding season

Fishery discards in the Belgian part of the North Sea are a source of food for Herring Gulls Larus argentatus and Lesser Black-backed Gulls L. fuscus. To understand the importance of discards for local L. argentatus and L. fuscus populations, single-item discard experiments were performed at four offshore distances from the gullery of the Port of Zeebrugge, at four different stages of the breeding season (May to August 2011). We compared flock composition during discarding with the distribution of Herring and Lesser Black-backed Gulls, with respect to offshore distance from the colony as reflected by an 11-year (2002-2013) dataset of standardised ship-based surveys. Consumption of discards depended on the type of fish that was discarded, but prey selectivity by adults was reduced during the chick rearing stage. A generalised linear mixed model identified the number of scavengers following the vessel, the proportion of adults and of Herring Gulls in the flock and the frequency of food robbery events interacting with the stage of the breeding season as affecting the variation in flatfish consumption. Shifts in scavenger flock composition and discard consumption between stages of the breeding season are likely linked to variation in food requirements of the gull population along the season and to dispersal patterns towards the end of summer. Nutrient requirements of breeding adults peak during the chick rearing stage, making this a key period in terms of dependence of the breeding parents on discarded fish as food source

Mass Mortality Caused by Highly Pathogenic Influenza A(H5N1) Virus in Sandwich Terns, the Netherlands, 2022

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

Combining video and GPS-tracking to study the spatial foraging distribution of a single-prey loading seabird

Seabirds are valuable indicators of marine ecosystem processes and studying seabird diets can shed light on natural or human-induced variability in food-web composition. Specifically single-prey loading seabird species such as terns have the potential to act as visual sentinels of prey availability offshore. However, obtaining diet information from remote bird colonies is often challenging and time consuming. In this pilot study we present a novel approach to combine two established methods to study seabird foraging ecology, providing a powerful and cost-effective tool to study the distribution of prey items available to seabirds. We combined GPS tracking data of Sandwich Terns (Thalasseus sandvicensis) with prey-observations from a hide in 2012 and 2013, and from semi-continuously recorded camera footage in 2017. By doing so, we identified 115 approximate catch locations of prey (86 herring/sprat Clupeidae, 29 sandeel Ammodytidae). Combining GPS-data and prey observations yielded detailed knowledge on the movements and chick diets of tracked birds as well as the spatial origin and lengths of captured prey items. Further catch distances of both Clupeidae and Ammodytidae resulted in deliveries of larger prey items and thus higher energy yield per trip, but also a higher energy expenditure per trip. We discuss the limitations and potential of our methodological approach to study foraging energetics during chick-provisioning of seabirds that carry prey items visible in their beaks

Attracted to the outside : a meso-scale response pattern of lesser black-backed gulls at an offshore wind farm revealed by GPS telemetry

Among seabirds, lesser black-backed gulls (Larus fuscus) are considered to be at high risk of colliding with offshore wind turbines. In this respect, we used GPS tracking data of lesser black-backed gulls caught and tagged in two colonies along the Belgian North Sea coast (Ostend and Zeebrugge) to study spatial patterns in the species’ presence and behaviour in and around the Thornton Bank offshore wind farm (OWF). We found a significant decrease in the number of GPS fixes of flying birds from up to a distance of at least 2000 m towards the middle of the wind farm. Non-flying birds showed a similar avoidance of the wind farm interior, yet presence strongly peaked right at the wind farm’s edge, demonstrated to represent gulls perching on the outer turbine jacket foundations. The findings of this study reveal a strong within-wind farm variability in bird density, a most crucial parameter in collision risk modelling. The method presented here is straightforward and similar studies conducted at other wind farm sites on a range of large gull species (Larus sp.) would allow to assess the potential and species-specific variation in meso-scale response patterns and to gain insight in the underlying ecological incentives, which in turn would provide widely applicable and much-needed input for (cumulative) collision impact assessments

Sensitivity assessment as a tool for spatial and temporal gear-based fisheries management

Assessment of ecosystem health is required in the ecosystem approach to fisheries management (EAFM). Mitigation measures that address impacts exceeding the acceptable level also require assessment. The various fishing métiers have different ecosystem impacts and this makes it difficult to assess them jointly. Sensitivity of the ecosystem to individual fishing métiers has been assessed previously, but to our knowledge, concurrent comparisons of different métiers on the same ecosystem have not been done. In this study, we combined the main characteristics of established approaches to sensitivity assessment into a single roadmap, called Sensitivity Assessment of Gear Effects (SAGE). SAGE is a widely applicable, three-step process to assess the ecological concerns of EAFM. The methodology used in the SAGE roadmap is built on a scoring system, which then results in a sensitivity index of the ecosystem components to the fishing métiers. The scoring system is based on a combination of expert judgement and data, both qualitative and quantitative. It allows for cross-evaluation of fishing métiers and ecosystem components. Sensitivity maps are created using the spatial and temporal distribution patterns of the ecosystem components in the index. The uncertainty of the sensitivity scores and maps are estimated through a pedigree index. The index is based on proxy representation, empirical basis, methodological rigour, theoretical understanding and degree of validation, all of which measure the strength of the research results. The proposed methodology is illustrated using a case study that compares the ecosystem effects of beam trawl and trammel net fisheries. The selected examples did not result in unexpected outcomes, but were rather chosen to evaluate the applicability of our methodology. They illustrate how a semi-quantitative framework, which includes the uncertainties associated with scientific assessments, can deliver holistic advice to fisheries managers in a fully transparent manner