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DIVER - German tracking study of seabirds in areas of planned Offshore Wind Farms at the example of divers
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... Of the 40 Common Murres found in fishing nets in this study, 16% had rings indicating that they were from Swedish colonies. A tracking project has shown that sea ducks and loons that are likely suffering from bycatch in the Baltic breed in the Russian Arctic (Dorsch et al. 2019, Karwinkel et al. 2020, Quillfeldt et al. 2021. Therefore, the negative effects of the Lithuanian fishery are manifested in breeding areas in other countries. ...
... Benthic prey might be successfully caught by grebes in shallow waters (Morkūnė et al. 2016), and this could be the reason why Crested Grebes were mostly bycaught in shallow coastal waters. Considering data of bird distribution at other sites, Red-throated Loons were choosing depths up to 20 m in the Baltic Sea (Dorsch et al. 2019). In general, the bycatch depth of different bird species depends not only on species-specific feeding preferences, but also on fishing depths and local specificities of prey distribution. ...
Bycatch, or the incidental capture of non-target species in fisheries, has been identified as one of the major threats affecting seabird populations worldwide. In the Baltic Sea, a globally important area for wintering seabirds, bycatch in gillnets represents an important cause of human-induced mortality for seabird species whose populations have declined significantly in recent decades. Although countries are required by European law to report official bycatch data, a lack of data on bycatch in small-scale fisheries impedes an assessment of the contribution of bycatch to declines of seabird populations. This study presents data on the total seabird bycatch in the small-scale coastal fishery for an entire country, Lithuania, in the southeastern Baltic Sea, during the 2015–2020 winter period. An average of 19.3% of the total fishing effort in net-meter days (15.5% of fishing days) were observed each winter season, resulting in observations of 909 bycaught birds from 15 species. Two species composed two-thirds of the total bycatch, Long-tailed Duck (Clangula hyemalis; 42.1%) and Velvet Scoter (Melanitta fusca; 35.4%). Bycatch composition varied with depth, with the majority of bycatch occurring in nets set at depths ≤ 10 m. Adult males dominated the bycatch of benthivorous sea ducks, whereas adult females composed the majority of piscivorous birds caught. Low numbers of juveniles in the bycatch may indicate different wintering sites for young birds. We estimate that between 1500 and 3000 seabirds were bycaught annually in the Lithuanian small-scale coastal fishery in the 2015–2020 period. Because this number is orders of magnitude larger than the bycatch officially reported by the Lithuanian authorities (six birds), our study highlights deficiencies in the country’s current bycatch reporting. In contrast to official statistics based on inadequate data, the unintended capture of seabirds in gillnets remains high, despite financial investments to minimize the impact of fisheries on biodiversity.
In Europe, the German Bight is one of the most important non-breeding areas for protected red-throated divers (Gavia stellata). It is unclear what attracts the birds to this area, especially as the food composition of seabirds outside the breeding season is notoriously difficult to study. To obtain information on prey species composition of red-throated divers in this area, faecal samples from 34 birds caught alive were analysed using DNA metabarcoding. Prey DNA was detected in 85% of the samples with a mean number of 4.2 ± 0.7 taxa per sample (n = 29). Altogether, we found a broad prey spectrum with 19 fish taxa from 13 families dominated by five groups: clupeids, mackerel, gadoids, flatfish and sand lances with clupeids being the most frequently detected prey. Our results indicate that red-throated divers are generalist opportunistic feeders in the German Bight, but pelagic schooling fish that aggregate at frontal zones and have a high energetic value might be favoured. Atlantic mackerel appears to be a more important prey for red-throated divers in this area than previously thought. The precision achievable using metabarcoding has revealed a number of prey species that are consumed by red-throated divers in the German Bight, which helps to explain the selection of this area by divers in winter and spring.
Ship traffic in Northwestern European seas is intense and continuing to increase, posing a threat to vulnerable seabird species as a result of disturbance. However, information on species-specific effects of ship traffic on seabirds at sea is limited, and tools are needed to prioritize species and areas to support the integration of conservation needs in Marine Spatial Planning. In this study, we investigated the responses of 26 characteristic seabird species in the German North and Baltic Seas to experimental ship disturbance using large datasets collected as part of the seabirds at Sea counts. We developed a Disturbance Vulnerability Index (DVI) for ship traffic combining indicators for species’ shyness, escape costs, and compensatory potential, and analyzed the relationships among shyness, escape costs, and vulnerability. The DVI was calculated using the following eight indicators: escape distance, proportion of escaping birds, proportion of birds swimming prior to disturbance, wing loading, habitat use flexibility, biogeographic population size, adult survival rate, European threat and conservation status. Species-specific disturbance responses differed considerably, with common scoters (Melanitta nigra) and red-throated loons (Gavia stellata) showing the longest escape distances and highest proportions of escaping individuals. Red-throated loon, black guillemot (Cepphus grylle), Arctic loon (Gavia arctica), velvet scoter (Melanitta fusca), and red-breasted merganser (Mergus serrator) had the highest DVI values, and gulls and terns had the lowest. Contrary to theoretical considerations, shyness correlated positively with escape costs, with the shyest species also being the most vulnerable among the species studied. The strong reactions of several species to disturbance by ships suggest the need for areas with little or no disturbance in some marine protected areas, to act as a refuge for vulnerable species. This DVI can be used in combination with distribution data to identify the areas most vulnerable to disturbance.
The increasing demand for robust marine bird abundance and distribution assessments coupled with technological advances has led to the development of digital survey techniques for birds. Although digital surveys for bird monitoring are becoming a standard method in some countries, their strengths and weaknesses and comparability with traditional visual surveys remain insufficiently documented and understood. Aiming to improve existing knowledge on digital video monitoring techniques, we conducted one parallel digital video survey with 2-cm ground resolution and a 544-m swath flown at 549 m and an aerial visual survey flown at 76 m over the southern Baltic Sea in March 2015. We assessed bird sighting rates, identification rates, observed densities, and model-based abundance estimates. The digital survey covered a larger area through direct registrations, provided higher numbers of bird sightings and identified species, and higher spatial accuracy than the visual survey. Overall species identification rates were similar between the survey methods; however, there were marked differences among bird taxonomic groups: more individuals were identified to species level in the digital survey dataset for the majority of taxonomic groups, except for grebes and auks. These advantages supplement other previously identified benefits of digital aerial surveys, such as the elimination of bird disturbance due to high flight altitude, reduced observer bias, and availability of raw data for quality assurance. Furthermore, higher numbers of direct bird sightings at a higher spatial resolution during digital surveys ensure better statistical analyses, including distribution modelling, of more species for the same survey effort.
The purpose of migration, regardless of the distance involved, is to exploit two or more environments suitable for survival or reproduction over time, usually on a seasonal basis. Yet individual organisms can practice the phenomenon differently, and birds deploy unique patterns of movement over particular segments of time. Incorporating the latest research on bird migration, this critical assessment offers a firm grasp of what defines an avian migrant, how the organism came to be, what is known about its behavior, and how we can resolve its enduring mysteries. The book clarifies key ecological, biological, physiological, navigational, and evolutionary concerns. It begins with the very first avian migrants, who traded a home environment of greater stability for one of greater seasonality, and uses the structure of the annual cycle to examine the difference between migratory birds and their resident counterparts. It ultimately connects these differences to evolutionary milestones that have shaped a migrant lifestyle through natural selection. Rather than catalogue and describe various aspects of bird migration, the book considers how the avian migrant fits within a larger ecological frame, enabling a richer understanding of the phenomenon and its critical role in sustaining a hospitable and productive environment. It concludes with a focus on population biology and conservation across time periods, considering the link between bird migration and the spread of disease among birds and humans, and the effects of global warming on migrant breeding ranges, reaction norms, and macroecology.
Expansion of offshore wind energy is vital for the reduction of CO2 emissions. However, offshore wind farms may negatively impact the environment without proper planning. Here we assess the robustness of the conclusions of earlier studies that the strictly protected red-throated diver, Gavia stellata, is strongly displaced from wind farms in the German Bight (North Sea). We modelled the distribution of divers based on two independent data sets, digital aerial surveys and satellite telemetry, in relation to the dynamic offshore environment and anthropogenic pressures. Both data types found that divers were strongly displaced from wind farms in suitable habitat. The displacement effect gradually decreased with distance from the wind farms (being very strong up to 5 km away), but a significant effect could be detected up to 10–15 km away. The telemetry data further indicated that the displacement distance decreased with decreasing visibility. The displacement distance was also shorter during the day than during the night, potentially as a response to aviation and navigation lights of the wind farms. These findings should be taken into consideration in marine spatial planning to avoid cumulative impacts on red-throated diver populations.
We describe parental feeding activities of Red-throated Loons (Gavia stellata) throughout the prefledging period at two freshwater nesting territories in coastal British Columbia. The nesting lake contained resident fish populations, but adult loons fed marine fish to their young, making an average of 11 flights per day (average duration 60 min per flight) to the ocean and returning each time with a single fish. Small shallow-bodied fish (Ammodytidae, Pholidae), which were easily swallowed by chicks, predominated in the diet during the 3 days following hatching. The total weight of fish fed to the chicks per day (8-194 g) increased over the prefledging period: adults returned fewer but larger fish (Embiotocidae) as the chick aged. Of the fish offered, 4% were too large for the chick to swallow.
Marine habitats are nowadays strongly affected by human activities, while for many species the consequences of these impacts are still unclear. The red-throated diver (Gavia stellata) has been reported to be sensitive to ship traffic and other anthropogenic pressures and is consequently of high conservation concern. We studied red-throated divers in the German Bight (North Sea) using satellite telemetry and digital aerial surveys with the aim of assessing effects of ship traffic on the distribution and movements of this species during the non-breeding season. Data from the automatic identification system of ships (AIS) were intersected with bird data and allowed detailed spatial and temporal analyses. During the study period, ship traffic was present throughout the main distribution area of divers. Depending on impact radius, only small areas existed in which ship traffic was present on less than 20% of the days. Ship traffic was dominated by fishing vessels and cargo ships, but also wind farm-related ships were frequently recorded. Red-throated divers were more abundant in areas with no or little concurrent ship traffic. Analysis of aerial survey data revealed strong effects of ship speed on divers: in areas with vessels sailing at high speed only a slow resettlement of the area was observed after the disturbance, while in areas with vessels sailing at medium speed the resettlement was more rapid during the observed time period of 7 hours. Data from satellite-tracking of divers suggest that large relocation distances of individuals are related to disturbance by ships which often trigger birds to take flight. Effective measures to reduce disturbance could include channeled traffic in sensitive areas, as well as speed limits for ships traveling within the protected marine area.
There have been efforts around the globe to track individuals of many marine species and assess their movements and distribution, with the putative goal of supporting their conservation and management. Determining whether, and how, tracking data have been successfully applied to address real-world conservation issues is, however, difficult. Here, we compile a broad range of case studies from diverse marine taxa to show how tracking data have helped inform conservation policy and management, including reductions in fisheries bycatch and vessel strikes, and the design and administration of marine protected areas and important habitats. Using these examples, we highlight pathways through which the past and future investment in collecting animal tracking data might be better used to achieve tangible conservation benefits.
Since 1979 the breeding success of c40 pairs in Hame, southern Finland has been monitored. Nests located on small islets produce more young than nests on shores. Reasons for unsuccessful nesting, including human disturbance, are considered. The red-throated diver population within the study area is on the increase. The most probable reason for this is the good breeding success, ie 1.15 offspring per pair per year.-from Authors
Seabirds select suitable habitats at sea, but these habitats may be strongly impacted by marine spatial planning, including the construction of offshore wind farms (OWFs) and the associated ship traffic. Loons (Gavia spp.) are particularly vulnerable to anthropogenic activities and are also of high conservation status, making them particularly relevant to marine planning processes. We investigated the effects of OWF construction and ship traffic on Loon distributions in the German North Sea on a large spatial scale, using a 'before-after' control impact analysis approach and a long-term data set. Many OWFs were built in or close to core areas of Loon distributions. Loons showed significant shifts in their distribution in the 'after' period and subsequently aggregated between two OWF clusters, indicating the remaining suitable habitat. The decrease in Loon abundance became significant as far as about 16 km from the closest OWF. Ship traffic also had a significant negative impact on Loons, indicating that OWFs deterred Loons through the combined effect of ship traffic and the wind turbines themselves. This study provides the first analysis of the extensive effects of OWFs and ships on Loons on a large spatial scale. The results provide an essential baseline for future marine spatial planning processes in the German North Sea and elsewhere.