Search

Introduction: Drones, or Unmanned Aerial Vehicles (UAVs), have emerged as valuable tools for wildlife monitoring, offering potentially non-intrusive observations in challenging terrains like marine ecosystems. Despite their potential, widespread use is impeded by regulatory constraints, especially in protected areas. Methods: This study aims to assess the impact of varying flight altitudes and flight approaches of two commercial drones on the behaviour of harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) and compare to existing findings for marine mammals. We conducted a comparative analysis of the response to flight altitude from 70 m gradually descending to 10 m and two different flight approaches between the DJI Phantom 4Pro and the Autel EVO II RTK drones in the Danish part of the Wadden Sea. Results: We found varying responses, where species-specific sensitivity and environmental conditions appeared to influence the behavioural reactions of the seals. Our results reveal that seal reactions to drones are complex and depend on several factors, such as flight altitude, drone model, received noise levels, approach, weather conditions, the animals' annual cycle, and geographic location. Discussion: The outcomes hold significance for refining regulatory policies governing drone flights in protected marine environments, balancing conservation efforts with technological advancements in wildlife monitoring and ensuring undisturbed observations of seals. [ABSTRACT FROM AUTHOR]

The management and conservation of biodiversity relies on information on both the abundance of species and the potential impact of threats. Globally, one of the largest threats towards marine biodiversity is bycatch in fisheries. Under the Marine Strategy Framework Directive (MSFD), EU Member States are required to assess the status of species, such as the harbour porpoise (Phocoena phocoena), in relation to their abundance and mortality due to bycatch every six years. The Vulnerable (HELCOM) Belt Sea population of harbour porpoise has been surveyed to determine its abundance six times using dedicated aerial or shipbased line-transect distance sampling surveys. Here, we estimated the first trend in population abundance over an 18 year period (2005-2022). Using the most recent abundance estimate, we computed a mortality limit applying the modified Potential Biological Removal (mPBR) method based on the regionally agreed conservation objective to restore or maintain 80% of carrying capacity over 100 years with an 80% probability. Over the past 18 years there has been a strong negative trend (-2.7% p.a.; 95% CI: -4.1%; + 1.3%) in abundance, with a 90.5% probability. The mortality limit was estimated to be 24 animals, which the current bycatch estimates (~900 porpoises/year from the commercial Danish and Swedish set net fishery fleets, with no data from Germany and other fishery types) exceed by far. The frequency and quality of data available on abundance for this population are higher than those available for the majority of marine species. Given the observed population decline and likely unsustainable levels of bycatch, the results presented here provide a strong basis to make informed, evidence-based management decisions for action for this population. Such action is needed urgently, before the dire situation of other porpoise species and populations around the globe is repeated. [ABSTRACT FROM AUTHOR]

The harbour seal (Phoca vitulina) is the most widely distributed pinniped, occupying a wide variety of habitats and climatic zones across the Northern Hemisphere. Intriguingly, the harbour seal is also one of the most philopatric seals, raising questions as to how it colonized its current range. To shed light on the origin, remarkable range expansion, population structure and genetic diversity of this species, we used genotyping‐by‐sequencing to analyse ~13,500 biallelic single nucleotide polymorphisms from 286 individuals sampled from 22 localities across the species' range. Our results point to a Northeast Pacific origin of the harbour seal, colonization of the North Atlantic via the Canadian Arctic, and subsequent stepping‐stone range expansions across the North Atlantic from North America to Europe, accompanied by a successive loss of genetic diversity. Our analyses further revealed a deep divergence between modern North Pacific and North Atlantic harbour seals, with finer‐scale genetic structure at regional and local scales consistent with strong philopatry. The study provides new insights into the harbour seal's remarkable ability to colonize and adapt to a wide range of habitats. Furthermore, it has implications for current harbour seal subspecies delineations and highlights the need for international and national red lists and management plans to ensure the protection of genetically and demographically isolated populations. [ABSTRACT FROM AUTHOR]

Knowledge about species-specific hearing is vital to assessing how anthropogenic noise impacts marine mammals. Unfortunately, no empirical audiogram exists for any mysticete whale. We therefore developed a catch-and-release method to assess hearing in a small mysticete, the minke whale (Balaenoptera acutorostrata). Stationary lead nets were placed to intercept migratory routes and direct the whales into an ocean basin enclosed by nets and islets, while another net was pulled across the entrance once a whale entered the basin. The minke whales were then slowly corralled into a modified aquaculture pen using a net suspended between two boats. Subsequently, the water volume available to the whales was gradually reduced by raising the pen net by hand until the whales were secured in a “hammock” between the floating pen ring and a raft. From the raft, researchers could access the whales to monitor their health, apply instruments for hearing tests, or perform other research objectives, and then attach tags to monitor the movements and diving behavior of the whale post-release. The method is a slow and controlled procedure, allowing continuous monitoring and quick release of the whales, if needed. In the first three field seasons employing the method, three minke whales were caught for research procedures. Initial hearing measurements using auditory evoked potentials were successfully completed. After release, the whales resumed migration, and dive behavior was considered normal. Our observations demonstrated that minke whales can be guided safely via moored net barriers, corralled into an aquaculture pen, and safely handled for research purposes, before being released back into the wild. [ABSTRACT FROM AUTHOR]