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Seal lice ( Echinophthirius horridus ) are bloodsucking ectoparasites of phocid seals and vectors of pathogens like the heartworm, Acanthocheilonema spirocauda . Grey and harbour seal populations are recovering in German waters and wildlife health surveillance is crucial for wildlife conservation. A new, high effort sampling protocol for seal lice was applied for grey and harbour seals along the German North- and Baltic Sea coast. Freshly dead seals were systematically sampled within a health monitoring of stranded seals over 12 months. Prevalence, intensity and distribution patterns of seal lice were analysed. 58% of harbour seals ( n  = 71) and 70% of grey seals ( n  = 10) were infected with seal lice. A majority of harbour seals displayed mild levels of infection, while three were moderately and two were severely infected. The head was the preferred predilection site, indicating that E. horridus prefers body areas with frequent access to atmospheric oxygen. Nits and different developmental stages were recorded in all age classes in grey and harbour seals in all seasons. For the first time, copulating specimens of E. horridus were recorded on a dead harbour seal, highlighting that E. horridus reproduces throughout the year on seals of all age classes in German waters.

Over the last decades, the European hare (Lepus europaeus) has become the subject of many interdisciplinary studies due to the sharp Europe-wide population decline. In European hares, the first stage of life until weaning and the subsequent dispersal have been sparsely studied, in particular, habitat selection, movements and survival rate, as juveniles´ precocial lifestyle is dominated by concealment, motionlessness and inconspicuousness. In this study, free-living juvenile European hares (leverets) were detected systematically by thermography (n = 394), radio-tagged or marked (n = 122) from birth until the fifth week of life to research their habitat usage and pre-dispersal movements. The day-resting places and night locations, as well as the distance moved by leverets with aging, were evaluated by generalized linear mixed effect models. In addition, the habitat preference was assessed by a conservative use-availability analysis. Up to the fifth week of life, 30.5% of all leverets used cultivated areas in the daytime. In contrast, the remaining 69.4% animals inhabitated linear or small planar structures in the daytime, with the edges of field tracks, hedges and some ruderal structures clearly being preferred. At nighttime, 93% of all juveniles, which occupied linear structures in the daytime, used the adjoining fields up to 20 m away from the next linear structure. Nocturnal distances of more than 60 m to the next edge rarely occurred before the end of the pre-weaning phase. The time of day and age have a significant influence on the distance moved by juvenile hares. With increasing age, leverets moved less during the day and roamed further at night. The results are largely consistent with the behavioral patterns found in the few previous studies on pre-weaning European hares and show the importance of hiding places for leverets in early life stages. This study should contribute to a better understanding of behavior in juvenile life-history stages of European hares that may help to identify vulnerable phases in their lifecycle. In addition, the findings can refine existing population models and improve conservation efforts.

IntroductionThe harbor porpoise populations of the North and Baltic Seas are highly impacted by human activities, including underwater-radiated noise, fisheries and pollution. These cumulative stressors can have various detrimental effects, such as reduced foraging success, altered behavior and an impaired immune system. Harbor porpoises especially suffer from diseases of the respiratory tract which are partly caused or exacerbated by high parasitic prevalence in the lungs that may ultimately affect diving ability and competitiveness due to insufficient oxygen uptake and supply to the locomotor musculature.MethodsTo investigate pathophysiological mechanisms and potential compensatory adaptations to pathogenic insults, we employed transcriptomics and compared lungs and muscles of harbor porpoises with compromised respiratory health to healthy individuals. Additionally, a de novo transcriptome assembly was generated to identify transcripts that may be involved in immune-related responses.Results and DiscussionNon-healthy harbor porpoises showed a distinct host-pathogen defense reaction in the lung, suggesting similarities to immune responses of humans suffering from lung diseases, which may be conserved along the mammalian lineage despite vastly different habitats. However, the lung transcriptomes did not indicate a Th2 immune response which is typically activated upon parasitic insults. Severely infected harbor porpoises may be overwhelmed or weakened by prolonged parasitic exposure and immune activation, possibly affecting simultaneous pathogenic clearance and tissue repair. The muscles of non-healthy harbor porpoises exhibited enhanced stress signaling and tightly regulated tissue degradation/regeneration, potentially reflecting a chronic inflammation state. Higher expression of hypoxia- and oxidative stress-associated transcripts in the muscle were consistent with hypoxia-induced transcriptional patterns and suggest a systemic pathological challenge. The de novo assembly identified significantly dysregulated non-coding RNAs in the lung and muscle which may be associated with regulatory processes. Several transcripts of the de novo assembly remained unidentified, thus their putative function needs to be elucidated. In marine mammals, the understanding of molecular immune responses still remains incomplete. This is the first study to describe the lung transcriptome of wild harbor porpoises in regard to pathophysiology. These insights contribute to the understanding of the interaction between anthropogenic impacts, infectious diseases and molecular immune responses in cetaceans, thus supporting cetacean health assessments and conservation efforts.

The harbour porpoise is the only cetacean species native to German waters. Since human pressures are suggested to shorten their reproductive lifespan, basic knowledge on reproduction is strongly required. One parameter is the onset of sexual maturity in female harbour porpoises. Therefore, we investigated the first signs of sexual maturity for a period of almost two decades (1990-2016). Ovaries from 111 female harbour porpoises from the German North Sea and Baltic Sea were examined for the presence and morphological structure of follicles, corpora lutea and corpora albicantia. Based on the ovarian characteristics we performed the first model-based estimation of age at sexual maturity for harbour porpoises from German waters. Additionally, we produced a demographical age structure based on all female strandings and bycatches from German coasts. Our results showed that corpora lutea and corpora albicantia as signs of former ovulation could be found in individuals at an age of 4.95 (± 0.6) years. No significant differences between specimens from the North Sea and Baltic Sea were detected. However, the average age at death differed significantly with 5.70 (± 0.27) years for North Sea animals and 3.67 (± 0.30) years for those in the Baltic Sea. Growing evidence exists that the shortened lifespan of Baltic Sea harbour porpoises is linked to an anthropogenically influenced environment with rising bycatch mortalities due to local gillnet fisheries. Thus, our findings support the idea of local management plans based on a model-based detection of age at sexual maturity and considering the anthropogenic impacts on the population for effective protection of harbour porpoises and the North Sea and Baltic Sea.

Marine mammals are sentinel species representing the “health” of our oceans on which we are dependent. There are many threats to marine mammals including infectious diseases that increase with climate change and pollution of the marine environment. Streptococcus phocae has frequently been isolated from diseased or dead marine mammals. However, its pathogenicity and contribution to disease in marine mammals is still unknown. As bacteria including (potential) pathogens has to deal with different host environments during colonization or infection, we investigated the survival of S . phocae in fresh porcine and phocid blood, in seawater and in the presence of macrophages and (epithelial) cells from harbor seals and pigs. Furthermore, we tested adherence on and invasion of different (marine) mammalian cells by S . phocae . Our results showed that S . phocae can survive in seawater for at least 11 and 28 days at 16°C and 4°C, respectively. It is able to grow in blood of harbor and grey seals, but not in porcine blood. Furthermore, S . phocae is adherent and invasive to cells from seals and pigs, while the portion of invasive cells was higher in seal derived cells. Macrophages of harbor seals were more efficient in killing S . phocae than porcine macrophages. Our results indicate that S . phocae has strategies enabling it to adapt to the marine environment and seal hosts.

Harbour seals are top predators in the North Sea and regarded as sentinels for ecosystem health. A few hundred also occur in adjacent estuaries, such as the Elbe estuary, Germany. However, only little is known about how these animals use this dynamic tidally influenced habitat, which has been under high anthropogenic pressure for decades. In this context, nine harbour seals ( Phoca vitulina ) from the Elbe estuary were equipped with biotelemetry devices to track their movements over multiple months. Harbour seal movements were characterised by short trips (trip length outside pupping season for females: 9.0 ± 1.12 km, males: 7.0 ± 1.24 km) as well as small home ranges (median 50% home range for females: 16.3 km 2 , males: 36.1 km 2 ) compared to harbour seals from marine regions. Within the estuary, the animals utilised the fairway, river branches and tributaries. During the pupping season in June and July, four seals showed strongly reduced trip lengths and durations, increased daily haul out durations as well as smaller home ranges. Even though a continuous exchange with harbour seals from the Wadden Sea likely occurs, most individuals in this study spent the entire deployment duration inside the estuary. This indicates that the Elbe estuary provides a suitable habitat for harbour seals, despite extensive anthropogenic usage, calling for further studies on the consequences of living in such an industrialised habitat.

A successful wildlife management requires monitoring. Including non-scientific volunteers into monitoring actions is a common way for obtaining long-term and comprehensive data. Hunters present a valuable target group as they are spread out nationwide in Germany and additionally, they provide a know-how regarding game species. Since 1990s, various German hunting associations established monitoring programs and motivated hunters to join, in order to record population sizes of huntable game species under standardized census methods. The aim of this study was to compare instructed hunters performed spotlight counts of European brown hares with thermography in three federal states (Lower-Saxony, Saxony-Anhalt, North Rhine-Westphalia) in 2015–2018 in Northern Germany. Therefore, we modelled the number of hares counted by both methods with the associated observed area. Moreover, we performed repeated thermographic counts in selected areas and performed distance sampling to test the deviations of estimated population densities within a short time period. Repeated infrared thermographic counts on three consecutive nights show a coefficient of variation from 6.6% to 15.5% with deviations of 2.2–2.7 hares per 100 ha, while the method of distance sampling reveals minor deviations of 0.9–1.7 hares per 100 ha and a coefficient of variation from 3.1–7.4%. The coefficient of variation value between spotlight and infrared thermographic count lies between 0 to 21.4%. Our model confirmed no significant differences between the European brown hare density estimations based on a spotlight count and an infrared thermographic count on the following night. The results provide insight into the dimension of the error margin of density estimations performed by spotlight counts. Therefore, we recommend to take possible counting errors into account and to ideally perform repeated counts to assess the error margin for each counting site. This would help for example to quantify the uncertainty in the calculation of mortality rates. Additionally, our results show that monitoring data generated by instructed hunters can provide reliable and valid data, if implemented and conducted in a standardized scientific way.

As many other wild living species, black grouse Tetrao tetrix has to cope with anthropogenic disturbances in many habitats. Impacts of tourism and outdoor recreation on grouse species Tetraoninae have been subject to several studies in mountainous habitats in Central Europe and the United Kingdom. The geographically isolated and critically endangered black grouse population of Lower Saxony (North Germany) has been consistently monitored but beyond that poorly studied. This also applies to the key habitats of the nature reserve Lüneburg Heath (Lüneburger Heide) which, in turn, serves as a recreational area as well. In this study, the impact of tourism activity on habitat use of black grouse was investigated using data of GPS-tracked individuals. Additionally, visitor numbers on public and (usually undisturbed) closed routes were monitored using infrared light barriers. The spatio-temporal distribution of locations and the recreational activity were evaluated by linear mixed-effects models. Tagged individuals avoided the vicinity of public routes and avoiding distances were directly related to intensity of human activity. There was no seasonal change of black grouse habitat use alongside public routes. However, towards closed routes, significantly higher distances appeared during peak phases of visitor numbers (August and September), implying temporary increased disturbance levels within a key refuge area. Diurnal adaptation of habitat use was strongly dependent on the route density within the home range. Individuals used the vicinity of public trails at night and dawn but evaded these habitats during peak human activity around noon and afternoon. Recreational disturbances appeared to significantly affect the effective habitat availability for black grouse in the nature reserve. Visual cover by vegetation, however, seemed to diminish negative effects emerging from hiking trails. This provides an effective protective measure which requires minimal effort for the local conservation management.

Successful species conservation and rising tourism in coastal ecosystems lead to more human-wildlife conflicts. Non-invasive conflict mitigation measures are needed to ensure human safety and wildlife conservation. The Helgoland Dune, a small German offshore island, is home to Germany’s largest grey seal ( Halichoerus grypus ) colony alongside popular tourist beaches, leading to frequent human-seal encounters. Previous physical incidents in the shared swimming zone have raised safety concerns. This study evaluated an acoustic deterrent system (ADS) using Targeted Acoustic Startle Technology (TAST) to reduce such interactions. During two field trials, the ADS emitted pulsed signals (2 s, 700–1500 Hz, 180 dB re 1 µPa) while a camera tracked seal movements. Analysing 22,086 positions via a cumulative link mixed model (CLMM) revealed seals were 3.57 times more likely (odds ratio, CI: 2.38–5.37, p-value < 0.001) to occupy the two farther distance categories (10–25 m, > 25 m) during signal emission, compared to the closest distance zone (< 10 m). Individual variability accounted for 94% (ICC) of behavioural differences. Results provide the first empirical evidence of the ADS’s effectiveness in a recreational context as a non-invasive deterrent tool, while maintaining seal access to surrounding habitat crucial to them.

Knowledge about parasite species of orcas, their prevalence, and impact on the health status is scarce. Only two records of lungworm infections in orca exist from male neonatal orcas stranded in Germany and Norway. The nematodes were identified as Halocercus sp. (Pseudaliidae), which have been described in the respiratory tract of multiple odontocete species, but morphological identification to species level remained impossible due to the fragile structure and ambiguous morphological features. Pseudaliid nematodes (Metastrongyloidea) are specific to the respiratory tract of toothed whales and are hypothesized to have become almost extinct in terrestrial mammals. Severe lungworm infections can cause secondary bacterial infections and bronchopneumonia and are a common cause of mortality in odontocetes. DNA isolations and subsequent sequencing of the rDNA ITS‐2 and mtDNA COI revealed nucleotide differences between previously described Halocercus species from common dolphin (H. delphini) and harbor porpoises (H. invaginatus) that were comparatively analyzed, pointing toward a potentially new species of pseudaliid lungworm in orcas. New COI sequences of six additional metastrongyloid lungworms of seals and porpoises were derived to elucidate phylogenetic relationships and differences between nine species of Metastrongyloidea. Rare orca lungworms were molecularly characterized as potential new pseudaliid nematode species using ITS2 and COI nucleotide data. Phylogenetic analyses highlight relationships between metastrongyloid lung nematodes of marine mammals.