ABSTRACT Harbour porpoises ( Phocoena phocoena ) in the North and Baltic Seas are increasingly impacted by anthropogenic pressures, including underwater noise, fisheries and pollution. These pressures correlate with declining population health, particularly affecting the respiratory system. Growing pathological lesions, partly resulting from high prevalence of parasitic infestations and subsequent diseases, can impair tissue function and oxygen supply to distant end-organs. In this study, we applied an integrative MultiOmics approach (proteomics, metabolomics, lipidomics) to analyse the lungs and muscles of 12 wild harbour porpoises with compromised respiratory health. Our aim was to identify dysregulated biological pathways across omics layers to advance insights into adaptive physiological responses and to define disease-associated molecular signatures that could assist health assessments. Our analysis revealed pronounced immune system and antioxidative responses in the lungs and muscles, indicated by enhanced immunoglobulins, plasmalogens and glutathione-related proteins. In the lungs, high cardiolipin levels and reduced collagen suggest impaired tissue structure and function, while tissue maintenance processes were elevated in the muscle. Both tissues exhibited metabolic alterations suggestive of energetic imbalance, including increased purine metabolism in the lung and decreased lipid metabolism in the muscle. Several dysregulated molecules were shared across tissues, pointing to pathophysiological effects. The proposed disease-associated molecular signatures included the protein SLC25A4, the metabolite O-phosphoethanolamine and the lipid TG O-16:0_16:0_20:4 for the lung, and the protein SPEG, the metabolite pipecolic acid, and the lipid BMP 18:1_22:6 in the muscle. Our findings elucidate the complexity of molecular mechanisms linking anthropogenic and environmental stressors with vulnerability and resilience in a marine sentinel species. Furthermore, this study highlights the potential of integrative omics to define disease-related marker panels, thereby supporting ongoing and future health monitoring and conservation efforts.

Abstract Effective management decisions rely on accurate insights into species’ population structure, with high-quality genetic material being essential. Stranded cetaceans are an important source of samples, but meeting quality standards remains challenging. Despite their frequent use in conservation genetics, no controlled studies have compared DNA yield and quality across tissue types and preservation methods. This is further compounded by cetaceans uniquely derived physiology, meaning standards obtained from other mammals might not apply. In this study, we compared DNA concentration, purity, and integrity when extracted from skin, muscle, and blubber samples preserved in 96% ethanol or frozen at − 20 °C. Samples were obtained from a tissue bank of stranded dolphins and classified into five decomposition condition categories following international guidelines. All samples underwent standardized protocols for DNA extraction, quantification, and quality control. Statistical analyses evaluated the influence of tissue type and preservation method on DNA quality. Skin consistently produced the highest DNA concentrations and acceptable purity levels, even in advanced decomposition stages. DNA integrity declined with decomposition, except in muscle, which retained higher integrity values in later stages. Both 96% ethanol and freezing at − 20 °C produced good results in early decomposition stages, while freezing was particularly important for maintaining DNA integrity in muscle in more advanced decomposition. Based on these findings, we propose two frameworks: one guiding researchers according to sequencing requirements, and another simplified version for stranding networks. These results contribute to standardized sampling protocols and improve the reliability and comparability of genetic analyses from stranded cetaceans.

Anthropogenic underwater noise is a pervasive pollutant in marine and aquaculture environments. However, its physiological and biochemical impacts on fish auditory systems remain poorly understood, particularly in species of ecological and aquaculture importance such as the European sea bass (Dicentrarchus labrax). Here, we combined auditory evoked potentials (AEPs) with untargeted metabolomics of inner ear endolymph to quantify noise-induced auditory threshold shifts and to identify molecular pathways affected by broadband noise exposure. A total of 114 sea bass were first assessed for baseline hearing sensitivity (100-600 Hz) and subsequently exposed to vessel-derived broadband noise concentrated below 1 kHz under two playback treatments: Medium-intensity exposure (SELcum 163-165 dB re 1 μPa2s, 30 min) and High-intensity exposure (SELcum 180 dB re 1 μPa2s, 60 min), with matched unexposed controls. Fish exposed to the High-intensity treatment showed auditory threshold shifts of 11-17 dB across all tested frequencies. Untargeted metabolomic profiling identified 752 metabolites, providing a comprehensive characterization of teleost endolymph metabolism. Noise exposure affected 199 metabolites, spanning lipids, amino acids, nucleotides, and peptides. Lipid-related subpathways, particularly sphingomyelins, plasmalogens, and long-chain acylcarnitines, were selectively enriched and formed a highly interconnected metabolic module. Notably, metabolic alterations were detected even in fish without pronounced hearing loss, indicating early inner ear responses to acoustic pollution. These results suggest that current assessments based solely on auditory thresholds may underestimate biological responses to noise exposure, highlighting the need for further investigation in marine and aquaculture contexts.

Climate change associated transformations of Arctic marine ecosystems are having detrimental impacts on Arctic endemic marine mammals. However, warming conditions are providing new habitats for temperate marine mammals, some of which are expanding into Arctic regions, posing a threat of novel pathogen introduction and disease transmission. We analyzed swab samples for Influenza A, morbilli- (Phocine distemper virus, PDV), and herpesvirus nucleic acid and performed microbiological screenings and serological analyses for antibodies for the same viral pathogens, the bacterial agents Brucella spp. and Leptospira spp. and the protozoan parasite Toxoplasma (T.) gondii from ringed (Pusa hispida), bearded (Erignathus barbatus), and the newly established harbor seals (Phoca vitulina) in Kongsfjorden, Svalbard. Antibodies against Phocine Herpesvirus-1 or antigenetically related phocine herpesviruses (PhHV) were detected in all species. Antibodies against Influenza A were only found in one ringed seal and antibodies against PDV were found in two harbor seals. Twelve harbor seals and two ringed seals tested positive for Herpesvirus DNA by PCR. Brucella spp. and Leptospira spp. antibodies were detected in multiple harbor seals and a single bearded seal. Three harbor, two ringed, and one bearded seal had antibodies against T. gondii. Our results indicate an overlap and possible transmission of pathogens between all investigated seal species. The introduction of new pathogens to the Arctic through temperate species' range expansions could have fatal consequences for immunologically naive Arctic seal populations and should be further investigated.

Abstract Grey seals are divided into two subspecies, Halichoerus grypus grypus in the Baltic Sea and H. grypus atlantica in the North Atlantic Ocean. Historically, intense hunting caused local extinctions of grey seals across their range and promoted geographical isolation of the subspecies. However, recent population recovery and recolonization have renewed their overlap in a contact zone in Danish and Swedish waters. Here, using whole-genome sequencing data from 119 individuals, we investigate the demographic history of grey seals, the divergence of the subspecies, and genomic signatures of local adaptation and potential hybridization in the contact zone. We estimate that divergence began approximately 10,000 years ago, with gene flow ceasing 2000 years ago. We detect peaks of high genetic differentiation near genes with putative functions in osmo- and thermoregulation, consistent with salinity and temperature differences between the Baltic Sea and the North Atlantic. As evidence of the geographic isolation breaking up, we report a hybrid individual in the southwest Baltic contact zone, with Baltic maternal and Atlantic paternal ancestry, and identify a migrant of Baltic origin in the North Sea. Our study illustrates how local environmental variation and long-term hunting pressure have contributed to divergence between mammal subspecies over a short evolutionary timescale, with recent population recovery, recolonization and hybridization reshaping gene flow dynamics. Broadly, our work emphasizes the importance of studying evolutionary processes amid anthropogenic influences, including both disturbances and conservation successes, where demographic fluctuations, range shifts, altered gene flow, and adaptation to changing environments interact in complex, potentially consequential ways.

The hooded seal (Cystophora cristata) is an Arctic phocid seal occasionally observed far outside its native range, including the European Atlantic shelf seas. This study presents the movements and diving behaviour of two female hooded seal pups after rehabilitation and release in the German North Sea. We tracked the animals using satellite telemetry to evaluate post-release survival and movement behaviour. Within one month, one seal travelled through the North Sea to the coast of United Kingdom, and then further northward to the Norwegian west coast, suggesting a successful return to Arctic waters. In contrast, the second seal remained in the North Sea and exhibited shallower and shorter dives over time, with extensive surface resting. She was ultimately found in poor condition in the United Kingdom and placed in permanent captivity. These cases highlight the species’ high dispersal capacity, yet also underline the challenges vagrant individuals face in suboptimal non-native habitats. The contrasting outcomes suggest that rehabilitation and release of such Arctic vagrants should be assessed case-by-case, considering the animal’s age, health, and timing of the release in relation to the expected prey availability. This study emphasizes the importance of satellite telemetry in evaluating post-release success and contributes to the broader discussion on the viability and ethics of rehabilitating extralimital marine mammals.

Abstract Top predators are crucial in shaping ecosystem dynamics by regulating key processes such as prey populations, energy transfer, and community structure, particularly in systems where multiple species compete for the same resources. Understanding their trophic niches and interactions is essential for effective conservation. In the southern North Sea, harbor seals, gray seals, and harbor porpoises are top predators with overlapping prey. This multi-method study examined resource partitioning using complementary stomach content analysis, metabarcoding, and carbon, nitrogen, and sulfur stable isotope analysis to refine habitat use, incorporating sulfur isotopes, for the first time in marine mammals of the southern North Sea. Gastrointestinal data from stranded harbor seals (n = 223), gray seals (n = 87), and harbor porpoises (n = 218), alongside 283 scat samples from wild seals, collected between 2014 and 2021, were analyzed. Harbor seal and gray seal showed high prey similarity (Jaccard index 0.71), while porpoises exhibited lower similarity with both seal species (Jaccard index 0.46 and 0.45). Interactions with prey guilds were strongest for demersal roundfish, flatfish, gobies, and sandeels. Bayesian isotope mixing models revealed consistent trophic differences among the three top predators, with seals occupying higher trophic positions than porpoises and showing minimal dietary change over time. Isotopic niche metrics indicated increasing overlap between porpoises and gray seals, particularly in δ34S/δ15N space, suggesting growing trophic similarity, while harbor seals showed a contraction in niche area. Also, stomach content data revealed that high-energy prey in porpoises declined as gray seal abundance increased. These results highlight trophic niche overlap and substantial interspecific interactions, potentially leading to competition under limited resources.

Taking wildlife into human care is a balancing act between benefits and harms, as handling and captivity can cause chronic stress that can lead to permanent physiological changes. Therefore, it is necessary to investigate stress levels during the rehabilitation of wild animals such as raptors. Fecal samples from 15 Common Buzzards (Buteo buteo) were taken to determine fecal glucocorticoid metabolite concentrations as a biomarker for stress across the rehabilitation phases. Significantly higher concentrations of fecal glucocorticoid metabolites were found during housing phase 1, when the birds were housed in small cages and handled at least once a day for medical treatment, compared to housing phase 2, when they were housed in larger and more undisturbed aviaries. The day of rehabilitation had no significant impact on fecal glucocorticoid metabolite concentrations alone or in interaction with the housing phases. The cause of admission (acute or chronic) and the eventual outcome for the birds (release or euthanasia) also had no statistically significant effect. The results suggest that handling and restraint could be main stressors during rehabilitation and should be critically evaluated throughout the rehabilitation process. Recommendations were derived from our findings to improve the welfare of birds of prey in wildlife rehabilitation.

Amphibian populations are undergoing dramatic global declines, with infectious diseases recognized as major contributors. While chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), and disease caused by ranaviruses are well known, herpesviruses in amphibians remain comparatively neglected. We conducted a passive survey using carcasses collected between 2022 and 2025 in Schleswig-Holstein, northern Germany. Dead amphibians (n = 187) were dissected. Skin, kidney, liver, and brain samples were screened for Bd, ranaviruses, bufonid herpesvirus 1 (BfHV1), and ranid herpesvirus 3 (RaHV3) by PCR. BfHV1 was detected in nearly half of the Bufo bufo (common toads; 48.6%), while RaHV3 was identified in 23.6% of the Rana temporaria (common frogs) examined. Bd was detected in a single B. bufo, while ranaviruses were not detected. BfHV1 was present in skin, liver, kidney, and brain samples, whereas RaHV3 was detected exclusively in skin samples. No macroscopical or histological lesions characteristic of herpesviruses or Bd were found. However, the carcass-based approach frequently limited detailed examination due to compromised sample quality. Our findings confirm the presence of amphibian herpesviruses (BfHV1 and RaHV3) in the region without associated lesions, raising questions about their potential to cause systemic infections. Furthermore, our results highlight the limitations of carcass-based surveillance and underscore the need for complementary diagnostic approaches, such as immunohistochemistry and meta-omics.

Haul-out behavior is a key component of the behavioral ecology of pinnipeds and serves essential resting functions. Various intrinsic and extrinsic factors have been shown to determine the occurrence of haul-out events. However, in the Baltic Sea, a nontidal, semi-enclosed shelf sea, the drivers of haul-out behavior in seals are not well characterized, especially in juveniles. In this study, 14 rehabilitated juvenile gray seals (Halichoerus grypus) were equipped with Argos satellite transmitters to enable post-release monitoring and to investigate the spatial and temporal aspects of haul-out behavior. The animals dispersed widely in the Baltic Sea and hauled out along coastal areas that largely overlapped with sites used by wild conspecifics. Seals tended to haul out during evening and night hours, with peak activity occurring after sunset. Both the probability and duration of haul-out events showed a tendency to increase with longer nights. No seasonal patterns or effects of sex or release year were identified. The association between haul-out behavior and nighttime suggests a possible link to prey activity patterns but does not preclude additional factors such as physiological rhythms, potential effects of rehabilitation, or inherited behavioral tendencies shaped by historical hunting pressure. Our findings indicate that such patterns may emerge early in life, independent of prior experience.

Quantifying and mitigating transboundary effects of anthropogenic activity is a key challenge in environmental management, particularly for wide-ranging species such as large predators, fish and migratory birds, relying on habitats across multiple national jurisdictions. This challenge is especially complex in marine ecosystems, where the movement of species and impacts across borders is largely unobserved. Central-place foragers, such as pinnipeds and seabirds, exemplify this complexity: abundance is typically assessed on local (regional or national) scales on land, yet at-sea movements and drivers of abundance occur on broader transboundary scales. Resolving this mismatch is critical to effective conservation, especially in areas such as the Northwest European Shelf (NWES), which features globally important predator populations (including two pinniped species) alongside growing anthropogenic pressures and a mosaic of national maritime borders. We model an unprecedented GPS dataset from 236 grey (Halichoerus grypus) and 606 harbour seals (Phoca vitulina) tracked in waters of seven countries across the NWES (United Kingdom, Ireland, France, Belgium, Netherlands, Germany and Denmark). Using regional habitat association models, we generate at-sea distribution estimates for both species at 5 km resolution, scaled to haulout counts, producing country-specific and NWES-wide density maps. Analysis of the extent to which seals making foraging trips from one country occupy the Exclusive Economic Zones (EEZs) of other countries revealed substantial transboundary overlap, particularly for grey seals, and harbour seals in the southern North Sea. A case study apportioning grey seal density within three adjacent offshore marine protected areas in different EEZs revealed that, where total density in a given area is required, overlooking transboundary distribution can underrepresent numbers by an order of magnitude. Synthesis and applications. This study provides the first comprehensive, regionally scalable distribution estimates for pinnipeds across the NWES and its constituent countries. The modelling framework is adaptable to other central-place and migratory species, supporting transboundary biodiversity assessments and international conservation policy. We discuss common limitations and misconceptions of species distribution estimates, highlight priorities for future work and underscore the need for transboundary efforts to manage wide-ranging species, providing a foundation for future ecological modelling and decision-making across shared ecosystems. Quantifier et att & eacute;nuer les effets transfrontaliers des activit & eacute;s anthropiques est un d & eacute;fi majeur dans la gestion environnementale, en particulier pour les esp & egrave;ces & agrave; large r & eacute;partition telles que les grands pr & eacute;dateurs, les poissons et les oiseaux migrateurs, qui d & eacute;pendent d'habitats r & eacute;partis sur plusieurs juridictions nationales. Ce d & eacute;fi est particuli & egrave;rement complexe dans les & eacute;cosyst & egrave;mes marins, o & ugrave; les d & eacute;placements des esp & egrave;ces et les impacts transfrontaliers sont largement inobserv & eacute;s. Les esp & egrave;ces & agrave; places centrales, telles que les pinnip & egrave;des et les oiseaux marins, illustrent bien cette complexit & eacute;: leur abondance est g & eacute;n & eacute;ralement & eacute;valu & eacute;e & agrave; l'& eacute;chelle locale (r & eacute;gionale ou nationale) sur terre, alors que leurs mouvements en mer et les facteurs qui d & eacute;terminent leur abondance se produisent & agrave; une & eacute;chelle transfrontali & egrave;re plus large. Il est essentiel de r & eacute;soudre ce d & eacute;calage pour assurer une conservation efficace, en particulier dans des zones telles que le plateau nord-ouest europ & eacute;en (NWES), qui abrite des populations de pr & eacute;dateurs d'importance mondiale (dont deux esp & egrave;ces de pinnip & egrave;des) et qui est soumise & agrave; des pressions anthropiques croissantes et & agrave; une mosa & iuml;que de fronti & egrave;res maritimes nationales. Nous avons mod & eacute;lis & eacute; un jeu de donn & eacute;es GPS sans pr & eacute;c & eacute;dent provenant de 236 phoques gris (Halichoerus grypus) et 606 phoques veaux-marins (Phoca vitulina) suivis dans les eaux de sept pays du NWES (Royaume-Uni, Irlande, France, Belgique, Pays-Bas, Allemagne et Danemark). & Agrave; partir de mod & egrave;les r & eacute;gionaux d'association d'habitats, nous avons g & eacute;n & eacute;r & eacute; des estimations de r & eacute;partitions en mer des deux esp & egrave;ces avec une r & eacute;solution de 5 km, mises & agrave; l'& eacute;chelle en fonction du nombre d'animaux recens & eacute;s sur les zones de repos terrestres, afin de produire des cartes de densit & eacute; sp & eacute;cifiques & agrave; chaque pays et & agrave; l'ensemble de la r & eacute;gion NWES. L'analyse de la r & eacute;partition des zones de chasse des phoques partant d'un pays et se superposant aux Zones & Eacute;conomiques Exclusives (ZEEs) d'autres pays a r & eacute;v & eacute;l & eacute; un chevauchement transfrontalier important, en particulier pour les phoques gris et les phoques veaux-marins dans le sud de la mer du Nord. Une & eacute;tude de cas portant sur la r & eacute;partition de la densit & eacute; des phoques gris dans trois zones marines prot & eacute;g & eacute;es adjacentes situ & eacute;es dans diff & eacute;rentes ZEE a r & eacute;v & eacute;l & eacute; que, lorsqu'il est n & eacute;cessaire de d & eacute;terminer la densit & eacute; totale dans une zone donn & eacute;e, le fait de n & eacute;gliger la r & eacute;partition transfrontali & egrave;re peut entra & icirc;ner une sous-estimation des chiffres d'un ordre de grandeur. Synth & egrave;se et applications: Cette & eacute;tude fournit les premi & egrave;res estimations compl & egrave;tes et adaptables & agrave; l'& eacute;chelle r & eacute;gionale de l Le cadre de mod & eacute;lisation est adaptable & agrave; d'autres esp & egrave;ces & agrave; place centrales et migratrices, permettant les & eacute;valuations transfrontali & egrave;res de la biodiversit & eacute; et les politiques internationales de conservation. Nous discutons des limites et des id & eacute;es fausses courantes concernant les estimations de la r & eacute;partition des esp & egrave;ces, soulignons les priorit & eacute;s pour les travaux futurs et insistons sur la n & eacute;cessit & eacute; d'efforts transfrontaliers pour g & eacute;rer les esp & egrave;ces & agrave; large r & eacute;partition, fournissant ainsi une base pour la mod & eacute;lisation & eacute;cologique et la prise de d & eacute;cision futures dans les & eacute;cosyst & egrave;mes partag & eacute;s.

Reference ranges for blood parameters are essential for diagnostic assessment and treatment decisions for harbor seals (Phoca vitulina) in rehabilitation or under permanent human care. Moreover, they are also important for evaluating the health status of free-ranging animals, thereby allowing conclusions about population health. To date, robust datasets of free-ranging presumably healthy individuals are rare. Here, we evaluated reference values for 14 hematologic and 21 serum biochemical parameters of 576 harbor seals that were wild-caught in the German North Sea over almost three decades. After the removal of outliers, nonparametric or bootstrapping methods were applied, depending on the sample size for each parameter, to estimate 95% reference intervals and their 90% confidence intervals. Additionally, we investigated the influence of three factors, as well as potential time trends, on each blood parameter using the Mann–Whitney-U test. Here, the factors which showed a moderate effect on only a few of the tested blood parameters were age class, sex, and season. LDH values were higher in juveniles than in multi-year animals, while creatine showed higher values in multi-year animals. Females showed higher values for iron, BUN, and triglycerides compared to males. Red cell distribution width (RDW), total-protein and cholesterol values were higher in spring than in autumn. No specific changes over time were determined for any of the blood parameters. This study enhances the knowledge on blood reference values of free-ranging harbor seals, delivering important baseline data especially for further health assessments of the Wadden Sea harbor seal population. Continuous health examinations of free-ranging marine mammal populations represent an important early warning tool for identifying potential threats affecting these animals. Therefore, they can provide valuable information to support effective management and conservation measures.

Live trapping is a common method in wildlife research and management, yet it poses inherent risks to animal welfare. This study systematically evaluated injury incidence and severity in coypus (Myocastor coypus) and raccoons (Procyon lotor) captured using three commercially available live trap types: a standard wooden box trap (WBT), a metallic, sheet metal trap (SMT), and a wire grid trap (WGT). A total of 55 coypus and 45 raccoons were examined following a trap confinement duration of a maximum of six hours. Injuries were assessed using standardized necropsy protocols and categorized by anatomical location, severity, and presumed cause. Results showed species-specific injury patterns, with raccoons exhibiting more frequent and severe injuries than coypus. Raccoons primarily sustained skin lesions and dental trauma, consistent with their manipulative, escape-oriented behavior, while coypu injuries were predominantly localized to the snout and incisors. Although not statistically significant, trap design influenced injury profiles: the WBT was associated with severe injuries in raccoons, particularly to the forelimbs and dentition, while the WGT prompted intense escape behaviors without a proportional increase in trauma. The SMT resulted in fewer external injuries but did present species-specific risks, such as claw-abrasion and tail entrapment. Approximately 93% of raccoons and 55% of coypus exhibited external injuries, including 14 severe cases and 5 confirmed fractures. These findings underscore the importance of species-specific trap assessment and design optimization to mitigate animal suffering. Given the limitations of traditional injury scoring systems and behavioral indicators when applied to wild animals, this study highlights the need for integrated, evidence-based welfare assessments in field settings. Future research should prioritize refinement of trapping methods and standardized welfare evaluation frameworks to support ethical and effective wildlife management.

Marine ecosystems are increasingly affected by anthropogenic stressors, including pollution with trace elements. Trace elements (TE) can bioaccumulate or in some cases biomagnify along the food chain, which can have harmful consequences for marine organisms. In recent years, fish parasites emerged as complementary bioindicators due to their ability to accumulate significantly higher concentrations of certain elements than their host or other established free-living bioindicators. As top predators, marine mammals are known to accumulate high TE levels. Thus, extending this approach to marine mammal host-parasite systems offers a promising, yet underexplored, approach for biomonitoring. Therefore, in this study we analysed the concentrations of eleven TE (Ag, As, Cd, Co, Cu, Fe, Mn, Pb, Sn, Sr and Zn) in harbour porpoises and their helminths, with a particular focus on nematodes. Our findings revealed that certain elements such as Fe, Mn, Zn, As, Co and Cd were accumulated to a higher degree in parasites than in host tissues. Additionally, differences in accumulation patterns were found between parasite groups and between individuals from the North Sea and Baltic Sea. The accumulation of TE in host tissue was influenced by a number of factors, including region and helminth infection.

Successful Reproduction is fundamental for species survival. In harbour seals, reproductive cycle includes the embryonic diapause. This study investigates seasonal and annual variations in reproductive parameters of harbour seals from the North and Baltic Sea to assess reproductive status, sexual maturity and broader reproductive dynamics. 1.523 females were found dead, or mercy killed along Germany`s coastline between 1995 and 2024. Out of these 383 were examined and categorized into three age groups (adult = 80, juvenile = 77, neonate = 226), as well as into two timelines (1995-2015 and 2016-2024). Ovaries were cut into 2 mm slices and examined for the presence or absence of Tertiary follicles, Corpus luteum, Corpus albicans and scars. Sexual maturity was first observed at 3.5 years - six months later than previously reported. Reproductive activity declined from age 13, earlier than previously assumed. A peak in ovarian weight shifted from mid-March (1995-2015) to late December (2016-2024), suggesting earlier reproductive activation. The period of minimal ovarian activity was delayed, indicating a prolonged reproductive window. Inconsistencies in Cl presence during expected embryonic diapause periods imply alterations in reproductive timing, potentially linked to prey availability or population structure. These results suggest a complex interplay between environmental pressures and reproductive physiology, with potential consequences for fitness, genetic diversity and population resilience. This study presents basic information for assessing harbour seal reproduction along Germany`s coastline and supports the need for long-term, regionally monitoring to guide effective management strategies to better understand the impacts of ongoing changes.