Harbour seals were extensively hunted in Denmark, but have only been driven to local extinction in one larger area, the South Funen Archipelago and Little Belt, where the species has been absent throughout the 20th century. Despite high growth rates of the Danish harbour seal populations after protection from hunting in 1976, seals have only been observed sporadically in the South Funen Archipelago and Little Belt until recent years, where recolonisation now causes conflicts with fisheries. Here, we review historical sources documenting the local extinction of harbour seals in the area during the 19th century and report the results of aerial surveys of haul-out sites during moulting seasons of 2021–2023 and pupping seasons of 2022 and 2023. Historical sources reveal that seal hunting was a common practice in southern Denmark, but catches dwindled to rarities during the 19th century. During recent surveys, seals were detected at six of the identified potential haul-out sites. Around Aarø Island, an average of 141 (range: 92–186) harbour seals were recorded over four moulting season surveys, constituting the majority (90%) of the total counts of the surveyed area. During the pupping seasons, a total of five pups was encountered at two different haulouts. As none of the haulouts are protected during the pupping and breeding seasons, protective measures may support this recolonisation of the historic harbour seal breeding range.

Grey seals from both the Atlantic and Baltic Sea subspecies are recovering from dramatic declines and recolonising former ranges, potentially leading to overlapping distributions and an emerging subspecies transition zone in Kattegat between Denmark and Sweden. The two subspecies have asynchronous moulting and pupping seasons. We present aerial survey data from 2011 to 2023 in Danish Kattegat during the Atlantic subspecies' moulting (March–April) and pupping (December–January) seasons, as well as the Baltic subspecies' moulting season (May–June). During the Atlantic subspecies' peak moulting season, 82% of the grey seals were recorded north of the island of Læsø (N57°18′, E11°00′). In contrast, during the Baltic moulting season in those years, only 9% of the grey seals were recorded here. This indicates a predominance of Atlantic grey seals in the north and Baltic grey seals in central and southern Kattegat. In 2022 and 2023, three pups were recorded around Læsø during early January, which coincides with the pupping season of northern Wadden Sea grey seals. Previously, pups have been recorded in the same locations during the Baltic pupping season, which demonstrates overlapping breeding ranges. Grey seals are known to have plasticity in the timing of pupping indicated by a west to east cline of progressively later pupping in the eastern North Atlantic. Historical sources document that the Baltic pupping season in Kattegat was earlier than it has been in recent years. Thus, the expanding ranges may be associated with convergence of Atlantic and Baltic subspecies' pupping seasons and potential hybridisation in this emerging transition zone.

Verminotic pneumonia caused by Parafilaroides spp. nematodes is an underreported disease in beached South American fur seals, with scant literature available on the characteristics of parafilaroidiasis, the nematode itself, as well as its occurrence in pinnipeds in Brazil. The present work aims to identify, describe and detail the histological features of the infection and molecular characteristics of verminotic pneumonia in the South American fur seal. Twenty-six specimens of Arctocephalus australis, found dead on the northern coast of Rio Grande do Sul in 2021, were analysed. These animals were identified and submitted to necropsy and histology. For the molecular identification of metastrongylids, lung fragments were subjected to DNA extraction, polymerase chain reaction targeting the Internal transcribed spacer 2 (ITS-2) gene and subsequent sequencing. In total, 12 animals presented with parasites in the lung parenchyma on histological evaluation, and only 1 showed a granulomatous lung lesion at necropsy. Microscopically, the nematodes were found mainly in the alveoli, associated with little or no inflammatory response, and they had morphological characteristics compatible with metastrongylids. Six ITS-2 gene quality sequences were obtained; after comparative analysis via BLAST, they showed similarity with sequences obtained from Parafilaroides sp. Therefore, verminotic pneumonia caused by Parafilaroides represents an important differential diagnosis of lung disease in South American fur seals found on the northern coast of Rio Grande do Sul.

El objetivo de este trabajo es discutir las técnicas y estrategias de caza empleadas para la captura de pinnípedos en la desembocadura del Río Santa Cruz (Santa Cruz, Patagonia), particularmente en la localidad arqueológica Punta Entrada. Ésta se caracteriza por poseer amplias concentraciones de material arqueológico a cielo abierto en las cuales los restos de pinnípedos de las especies Otaria flavescens y Arctocephalus australis dominan los conjuntos zooarqueológicos, evidenciando que estos animales fueron una presa principal de los cazadores-recolectores durante los últimos 2.000 años aP. Los estudios del registro artefactual lítico sugieren el uso de diversos sistemas de armas combinados, entre los cuales se incluyen aquellos de circulación regional y uso general (lanzas) y otros netamente costeros y de uso específico, como son los rompecráneos, informando así la existencia de estrategias de caza particulares para estos animales y de artefactos destinados a tal fin.

Acanthocephalans are common intestinal parasites of marine mammals, the most widespread of which is the genus Corynosoma. In this study, parasite infrapopulations of two closely related species of Corynosoma were examined: Corynosoma enhydri from sea otters (Enhydra lutris) in Alaska (n = 12) and California (n = 19), and Corynosoma strumosum from seals in Germany (n = 22). Prevalence of C. enhydri was 100% in Californian otters, with a mean abundance of 30, and 83% in Alaskan otters, with a mean abundance of 232. In seals, C. strumosum had a prevalence of 65%, with a mean abundance of 33. Female C. enhydri dominated both Californian (82%) and Alaskan (79%) infections, while, in seals, female C. strumosum made up 68% of the parasite population. Reproduction rates for C. enhydri, with 16% (California) and 18% (Alaska) of females mated, were low compared to C. strumosum in seals, of which 40% of females were mated. Habitat selection also differed significantly between the two species. Corynosoma enhydri was found most frequently in the second and third fifths of the small intestine, while C. strumosum was found most frequently in the fourth. The differences in habitat selection and prevalence analysed in this study may be related to a trade-off between growth and reproduction between the two species.

Marine mammals are long-lived top predators with vagile lifestyles, which often inhabit remote environments. This is especially relevant in the oceanic waters around New Zealand and Australia where cetaceans and pinnipeds are considered as vulnerable and often endangered due to anthropogenic impacts on their habitat. Parasitism is ubiquitous in wildlife, and prevalence of parasitic infections as well as emerging diseases can be valuable bioindicators of the ecology and health of marine mammals. Collecting information about parasite diversity in marine mammals will provide a crucial baseline for assessing their impact on host and ecosystem ecology. New studies on marine mammals in New Zealand and Australian waters have recently added to our knowledge of parasite prevalence, life cycles and taxonomic relationships in the Australasian region, and justify a first host–parasite checklist encompassing all available data. The present checklist comprises 36 species of marine mammals, and 114 species of parasites (helminths, arthropods and protozoans). Mammal species occurring in New Zealand and Australian waters but not included in the checklist represent gaps in our knowledge. The checklist thus serves both as a guide for what information is lacking, as well as a practical resource for scientists working on the ecology and conservation of marine mammals.

Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only phocid species found in Mexico. There is evidence that harbour seals at other latitudes exhibit non-migratory behaviour; however, there is lack of knowledge regarding this species' movements in Mexico. In contrast, elephant seal migrations to high latitudes are documented. In order to analyse this behaviour in harbour seals, hair samples (N = 19) were collected from weaned, or nearly weaned, pups on Natividad Island, Baja California (BC), during the 2013 breeding season (February). Lanugo samples (N = 20) were also collected from elephant seal pups on the San Benito Archipelago (60 km north of Natividad) during the same season, providing information on maternal foraging during the last 4–5 months before sampling. Of the two species, BC harbour seals had higher isotope values, reflecting their non-migratory behaviour. These differences may be due to the depleted base values in the higher latitude foraging areas used by northern elephant seals relative to the areas around Natividad frequented by harbour seals. A lower trophic position by elephant seals was considered but taken as an unlikely explanation for this variation. Bayesian analysis confirmed the distinction, with a low overlap value (0.4) and different isotopic spaces (Phoca: 0.5, Mirounga: 1.6). Building upon previous studies of the trophic ecology of the two phocids that inhabit the region, we provide new information by comparing the two species during the same season using the same tissue type sampled from individuals of similar age classes.

A grey seal (Halichoerus grypus), representative of the North Atlantic species, has been recorded in the north-east Black Sea. It is the first documented case of successful long-term survival of an exotic pinniped. We have been receiving data about regular sightings of the seal identified as the observed individual since 2001. It is a 160–170 cm long adult female. The seal used an underwater cave as a shelter. The most likely way of introduction of the grey seal to the Black Sea is escape from captivity. According to available data (body size and moulting seasonality), we tentatively identify it as a representative of the Baltic subspecies. The biotope requirements of the grey seal and monk seal are similar: both species use coastal karst caves and grottos. In addition, the seal's presence in this region is a marker of the lack of anthropogenic disturbance. Thus, the survival of a seal in this region indicates the possibility of successful re-colonization of the Black Sea by monk seals.

Knowledge about the diet of fish-eating predators is critical when evaluating conflicts with the fishing industry. Numerous primary studies have examined the diet of grey seals Halichoerus grypus and common seals Phoca vitulina in a bid to understand the ecology of these predators. However, studies of large-scale spatial and temporal variation in seal diet are limited. Therefore this review combines the results of seal diet studies published between 1980 and 2000 to examine how seal diet varies at a range of spatial and temporal scales. Our results revealed extensive spatial variation in gadiform, perciform and flatfish consumption, likely reflecting variation in prey availability. Flatfish and gadiform consumption varied between years, reflecting changes in fish assemblages as a consequence of factors such as varying fishing pressures, climate change and natural fluctuations in populations. Perciform and gadiform consumption varied seasonally: in addition there was a significant interaction between season and seal species, indicating that grey and common seals exhibited different patterns of seasonal variation in their consumption of Perciformes and Gadiformes. Multivariate analysis of grey seal diet revealed spatial variation at a much smaller scale, with different species dominating the diet in different areas. The existence of spatial and temporal variation in seal diet emphasizes that future assessments of the impact of seal populations should not be based on past or localized estimates of diet and highlights the need for up-to-date, site specific estimates of diet composition in the context of understanding and resolving seal/fisheries conflict.

The present knowledge of pinnipeds’ distribution is principally based on the location of breeding colonies. Several species of pinnipeds have shown the ability to undertake long travels to different and unusual locations, where they are frequently interpreted as vagrants. A total of seven species of pinnipeds are known to occur along the Brazilian coast: four belong to the family Otariidae and three to the family Phocidae. From 1954 to 2008 a total of 54 records of pinnipeds were reviewed for the coast of Rio de Janeiro State, ten of them were new records, representing 18.2% of the total. The most common species registered in the study area was Arctocephalus tropicalis (49.1%; N = 27) followed by Mirounga leonina (20%; N = 11). The other species recorded were Lobodon carcinophaga, Otaria flavescens, Arctocephalus australis and Hydrurga leptonyx. From 51 pinniped specimens with information on periods of occurrence, 76.5% (N = 39) were reported during winter, and the other 12 specimens were equally distributed over the three other seasons. Most sub-Antarctic fur seals (88%) and southern elephant seals (83%) were males. The majority of the species were classified as sexually immature. The seasonal pattern of the pinnipeds found on the coast of Rio de Janeiro State is related to the intensive northward flow of the Malvinas/Falkland Current during winter. In addition, the potential to swim long distances together with the lack of physical barriers in the marine environment could help the dispersion of the seals to distant regions far from their traditional breeding or feeding regions.

Signy Island has experienced a dramatic increase in fur seal numbers over recent decades, which has led to the devastation of lowland terrestrial vegetation, with the eradication of moss turfs and carpets being the most prominent feature. Here we demonstrate that fur seals also affect the other major component of this region’s typical cryptogamic vegetation, the lichens, although with a lower decrease in variability and abundance than for bryophytes. Classification (UPGMA) and ordination (Principal Coordinate Analysis) of vegetation data highlight differences in composition and abundance of lichen communities between areas invaded by fur seals and contiguous areas protected from these animals. Multivariate analysis relating lichen communities to environmental parameters, including animal abundance and soil chemistry (Canonical Correspondence Analysis), suggests that fur seal trampling results in the destruction of muscicolous-terricolous lichens, including several cosmopolitan and bipolar fruticose species. In addition, animal excretion favours an increase in nitrophilous crustose species, a group which typically characterizes areas influenced by seabirds and includes several Antarctic endemics. The potential effect of such animal-driven changes in vegetation on the fragile terrestrial ecosystem (e.g. through modification of the ground surface temperature) confirms the importance of indirect environmental processes in Antarctica.

Pre-weaning pup mortality of grey seals Halichoerus grypus in a breeding colony (North Rona, Scotland, U.K.) was examined in relation to the density of local adult females over two breeding seasons. Accurate, fine-scale maps of daily seal locations within a GIS database permitted the extraction of measures of female density determined at a range of spatial scales from 5 to 50 m around each pup on the date of death. Adult densities around live pups provided the null distribution of adult densities, which were tested against the distribution of densities where deaths occurred. Pre-weaning pup mortality at this colony was not related to any of our density measures. The proportion of pups dying each day showed no seasonal trends. Analysis of topographic features from a sub-meter digital terrain model for locations where deaths occurred suggested that there were fewer mortalities in prime pupping habitats. This could have been a direct effect of habitat or the relative quality of mothers in these habitats. The distance separating mothers and pups tended to be greater on the periphery of the colony compared to more central areas. Pups in the peripheral areas may be more exposed to predation by gulls.

Many sea-birds are dependent for breeding on islands free from both mammalian predators and high levels of human disturbance. Yet human use of small islands appears to be increasing in many parts of the world, including the >150 islands in the Gulf of California, México. For this reason, the frequency and activities of human visitors to San Pedro Mártir Island, one of the most important sea-bird nesting sites in México, were studied over the course of 14 months of field work between 1990 and 1992. On average >350 people per month visited the near-shore waters. The most important visitors were: (1) commercial fishers in small open boats called pangas; (2) commercial fishers in larger ships; (3) private sport-fishers; and (4) commercial environmental-tourism groups. Private sport-fishing boats were most frequently observed, but private sport-fishers rarely landed on shore and caused little apparent disturbance to nesting or roosting sea-birds or California sea-lions (Zalophus californicus). Commercial companies concerned with environmental tourism also caused little apparent disturbance to sea-birds or sea-lions, but only because the company that brought the majority of 'ecotourists' developed and followed guidelines to minimize disturbance. Disturbance caused by all tourists can be reduced at minimal cost to both tourists and protected-area managers. Commercial fishers were responsible for most of the apparent disturbances to sea-birds and sea-lions; decreasing this apparent impact will be more difficult. Most apparent human impact was found to be short term and localized. However, commercial fishers and scientific researchers have the potential to cause long-term changes to the terrestrial ecology of the island by introducing exotic species.

Lactating New Zealand sea lions (Phocarctos hookeri) have recently been reported to be the longest and deepest-diving otariid. An unusually large proportion of dives exceeded a theoretical aerobic dive limit, predicted from estimated oxygen stores and measurements of diving metabolic rate. We investigated swimming speed, a key variable in both the management of oxygen stores and foraging strategies, and its relation to diving behaviour in New Zealand sea lions. Diving behaviour was nearly continuous with short inter-dive intervals. Mean diving swimming speeds ranged from 1.6 to 2.4 m/s. Mean surface swimming speeds ranged from 0.9 to 1.8 m/s and were significantly lower than diving speeds in all subjects. New Zealand sea lions spend significant but variable amounts of time resting at the surface. Diving and swimming speed patterns were consistent with foraging on the benthos. Time in the foraging zone was maintained in deeper dives by increasing dive duration. This increased duration cannot be accounted for by a decreased metabolic rate resulting from slower swimming speeds, as speeds increased with the maximum depth of dives. Patterns of swimming speed and acceleration suggest the use of a gliding phase during descent. For most females, the extended duration of deeper dives did not impact on surface times, suggesting the use of aerobic metabolism. Females exhibited significantly slower swim speeds during the bottom segments of foraging dives than during descent or ascent. These findings suggest that swimming behaviour should be considered a critical component when modelling energetic costs for diving animals.

The gross and microscopic anatomy of the Cape fur seal heart, lung, liver, spleen, stomach, intestine and kidneys (n = 31 seals) is described. Absolute and relative size of organs from 30 male seals are presented, with histological examination conducted on 7 animals. The relationship between log body weight, log organ weight and age was investigated using linear regression. Twenty five animals were of known age, while 6 were aged from counts of incremental lines observed in the dentine of tooth sections. For the range of ages represented in this study, body weight changes were accurately described by the exponential growth equation, weight = wort, with body weight increasing by 23% per annum until at least 9–10 y of age. Organ weight increased at a rate of between 25% and 33% per annum until at least 9–10 y of age, with the exception of the intestines, where exponential increase appeared to have ceased by about 7 y. The relationship between body weight and organ weight was investigated using logarithmic transformations of the allometric equation, y = axb, where the exponent b is 1 if organ weight is proportional to body weight. Most organs increased in proportion to the body. However, the heart, liver and spleen had exponents b > 1, suggesting that these organs increased at a faster rate than the body. The basic anatomical features of the viscera were similar to those of other pinnipeds, with some exceptions, including the arrangement of the multilobed lung and liver. Apart from the large liver and kidneys, relative size of the organs did not differ greatly from similar sized terrestrial carnivores. The histological features of the organs were generally consistent with those previously described for this species and other otariids. The heart, as in other pinnipeds, was unlike that of cetacea in not having unusually thick endocardium or prominent Purkinje cells. Notable histological features of the lungs included prominent fibrous septa, prominent smooth muscle bundles, cartilage extending to the level of the alveolar sacs and ample lymphoid tissue. The spleen had a thick capsule, well developed trabeculae and plentiful plasma cells. Abundant parietal cells were present in the fundic glands and lymphoid follicles were present in the gastric lamina propria, particularly in the pyloric region. Small intestinal villi were very long but this could have resulted from underlying chronic inflammation. Lymphoid follicles were prominent in the colon. The kidney reniculi each had a complete cortex, medulla and calyx, but a sportaperi medullaris musculosa was not identified.

The mammalian spleen consists of white and red pulp and serves at least the dual purpose of immunological functions and filtration, and subsequent lysis of abnormal red blood cells (RBCs) from the blood. Seals are known to have very large spleens with a mass that, when fully dilated, amounts to about 2–4% of body mass. The red pulp in these animals serves as a temporary store for large amounts of (oxygenated) RBCs, which may be released during diving. In the present study the spleens of four hooded seals, which are known to be able to stay submerged for almost 1 h and reach depths in excess of 1000 m, were examined histologically. The hooded seal red pulp was found to contain perforated arterioles that communicate with interconnected fenestrated venous sinuses through which the blood commutes with an extravascular room. It is proposed that this extravascular room is engorged with blood in response to withdrawal of alpha-adrenergic nervous tone to the splenic capsular smooth muscle, concomitant with dilatation of the splenic artery and increased splenic venous resistance. This will result in capsular dilatation and increased inflow of blood to the extravascular room, where RBCs may adhere reversibly to a mesh of reticular fibres, while the plasma fraction can escape back into circulation by way of the fenestrations. In preparation for the release of the RBCs, the opposite will happen – the capsula and the splenic artery constrict gradually, while the splenic veins dilate, and the RBCs are washed out. It is suggested that the release of the RBCs from the reticular fibres is facilitated by the release of a hitherto unknown substance, in response to beta-adrenergic nervous stimulation.

We use information on the at-sea distribution of radio-tagged seals to identify the summer foraging areas used by 31 harbour seals from two different haul-out sites in the Moray Firth, N.E. Scotland. We then determine whether seals tend to occur over particular sediment types or water depths as hypothesized by Härkönen (1987b), and assess whether local geographical variations in diet composition can be related to local differences in available foraging habitat.

The majority of seals foraged within 30 km of their haul-out site, consequently there was broad overlap between the foraging areas used by animals from the same site, but little overlap in the areas used by seals from different sites. Most seals foraged in water depths of 10-50 m with mainly sandy sea-bed sediments. Data on the distribution of dive depths of five seals which were fitted with time-depth-recorders indicated that seals were generally diving on, or close to, the sea-bed. Occasional pelagic dives between the more common benthic dives were also observed. Between-site differences in the seals' use of different water depths and sea-bed sediments suggest that local geographical variations in diet were related to local differences in foraging habitats, but that habitat use also differed between individual seals.