Harbour and grey seals rely on acoustic signals to mate, socialise and defend their territory. Previous studies have focused on their behaviour, movements and communication from the coast, leaving a ...knowledge gap in the offshore environments, and therefore being unable to determine the proper use they give to those areas and the risks they face around them. Acoustic data collected with a SoundTrap were analysed to assess the detectability of both species in the Malin Sea. Vocalisations were classified based on aural and visual features, as well as using non-parametric classification trees. Differences in the vocalisation rate of grey seals per diel, season and tidal state were also assessed through Generalised Linear Mixed Models, obtaining significant results, and finding similarities in the vocalisations of grey seals with the Scottish and Irish populations. A small sample of adult and pup harbour seals was detected, and differences in call type and number of detections per type were found across the seasons. These results show the importance of the area for both species, and lay the foundations for future studies, which will help to implement proper conservation measures such as Marine Protected Areas.
Two-phase mechanical face seals with laser surface texturing (LST) on their end faces were investigated using a test rig with a transparent rotating ring. Cavitation occurred in some of the dimples ...and annular vaporization regions attached to the dimples were observed. The speed limit of the LST seals with suitable parameters was obviously higher than that of a seal with a plain end face, while those with sub-optimal LST parameters exhibited a lower speed limit. These results reveal that LST shows potential in two-phase mechanical face seals, but the LST parameters should be carefully considered.
•We study two-phase mechanical seal using a test rig with transparent seal runner.•We examine the relation between tribology performance and phase distribution.•The plain-face seal has a speed limit above which it becomes unstable.•LST seals with suitable parameters improve the performance of mechanical seals.•LST shows potential in two-phase mechanical seals.
Full text
Available for:
GEOZS, IJS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Despite decades of research, surprisingly little is known about the mechanism(s) by which an individual's genotype is encoded in odour. Many studies have focused on the role of the major ...histocompatibility complex (MHC) owing to its importance for survival and mate choice. However, the salience of MHC-mediated odours compared to chemicals influenced by the rest of the genome remains unclear, especially in wild populations where it is challenging to quantify and control for the effects of the genomic background. We addressed this issue in Antarctic fur seals by analysing skin swabs together with full-length MHC DQB II exon 2 sequences and data from 41 genome-wide distributed microsatellites. We did not find any effects of MHC relatedness on chemical similarity and there was also no relationship between MHC heterozygosity and chemical diversity. However, multilocus heterozygosity showed a significant positive association with chemical diversity, even after controlling for MHC heterozygosity. Our results appear to rule out a dominant role of the MHC in the chemical encoding of genetic information in a wild vertebrate population and highlight the need for genome-wide approaches to elucidate the mechanism(s) and specific genes underlying genotype-odour associations.
Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic ...persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their abundance and population trends. We modelled the density and distribution of pack-ice seals as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our density surface modelling approach used data from aerial surveys of pack-ice seals collected in the 2013/14 austral summer. Crabeater seals
Lobodon carcinophaga
, the most numerous pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice near the continental shelf break, but were almost absent in areas of similar sea ice concentration in the southern extent of the Weddell Sea. The highest densities of Weddell seals
Leptonychotes weddelli
, which were less abundant than crabeater seals within the pack-ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative abundance of their main prey (Antarctic krill
Euphausia superba
and Antarctic silverfish
Pleuragramma antarctica
) obtained from concurrent ecosystem surveys. Ross seals
Ommatophoca rossii
and leopard seals
Hydrurga leptonyx
were not detected at all and are apparently rare within the southern Weddell Sea. These results can contribute to biodiversity assessments in the context of marine protected area planning in this region of the Southern Ocean.
Host‐specialist parasites of endangered large vertebrates are in many cases more endangered than their hosts. In particular, low host population densities and reduced among‐host transmission rates ...are expected to lead to inbreeding within parasite infrapopulations living on single host individuals. Furthermore, spatial population structures of directly‐transmitted parasites should be concordant with those of their hosts. Using population genomic approaches, we investigated inbreeding and population structure in a host‐specialist seal louse (Echinophthirius horridus) infesting the Saimaa ringed seal (Phoca hispida saimensis), which is endemic to Lake Saimaa in Finland, and is one of the most endangered pinnipeds in the world. We conducted genome resequencing of pairs of lice collected from 18 individual Saimaa ringed seals throughout the Lake Saimaa complex. Our analyses showed high genetic similarity and inbreeding between lice inhabiting the same individual seal host, indicating low among‐host transmission rates. Across the lake, genetic differentiation among individual lice was correlated with their geographic distance, and assignment analyses revealed a marked break in the genetic variation of the lice in the middle of the lake, indicating substantial population structure. These findings indicate that movements of Saimaa ringed seals across the main breeding areas of the fragmented Lake Saimaa complex may in fact be more restricted than suggested by previous population‐genetic analyses of the seals themselves.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
To improve the pressure capability of ordinary ferrofluid seals with a large gap, a novel type of converging stepped ferrofluid seals was proposed. The leakage positions and the magnetic field ...distributions in the sealing gaps of the new device are studied computationally by means of the finite-element method. The theoretical pressure capabilities of the seal are calculated based on a new expression introduced for the particular new seal geometry and for different sealing gaps. Computational results for effects of the radial and axial sealing gaps on the pressure capabilities of the seal are compared to the experimental results obtained from measurements employing a prototype of the proposed new seal. A good agreement between theoretical and experimental results is obtained. It is found that the pressure capabilities of the new seal depend on the height of the radial sealing gap and on the width of the axial sealing gap.
Ferrofluid rotary seals are mechanical contact-free magnetic liquid seals that are characterised by their simple structure, low friction and ability to hermetically seal. Although ferrofluid rotary ...seals for sealing vacuum and gases are part of a well established industry, the sealing of liquids has not been implemented yet. Literature learns that degradation of the ferrofluid seal over time when it dynamically contacts a liquid results into premature seal failure. This paper presents a new type of ferrofluid rotary seal in which a ferrofluid replenishment system is implemented that renews the ferrofluid in the sealing ring while sealing capacity is maintained. By replacing the degraded ferrofluid in the seal at a sufficient rate, service life of the ferrofluid rotary seal can theoretically be unlimited. An analytical model and FEM analysis are used to design the ferrofluid sealing device and to predict its sealing capacity. An experimental test setup has been built on which the sealing capacity and service life of the device has been tested for different sealing conditions. It is demonstrated that the ferrofluid replenishment system successfully extends and controls the service life of the ferrofluid rotary seal that dynamically seals pressurised water.
•This paper presents a solution for the premature failure of ferrofluid rotary seals that seal liquids.•Theoretically, when the ferrofluid seals are renewed at a sufficient rate, service life of the ferrofluid seal is unlimited.•It is demonstrated that ferrofluid can be transported between ferrofluid seals while the sealing capacity is maintained.
Full text
Available for:
GEOZS, IJS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Dynamic seals are one of the critical components of Absorber Rod Drive Mechanism of Fast Breeder Reactors, requiring separate experimental development. Their significance can't be overemphasized ...considering that the availability and re-usability of Control Rod Drive Mechanisms of Fast Breeder Test Reactor is governed by the failure rate of dynamic seals (bellows). For prototype and subsequent Fast Breeder Reactors in India, choice of the dynamic seal is changed to an in-house designed & developed labyrinth type V-ring seal. The present work is related to the numerical investigations carried out to gain insights into the sealing mechanism and the thermal behaviour of these seals. The results indicate that the seal geometry is very important for obtaining optimum performance. By changing the geometry of the present seal, performance enhancement by more than 50% in important indices is obtained. Further, the results point out that caution shall be exercised when the seal material & its operating temperature are changed. Also, the numerical model developed in this study will be useful for developing more robust dynamic seals in future.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Evidence for an Allee effect in a declining fur seal population Nagel, Rebecca; Stainfield, Claire; Fox-Clarke, Cameron ...
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
03/2021, Volume:
288, Issue:
1947
Journal Article
Peer reviewed
Open access
Allee effects play an important role in the dynamics of many populations and can increase the risk of local extinction. However, some authors have questioned the weight of evidence for Allee effects ...in wild populations. We therefore exploited a natural experiment provided by two adjacent breeding colonies of contrasting density to investigate the potential for Allee effects in an Antarctic fur seal (
) population that is declining in response to climate change-induced reductions in food availability. Biometric time-series data were collected from 25 pups per colony during two consecutive breeding seasons, the first of which was among the worst on record in terms of breeding female numbers, pup birth weights and foraging trip durations. In previous decades when population densities were higher, pup mortality was consistently negatively density dependent, with rates of trauma and starvation scaling positively with density. However, we found the opposite, with higher pup mortality at low density and the majority of deaths attributable to predation. In parallel, body condition was depressed at low density, particularly in the poor-quality season. Our findings shed light on Allee effects in wild populations and highlight a potential emerging role of predators in the ongoing decline of a pinniped species.
•We review the of pathogens in select marine and terrestrial key species of the Baltic Sea.•This review is the first to merge and present available information and baseline data for the Baltic ...Sea.•Pathogens including parasites, bacteria and virus were reviewed.
Here we review the state-of-the-art of pathogens in select marine and terrestrial key species of the Baltic Sea, i.e. ringed seal (Pusa hispida), harbour seal (Phoca vitulina), grey seal (Halichoerus grypus), harbour porpoise (Phocoena phocoena), common eider (Somateria mollissima), pink-footed goose (Anser brachyrhynchus) and white-tailed eagle (Haliaeetus albicilla). This review is the first to merge and present available information and baseline data for the FP7 BONUS BaltHealth project: Baltic Sea multilevel health impacts on key species of anthropogenic hazardous substances. Understanding the spread, prevalence and effects of wildlife pathogens is important for the understanding of animal and ecosystem health, ecosystem function and services, as well as human exposure to zoonotic diseases. This review summarises the occurrence of parasites, viruses and bacteria over the past six decades, including severe outbreaks of Phocine Distemper Virus (PDV), the seroprevalence of Influenza A and the recent increase in seal parasites. We show that Baltic high trophic key species are exposed to multiple bacterial, viral and parasitic diseases. Parasites, such as C. semerme and P. truncatum present in the colon and liver Baltic grey seals, respectively, and anisakid nematodes require particular monitoring due to their effects on animal health. In addition, distribution of existing viral and bacterial pathogens, along with the emergence and spread of new pathogens, need to be monitored in order to assess the health status of key Baltic species. Relevant bacteria are Streptococcus spp., Brucella spp., Erysipelothrix rhusiopathiae, Mycoplasma spp. and Leptospira interrogans; relevant viruses are influenza virus, distemper virus, pox virus and herpes virus. This is of special importance as some of the occurring pathogens are zoonotic and thus also pose a potential risk for human health. Marine mammal handlers, as well as civilians that by chance encounter marine mammals, need to be aware of this risk. It is therefore important to continue the monitoring of diseases affecting key Baltic species in order to assess their relationship to population dynamics and their potential threat to humans. These infectious agents are valuable indicators of host ecology and can act as bioindicators of distribution, migration, diet and behaviour of marine mammals and birds, as well as of climate change and changes in food web dynamics. In addition, infectious diseases are linked to pollutant exposure, overexploitation, immune suppression and subsequent inflammatory disease. Ultimately, these diseases affect the health of the entire ecosystem and, consequently, ecosystem function and services. As global warming is continuously increasing, the impact of global change on infectious disease patterns is important to monitor in Baltic key species in the future.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
