Abstract
Seals and fish-eating birds have increased in the Baltic Sea and there is concern that they compete with fisheries. Using data from around year 2010, we compare consumption of different fish ...species by seals and birds to the catch in the commercial and recreational fishery. When applicable this is done at the geographical resolution of ICES subdivisions. Predation by birds and mammals likely has limited impact on the populations of the commercially most important species (herring, sprat, and cod). In the central and southern Baltic, seals and birds consume about as much flatfish as is caught by the fishery and competition is possible. Birds and seals consume 2-3 times as much coastal fish as is caught in the fishery. Many of these species are important to the fishery (e.g. perch and whitefish) and competition between wildlife and the fishery is likely, at least locally. Estimated wildlife consumption of pike, sea trout and pikeperch varies among ICES subdivisions and the degree of competition for these species may differ among areas. Competition between wildlife and fisheries need to be addressed in basic ecosystem research, management and conservation. This requires improved quantitative data on wildlife diets, abundances and fish production.
•Skull measurements are not possible for the sex identification of ringed seals.•Males have higher BMD (bone mineral density) than females in the Greenland Sea.•BMD of the ringed seal skulls varies ...between Baltic Sea and Greenland Sea.•BMD increased with increasing PCB concentrations in the Baltic Sea.
Bone is remodelled constantly through a balance of bone formation and resorption. This process can be affected by various factors such as hormones, vitamins, nutrients and environmental factors, which can create an imbalance resulting in systemic or local bone alteration. The aim of the present study was to analyse the changes in bone mineral density (BMD) over time in skulls of ringed seals (Pusa hispida) from the Baltic and Greenland using museum samples. Overall, 303 skulls (102 Male, 89 Female, 112 unknown) were used for bone investigations and were divided into three periods according to collection year: before 1958 (n = 167), between 1958 and 1989 (n = 40) and after 1994 up to 2019 (n = 96). All skulls were examined by dual-energy X-ray absorptiometry to obtain the BMD. Skull BMD of the Baltic seals was positively correlated with the historical polychlorinated biphenyls (PCB) contamination having potential effects on the constitution of bones. BMD fluctuated between the three study periods (LM: p-value < 0.001, F-value = 47.5) with the lowest BMD found between 1897 and 1957, in the Gulf of Bothnia, where the highest peak of contaminant concentration was in the second period. BMD levels increased with increasing PCB concentration (LM: p < 0.001). The Greenland population showed significant lower BMD levels in the pollution and post-pollution period than the Baltic population (LM: p < 0.001). It also revealed a higher BMD in males than in females (LM: p = 0.03). In conclusion, the variations between 1829 and 2019 in the Baltic Sea and Greenland may to a certain extent reflect normal fluctuations; however, this study revealed several factors affecting BMD, including sex and PCB levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Mediterranean monk seal Monachus monachus, categorized as Endangered on the IUCN Red List, comprises 600–700 individuals in the eastern Mediterranean Sea and eastern Atlantic Ocean. Habitat ...degradation is a severe threat to the species. In 2016 and 2017, coastline surveys were conducted in Gökova Bay, south-west Turkey, to identify suitable monk seal habitat. A significant factor hindering recovery of the monk seal population of this Turkish coast and the nearby Greek islands is the limited number of marine caves suitable for resting and/or pupping. We identified four caves as possible monk seal resting and pupping caves. An additional cave with all essential features for seal usage except a ledge was also identified. An artificial ledge was built in this cave in July 2019 and seal usage was monitored by camera trap until September 2020. A total of 405 camera-trap events were analysed to examine presence of any monk seals on the ledge, and to understand the purpose (resting and/or pupping), frequency of use, sex and age group of any individuals using the cave. One juvenile used the cave four times for resting (420 minutes in total), predominantly nocturnally. This is the first construction of a dry ledge in a cave of this kind for monk seals. The camera recordings suggest this approach could provide habitat for this species in areas where there is insufficient dry protected area on land.
•The NHBF was used to improve the combustion and emission performance of rotary engine.•A calculation model of a peripheral portedrotary engine considering ASL was established.•The mixture formation ...and combustion process of NHBF under the action of ASL were analyzed.•The ideal blend fuel distribution which can improve the combustion efficiency was given.•The optimized hydrogen injection strategy was provided for improving the engine performance.
Natural gas/hydrogen blended fuel (NHBF) is considered to be one of the ideal alternative fuels for rotary engine, which can effectively reduce the carbon emission of the rotary engine. The purpose of this paper is to numerically study the influence of hydrogen injection timing (HIT) and hydrogen injection angle (HIA) on mixture formation, flame propagation, and NO emission in the cylinder. In addition, considering that the apex seal leakage (ASL) of rotary engine is difficult to avoid, the NHBF in the cylinder will inevitably leak from the apex seal leakage gap to the adjacent cylinders. Therefore, the NHBF leakage under the action of ASL should be considered. In this paper, a 3D dynamic model of the NHBF rotary engine considering the action of ASL was established. Further, the diffusion and combustion processes of NHBF in the cylinder with different HITs and HIAs were calculated. The results showed that the HIT and HIA can significantly change the flame propagation process by changing the fuel stratification pattern in the cylinder. For improving the combustion efficiency of the engine, the HIA of +45° and HIT of 155°CA (BTDC) adopted by Case:155 + 45 should be set as the hydrogen injection strategy. This is mainly because that for Case: 155 + 45, both natural gas and hydrogen are mainly distributed in the FOC, and the concentration of hydrogen and natural gas near the spark plug is also high. However, the defect of Case:155 + 45 is the significant increase of NO emission.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► The coefficient of friction of a-C coatings was in the range of 0.10 to 0.15 under cryogenic environment. ► The coatings had a graphite-like characteristic and were available to cryogenic ...environments. ► The deposition of the a-C coatings could significantly reduce the specific wear rate of seal rings. ► We explore the suitability of a-C coatings used in cryogenic mechanical seal.
The service life and the reliability of contact mechanical seal are directly affected by the wear of seal pairs (rotor vs. stator), especially under the cryogenic environment in liquid rocket engine turbopumps. Because of the lower friction and wear rate, amorphous carbon (a-C) coatings are the promising protective coatings of the seal pairs for contact mechanical seal. In this paper, a-C coatings were deposited on 9Cr18 by pulsed DC magnetron sputtering. The tribological performances of the specimen were tested under three sealed fluid conditions (air, water and liquid nitrogen). The results show that the coatings could endure the cryogenic temperature while the friction coefficients decrease with the increased contact load. Under the same contact condition, the friction coefficient of the a-C coatings in liquid nitrogen is higher than that in water and that they are in air. The friction coefficients of the a-C coatings in liquid nitrogen range from 0.10 to 0.15. In the cryogenic environment, the coatings remain their low specific wear rates (0.9×10−6 to 1.8×10−6mm3N−1m−1). The results provide an important reference for designing a water lubricated bearing or a contact mechanical seal under the cryogenic environment that is both reliable and has longevity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
There is global interest in marine renewable energy from underwater tidal turbines. Due to overlap in animal habitat with locations for tidal turbines, the potential for collisions has led to concern ...around strike risk. Using data from tagged harbor seals collected before construction and after operation of the SeaGen tidal turbine in Northern Ireland, this study quantifies risks of an operational turbine to harbor seals by taking into account turbine characteristics, tidal state, and seal behavior. We found 68% spatial avoidance (95% C.I., 37%, 83%) by harbor seals within 200 m of the turbine. When additionally accounting for variation in seal occupancy over depth and tidal flows, there is an overall reduction in collision risk from 1.29 to 0.125 seals per tidal cycle (90.3% reduction; (95% C.I., 83%, 98%)) compared to risk calculated under assumptions of uniform habitat use. This demonstrates the need to incorporate environmental conditions to properly assess strike risk.
•Strike risk is reduced by slower rotational blade speeds of tidal turbines.•Harbor seals predominately swam at surface and seafloor layers in this tidal region.•Harbor seals were 68% less likely to occupy habitat within 200 m of turbine.•Perceived risk is reduced by 90.3% using empirical data of dive and surface locations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Long and deep dives in marine mammals are enabled by high mass-specific oxygen stores and the dive response, which reduces oxygen consumption in concert with increased peripheral vasoconstriction and ...a lowered heart rate during dives. Diving heart rates of pinnipeds are highly variable and modulated by many factors, such as breath holding (apnea), pressure, swimming activity, temperature and even cognitive control. However, the individual effects of these factors on diving heart rate are poorly understood because of the difficulty of parsing their relative contributions in diving pinnipeds. Here, we examined the effects of apnea and external sensory inputs as autonomic drivers of bradycardia. Specifically, we hypothesized that (1) water stimulation of facial receptors would - as is the case for terrestrial mammals - enhance the dive response, (2) increasing the facial area stimulated would lead to a more intense bradycardia, and (3) cold water would elicit a more pronounced bradycardia than warm water. Three harbor seals (
) and a California sea lion (
) were trained to breath hold in air and with their heads submerged in a basin with variable water level and temperature. We show that bradycardia occurs during apnea without immersion. We also demonstrate that bradycardia is strengthened by both increasing the area of facial submersion and colder water. Thus, we conclude that the initiation of the dive response in pinnipeds is more strongly related to breath holding than in terrestrial mammals, but the degree of the dive response is potentiated autonomically via stimulation of facial mechano- and thermo-receptors upon submergence.
In 2012, climate-warming related decreases in sea ice led to listings of ringed Pusa hispida and bearded seals Erignathus barbatus as threatened under the United States Endangered Species Act (ESA) ...prior to evidence of population declines. These and 2 other ice-associated species (spotted Phoca largha and ribbon seals Histriophoca fasciata) are vital subsistence re sources to coastal Alaska Native communities. ESA-related assessments concluded that subsistence removals (seals that were harvested as well as those that were struck and lost) were sustainable; however, limited data precluded a quantitative evaluation. Potential biological removal (PBR), defined as the maximum number of animals that can be removed from a stock while allowing the stock to reach or maintain its optimal sustainable size, is typically used to determine whether human-caused mortality is sustainable. Although developed to address commercial fisheries bycatch, PBR serves as a conservative measure of sustainability. We compiled annual subsistence removal of ice seals in Alaska between 1992 and 2014 for 41 of 55 ice seal hunting communities and used per capita (based on the 2015 human population) removal estimates from surveyed communities to estimate regional and statewide average removals. We used average per capita values of harvest, combined with struck and lost, for surveyed communities (average removals) to extrapolate to unsurveyed communities. To account for underreported harvest, we also extrapolated using maximum harvest values, providing a liberal estimate. Both the average and liberal estimates of removals were below PBR for all 4 species. Thus, the best available data indicate that subsistence hunting is currently sustainable for all 4 species of ice seals.
•Acidic and alkaline solution exhibited inhibitory effect against cavitation.•Acidic solutions have higher inhibitory effect than alkaline solutions.•The cavitation degree and flow length increased ...with higher deviation from pH = 7.•The cycle period reduced with higher offset value from pH = 7.•Acidic solutions should be used as reference for magneto-hydraulic sealing design.
Owing to the different pH values of water resources in different places, it is not practical to design hydraulic–mechanical magneto-hydraulic sealing devices under clean water conditions. This study used a Venturi structure to analyze the relationship between the solution pH and cavitation. A high-speed camera and turbine flowmeter were used to record the primary cavitation flow rate, shedding period of the cavitation cloud, and flow direction length of the cavitation cloud of solutions with different pH values. The results showed that acidic and alkaline solutions can inhibit the occurrence of primary cavitation. Compared with clean water, acidic and alkaline solutions have longer cavitation cloud flow length, shortened cavitation cycle, and higher degree of cavitation. In detail, the degree of cavitation in the acidic solution is stronger than that in the alkaline solution. Therefore, the amplitude of the pressure pulsation in an acidic solution should be taken as the reference when designing a hydro-mechanical magneto-hydraulic sealing device.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Teeth-on-rotor (TOR) and teeth-on-stator (TOS) layouts are compared in this paper to explore better arrangement for different labyrinth seals. The diaphragm labyrinth seal (DLS) and hole diaphragm ...labyrinth seal (HDLS) are both redesigned into TOR and TOS layouts. To accurately predict the rotordynamics and leakage performance of different seals, a one-motion transient computational fluid dynamics (CFD) method based on the simplified multi-frequency transient method is proposed. A comparison of the experimental results, two-motion transient CFD method and proposed method showcase the better accuracy of the current method in rotordynamic performance prediction. The results shows the better rotordynamic characteristics of the TOS layout for different layouts and of the HDLS type seals for three labyrinth type seals. Even though, the TOR layout cannot increase the stability of the rotor system, a clear circumferential velocity reduction in the DLS and HDLS seals can be observed in both the TOS and TOR layouts. However, the changes in leakage performance for DLS and HDLS seals are different from those for traditional LSs. Unlike TOR-LS and TOR-HDLS, which exhibit relatively large increases in leakage compared with the TOS layout, TOR-DLS achieves a maximum 1.7% leakage reduction at a 15000 rpm rotation speed. A decrease in the jet flow length and increase in the turbulence kinetic energy in TOR-DLS compared with those in TOS-DLS further explain this abnormal phenomenon.
•A one-motion transient computational fluid dynamics(CFD) method was verified to have the better accuracy.•Teeth-on-rotor(TOR) and teeth-on-stator(TOS) layouts were considered in traditional and modified labyrinth seals (LS).•Better stability of diaphragm labyrinth seal(DLS) and hole diaphragm labyrinth seal(HDLS) is observed in both layouts.•TOS-HDLS achieves the best leakage stoppage performance by maximum area of turbulence kinetic energy(TKE).•Only TOR-DLS can decrease 1.7% leakage of TOS-LS by decrease of axial jet and increase of TKE, in three TOR seals.
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GEOZS, IJS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZAGLJ
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