Mass stranding events (MSEs) of beaked whales (BWs) were extremely rare prior to the 1960s but increased markedly after the development of naval mid-frequency active sonar (MFAS). The temporal and ...spatial associations between atypical BW MSEs and naval exercises were first observed in the Canary Islands, Spain, in the mid-1980s. Further research on BWs stranded in association with naval exercises demonstrated pathological findings consistent with decompression sickness (DCS). A 2004 ban on MFASs around the Canary Islands successfully prevented additional BW MSEs in the region, but atypical MSEs have continued in other places of the world, especially in the Mediterranean Sea, with examined individuals showing DCS. A workshop held in Fuerteventura, Canary Islands, in September 2017 reviewed current knowledge on BW atypical MSEs associated with MFAS. Our review suggests that the effects of MFAS on BWs vary among individuals or populations, and predisposing factors may contribute to individual outcomes. Spatial management specific to BW habitat, such as the MFAS ban in the Canary Islands, has proven to be an effective mitigation tool and mitigation measures should be established in other areas taking into consideration known population-level information.
First observed in the classical era, a population of sperm whales (Physeter macrocephalus) persists to this day in the deep waters of the Mediterranean Sea. Genetic and observational evidence support ...the notion that this is an isolated population, separated from its Atlantic neighbours. These whales depend on mesopelagic squid for food, and appear to occupy a very similar ecological niche to sperm whales in the open oceans. Recent evidence proving that individuals can pass between the eastern and western deep water basins confirms that this is a single population, not isolated into western and eastern stocks. We lack robust information on their population status, but they could number in the hundreds rather than thousands, and current densities appear to be much lower than those reported in the 1950s, suggesting that we should be very concerned about the conservation status of this population. This makes it vitally important to address the serious threats posed by ship strikes and entanglement in fishing nets, especially driftnets, and to carefully monitor other potential sources of anthropogenic impact. A step change in funding to collect better data and a clear shift in policy priorities are needed if we are to be serious about conserving this population.
Mass strandings of live whales have been explained by proposing many 'natural' or human-related causes. I found that a recent stranding of Cuvier's beaked whale coincided closely in time and location ...with military tests of an acoustic system for submarine detection being carried out by the North Atlantic Treaty Organization (NATO).
The Mediterranean Sea provides habitat for globally threatened cetaceans. The Hellenic Trench is an Important Marine Mammal Area, providing core habitat for sperm whales
Physeter macrocephalus
and ...Cuvier’s beaked whales
Ziphius cavirostris
. Surveys have characterized distributions of these species in near-shore areas (<2000 m deep). Sparse survey effort in deeper waters during winter has allowed speculation that it is not an important habitat in winter. We used passive acoustic monitoring from towed arrays to document cetaceans during summer and winter, covering 18366 km of trackline off the Peloponnese and Crete. We confirmed the acoustic presence of 5 odontocetes: sperm whales (n = 49 encounters; mean depth (
x
̄): 3360 m; range (
R)
: 1250 to 4210 m), Cuvier’s beaked whales (n = 4;
x
̄: 3070 m;
R
: 1970 to 3770 m), Risso’s dolphins
Grampus griseus
(n = 5;
x
̄: 3340 m;
R
: 2250 to 4440 m), striped dolphins
Stenella coeruleoalba
(n = 2;
x
̄: 2980 m;
R
: 2490 to 3470 m) and rough-toothed dolphins
Steno bredanensis
(n = 1; 3650 m). We also encountered 224 unidentified delphinids, including a potential blackfish (3020 m). We confirmed that these species are present in the Hellenic Trench throughout the year. Given the impact of multiple threats on sperm and Cuvier’s beaked whales in the Hellenic Trench, we suggest that policymakers follow the precautionary approach in managing human activities in the area. Ongoing seismic surveys, hydrocarbon extraction and uncontrolled shipping could have potentially negative effects on these species at the population level and we advise caution in permitting such activities in future
Cuvier's beaked whale (Ziphius cavirostris G. Cuvier, 1823) is the only beaked whale species commonly found in the Mediterranean Sea. Until recently, species presence in this area was only inferred ...from stranding events. Dedicated cetacean surveys have increased our knowledge of the distribution of Cuvier's beaked whales, even though many areas still remain unexplored. Here, we present an updated analysis of available sighting and stranding data, focusing on the atypical mass strandings that have occurred in the Mediterranean Sea since 1963. We describe in detail the five more recent events (2006-14), highlighting their relationship with naval exercises that used mid-frequency active sonar. The distribution of the species is apparently characterized by areas of high density where animals seem to be relatively abundant, including the Alborán Sea, Ligurian Sea, Central Tyrrhenian Sea, southern Adriatic Sea and the Hellenic Trench, but other such areas may exist where little or no survey work has been conducted. Population size has been estimated for the Alborán and Ligurian seas. Habitat modelling studies for those areas, confirmed the species preference for the continental slope and its particular association with submarine canyons, as has also been found to be the case in other areas of the world. The application of results from habitat modelling to areas different from their calibration sites is proposed as a management tool for minimizing the potential impacts of human activities at sea. Military sonar is known worldwide as a threat for this species and is suggested to be a major threat for Cuvier's beaked whale in the Mediterranean Sea.
The sperm whale is one of the very few deep diving mammal species in the Mediterranean Sea. Following a rare mass stranding of male sperm whales in the Adriatic Sea in December 2009, ...photo-identification methods were used in order to investigate previous sightings of the stranded whales in the region. Fluke photos of the stranded whales were compared with those of 153 and 128 free-ranging individuals photographed in the western and eastern Mediterranean basins, respectively. Three out of the seven stranded whales had been previously photo-identified and some of them more than once. To reach the stranding place, two of these re-identified whales performed long-range inter-basin movements of about 1600–2100
km (in a straight line) either through the Strait of Sicily or the Strait of Messina. In addition, comparisons among all whales photographed in the two Mediterranean basins revealed that one more individual first photographed in the western basin (1991) was re-identified 13 years later in the eastern basin (2004). These three cases provide the first conclusive evidence of inter-basin movement of sperm whales in the Mediterranean Sea. Inter-basin gene flow is important for the survival of the small and endangered Mediterranean sperm whale population. Mitigating the disturbance created by human activities in the straits area is crucial for its conservation.
► Sperm whales’ life-history can be followed over decades through photo-identification. ► Mediterranean sperm whales perform long-range inter-basin movements. ► All recorded movements concerned males passing from the western to the eastern basin. ► Crossings of the central Mediterranean straits are important for this population. ► Mitigating disturbing human activities in the straits is crucial for its conservation.
On the zeros of derivatives of Bessel functions Frantzis, Dimitris A.; Kokologiannaki, Chrysi G.; Petropoulou, Eugenia N.
Integral transforms and special functions,
06/2024, Letnik:
35, Številka:
5-6
Journal Article
Recenzirano
The positive zeros of
$ J'''_{\nu }(x) $
J
ν
‴
(
x
)
and
$ J_{\nu }^{(n+1)}(x) $
J
ν
(
n
+
1
)
(
x
)
are studied by using classical analysis and the properties of
$ J_{\nu }(x) $
J
ν
(
x
)
. It is ...proved that
$ J'''_{\nu }(x) $
J
ν
‴
(
x
)
has a unique zero in specific intervals. Regarding
$ J_{\nu }^{(n+1)}(x) $
J
ν
(
n
+
1
)
(
x
)
, it is proved that its positive zero
$ j_{\nu,m}^{(n+1)} $
j
ν
,
m
(
n
+
1
)
is an increasing function with respect to ν, for
$ \nu \gt n $
ν
>
n
. Moreover, the first two Rayleigh sums for
$ j_{\nu,m}^{(n)} $
j
ν
,
m
(
n
)
are calculated. The obtained results extend and complement previously known results and also answer an open problem regarding the monotonicity of
$ j_{\nu,m}^{(n)} $
j
ν
,
m
(
n
)
. As a consequence of these results, a lower bound for
$ j_{\nu,1}^{(n+1)} $
j
ν
,
1
(
n
+
1
)
is deduced, as well as an inequality between
$ j_{\nu,1}^{(n+1)} $
j
ν
,
1
(
n
+
1
)
and
$ j_{\nu,1}^{(n)} $
j
ν
,
1
(
n
)
.
This paper compares the relative performances of three different thermally activated, environmentally friendly cooling systems, e.g. a silica-gel–water adsorption system, a LiBr–H
2O absorption ...system and a desiccant air system. The adsorption and absorption systems in the current study employ water as the refrigerant, while the desiccant system cools atmospheric air directly. Each of these systems can be utilized at relatively low heat source temperatures such as achieved by flat plate solar collectors, but it is unclear which of these systems is best suited to what range of heat source temperature. Our study explores answers to this question by generating quantitative results comparing their relative thermal performance, i.e. COP and refrigeration capacity, and a qualitative comparison based on the size, maturity of technology, safe operation etc. In order to provide a fair comparison between the fundamentally different systems, a
UA (overall heat transfer coefficient multiplied by the heat transfer area) value of 1.0
kW
°C
−1 is considered for the heat exchanger that transfers heat from the supplied hot water. Furthermore, to compare systems of similar size, the mass of silica-gel in the adsorption and desiccant systems and the mass of LiBr–H
2O solution in the absorption system were specified such that each system provides the same amount of refrigeration (8.0
kW) at a source temperature of 90
°C. It is found that the absorption and adsorption cooling systems have a higher refrigeration capacity at heat source temperatures below 90
°C, while the desiccant air system outperforms the others at temperatures above 90
°C.
Mapping of ecosystem components (natural and socioeconomic) is a prerequisite for ecosystem-based marine spatial management (EB-MSM). To initiate the process of EB-MSM in the Greek Ionian Sea and the ...adjacent gulfs, the main relevant ecosystem components were mapped based on existing spatial information and expert judgment. The natural components mapped included habitat types and species targeted for conservation, according to national and European legislation and international agreements. Main human activities/pressures related to fisheries, aquaculture, tourism, and industry were also mapped. In order to assess the quality of data used to map ecosystem components and therefore take into consideration the inherent uncertainty, an assessment of 5 semi-quantitative data indicators based on a pedigree matrix was conducted. Through this qualitative approach we gained information related to the sources, acquisition and verification procedures, statistical properties, and temporal & geographical correlation, along with the collection process quality of the ecosystem components under study. A substantial overlapping between ecological features and human activities was identified, confirming the need for a well-planned approach to marine space management, in order to mitigate conflicts for marine resources and conserve marine ecosystems and their associated goods and services.
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