Using national and international research survey data and applying a combination of models and mapping tools, this study revealed temperature and depth as the crucial environmental drivers of both ...the distribution and the abundance of four benthopelagic chondrichthyans inhabiting Norwegian and Icelandic waters: rabbitfish (Chimaera monstrosa), velvet‐belly lanternshark (Etmopterus spinax), blackmouth catshark (Galeus melastomus) and spurdog (Squalus acanthias). C. monstrosa and E. spinax seem to prefer similar spatial and ecological habitats, that is deep and cold waters. In contrast, G. melastomus and S. acanthias both prefer similar ecological habitats, that is warmer and shallower waters; nonetheless, they exhibit a different spatial distribution pattern. The species' varied habitat and spatial preferences may lead to different levels of exposure to fishing activities and associated by‐catch risks. Findings of the species' spatial distributions and their driving forces are expected to inform the sustainable management of these species and the ecosystems they inhabit.
In many fisheries, such as trawl fisheries, sharks appear among the catches as bycatch or discards, and these species include velvet belly (
Etmopterus spinax
) and blackmouth catshark (
Galeus ...melastomus
). The objective of this study was to research the feeding habits of both species in the Gulf of Cádiz and to identify possible differences in diet depending on size and time of day. The most frequent sizes were 12–16 cm for
E. spinax
and 14–20 cm for
G. melastomus.
Both species preyed mainly on euphausiaceans and teleosts; their Index of Relative Importance (IRI) per species were as follows:
E. spinax
42.30% IRI, 21.66% IRI;
G. melastomus
52.33% IRI, 27.26% IRI, respectively. Only
Etmopterus spinax
showed significant variation in diet as a function of the time of day (
p
< 0.05), although both species showed similar patterns of feeding throughout the day. With respect to size,
E
.
spinax
consumes more cephalopods and teleosts as its size increases, while
G
.
melastomus
increases its consumption of decapods.
The feeding ecology of eight demersal elasmobranchs, three sharks (Etmopterus spinax, Scyliorhinus canicula and Galeus melastomus) and five batoids (Myliobatis aquila, Leucoraja naevus, Raja ...polystigma, R. miraletus and R. clavata), from the Balearic Sea (western Mediterranean) was analyzed. For each species, the diet and feeding habits were characterized by depth strata using quantitative indices such as diet overlap, diet breadth and prey diversity. Diet variation with size and depth were also tested for the most abundant species. For shelf-living species, natantian and reptantian crustaceans together with teleosts were the most important preys. On slope bottoms, euphausiids were the preferential prey for S. canicula and G. melastomus, while E. spinax fed mainly on cephalopods. The most specialist and generalist diet corresponded to G. melastomus living on the upper slope and S. canicula from the continental shelf, respectively. High overlap was found between all the skates on the continental shelf and the sympatric sharks S. canicula and G. melastomus on the slope. Significant overlap was also found between S. canicula and R. clavata on the continental shelf. Size was found to significantly affect the diet of S. canicula, G. melastomus and R. clavata, whereas depth affected exclusively S. canicula.
Main biological features were assessed for the first time in the deep‐water shark Etmopterus spinax from Hellenic waters by examining 150 individuals caught incidentally in the bottom‐trawl ...commercial fishery off Skyros island. Females outnumbered males and the overall sex ratio was 1.38:1. Females ranged from 122 to 311 mm in total length (LT) and males from 129 to 270 mm LT, both exhibiting positive allometric growth. Total length–total mass relationships and frequency distributions did not show significant differences between females and males. Sexual dimorphism was not either found by analysing 56 different morphological characteristics. The effect of sex and season was more prominent on the gonadosomatic and hepatosomatic indices compared to the relative condition factor. Most of the individuals were sexually immature, with two specimens classified as mature, one gravid female reaching 311 mm LT with undeveloped gonads and enlarged uteri with embryos, and one male reaching 270 mm LT with enlarged gonads and rigid claspers with hooks. The present study highlights the importance of the sampling location as a breeding and nursery ground for E. spinax in the eastern Mediterranean Sea that should be taken into account for the species' conservation considering its intrinsic characteristics, which make it vulnerable to fishing pressure.
The velvet belly lanternshark, Etmopterus spinax, is a deep-sea bioluminescent squaloid shark, found predominantly in the Northeast Atlantic and Mediterranean Sea. It has been exposed to relatively ...high levels of mortality associated with by-catch in some regions. Its late maturity and low fecundity potentially renders it vulnerable to over-exploitation, although little remains known about processes of connectivity between key habitats/regions. This study utilised DNA sequencing of partial regions of the mitochondrial control region and nuclear ribosomal internal transcribed spacer 2 to investigate population structure and phylogeography of this species across the Northeast Atlantic and Mediterranean Basin. Despite the inclusion of samples from the range edges or remote locations, no evidence of significant population structure was detected. An important exception was identified using the control region sequence, with much greater (and statistically significant) levels of genetic differentiation between the Mediterranean and Atlantic. This suggests that the Strait of Gibraltar may represent an important bathymetric barrier, separating regions with very low levels of female dispersal. Bayesian estimation of divergence time also places the separation between the Mediterranean and Atlantic lineages within the last 100,000 years, presumably connected with perturbations during the last Glacial Period. These results demonstrate population subdivision at a much smaller geographic distance than has generally been identified in previous work on deep-sea sharks. This highlights a very significant role for shallow bathymetry in promoting genetic differentiation in deepwater taxa. It acts as an important exception to a general paradigm of marine species being connected by high levels of gene-flow, representing single stocks over large scales. It may also have significant implications for the fisheries management of this species.
•First analysis of connectivity in the velvet belly lanternshark, a vulnerable deep sea shark.•Identification of a major oceanographic barrier to gene-flow.•Important implications for biogeography, fisheries management & conservation.
Multiple paternity seems common within elasmobranchs. Focusing on two deep‐sea shark species, the velvet belly lanternshark (Etmopterus spinax) and the slendertail lanternshark (Etmopterus molleri) ...we inferred the paternity in 31 E. spinax litters from Norway (three to 18 embryos per litter) and six E. molleri litters from Japan (three to six embryos), using 21 and 10 specific microsatellites, respectively. At least two E. spinax litters were sired from multiple fathers each, with highly variable paternal skew (1:1 to 9:1). Conversely, no clear signal of genetic polyandry was found in E. molleri.
We conducted interviews of a representative sample of 106 retired fishers in Italy, Spain and Greece, asking specific questions about the trends they perceived in dolphin and shark abundances between ...1940 and 1999 (in three 20 year periods) compared to the present abundance. The large marine fauna studied were not target species of the commercial fleet segment interviewed (trawl fishery). The fishers were asked to rank the perceived abundance in each period into qualitative ordinal classes based on two indicators: frequency of sightings and frequency of catches (incidental or intentional) of each taxonomic group. The statistical analysis of the survey results showed that both incidental catches and the sighting frequency of dolphins have decreased significantly over the 60+ years of the study period (except for in Greece due to the recent population increase). This shows that fishers' perceptions are in agreement with the declining population trends detected by scientists. Shark catches were also perceived to have diminished since the early 1940s for all species. Other long-lived Mediterranean marine fauna (monk seals, whales) were at very low levels in the second half of the 20(th) century and no quantitative data could be obtained. Our study supports the results obtained in the Mediterranean and other seas that show the rapid disappearance (over a few decades) of marine fauna. We show that appropriately designed questionnaires help provide a picture of animal abundance in the past through the valuable perceptions of fishers. This information can be used to complement scientific sources or in some cases be taken as the only information source for establishing population trends in the abundance of sensitive species.
Counterilluminating animals produce a ventral light to hide their silhouette in the water column. This midwater camouflage technique requires a fine and dynamic control of the wavelength, angular ...distribution, and intensity of their luminescence, which needs to continuously match ambient downwelling light. Recently, extraocular opsins have been suggested to play a role in the bioluminescence control of several organisms, such as squids, comb jellies, or brittle stars, providing a way for photogenic structures to perceive their own light output. By analysing a growing embryonic series of the velvet belly lanternshark,
Etmopterus spinax
, we show that the development of lanternshark luminescence competence is associated with the expression of encephalopsin within epidermal cells and in the light-regulating structure of the photogenic organs. Such an intra-uterine expression of encephalopsin strongly supports this blue-sensitive extraocular opsin to allow bioluminescence perception in lanternshark photophores and suggests a clear physiological interaction between photoemission and photoperception.
Aim
Trypanorhyncha cestodes comprise a wide range of heteroxenous parasites infecting elasmobranchs as definitive hosts. Limited data exist on the larval infection of these cestodes and the role of ...intermediate and paratenic hosts in the life cycle of these parasites. We investigated the factors that determine the occurrence and the level of infection of Grillotia plerocerci in the skeletal muscles of various benthonic sharks and analyzed the parasites through an integrative taxonomic approach.
Location
Mediterranean Sea.
Methods
Sharks obtained as bycatch of commercial trawling activities (i.e., Etmopterus spinax, Galeus melastomus, and Scyliorhinus canicula) were used in this study. Data from a limited number of Dalatias licha and Scyliorhinus stellaris were also included. Grillotia plerocerci were molecularly characterized using the partial 28S large subunit rDNA. Boosted regression trees were used to model the relationship between the abundance of infection with both morphological and physiological predictors in each host.
Results
Plerocerci of Grillotia were detected in all shark species except S. stellaris. Host species significantly differed in terms of parasite abundance, with the highest and lowest prevalence and abundance of infection detected in G. melastomus and E. spinax, respectively. The relative influence of the traits involved in explaining the parasite abundance was related to the host size in G. melastomus, while both morphology‐ and physiology‐related traits explained the patterns observed in E. spinax and S. canicula. The 28S rDNA sequences shared an identity of ∼99.40% with a Grillotia species previously found in the Mediterranean Sea. At intraspecific level, two different genotypes were found. A first type was retrieved only from D. licha, whereas a second type was found in G. melastomus, E. spinax, and S. canicula.
Main conclusions
Present results suggest that the two genotypes could be involved in different consumer‐resource systems and confirm most of the examined shark species as transport hosts of Grillotia species for unknown larger top predators.
This study investigated the factors that determine the occurrence and the level of infection of Grillotia (Cestoda) plerocerci in the skeletal muscles of various benthonic sharks and analyzed the parasites through an integrative taxonomic approach. Plerocerci of Grillotia were detected in all shark species except Scyliorhinus stellaris. Present results suggest that the two genotypes here found could be involved in different consumer‐resource systems and confirm most of the examined shark species as transport hosts of Grillotia species for unknown larger top predators.
The Santa Maria di Leuca (SML) coral banks represent a rare example of living
Lophelia-Madrepora-bearing coral mounds in the Mediterranean Sea. They are located between 350 and 1100
m in depth, in ...the northern Ionian Sea (eastern-central Mediterranean). Using a multi-beam echo sounder, side-scan sonar, high-resolution seismics and underwater video, the zones were identified for the sampling demersal fauna without damaging the coral colonies. During September–October 2005 experimental samplings were carried out with longlines and trawl nets inside the coral habitat and outside, where fishery exploitation occurs. No significant differences were shown between the abundance of fish recorded using longlines in the coral and non-coral habitat even though some selachians and teleosts were more abundant in the former than in the latter. Large specimens of rockfish (
Helicolenus dactylopterus) and blackspot seabream (
Pagellus bogaraveo) were commonly caught using longlines in the coral habitat. Data from trawling revealed refuge effects in the coral habitat and fishing effects outside. Significant differences were detected between the recorded abundances in the two study areas. Greater densities and biomasses were obtained inside the coral area, and fish size spectra and size distributions indicate a greater abundance of large fish inside the coral habitat. The SML coral habitat is a spawning area for
H. dactylopterus. The remarkable density of the young-of-the-year of the deep-water shark
Etmopterus spinax as well as of
Merluccius merluccius,
Micromesistius poutassou,
Phycis blennoides and
H. dactylopterus, indicates that the coral habitat also acts as nursery area for these demersal species, which are exploited outside. Considering the evidence of the negative impact of bottom trawling and, to a lesser extent, of longlining, the coral banks can provide a refuge for the conservation of unique species and habitats as well as in providing benefit to adjacent fisheries through the spill-over effect both of eggs, larvae, juveniles and adults.
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