The deep-sea lantern shark Etmopterus spinax occurs in the northeast Atlantic on or near the bottoms of the outer continental shelves and slopes, and is regularly captured as bycatch in deep-water ...commercial fisheries. Given the lack of knowledge on the impacts of fisheries on this species, a demographic analysis using age-based Leslie matrices was carried out. Given the uncertainties in the mortality estimates and in the available life history parameters, several different scenarios, some incorporating stochasticity in the life history parameters (using Monte Carlo simulation), were analyzed. If only natural mortality were considered, even after introducing uncertainties in all parameters, the estimated population growth rate (λ) suggested an increasing population. However, if fishing mortality from trawl fisheries is considered, the estimates of λ either indicated increasing or declining populations. In these latter cases, the uncertainties in the species reproductive cycle seemed to be particularly relevant, as a 2-year reproductive cycle indicated a stable population, while a longer (3-year cycle) indicated a declining population. The estimated matrix elasticities were in general higher for the survivorship parameters of the younger age classes and tended to decrease for the older ages. This highlights the susceptibility of this deep-sea squaloid to increasing fishing mortality, emphasizing that even though this is a small-sized species, it shows population dynamics patterns more typical of the larger-sized and in general more vulnerable species.
This study aims to assess the litter ingestion in some demersal elasmobranchs, combining a classical gastro-intestinal tract (GIT) analysis with a procedure methodology to reduce airborne fibres ...contamination. In order to prevent the overestimation of litter ingestion, we applied severe mitigation measures to avoid airborne contamination during the analyses, integrating a new approach for the correction of estimates of fibres abundance using control procedure. In this study, we assessed the anthropogenic litter ingestion in four elasmobranch species from the southern Tyrrhenian Sea: Scyliorhinus canicula (n= 27), Etmopterus spinax (n= 16), Galeus melastomus (n= 12) and Raja clavata (n= 6). The gastro-intestinal tract of each specimen was analysed by visual sorting and the polymers identified by FT-IR spectroscopy technique. Overall, 19 litter particles were found in the gastro-intestinal tract of 13 demersal elasmobranchs (%O= 21) and for the first time, evidence of litter ingestion by R. clavata in Mediterranean waters was also reported. In G. melastomus and R. clavata all anthropogenic particles were plastics, whereas in S. canicula other litter categories were also found. No litter ingestion was instead observed in E. spinax. More than 50% of litter particles belonged to microlitter category (< 5 mm). Polyamide was the only polymer typology found in all examined species. We described the procedures to control the airborne contamination applied at each step of laboratory analysis and, thanks to the application of our control method, it was possible to exclude the 95% of fibres found in samples from the assessment. Moreover, we compared fibres abundances observed in samples and controls. This study, combining an approach for minimizing the bias associated to airborne fibre contamination, provided a reliable assessment of marine litter ingestion in demersal elasmobranchs.
Bioluminescence is a common ecological trait among many marine organisms, including three shark families: Etmopteridae, Dalatiidae, and Somniosidae. The kitefin shark, Dalatias licha (Bonnaterre, ...1788), from the Dalatiidae family is the largest known luminous vertebrate. This study compares the light organ ultrastructure of D. licha with that of Etmopterus spinax, the type species of Etmopteridae, to gain a deeper understanding of the light emission process and its evolutionary conservation within shark families. The ultrastructure of D. licha’s photophores and the morphological changes that occur after hormonal stimulation (via melatonin and α-MSH, which stimulate or inhibit the bioluminescence, respectively) were examined. The photophores consist of a spherical pigmented sheath surrounding a unique, regionalized light-emitting cell (photocyte). The photocyte’s basal area contains a specific area filled with granular inclusions that resemble the glowon-type microsources of E. spinax, suggesting that this area is the intracellular site of light emission. An acidophilic secretion, not present in Etmopteridae, is also observed within the granular area and may be involved in photogenesis. The ultrastructure analysis reveals no lens cells or reticular layer, unlike in Etmopteridae photophores, indicating a simpler organization in Dalatiidae photophores. Melatonin stimulation causes the removal of pigments from the photophore-associated melanophores and an increase in the granular inclusion diameter and coverage in the granular area, further showing that this last area is the potential site of light emission, while α-MSH stimulation causes the extension of the melanophore pigments and a decrease in the granular inclusion diameter and coverage. These results support the evolutive conservation of photophore functional organization across luminous etmopterid and dalatiid sharks.
Bioluminescence relies on the oxidation of a luciferin substrate catalysed by a luciferase enzyme. Luciferins and luciferases are generic terms used to describe a large variety of substrates and ...enzymes. Whereas luciferins can be shared by phylogenetically distant organisms which feed on organisms producing them, luciferases have been thought to be lineage-specific enzymes. Numerous light emission systems would then have co-emerged independently along the tree of life resulting in a plethora of non-homologous luciferases. Here, we identify for the first time a candidate luciferase of a luminous echinoderm, the ophiuroid Amphiura filiformis. Phylogenomic analyses identified the brittle star predicted luciferase as homologous to the luciferase of the sea pansy Renilla (Cnidaria), contradicting with the traditional viewpoint according to which luciferases would generally be of convergent origins. The similarity between the Renilla and Amphiura luciferases allowed us to detect the latter using anti-Renilla luciferase antibodies. Luciferase expression was specifically localized in the spines which were demonstrated to be the bioluminescent organs in vivo. However, enzymes homologous to the Renilla luciferase but unable to trigger light emission were also identified in non-luminous echinoderms and metazoans. Our findings strongly indicate that those enzymes, belonging to the haloalkane dehalogenase family, might then have been convergently co-opted into luciferases in cnidarians and echinoderms. In these two benthic suspension-feeding species, similar ecological pressures would constitute strong selective forces for the functional shift of these enzymes and the emergence of bioluminescence.
Etmopterus spinax
(Linnaeus, 1758) and
Etmopterus molleri
(Whitley, 1939) are two bioluminescent deep-sea sharks, usually caught in large numbers as bycatch by deep-water fisheries. Yet, no study has ...ever involved population status of these two species using genetic tools. In order to investigate population genetic structure, diversity and connectivity of these two lanternsharks, 29 and 19 microsatellite loci were isolated from
E. spinax
DNA library for
E. spinax
and
E. molleri
, respectively. These loci were tested on 32
E. spinax
individuals from the North Sea and seven
E. molleri
from the East China Sea. The number of alleles per locus ranged from 2 to 13. The observed heterozygosity ranged from 0.031 to 0.839 for
E. spinax
and from 0.000 to 1.000 for
E. molleri
, while the expected heterozygosity ranged from 0.031 to 0.903 and from 0.143 to 0.821, respectively. Almost all loci (24 and 16, respectively) were at Hardy–Weinberg equilibrium for both species and no linkage disequilibrium among loci was detected. These loci represent useful tools to better understand the population structure of these two species. Besides, they could also be suitable for other lanternsharks in general, as these latter remain largely understudied, specially in terms of understanding the basic science that will serve into their conservation.
Fishing with demersal towed gears can have dramatic effects on the structure and functioning of marine ecosystems. We studied the ecosystem effects of the deep-sea red shrimpAristaeomorpha ...foliaceatrawl fishery (500 to 800 m) in the Strait of Sicily, at the population and community level by sampling in trawled and non-trawled sites as determined by vessel monitoring system (VMS) fishing effort data. The study was conducted within the Maltese 25 nautical mile Fisheries Management Zone as part of the ongoing MEDITS trawl survey. Samples were collected using an experimental otter trawl net with a cod-end stretched mesh size of 20 mm, from 7 stations located in trawled sites (mean depth 616 ± 26 m) and from 7 stations in non-trawled sites (mean depth 556 ± 40 m). Population and community indicators were compared across the trawled and non-trawled sites. Populations ofA. foliaceaandEtmopterus spinaxdid not show any differences in biomass between the trawled and non-trawled sites, whereas the biomass ofPlesionika martia,Nephrops norvegicus,Helicolenus dactylopterus dactylopterusandGaleus melastomuswas 4 times, 16 times, 6 times and 2 times higher, respectively, at the non-trawled sites. Changes in length structure were also detected for all species except forE. spinax. At the community level, higher biomass, density and diversity indices were recorded at the non-trawled sites. Despite the clear evidence of ecosystem changes due to fishing, the main target species,A. foliaceaandP. martia, had a high resilience to trawling activities. Setting up trawling lanes as a management option would likely minimise negative impacts on species with slow growth rates and low resilience.
The chemistry of the luminous system in a shark is addressed for the first time. Assuming that many luminous species acquire their luminous substrate (luciferin) through the food chain, we ...investigated the feeding habits of a Norwegian population of the lantern shark Etmopterus spinax Linnaeus, 1758 in order to identify potential alimentary sources of luciferin in this species. Among the major groups of preys found in the diet of E. spinax, we identified three potential sources of luciferin: the euphausiid Meganyctiphanes norvegica Sars, 1857 (tetrapyrrole luciferin), the shrimp Pasiphaea multidentata Esmark, 1866 (coelenterazine) and the teleost Maurolicus muelleri Gmelin, 1789 (coelenterazine). Their luciferins were tested for their presence in the digestive tract and photogenic organs of E. spinax as well as for their cross-reaction with a putative shark catalyst. Although not detected in the diet, the cypridinid luciferin, the third most widespread marine luciferin, was also assayed. As a result, only the coelenterazine was unambiguously detected in the digestive tract of E. spinax and none of the tested luciferins reacted with the shark catalyst extract. Our results support the hypothesis of an unknown luminous system in this shark species, involving either a known luciferin in a specific active or storage form, or an unknown light-emitting molecule.
•Feeding habits of the lantern shark Etmopterus spinax has been investigated.•Luminous substrates from prey were identified and assayed on shark tissues.•One luminous substrate was detected but none reacts with the putative shark catalyst.•An unknown luminous system is hypothesized in this lantern shark species.
Feeding habits of blackmouth catshark Galeus melastomus and velvet belly lantern shark Etmopterus spinax were studied throughout the Spanish Mediterranean, from the Alboran Sea to the Gulf of Lion, ...between 400 and 790 m depth. Diets were studied taking into account size and depth differences. Included within the trophic guild of non-migratory macroplankton feeders, both species preferably exploited mesopelagic resources (mainly natantian decapods, euphausiids, mesopelagic fish and cephalopods). G. melastomus mostly preyed on decapod crustaceans (46% in terms of IRI), with cephalopods, euphausiids and mesopelagic fish as a secondary prey item. The diet of E. spinax was composed primarily of mesopelagic fish (61.4% in terms of IRI), with decapod crustaceans and cephalopods of secondary importance. Both species showed ontogenetic changes in their diets: small blackmouth catshark specimens (between 150 and 350 mm total length) mainly consumed cephalopods, medium size individuals (351-450 mm TL) consumed decapod crustaceans, while larger specimens (larger than 451 mm TL) seemed to be more generalist-feeders. Smaller specimens of E. spinax (150-250 mm TL) mostly fed on small crustaceans and cephalopods, whilst an increase in the consumption of mesopelagic fish (mycthophids and Stomiiformes) was detected in larger individuals (251-450 mm TL). Diet of G. melastomus also changed throughout the narrow depth range explored, mainly consumed euphausiids and mesopelagic fish between 400 and 500 m depth, whilst preferably exploiting natantian decapods and cephalopods below 500 m of depth. However, this trend may be correlated to the larger-deeper trend found for this species. Slight but not significant differences were found in E. spinax diet by depth, with euphausiids mainly consumed at lower depths (400-500 m). In a multispecies MDS analysis, diets of G. melastomus and E. spinax were separated and the anosim test proved evidence for significant differences in the diets of the two species (R = 0.25; P = 0.05), mainly attributed to the stronger pelagic habits of E. spinax in comparison with G. melastomus. Low overlap (by Schoener Index) also occurred when comparing specimens of the same size range. In general, the higher occurrence of benthic prey in the diet of G. melastomus (i.e. the brachyuran crab Geryon longipes, the thalassinid shrimp Calocaris macandrae) than in E. spinax pointed to a stronger pelagic behavior for the velvet belly lantern shark. Both multivariate analysis and the Levins Index pointed to a narrow niche breadth for the two sharks. A trend of increasing fullness was found for both species in the highly productive areas of the Alboran Sea and Vera Gulf, probably related to higher resource availability, enhanced by local upwellings.
Many midwater animals emit ventral light to hide their silhouette in the water column. This phenomenon known as counterillumination typically requires fine control over light emission since it needs ...a luminescence that closely matches the properties of downwelling light (intensity, angular distribution and wavelength). Here we provide evidence that, although lacking complex structures of counterilluminating animals, the deepwater luminescent shark
Etmopterus spinax could, in Norwegian fjords, efficiently cloak its silhouette from downwelling ambient light to remain hidden from predator and prey. This represents the first experimentally tested function of luminescence in a shark and illustrates how evolution can take different routes to converge on identical complex behavior.
In this paper, the population biology of the velvet belly lanternshark Etmopterus spinax was studied and life‐history coefficients determined. Age was estimated from sections of the second dorsal ...spine and validated by marginal increment analysis. Males attained a maximum age of 8 years while 11 year‐old females were found. Several growth models were fitted and compared for both size‐at‐age and mass‐at‐age data, showing that even though this is a small‐sized species, it has a relatively slow growth rate. This species matures late, specifically at 49·6 and 42·5% of the maximum observed ages for males and females, respectively. It has a low fecundity, with a mean ovarian fecundity of 9·94 oocytes and a mean uterine fecundity of 7·59 embryos per reproductive cycle. This species seems to have a long reproductive cycle, and even though no conclusive data were obtained, a 2–3 year cycle is possible. The estimated coefficients indicate that this species has a vulnerable life cycle, typical of deepwater squalid sharks. Given the high fishing pressures that it is suffering in the north‐east Atlantic, this fish may already be facing severe declines or in risk of facing them in the near future.
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