Morfometría corporal, diversidad natatoria y nicho de los tiburones demersales: estudio comparativo en el mar Mediterráneo

Seven demersal shark species belonging to six families, obtained from the southern Mediterranean Sea, were selected as representative of different putative swimming modes, inhabited depths and trophic levels. Caudal fin morphometrics (caudal fin span, area and aspect ratio), hepatosomatic index and muscular-skeletal amount per unit length were estimated and compared within and among species by means of both parametric and non-parametric multivariate and univariate statistical procedures. Intra-specific variation was related to size and, for one species only, also to sex. Two inter-specific patterns of variation were observed: the first pattern was interpreted as a swimming ability gradient between slow benthic and more pelagic species, as a function of caudal morphometry and body characteristics; the second pattern is related to the depth the species inhabit and/or their trophic level. These two hypotheses were tested with the current data and literature information, and discussed in the context of shark swimming modes, habit and environment. Based on observed differences in caudal fin morphometrics, liver and muscular masses, this paper is the first to provide a quantitative and comparative dataset for demersal sharks as a group, and attempts to describe sample variability as a function of expected swimming ability and occupied niche (depth inhabited and/or trophic level).Siete especies de tiburones demersales, pertenecientes a 6 familias, capturadas en el sur del mar Mediterráneo, fueron seleccionadas como representantes de diferentes modos de natación, profundidad que suelen habitar y niveles tróficos. La morfometría de la aleta caudal (longitud, área y relación de aspecto), el índice hepato¬somático y la relación entre músculo y esqueleto por unidad de longitud fueron determinados y comparados entre los indivi¬duos y entre especies a través de procedimientos estadísticos paramétricos y no paramétricos, multivariados y univariados. La variación intra-específica se relacionó con el tamaño y, para una única especie, también con el sexo. Se observaron dos patrones interespecíficos de variación: el primero fue interpretado como un gradiente de la capacidad de natación entre es-pecies bentónicas y las más pelágicas, en función de la morfometría caudal y de las características corporales. El segundo se debió principalmente a la profundidad habitada y / o el nivel trófico. Asociando los datos actuales a la información existente en la literatura, estas dos hipótesis se comprobaron y se examinaron en el contexto del tipo de natación del tiburón y el am¬biente marino. Apartir de las diferencias observadas en la morfometría de la aleta caudal, el hígado y las masas musculares, este documento ofrece por primera vez una base de datos cuantitativos y comparativos sobre los tiburones demersales, como grupo, intentando describir la variabilidad muestral como una función de la capacidad de natación esperada y de los nichos ocupados (profundidad habitada y/ o nivel trófico)

Looking into the prevalence of bycatch juveniles of critically endangered elasmobranchs: a case study from pelagic longline and trammel net fisheries of the Asinara Gulf (western Mediterranean)

Bycatch of cartilaginous species is considered one of the main drivers for the dramatic declines observed in many populations. Pelagic longlines and passive nets impact many species depending on their life stage and habitat use. Here, we present an updated list of incidental catches collected through a 4-year fishery-dependent survey. We documented the bycatch of four critically endangered species, particularly 13 individuals of Isurus oxyrinchus, Prionace glauca, and Mobula mobular by longlines and one specimen of Lamna nasus by trammel nets in the Asinara Gulf (Northern Sardinia, Italy). As almost all specimens were juveniles or newborns, we explored and discussed the potential drivers explaining their prevalence in the sample. Despite our low sample size, of the four possible options discussed, the role of the Asinara Gulf as an Important Shark and Ray Area (ISRA) for large pelagic elasmobranch species is one worth considering

Unexpected Records of Newborn and Young Sharks in Ligurian and North Tyrrhenian Seas (North-Western Mediterranean Basin)

Between 2007 and 2022, 112 specimens of newborn and young pelagic sharks were recorded in the waters of Tuscany Region, in the South Ligurian–North Tyrrhenian Seas (north-western Mediterranean basin). The sharks belonged to the Carcharhinus plumbeus (n = 14), Prionace glauca (n = 66), Isurus oxyrinchus (n = 16), Mobula mobular (n = 5) Alopias vulpinus (n = 7) and Hexanchus griseus (n = 4) species. Each animal was correctly identified thanks to the photographs or videos collected. All specimens were incidentally captured with set nets in inshore shallow waters, except bluntnose six-gill sharks, which were bycatch of deep-water bottom-trawl fishery. Body mass, sex, total length and biometric measurements were recorded in 34 baby sharks following the Mediterranean Large Elasmobranches Monitoring (MEDLEM) protocol. The presence of very evident and often non-healed umbilical scar confirmed that some of the sample specimens were newborn. Further confirmation came from the comparison between the total length observed and the size at birth known for the sampled species as reported in the literature. Some baby sharks were preserved in the Museums of Natural History of Pisa and Florence University collections. The importance of the coastal area studied as a possible shark nursery is discussed

Gospodarski ulov, reprodukcija i prehrambene navike raže zvjezdopjege Raja asterias (Chondrichthyes: Rajidae) u priobalju Tirenskog mora (Italija, sjeverni Mediteran)

A total of 52 “rapido” (towed toothed beam gears) trawls were monitored in late winter-summer of the 1999-2000 period to assess the R. asterias size structure at this time of higher yields as well as 36 fishing operations performed by “volantina” (trawl nets with fairly high vertical opening) during distinct seasons on the continental shelf off the fishing harbour of Fiumicino (central western Italy) to gain data also for that gear. Daily yields recorded for the only boat locally authorised to use “rapido” nets gave median values of 32.0 individuals and 24.35 kg vs. 2.5 rays and 2.80 kg for trawlers fishing at the same time. Comparison of the body sizes at which 50% of the skates had been found mature in our samples (265 gonads examined) showed that most specimens caught by the “rapido” nets were in their juvenile stage. Examination of stomach contents from 129 skates confirmed previous reports that they mainly feed on crustaceans and bony fish and the role of the latter in the diet progressively increases as R. asterias specimens grow older and larger.Istraživana su ukupno 52 potega dredžama (“rapido”) u kasnom zimskom-ljetnom periodu 1999.-2000. godine kako bi se ustanovila veličina raže zvjezdopjege, R. asterias u vrijeme većeg ulova. Obavljeno je 36 ribarstvenih uzorkovanja pomoću “volantina” (koće većeg okomitog raspona) tijekom različitih godišnjih doba na kontinentalnom šelfu pokraj luke Fiumicino (srednji zapadni dio Italije) kako bi se dobili podaci i o ovom ribarskom alatu. Dnevni ulov zabilježen na brodu registriranom za uporabu “rapido” mreža iznosio je 32.0 jedniki i 24.35 kg od toga 2.5 kg raža i 2.80 kg koćarskog ulova istovremeno. Usporedbom veličine tijela uzoraka 50% raža je bilo zrelo (265 ispitanih gonada) što ukazuje na činjenicu da je većina ulovljenih primjeraka “rapido” mrežom bilo u juvenilnom stadiju. Ispitivanje želučanog sadržaja kod 129 raža potvrdilo je dosadašnja izvješća da se pretežito hrane rakovima i koštunjičavim ribama, koje su zastupljenije u prehrani starijih i većih primjeraka R. asterias

First evidence of population genetic structure of the deep-water blackmouth catshark Galeus melastomus Rafinesque, 1810

Genetic connectivity at large spatial scales. Given the lack of species-specific nuclear markers, a total of 129 microsatellite loci (Simple Sequence Repeats, SSRs) were cross-amplified on blackmouth catshark specimens collected in eight geographically distant areas in the Mediterranean Sea and North-eastern Atlantic Ocean. A total of 13 SSRs were finally selected for genotyping, based on which the species exhibited signs of weak, but tangible genetic structure. The clearcut evidence of genetic differentiation of G. melastomus from Scottish waters from the rest of the population samples was defined, indicating that the species is genetically structured in the Mediterranean Sea and adjacent Southern North-eastern Atlantic. Both individual and frequency-based analyses identified a genetic unit formed by the individuals collected in the Tyrrhenian Sea and the Strait of Sicily, distinguished from the rest of the Mediterranean and Portuguese samples. In addition, Bayesian analyses resolved a certain degree of separation of the easternmost Aegean sample and the admixed nature of the other Mediterranean and the Portuguese samples. Here, our results supported the hypothesis that the interaction between the ecology and biology of the species and abiotic drivers such as water circulations, temperature and bathymetry may affect the dispersion of G. melastomus, adding new information to the current knowledge of the connectivity of this deep-water species and providing powerful tools for estimating its response to anthropogenic impacts

Feeding in Deep Waters: Temporal and Size-Related Plasticity in the Diet of the Slope Predator Fish Coelorinchus caelorhincus (Risso, 1810) in the Central Tyrrhenian Sea

In-depth studies on the effect of size and period in the diet of the hollow-snout grenadier Coelorinchus caelorhincus in the Mediterranean Sea are scant and incomplete. We obtained 75 specimens of this species from the discard of deep trawl fishing on the slope of the central Tyrrhenian Sea. As corollary data, we estimated the length–weight relationship, the size frequency distribution, and composition of sexual maturity stages of the sampled individuals. We deepened stomach content analysis aiming at the evaluation of size and period’s effect in the fish diet by Costello’s interpretation of dietary indexes and correspondence analysis. The corollary results suggested negative allometric growth (b = 2.69), an asynchronous reproductive strategy (paucity of mature individuals) and a size-related bathymetrical distribution for this species (prevalence of small and intermediate-sized specimens). The prey importance index (PII) revealed that the hollow-snout grenadier is a generalist feeder on cephalopods (PII: 0–1200), fish (PII: 0–1000), crustaceans (PII: 4000–6000), and polychaetes (PII: 400–1800), and a light specialist at population level on the dominant prey among them. At the micro-taxa level, the species was found to be a generalist feeder on 10 groups of rare prey and a light specialist at population level on amphipods (PII: 1300–3200). Overall, results indicated the presence of two feeding gradients that determined an intermingled effect of size and period on fish diet. In particular, intraspecific competition and stability of food resources appeared as the factors that significantly harmonize the diet of Coelorinchus caoelorhincus in the context of the ecotrophic constraints of a deep-sea species

Macro-litter ingestion in deep-water habitats. Is an underestimation occurring?

Marine litter affects marine organisms, posing threats to biodiversity conservation and to ecosystem structure and functioning. Providing a suitable assessment of marine litter effects on marine life through bioindicator species is crucial to drive an effective waste management policy. However, to date no standardized tool has been developed to describe and monitor the impact of marine macro-litter on marine life within deep-water habitats. Modifying the protocol proposed to monitor macro-litter ingestion by the loggerhead sea turtle Caretta caretta, we perform a preliminary investigation on the suitability of different elasmobranch species for monitoring macro-litter ingestion in deep-sea. A total of 122 specimens representing 7 elasmobranch species were collected and examined. External visual inspections documented no clear evidences of disease due to marine litter entanglement. A total of 7 ingested litter items were found in the stomach or in the esophagus of 6 specimens of 4 different species (frequency of occurrence = 4.9%), with a maximum number of 2 items per specimen. No litter items were found in the intestinal contents, as well as no evidence of gastrointestinal blockages due to litter items were detected. The low number of collected litter items suggests that the number of samples required is too large for a feasible monitoring program. Moreover, we observed that the anatomy of the intestinal spiral valve may represent an obstacle to the transit of macro-litter items, which could be spontaneously regurgitated as it happens in the selective elimination of undigested remains, such as bones and scales. Therefore, macro-litter retention time in the gastrointestinal tract of elasmobranchs could be brief and shorter than retention time of food. This may lead to an underestimation of macro-litter ingestion frequency by deep-water elasmobranchs. This study reports the first evidence of plastic ingestion by the kitefin shark Dalatias licha

Feeding in Deep Waters: Temporal and Size-Related Plasticity in the Diet of the Slope Predator Fish <i>Coelorinchus caelorhincus</i> (Risso, 1810) in the Central Tyrrhenian Sea

In-depth studies on the effect of size and period in the diet of the hollow-snout grenadier Coelorinchus caelorhincus in the Mediterranean Sea are scant and incomplete. We obtained 75 specimens of this species from the discard of deep trawl fishing on the slope of the central Tyrrhenian Sea. As corollary data, we estimated the length–weight relationship, the size frequency distribution, and composition of sexual maturity stages of the sampled individuals. We deepened stomach content analysis aiming at the evaluation of size and period’s effect in the fish diet by Costello’s interpretation of dietary indexes and correspondence analysis. The corollary results suggested negative allometric growth (b = 2.69), an asynchronous reproductive strategy (paucity of mature individuals) and a size-related bathymetrical distribution for this species (prevalence of small and intermediate-sized specimens). The prey importance index (PII) revealed that the hollow-snout grenadier is a generalist feeder on cephalopods (PII: 0–1200), fish (PII: 0–1000), crustaceans (PII: 4000–6000), and polychaetes (PII: 400–1800), and a light specialist at population level on the dominant prey among them. At the micro-taxa level, the species was found to be a generalist feeder on 10 groups of rare prey and a light specialist at population level on amphipods (PII: 1300–3200). Overall, results indicated the presence of two feeding gradients that determined an intermingled effect of size and period on fish diet. In particular, intraspecific competition and stability of food resources appeared as the factors that significantly harmonize the diet of Coelorinchus caoelorhincus in the context of the ecotrophic constraints of a deep-sea species

Application of laser photogrammetry on C. carcharias in natural environment

Most morphometric methods of investigation used on large marine organisms are intrusive, as they involve the capture or the killing of the animal. In the last decade new methods and new technologies have been developed able to supply the same morphometric data avoiding contact with the animal. The result of these efforts was the introduction also in the ecological field of laser photogrammetry. Photogrammetry is a non-invasive remote sensing technique that uses digital photography or images to measure objects or, in the case of animals, morphometry. Laser photogrammetry uses two laser beams, parallel to each other, to obtain the real dimensions of a body starting from a digital image. The objective of the present study is to provide a contribution to the definition and validation of the method for the study of white sharks. Data were collected during XIV° Scientific Expedition in South Africa (2017) managed by Centro Studi Squali and Unical to study the behaviour of Carcharodon carcharias. We proceeded to create a system suitable for the study of the white shark, being careful to the problems highlighted in the literature. The realized instrument was equipped with two filming means, in this way the attention was focused on two aspects: the real effectiveness of laser photogrammetry and the efficiency of using a reflex camera compared to an action-cam. The tool made allowed to obtain valid data. From these, estimates of the total lengths of the samples encountered were obtained by processing the frames considered valid using an appropriately defined protocol. The results obtained by the two imaging systems were compared with each other and with the data derived from the visual estimation (traditionally used not invasive method). The comparison of results allowed some indications regarding the effectiveness of the new morphometric measurement system and its degree of reliability

Microplastics in the Deep: Comparing Dietary and Plastic Ingestion Data between Two Mediterranean Bathyal Opportunistic Feeder Species, <i>Galeus melastomus</i>, Rafinesque, 1810 and <i>Coelorinchus caelorhincus</i> (Risso, 1810), through Stomach Content Analysis

Marine plastic pollution is currently an issue of mounting concern around the world. Stomach content of marine fish has been increasingly used as a valid proxy for detecting the presence of such a pollutant in marine biota, both for coastal and deep-water environments. Although ingestion of microplastics has been reported in an increasing number of species, the patterns of ingestion still remain unclear, depending closely on the interaction between the species and types of microplastics involved. In this context, we analysed and compared the stomach contents of two bathyal dwelling opportunistic feeder species namely Galeus melastomus and Coelorinchus caelorhincus. In particular, we analysed microplastic items according to their dimension, morphology and colour, and diet’s variation with size obtained through prey identification. Both species showed a higher frequency of occurrence of the blue filament-like middle-sized microplastics (1.01–4.75 mm) compared with the other categories, although this pattern was much more marked in C. caelorhincus than in G. melastomus. The latter conversely showed a larger array of ingested plastic items in terms of shape and colour. Matching plastic ingestion with dietary data suggested potential predator confusion occurring in C. caelorhincus through active mis-selection of a defined type of microplastic instead of some particular family of polychaetes, which resemble in shape, size, and color to that type. Otherwise, G. melastomus appeared more prone to a random ingestion of a larger array of microplastic items because of a more generalistic and less selective feeding strategy. Although further validation is needed, stomach contents of the two species showed evidence strong enough to be considered as potential bioindicator species of microplastic pollution, as required by the Marine Strategy Framework Directive for monitoring this pollutant in the marine environment