Elasmobranch Diversity Research Articles

​An Annotated Checklist of Elasmobranchs Along the Coromandel Coast of Tamil Nadu, Southeast Coast of India

Background: Elasmobranch is one of the largest marine fish resources, consisting of sharks, sawfishes, rays and skates. A worldwide estimate of elasmobranch diversity reveals 815 species coming under 9 orders, 42 families and 164 genera, of which 359 species are sharks and 456 are skates and rays. Hence, it has been planned to investigate the biodiversity and fishery of elasmobranchs along the Coromandel Coast of Tamil Nadu, Southeast India. Methods: Elasmobranch specimens were collected during June 2019 to March 2020 from three main landing centres of Coromandel Coast of Tamil Nadu viz Royapuram (Chennai), Cuddalore and Nagapattinam Fishing Harbours. Sampling was done fortnightly in the above three landing centres. The specimens were collected from the catches of trawl nets, bottom set gillnets and hook and lines. The specimens were identified morphologically in the landing centres itself based on the valid taxonomic keys. Result: In the present study, 67 species of elasmobranch belonging to 7 orders, 21 families and 46 genera were recorded. Of the 7 orders, Carcharhiniformes had the largest number of species (27). Among the 25 families, Carcharhinidae (21) had the largest representation.

Baited Remote Underwater Video Surveys to assess relative abundance of sharks and rays in a long standing and remote marine protected area in the Arabian Gulf

Marine Protected Areas (MPAs) are increasingly advocated for the protection of key functional groups like elasmobranchs (sharks and rays). However, substantial uncertainty remains regarding which species can benefit from MPAs, crucial information to support policy and management plans. Using Baited Remote Underwater Video Surveys (BRUVS), a study was conducted on Sir Bu Nair Island in the United Arab Emirates encompassing a range of depths and habitat types within the MPA borders. A total of 96 deployments with 117 video hours recorded were analysed to assess the diversity, relative abundance and habitat associations of elasmobranchs. Surveys recorded 40 elasmobranchs including two species of sharks and seven species of rays. Overall, catch per unit effort for elasmobranchs was slightly higher overall, lower for sharks, and higher for rays compared to a similar study using BRUVS across United Arab Emirates waters. Two reef-associated species in early life stages, blacktip reef shark (Carcharhinus melanopterus) and Halavi guitarfish (Glaucostegus halavi) listed as Near Threatened and Critically Endangered on the IUCN Red List of Threatened Species respectively showed the highest frequency of occurrence of species representing 44.4% of all sightings. These results show the value of this MPA in protecting critical habitats for elasmobranchs while suggesting its limitation in protecting adult life stages and other elasmobranchs with wider ranging movements that are likely threatened by fishing in waters adjacent to the MPA. This study provides critical information to support the development of a Sir Bu Nair management plan and highlights further research needs around the island. Finally, it reinforces the need of additional management measures to protect and promote the recovery of elasmobranchs in the United Arab Emirates and broader Arabian Gulf.

Scarce ctenacanthiform sharks from the Mississippian of Austria with an analysis of Carboniferous elasmobranch diversity in response to climatic and environmental changes

ABSTRACT The Carboniferous is characterized by drastic climatic and environmental fluctuations, which include multiple phases of glaciation resulting in an icehouse climate. Additionally, dynamic continental reconfigurations forced the contraction of the Rheic Ocean resulting in the closure of the Rheic–Tethyan Gateway, which precluded further faunal exchanges between the North American and Eurasian marine realms. Interestingly, cartilaginous fishes seem to be relatively immune to these drastic climatic and environmental changes. The Eurasian fossil record of Paleozoic sharks is strongly biased towards intensively sampled localities from England, Ireland, Scotland, and the Russian Platform. Here we present rare dental material from the Serpukhovian (early Carboniferous) of Austria, adding new information to the paleogeographic distribution of ctenacanthiform sharks. The new material revealed the first record of the genus Saivodus in Central Europe and allowed us to recognize a new species, Cladodus gailensis sp. nov., and a remnant of fossilized cartilage. In an attempt to identify possible linkages between climatic or environmental fluctuations on shark diversity throughout the Carboniferous, we provide a synopsis of the distribution and diversity of elasmobranchs based on primary literature. This preliminary assessment at genus level indicates two pronounced events of extinction, with the first one occurring during the latest Mississippian and the second one towards the end of the Pennsylvanian. The first extinction event distinctly correlates with the known diversity decline of other marine inhabitants and the second occurred during an unstable period of multiple phases of glaciation.

Monitoring elasmobranch assemblages in a data-poor country from the Eastern Tropical Pacific using baited remote underwater video stations

Understanding how threatened species are distributed in space and time can have direct applications to conservation planning. However, implementing standardized methods to monitor populations of wide-ranging species is often expensive and challenging. In this study, we used baited remote underwater video stations (BRUVS) to quantify elasmobranch abundance and distribution patterns across a gradient of protection in the Pacific waters of Costa Rica. Our BRUVS survey detected 29 species, which represents 54% of the entire elasmobranch diversity reported to date in shallow waters (< 60 m) of the Pacific of Costa Rica. Our data demonstrated that elasmobranchs benefit from no-take MPAs, yet large predators are relatively uncommon or absent from open-fishing sites. We showed that BRUVS are capable of providing fast and reliable estimates of the distribution and abundance of data-poor elasmobranch species over large spatial and temporal scales, and in doing so, they can provide critical information for detecting population-level changes in response to multiple threats such as overfishing, habitat degradation and climate change. Moreover, given that 66% of the species detected are threatened, a well-designed BRUVS survey may provide crucial population data for assessing the conservation status of elasmobranchs. These efforts led to the establishment of a national monitoring program focused on elasmobranchs and key marine megafauna that could guide monitoring efforts at a regional scale.

Richness and distribution patterns of elasmobranchs in the San Andres, Providencia and Santa Catalina Archipelago: is this area a hotspot of these species in the greater Caribbean?

Hotspots identification can be used to establish protected or priority areas for conservation at different geographic scales. We aimed to determine if San Andres, Providencia and Santa Catalina Archipelago could be considered as a hotspot of elasmobranch diversity within the Greater Caribbean. For that, we updated the elasmobranch species richness and analyze its distribution pattern, evaluated the assembly structure and composition and estimated the occurrence probability of the more abundant species of the Archipelago. A total of 46 species, 33 of sharks and 13 of batoids were recorded, with 8 categorized as threatened by IUCN. Quadrants of San Andres and Providencia islands presented the highest richness with 16 species. Oceanic environments differed significantly in composition and abundance from the other four large areas evaluated. Northern banks were the most favorable environments for large-sized pelagic sharks while San Andres and Providencia Islands were for batoids; this difference could be due to the pelagic and benthic habits, respectively, and their relation with availability of substrate, food and sheltered areas. Our study confirmed that the Archipelago has at least 21% of the total richness of the northwestern Atlantic region, 43% of that of the Greater Caribbean and 49% of that registered in the Colombian Caribbean Coast, suggesting that the Archipelago is a potential richness hotspot in the Caribbean region. This high elasmobranch diversity could be due, among others, to its status as a Biosphere Reserve, to its high diversity of habitats and more recently to the establishment of the shark fishing ban.

A baited remote underwater video system (BRUVS) assessment of elasmobranch diversity and abundance on the eastern Caicos Bank (Turks and Caicos Islands); an environment in transition

The present study was undertaken to assess the diversity and abundance of elasmobranch fishes in coral reef and sand flat environments on the eastern Caicos Bank, with a view to informing marine spatial planning as the island of South Caicos and its environs transition to a tourism-based economy. Using baited remote underwater video systems (BRUVS), the nurse shark Ginglymostoma cirratum, Caribbean reef shark Carcharhinus perezi, spotted eagle ray Aetobatus narinari, southern stingray Hypanus americanus, lemon shark Negaprion brevirostris, tiger shark Galeocerdo cuvier, blacknose shark Carcharhinus acronotus, and great hammerhead shark Sphyrna mokarran were observed to use these waters, with G. cirratum and C. perezi being particularly abundant. Species diversity and overall abundance was greater in the reef environment than on the sand flats, but G. cirratum was equally abundant in both environments. Furthermore, even reef-associated species such as C. perezi were occasionally encountered on the flats a considerable distance from the reef. This indicates that although marine conservation efforts in the Turks and Caicos Islands should continue to focus on coral reef areas, less dramatic environments such as sand flats should not be ignored.

Diversity and paleoenvironmental implications of an elasmobranch assemblage from the Oligocene-Miocene boundary of Ecuador.

The occurrence and diversity of elasmobranchs from the Oligocene–Miocene boundary from Tropical America is poorly known in comparison with the paleodiversity from younger Neogene intervals of the region. Here we describe a new elasmobranch assemblage from the rich fossil site of Montañita-Olón (Dos Bocas Formation, Santa Elena, Ecuador), where other vertebrates have already been described: for example, sea turtles and cetaceans. We report a total of 27 elasmobranch taxa, 19 of which are new fossil records for Ecuador, 10 new records for the Central Eastern Pacific and four new records for South America. Additionally, in order to reconstruct the environment where these marine remains were deposited, we performed abundance, paleobathymetric and habitat preference analyses, concluding that they were likely deposited in an outer neritic (open shelf) environment. The study of Oligocene and early Miocene marine elasmobranchs faunas in Tropical America is key to addressing the issues in the evolutionary history of this group.

Elasmobranchs from the upper Paleocene of Togo

Bulk sampling and surface collecting of two glauconitic horizons located in Southern Togo yielded a diverse elasmobranch fauna described here. This fauna includes 30 species dominated by carcharhiniforms (eleven species), myliobatiforms (nine species) and lamniforms (five species); it also comprises three orectolobiforms, whereas the squatiniforms and rhinopristiforms are represented by one species each. Although the poor preservation of the specimens hampered numerous species-level identifications, the vast majority of taxa identified were formerly reported from the Paleocene–Ypresian interval, four of which being exclusively known from the upper Paleocene. This, along with the six associated benthic foraminifera species, indicates a late Thanetian age for the sampled horizons and provide age constraints on a geographically widespread benchmark horizon in Western Africa. The composition of the elasmobranch assemblage shows strong resemblances with upper Paleocene faunas from Morocco and differs markedly from known assemblages from geographically closer localities in Niger and Nigeria, which suggests strong palaeoenvironmental control on the distribution of Thanetian elasmobranch diversity.

Shark and ray community structure in a turbid, nearshore coral reef habitat

The coastline of northern Australia may be a refuge for elasmobranchs threatened or extirpated from much of their former ranges across South-East Asia. In this study, we used baited remote underwater video stations to survey the abundance, size and assemblage of elasmobranchs in the Cobourg Marine Park in northern Australia. Two sites were sampled inside the park and one site was sampled outside the park, covering two management zones: open and partially protected. During the austral summer, 85 individuals of 12 species of elasmobranch were observed over 12 days. No significant differences were observed among sites in either size or abundance for common species. Videos were dominated by Carcharhinus melanopterus (relative abundance±s.d., 0.29±0.90h–1), Nebrius ferrugineus (0.03±0.24h–1) and Urogymnus granulatus (0.08±0.28h–1), which comprised &amp;gt;81% of all individuals. Environmental variables had no measurable effect on the abundance of elasmobranchs. The abundance and diversity of elasmobranchs in Cobourg Marine Park is high compared with other similar turbid, inshore areas of northern Australia. The large number of juveniles observed in our surveys also suggests the possibility of a nursery area.

Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia

Bulk sampling of an indurated glauconic sandstone horizon from Djebel el Kebar, Central Tunisia, yielded a moderately diversified assemblage of elasmobranchs (sharks and rays), dating from the late Middle Eocene (mid Bartonian). Here, 10 new taxa (nine new species and three new genera) are described among a total diversity of 33 species. These new taxa highlight the rise of mid-large predator lineages of modern nearshore seas and fill a substantial gap in the sporadic fossil record of the late Middle Eocene. Comparisons of this assemblage with other Middle-Late Eocene faunas from the Tethys seaway indicate that this Tunisian fauna shares more similarities with Late Eocene than with early Middle Eocene assemblages. This suggests that the major shift observed in tropical elasmobranch communities from the Late Eocene, with for instance the appearance of large Carcharhinids replacing Lamniforms, began during the late Middle Eocene. Such a biotic shift could be linked to the warm conditions recorded ca. 41 Ma, known as the Middle Eocene Climatic Optimum (MECO), which was characterized by a short temperature increase of all marine waters.

DNA analysis of elasmobranch products originating from Bangladesh reveals unregulated elasmobranch fishery and trade on species of global conservation concern.

Trade involving elasmobranch products in Bangladesh is a four-decade-long practice in large scale and there is little understanding of its impact on species composition, population, and subsequent conservation. Capacity for monitoring and identification is lacking in landing and shark processing centres. A rapid survey and collection of tissue samples were performed in three landings and nine shark processing centres between 2016 and 2017 in the south-eastern coastal region of Bangladesh. Sequencing for a 707-bp fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene was used to assess the taxonomic status and species composition from 71 elasmobranch tissue samples collected from the shark processing centre only. Good quality COI sequences were obtained for 34 specimens representing 21 species—the majority of which are threatened with extinction. A total of ten species of sharks (Carcharhinus brevipinna, C. amboinensis, C. leucas, C. sorrah, C. amblyrhynchoides, Chiloscyllium burmensis, Galeocerdo cuvier, Rhincodon typus, Scoliodon laticaudus, and Sphyrna lewini), eleven species of rays (Aetomylaeus maculatus, Gymnura poecilura, Mobula mobular, M. kuhlii, Neotrygon indica, Pateobatis uarnacoides, Rhinoptera javanica, and R. jayakari), including three species of guitarfish (Glaucostegus granulatus, G. obtusus, and G. typus), were identified. Four species (14.7% of samples) were found to be listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in Appendix II. Sixteen species (59% of the specimens) were threatened with extinction according to IUCN Red List, whereas 41% were data deficient or not assessed. The results have important implications for the management of regional fisheries and the conservation of elasmobranchs as they 1) represent a preliminary understanding of elasmobranch diversity in trade; 2) depict a lack of awareness and monitoring; and 3) demonstrate a need for urgent monitoring and regulation of elasmobranch trade in Bangladesh.

Elasmobranch diversity, conservation and management along Wadge Bank, South India

The study was undertaken to document the elasmobranch diversity and their abundance along Wadge Bank. Species were collected fortnightly during June 2015 to May 2016 from three landing centres viz., Chinnamuttom,Colachel and Vizhinjam of Wadge Bank. A total of 1,575 specimens were collected during the period and 44 species were identified belonging to 8 orders, 13 families and 25 genera. Among the recorded \families,Carcharhinidae is the most dominant family with 12 species. The Colachel landing centre was rich in diversity with 43 species followed by Chinnamuttom 39 species and Vizhinjam26 species. The highest Shannon Weiner diversity (H’ value) was observed at Colachel (4.17) followed by Chinnamuttom (4.11) and Vizhinjam (3.76). The Margalef’s species richness (‘d’) value was assessed at Colachel (4.55) followed by Chinnamuttom (4.01) and Vizhinjam (2.91). The Pielou’s evenness (J’) estimated was 0.7786, 0.7700 and 0.8005respectively, for Chinnamuttom, Colachal and Vizhinjam. The highest taxonomic diversity value was observed at Colachel (60.33) and the lowest during at Vizhinjam (54.08). Among the three landing centres studied, the total phylogenetic diversity (sPhi+) was found to be the lowest at Vizhinjam (940) and highest at Colachel landing centre (1720). Bray Curtis similarities measure was also calculated, fish communities were separated into several clusters based on seasons. The conservation of elasmobranchs and the management measures to be followed along the Wadge Bank is also discussed.

A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns

Here we describe a new, previously unrecognized elasmobranch microfossil assemblage consisting of isolated dental material from late Pliensbachian marginal marine, near-shore deposits of Grimmen in north-eastern Germany. The faunal composition indicates close affinities to other European pre-Toarcian elasmobranch-bearing localities, as it is predominantly composed of Hybodontiformes (Hybodus reticulatus?, H. hauffianus?, Lissodus sp.), Synechodontiformes (Palidiplospinax enniskilleni, P. occultidens, Paraorthacodus sp., Sphenodus sp.), and Hexanchiformes (Notidanoides sp.), as well as teeth attributable of the enigmatic Early Jurassic galeomorph shark Agaleus dorsetensis. In addition, the here reported elasmobranch tooth assemblage includes the oldest undisputable fossil records of Orectolobiformes and Batomorphii, each being represented by a single complete tooth only. The orectolobiform specimen is reminiscent of hemiscyllids but left in open nomenclature due to its very generalized morphology preventing any taxonomic identification. The batomorph tooth, conversely, is characterized by a unique combination of morphological features, which allows the introduction of new genus and species, Antiquaobatis grimmenensis gen. et sp. nov. The fossil assemblage presented here contributes to our current knowledge of late Early Jurassic chondrichthyan diversity and distributional patterns, providing some support for the hypothesis that most modern neoselachian lineages were initially linked to marginal marine, near-shore environments, before moving into open marine, offshore habitats by the Toarcian.

Elasmobranch catch composition of North Sumatera Fishers

Indonesia is known to contribute nearly 20% of elasmobranch diversity in the world. Presently, elasmobranch biodiversity research had only conducted in particular waters. However, the distribution of Elasmobranch distributed throughout all Indonesia including in the waters of North Sumatra province. This study aims to examine the diversity of Elasmobranch in North Sumatera waters as Elasmobranch preliminary study. We used landing monitoring method in three landing sites from May to June 2018. We recorded species, total length, and fishing unit information. Sharks and rays commonly were caught by net in coastal waters. We found 8 species from 323sharks and Rays which caught and landed. Sharks were dominated by big eye six gill sharks and rays were dominated by pale-edge stingray. Based on length data, we found that sharks and rays which landed also dominated by immature individual. This condition should be concerned in order to it is conservation management related to gear selectivity, considering coastal area is an important habitat for Elasmobranch.

Risks to biodiversity and coastal livelihoods from artisanal elasmobranch fisheries in a Least Developed Country: The Gambia (West Africa)

Developing nations in tropical regions harbour rich biological resources on which humans depend for food, income and employment, yet data to aid their management is often lacking. In West Africa, the diversity and fisheries of elasmobranchs are poorly documented, despite them being known to be economically important and vulnerable to overexploitation. Rapid qualitative surveys of fish processing and landing sites in The Gambia from 2010-2018 revealed valuable new data on species composition, biology, relative abundance, fisheries and utilisation by humans. Diversity and abundance was dominated by batoids, with a major component comprising a large guitarfish (Glaucostegus cemiculus) that was apparently targeted, and a small whipray (Fontitrygon margaritella). Nearly all taxa recorded are classified by the IUCN Red List as Critically Endangered (angel sharks Squatina spp.), Endangered, Data Deficient, or Not Evaluated; several were endemic, of exceptional evolutionary distinctness, cryptic, possibly undescribed, and rare (including stingray Hypanus rudis not apparently recorded since description in 1870). Significant threats to biodiversity, coastal livelihoods and possibly food security are identified based on the apparent importance of elasmobranch fisheries and processing; the known inability of key taxa to withstand intensive fisheries; ‘fishing down the food web’ by intensive utilisation of F. margaritella; and the absence or rarity of previously common elasmobranch species that may be severely depleted in the region. This study provides data that may act as a starting point to aid sustainability accreditation of local fin-fisheries, and demonstrates the value of inexpensive and low-resolution data collection in developing countries.

Conservation genetics of elasmobranchs of the Mexican Pacific Coast, trends and perspectives.

One of the most critical threats to biodiversity is the high extinction rate driven by human activities. Reducing extinction rates requires the implementation of conservation programmes based on robust scientific data. Elasmobranchs are important ecological components of the ocean, and several species sustain substantial economic activities. Unfortunately, elasmobranchs are one of the most threatened and understudied animal taxa. The Mexican Pacific Coast (MPC) is a region with high elasmobranch diversity and is the seat of major elasmobranch fisheries. But it is also a developing region with several conservation and management challenges which require national and international attention. Here, we review the conservation genetics literature of elasmobranchs from the MPC. We present a synthesis of the works using samples from the region and emphasize the main gaps and biases in these data. In addition, we discuss the benefits and challenges of generating genomic information to improve the management and conservation of an elasmobranch biodiversity hotspot in a developing country. We found 47 elasmobranch genetic articles that cover <30% of the elasmobranch diversity in the region. These studies mainly used mitochondrial DNA sequences to analyse the genetic structure of commercially important and abundant species of the order Carcharhiniformes. Some of these papers also assessed mating systems, demographic parameters, and taxonomic uncertainties, all of which are important topics for efficient management decisions. In terms of conservation genetics, elasmobranchs from the MPC remain understudied. However, high-throughput sequencing technologies have increased the power and accessibility of genomic tools, even in developing countries such as Mexico. The tools described here provide information relevant for biodiversity conservation. Therefore, we strongly suggest that investment in genomic research will assist implementation of efficient management strategies. In time, this will reduce the extinction risk of the unique elasmobranch biodiversity from the MPC.

Elasmobranch diversity with preliminary description of four species from territorial waters of Bangladesh

There is a significant lack of data regarding the biodiversity of elasmobranchs in the territorial waters of Bangladesh, since that sharks and rays are not targeted by commercial fishing industry, but rather encountered as a bycatch. This paper updated the diversity of elasmobranchs in the territorial waters of Bangladesh. The study was carried out to identify two coastal areas of Patharghata, Barguna and Cox's Bazar between October, 2015 and September, 2016. Using fish landing station survey techniques, total 20 species of elasmobranch were encountered, including eight species of sharks and 12 species of batoids, under 14 genera, ten families. This is the most expended field based records of elasmobranch fishes of Bangladesh.&#x0D; Bangladesh J. Zool. 46(2): 185-195, 2018

Recent records of large tooth sawfish Pristis pristis (Linnaeus, 1758) from Parerhat of Pirojpur district in the southwestern Bangladesh

Sawfishes are the most endangered cartilaginous fishes on earth with alarming global population decline due to by-catch and socio-economic value. A study on elasmobranch diversity in one of the landing sites of Bangladesh observed annual sawfish captures (n = 5) adjacent to the Sundarbans, the largest mangrove forests in the world, between June 2017 and March 2018. Only largetooth sawfish Pristis pristis was recorded in this study. Data were collected from interviews with fishermen, literature review, media reports and through monthly fish landing record sheet used during the study period. Findings of this study shows that 80% (n = 4) sawfish species were captured in dry season (November to March) and 20% (n = 1) in wet season (June to October). Findings from the semi-structured interviews (n = 50) reported that 54% of the respondents were not aware of the value (ecological as well as economic) of sawfish species whereas 46% of the respondents mentioned sawfish as an important species as its flesh used to cure cancer. Although this report does not reflect the annual capture of sawfish from all over the country, this catch pattern is alarming and needs immediate action to develop a monitoring programme to assess sawfish landings in this area. Priority research is also needed to understand sawfish life history, identify their critical habitats and raise awareness to conserve sawfish species.&#x0D; Bangladesh J. Zool. 46(2): 255-262, 2018

Low abundance of sharks and rays in baited remote underwater video surveys in the Arabian Gulf

Data on the diversity and relative abundance of elasmobranchs (sharks and rays) in the Arabian Gulf have been limited to fishery-dependent monitoring of landing sites. Understanding the diversity and abundance of sharks and rays is, however, crucial to inform policy and management plans. Baited Remote Underwater Video Surveys (BRUVS) were conducted in 2015–2016 across the United Arab Emirates Arabian Gulf waters encompassing a range of depths and habitat types. Data from 278 BRUVS (757 hours soak time) were analysed to gather information on diversity, relative abundance, species distribution, and habitat associations. Surveys recorded 213 individuals from 20 species of sharks and rays at 129 stations. The frequency of occurrence of species usually discarded by fishers such as the Arabian carpetshark (Chiloscyllium arabicum) and stingrays (Himantura spp.) was high, accounting for 60.5% of observed elasmobranchs. Despite the large survey area covered and extensive sampling effort, the relative abundance of sharks and rays was low at 0.28 elasmobranchs per hour, 0.13 sharks per hour, and 0.15 rays per hour. This CPUE was reduced to one of lowest recorded abundance on BRUVS from around the world when removing the two discarded species from the analysis (0.11 elasmobranchs per hour). These results likely reflect the intense fishing pressure and habitat loss contributing to population declines of many elasmobranchs in the Arabian Gulf. Findings provide a baseline for future work and can support the design of conservation strategies for sharks and rays in the UAE.

On the need of providing tooth morphology in descriptions of extant elasmobranch species.

Elasmobranchii is a clade of chondrichthyans (cartilaginous fishes) that comprises sharks, skates and rays represented today by approximately 1,200 species. Chondrichthyans have a long evolutionary history dating back to the Late Ordovician (ca. 450 million years ago [Mya]) based on isolated dermal denticles (Janvier 1996). Other remains such as articulated skeletons and teeth are known from the Lower Devonian (ca. 410 Mya: Mader 1986; Miller et al. 2003). The fossil record of modern elasmobranchs (Neoselachii) can be traced back to the Early Permian (ca. 290 Mya) and is represented by isolated teeth (Ivanov 2005), with fossils of crown group sharks and rays appearing in Lower Jurassic (ca. 200 Mya) rocks (e.g., Cappetta 2012). Since their appearance in the geological record, elasmobranchs are mainly represented by isolated teeth, whereas articulated skeletons are very rare and restricted to a small number of fossil localities (e.g., Cappetta 2012). The scarcity of skeletal remains in their fossil record is due to their poorly mineralized cartilaginous skeleton that requires special taphonomical conditions to be preserved. Elasmobranch teeth, in contrast, are composed of highly mineralized tissues (hydroxyapatite) that have a strong preservation potential (Shimada 2006). In addition, elasmobranchs replace their teeth continuously over the course of their life span (polyphyodonty) and therefore shed thousands of teeth in their lifetime (Reif et al. 1978; Schnetz et al. 2016) leading to large numbers of potential fossils. These morphologically highly diverse isolated teeth constitute much of the rich fossil record of elasmobranchs, and largely form the basis of our understanding of elasmobranch diversity and evolution through geological time.