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Biogeographic regionalization identifies natural species assemblages of a given region. In this study, the geographic distribution of chondrichthyan species richness and species assemblages for the Southwest Atlantic were identified. The geographic distribution of 103 chondrichthyans was estimated through modelling. Based on the obtained binary maps, the distribution of chondrichthyan richness was obtained at four taxonomic levels: class Chondrichthyes (chondrichthyans), subclass Holocephali (chimaeras), division Selachii (sharks), and division Batomorphi (batoids). The continental shelf off Uruguay and southern Brazil presented the highest levels of chondrichthyan richness, and a smaller peak was found in El Rincón (northern Argentina). Shark richness concentrated mainly off Lagoa dos Patos (southern Brazil). Batoid richness was maximal off Uruguay and northern Argentina, including modes in El Rincón, San Jorge Gulf, and slope of the Argentinean shelf. Classification analyses revealed the presence of a hierarchical regionalization, with three main and six minor assemblages. Main assemblages are hierarchically identifiable as provinces and minor ones as ecoregions or districts. Two of the main assemblages correspond with the Argentinean and Magellanic Provinces; the third one is identified here for the first time, the Patagonian Slope Province. This regionalization provides the basis for the design of protected area networks for conservation or management purposes. Fil: Sabadin, David Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Barbini, Santiago Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Figueroa, Daniel Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Kittlein, Marcelo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Elasmobranchs (sharks, skates and rays) are of broad ecological, economic, and societal value. These globally important fishes are experiencing sharp population declines as a result of human activity in the oceans. Research to understand elasmobranch ecology and conservation is critical and has now begun to explore the role of body-associated microbiomes in shaping elasmobranch health. Here, we review the burgeoning efforts to understand elasmobranch microbiomes, highlighting microbiome variation among gastrointestinal, oral, skin, and blood-associated niches. We identify major bacterial lineages in the microbiome, challenges to the field, key unanswered questions, and avenues for future work. We argue for prioritizing research to determine how microbiomes interact mechanistically with the unique physiology of elasmobranchs, potentially identifying roles in host immunity, disease, nutrition, and waste processing. Understanding elasmobranch–microbiome interactions is critical for predicting how sharks and rays respond to a changing ocean and for managing healthy populations in managed care. Supplementary Information The online version contains supplementary material available at 10.1186/s42523-021-00121-4.

Sharks, skates, rays and chimaeras (chondrichthyans) are of high conservation concern; especially obligate freshwater chondrichthyans, given their restricted ranges, proximity to humans, and threatened habitat. The biological traits that increase chondrichthyan susceptibility to extinction are well known. Less attention has been put on the human determinants of chondrichthyan conservation status. Socio-economic development, scientific research, and exploitation affect natural resource management and conservation. We assessed the relationship between these factors and chondrichthyan conservation. We ran generalized linear models with number of Threatened (THR), Least Concern (LC), and Data Deficient chondrichthyans as dependent variables, and indicators of socio-economic development (governance, human security, human development, and corruption indices), scientific research (number of papers on chondrichthyans), and exploitation (total, industrial, and foreign catch of chondrichthyans), as independent variables. Human density instead of exploitation was a predictor for obligate freshwater chondrichthyans. Socio-economic development (regardless of the index used) and scientific research were associated to desirable conservation status, such as low THR and high LC, for both marine and obligate freshwater species. Exploitation and human density (for obligate freshwater chondrichthyans) were associated to negative conservation status, i.e. high THR and low LC. Current human density projections translated into a 69% decrease in obligate freshwater chondrichthyans LC by 2050. Development produces desirable conservation status for chondrichthyans, but resource overconsumption must be reduced. Scientific research appears to assist sustainable use of chondrichthyan resources, and should be promoted in developing countries. Assessment and conservation of obligate freshwater chondrichthyans, and freshwater biota in general, must be pursued with urgency. Fil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Barbini, Santiago Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Scarabotti, Pablo Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Sabadin, David Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Skates are a diverse group within the chondrichthyans and comprise a large component of the bycatch in many demersal fisheries. The distribution of the Deepsea Skate, Bathyraja abyssicola, is presently known to be limited to the northern temperate Pacific Ocean. We filmed B. abyssicola from a remote operated vehicle during surveys undertaken on a seamount located north of Darwin Island within the Galapagos Marine Reserve in 2015. This sighting represents the first record of B. abyssicola in the Galapagos Marine Reserve and the first record of the species from anywhere in the tropical eastern Pacific Ocean. The large range extension of this species to tropical low-latitude waters of the Pacific Ocean is a critical contribution to conservation biology of this poorly known species, especially since deepwater skates and rays are generally over-exploited. This new record also highlights our limited knowledge of unique deepwater ecosystems in general and those of the Galapagos Islands in particular.

16 pages, 7 figures, 4 tables, supplementary material http://dx.doi.org/10.3354/meps11494, Deficiencies in basic ecological information on uncommon and endangered elasmobranch fishes impair the assessment of their ecological role in marine ecosystems. In this study, we examined the feeding ecology (diet composition and trophic level) and trophic relationships of 22 elasmo branchs (2 Carcharhiniformes, 1 Hexanchiformes, 1 Lamniformes, 3 Myliobatiformes, 6 Rajiformes, 6 Squaliformes and 3 Torpediniformes) present in the western Mediterranean Sea. To obtain a comprehensive view of the feeding ecology of these species, we combined different approaches: stable isotope analyses (δC and δN values), stomach content analyses and published sources. Our results revealed differences in feeding strategies among elasmobranch groups: skates (Rajiformes) mainly consume crustaceans; sharks (Carcharhiniformes, Hexanchiformes, Squaliformes and Lamniformes) prefer mixed diets composed of cephalopods, crustaceans and fishes; electric rays (Torpediniformes) feed mostly on fishes; and the diet of stingrays (Myliobatiformes) varies between species. Sharks and electric rays show higher trophic positions than skates, and the former occupy similar positions to other apex predators. Skates are more similar to other mesopredator fishes. These new findings offer essential information on the ecological role of several elasmobranchs in the western Mediterranean Sea and provide useful data for managers for future conservation strategies, C.B. was supported by a predoctoral fellowship CONICYT-Becas Chile. M.C. was partially supported by the Marie Curie Career Integration Grant Fellowships of the BIOWEB project and by a postdoctoral contract of the Ramon y Cajal Program (Spanish Ministry of Economy and Competitiveness). J.N. was supported by the projects Estación Biológica de Doñana-Severo Ochoa (SEV-2012-0262) and ESFRI-Life-Watch. This study forms a contribution to the project ECOTRANS (CTM2011-26333, Spanish Ministry of Economy and Competiveness, Spain) and to the PhD thesis of C.B.

Turan, Cemal/0000-0001-9584-0261; Erguden, Deniz/0000-0002-2597-2151 WOS: 000358550200005 Total biomass, species composition, depth distribution, seasonal distribution and abundance of elasmobranchs were examined by commercial bottom trawls between 2009 and 2010 from Iskenderun Bay, Turkish coast of the northeastern Mediterranean. From 52 bottom trawl surveys, it was estimated that elasmobranchs represented 23% (190.1 kg.km(-2)) of total fish biomass (840.8 kg.km(-2)) in Iskenderun Bay. Dasyatis pastinaca, Gymnura altavela, Raja clavata and Rhinobatos spp. (Rhinobatos rhinobatos and Glaucostegus cemiculus) showed high occurrence and represented each between 11.10 and 38.46% of the whole elasmobranch biomass. The other species, Dipturus oxyrinchus, Raja miraletus, Torpedo marmorata and Torpedo torpedo, represented each between 0.12 and 2.82% of the total elasmobranchs biomass. Shark species, Mustelus mustelus, Scyliorhinus stellaris, Scyliorhinus canicula, Galeus melastomus and Squatina squatina, represented each between 0.45 and 1.7% of the whole elasmobranchs biomass. When seasonal distribution was examined, total catch of fish were 32.38, 23.24, 10.71 and 33.65%, of which elasmobranchs species constitute 24.11, 34.12, 20.42 and 21.34% in autumn, winter, spring and summer respectively. Single or sporadic captures were also recorded for Isurus oxyrinchus, Carcharhinus plumbeus, Carcharhinus altimus, Oxynotus centrina, Raja radula, Rhinoptera marginata and Pteromylaeus bovinus.

O presente estudo foi realizado no litoral entre a divisa dos Estados do Paraná e Santa Catarina, em duas comunidades pesqueiras artesanais que integram os municípios de Guaratuba (PR) e Itapoá (SC). Foram acompanhadas as atividades pesqueiras das comunidades, entre julho de 2001 e março de 2003, com o objetivo de: listar as espécies de elasmobrânquios capturadas pelas comunidades em questão; avaliar o uso comercial das espécies; observar a ocorrência sazonal das espécies nos desembarques; estimar a freqüência relativa de captura por aparelho de pesca; e inferir sobre a biologia reprodutiva das espécies. Durante o período estudado foram capturados: Carcharhinus falciformis, Galeocerdo cuvier, Rhizoprionodon lalandii, R. porosus, Sphyrna lewini, S. zygaena, Squatina guggenheim, Narcine brasiliensis, Rhinobatos percellens, Zapteryx brevirostris, Rioraja agassizii, Dasyatis americana, D. guttata, D. hipostigma, Gymnura altavela, Myliobatis goodei, Rhinoptera bonasus e R. brasiliensis. Quanto à comercialização das espécies, foi observado que todos os tubarões capturados na área de estudo são comercializados, dentre as raias, apenas Rhinobatos percellens e Zapteryx brevirostris. Nos desembarques, a ocorrência de elasmobrânquios foi maior durante o inverno e a primavera. A maioria das capturas ocorreu com redes de emalhe, o arrasto camaroneiro pouco capturou. Os dados do presente trabalho indicaram a utilização da área estudada para o parto das espécies G. cuvier, R. lalandii, R. porosus, S. lewini, N. brasiliensis e R. agassizii; para o crescimento de todas as espécies amostradas; e para a gestação de R. percellens e Z. brevirostris. É sugerido que medidas que visem a proteger as espécies sejam tomadas, sem trazer prejuízos e conflitos para as comunidades de pescadores. This study was done in the South coast of Parana State and North coast of Santa Catarina State, Brazil, in two artisanal fishermen communities. Between July, 2001 and March, 2003 the fishing activities were observed aiming to: report the elasmobranchs caught species; report which species are commercialized; observe the seasonal occurrence of the species in the landings; estimate the frequency of capture by different fishing gears; and infer about the reproductive biology of the species. During the studied period were captured: Carcharhinus falciformis, Galeocerdo cuvier, Rhizoprionodon lalandii, R. porosus, Sphyrna lewini, S. zygaena, Squatina guggenheim, Narcine brasiliensis, Rhinobatos percellens, Zapteryx brevirostris, Rioraja agassizii, Dasyatis americana, D. guttata, D. hipostigma, Gymnura altavela, Myliobatis goodei, Rhinoptera bonasus and R. brasiliensis. It was observed that all sharks and only two ray species (R. percellens and Z. brevirostris) are commercialized. In the landings, elasmobranchs were more frequent during winter and spring. Most catches were done by gillnets, while just a few captures were done by shrimp trawls. The data indicated that the studied area is used by G. cuvier, R. lalandii, R. porosus, S. lewini, N. brasiliensis and R. agassizii to give birth; by all species for growing; and during the gestation of R. percellens and Z. brevirostris. It is suggested that actions aiming to protect the species must be taken, without harming and conflicts for the fishermen communities.

Made available in DSpace on 2019-09-12T16:53:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2005 Specimens of the zipper sand skate Psammobatis extenta were collected in the region of Ubatuba off the northern coast of the State of Sao Paulo, Brazil, monthly for once year (January - December 2000), at 25- to 40-m isobaths. A total of 123 individuals were caught. The total length (TL) of females averaged 224.6 mm, and of males 217 mm. The overall sex ratio was 1:1. Analysis of the length-weight relationship indicated the existence of positive allometry in females, and isometry in males. The length at onset of sexual maturity was determined for both sexes; females reached sexual maturity at smaller sizes than males (TL50 = 230.7 and TL50 = 237.7 mm respectively). Females showed functional parity of both ovaries and uteri. Females that were pregnant or were carrying vitellogenic oocytes were observed during nine of 12 months of the survey, indicating a continuous reproductive cycle. Psammobatis extenta was most abundant from January to April, and again from June to October. Most individuals were collected at the 40-m isobath. Both adults and neonates were collected in the study area. However, adolescent skates were scarce, which either indicates differential occupation of the area, or suggests that the shallow waters of the continental shelf are used as breeding grounds. Universidade de Taubaté (Unitau), , Dept Biol, Zool Lab, BR-12030010 Taubate, SP, Brazil; Univ Estadual Paulista, UNESP, Dept Zool, BR-18618000 Botucatu, SP, Brazil

Over the past 50 years, economic and technological developments have dramatically increased the human contribution to ambient noise in the ocean. The dominant frequencies of most human-made noise in the ocean is in the low-frequency range (defined as sound energy below 1000Hz), and low-frequency sound (LFS) may travel great distances in the ocean due to the unique propagation characteristics of the deep ocean (Munk et al. 1989). For example, in the Northern Hemisphere oceans low-frequency ambient noise levels have increased by as much as 10 dB during the period from 1950 to 1975 (Urick 1986; review by NRC 1994). Shipping is the overwhelmingly dominant source of low-frequency manmade noise in the ocean, but other sources of manmade LFS including sounds from oil and gas industrial development and production activities (seismic exploration, construction work, drilling, production platforms), and scientific research (e.g., acoustic tomography and thermography, underwater communication). The SURTASS LFA system is an additional source of human-produced LFS in the ocean, contributing sound energy in the 100-500 Hz band.When considering a document that addresses the potential effects of a low-frequency sound source on the marine environment, it is important to focus upon those species that are the most likely to be affected. Important criteria are: 1) the physics of sound as it relates to biological organisms; 2) the nature of the exposure (i.e. duration, frequency, and intensity); and 3) the geographic region in which the sound source will be operated (which, when considered with the distribution of the organisms will determine which species will be exposed). The goal in this section of the LFA/EIS is to examine the status, distribution, abundance, reproduction, foraging behavior, vocal behavior, and known impacts of human activity of those species may be impacted by LFA operations. To focus our efforts, we have examined species that may be physically affected and arefound in the region where the LFA source will be operated. The large-scale geographic location of species in relation to the sound source can be determined from the distribution of each species. However, the physical ability for the organism to be impacted depends upon the nature of the sound source (i.e. explosive, impulsive, or non-impulsive); and the acoustic properties of the medium (i.e. seawater) and the organism.Non-impulsive sound is comprised of the movement of particles in a medium. Motion is imparted by a vibrating object (diaphragm of a speaker, vocal chords, etc.). Due to the proximity of the particles in the medium, this motion is transmitted from particle to particle in waves away from the sound source. Because the particle motion is along the same axis as the propagating wave, the waves are longitudinal. Particles move away from then back towards the vibrating source, creating areas of compression (high pressure) and areas of rarefaction (low pressure). As the motion is transferred from one particle to the next, the sound propagates away from the sound source. Wavelength is the distance from one pressure peak to the next. Frequency is the number of waves passing per unit time (Hz). Sound velocity (not to be confused with particle velocity) is the impedance is loosely equivalent to the resistance of a medium to the passage of sound waves (technically it is the ratio of acoustic pressure to particle velocity). A high impedance means that acoustic particle velocity is small for a given pressure (low impedance the opposite). When a sound strikes a boundary between media of different impedances, both reflection and refraction, and a transfer of energy can occur. The intensity of the reflection is a function of the intensity of the sound wave and the impedances of the two media. Two key factors in determining the potential for damage due to a sound source are the intensity of the sound wave and the impedance difference between the two media (impedance mis-match). The bodies of the vast majority of organisms in the ocean (particularly phytoplankton and zooplankton) have similar sound impedence values to that of seawater. As a result, the potential for sound damage is low; organisms are effectively transparent to the sound – it passes through them without transferring damage-causing energy.Due to the considerations above, we have undertaken a detailed analysis of species which met the following criteria:1) Is the species capable of being physically affected by LFS? Are acoustic impedence mis-matches large enough to enable LFS to have a physical affect or allow the species to sense LFS?2) Does the proposed SURTASS LFA geographical sphere of acoustic influence overlap the distribution of the species?Species that did not meet the above criteria were excluded from consideration. For example, phytoplankton and zooplankton species lack acoustic impedance mis-matches at low frequencies to expect them to be physically affected SURTASS LFA.Vertebrates are the organisms that fit these criteria and we have accordingly focused our analysis of the affected environment on these vertebrate groups in the world’s oceans: fishes, reptiles, seabirds, pinnipeds, cetaceans, pinnipeds, mustelids, sirenians (Table 1).