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Copyright of Global Change Biology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Cybium: International Journal of Ichthyology is the property of Societe Francaise d'Ichtyologie (SFI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The California horn shark (Heterodontus francisci) is a small demersal species distributed from southern California and the Channel Islands to Baja California and the Gulf of California. These nocturnal reef predators maintain small home-ranges as adults and lay auger-shaped egg cases that become wedged into the substrate. While population trends are not well documented, this species is subject to fishing pressure through portions of its range and has been identified as vulnerable to overexploitation. Here, we present a survey of 318 specimens from across the range, using mtDNA control region sequences to provide the first genetic assessment of H. francisci. Overall population structure (ΦST = 0.266, P < 0.001) is consistent with limited dispersal as indicated by life history, with two distinct features. Population structure along the continuous coastline is low, with no discernable breaks from Santa Barbara, CA to Bahia Tortugas (Baja California Sur, Mexico); however, there is a notable partition at Punta Eugenia (BCS), a well-known biogeographic break between tropical and subtropical marine faunas. In contrast, population structure is much higher (max ΦST = 0.601, P < 0.05) between the coast and adjacent Channel Islands, a minimum distance of 19 km, indicating that horn sharks rarely disperse across deep habitat and open water. Population structure in most elasmobranchs is measured on a scale of hundreds to thousands of kilometers, but the California Horn Shark has population partitions on an unprecedented small scale, indicating a need for localized management strategies which ensure adequate protection of distinct stocks. [ABSTRACT FROM AUTHOR]

The Cephaloscyllium ventriosum shark is present in the artisanal fisheries of elasmobranchs on the western coast of Baja California Sur, Mexico. The main characteristics of the sexual maturation of this species based on individuals captured from off north‐west Mexico in 2013–2016 are described. The size at maturity of this species was determined for the first time (total length 82 cm for females and 76 cm for males). Most females had one egg case per one uterus, and two per one uterus was an isolated event of low incidence. From the histological analysis of females, it was possible to show sperm storage in the oviducal gland. Fully developed sperm in immature organisms were identified in the testes. The main indicator of the maturity stage of males and their mating activity is the clasper. The present study provides evidence for a reliable estimation of the sexual maturity of these organisms, demonstrating the need for the combination of macroscopic and microscopic methods. [ABSTRACT FROM AUTHOR]

Devil rays of the genus Mobula are subject to fishing exploitation worldwide and are considered vulnerable to overexploitation due to population reduction, which is evidenced by a decline in the number of catches of these animals.Limited biological knowledge on these species has forced the use of precautionary conservation measures in countries where intensive fishing occurs.This study aimed to describe biological data of interest for estimating the feasibility of the recovery of Mobula populations, emphasizing the reproductive activity of three endangered species of the genus Mobula (Mobula munkiana, Mobula thurstoni, and Mobula mobular) in the Gulf of California.Reproductive organs were collected during 7 years of commercial fishing (2001–2007), and data on population structure, sex ratio, gamete production, and the number of offspring per breeding period were obtained.Maturity stages were determined through histological analysis of the gonads for both sexes, and the size at maturity was estimated based on anatomical and histological characteristics of the specimens caught.Considering the wide global distribution of Mobula species, there is an urgent need to apply strict conservation measures, such as established fishery closures during the breeding season or the establishment of catch periods after specimens have reached sexual maturity, especially in the countries where these animals are caught. [ABSTRACT FROM AUTHOR]

Nitrogen stable isotopes ratios (δ15N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk‐sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were 15N enriched compared to the same tissues in the pregnant female, using the difference in δ15N (Δδ15N) between embryo and adult. Mean Δδ15N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus, embryo liver tissue was significantly 15N enriched in comparison with liver of the pregnant female (Δδ15N mean = 1.22‰), whereas embryo muscle was 15N depleted relative to the muscle of the pregnant female (Δδ15N mean = −1.22‰). Both species presented a significant positive linear relationship between Δδ15N and embryo total length (LT). The results indicated that embryos have different Δδ15N depending on their reproductive strategy, tissue type analysed and embryo LT. [ABSTRACT FROM AUTHOR]

The study of the reproductive aspects of chondrichthyans through the analysis of steroid hormones has been carried out for more than five decades in several species around the world. This scientific knowledge constitutes the basis of the reproductive endocrinology of chondrichthyans, which has provided information regarding their sexual maturation, gametogenesis, mating seasons, gestation periods, and parturition. The present review summarises the existing literature on steroid hormones in chondrichthyan reproduction and identifies future research directions addressing critical knowledge gaps in the reproductive physiology of this taxon. A total of 59 peer reviewed scientific papers from 1963 to 2020 were reviewed and the following parameters analysed: species, steroid hormones, biological matrix, field sampling (year, location), and methodology (assays, sample size, precision, and recoveries). We provided a summary of the methods, biological matrices, and the functions of up to 19 hormones on the biology of 34 species of chondrichthyans that have been analysed to date. The majority of the studies used radioimmunoassay as the main methodology (76.3%; n = 45/49); while the most frequent biological matrix used was plasma (69.5%; n = 41/49). A Kernel's heat map was generated to present the scientific effort according to geographic location and evidenced a lack of research in high biodiversity areas for chondrichthyans worldwide. The implications of the study of steroid hormones for the conservation of chondrichthyans are discussed, as only 2.9% of the species of this group have been analysed and most of the scientific effort (93.2%; n = 55/59 papers) has focused on the analysis of less than six hormones. [ABSTRACT FROM AUTHOR]

Abstract The regulation of mesh size is important for the effective and sustainable management of fisheries using gillnets, which are the main fishing gear used in artisanal elasmobranch fisheries throughout northwestern Mexico. Gillnet selectivity studies focusing on elasmobranchs have generally evaluated the impact on target species, and information on bycatches remains scarce. This study assessed the impact of gillnet selectivity on both target elasmobranch species and bycatches, by varying the mesh size of gillnets. Sampling was performed from 2009 to 2015 in five artisanal fishing grounds located along the northwestern coast of Mexico. The species composition and ecological parameters of the elasmobranch communities that were caught, as well as the size structure and estimated selectivity models for the main species caught, were compared between four mesh sizes: 10.16, 15.24, 20.32 and 25.4 cm (stretched opening). Overall, 32 elasmobranch species were caught, nine of which were common to all mesh sizes. Our results indicate that the species composition of the catch varied with mesh size. While the small-sized sharks Mustelus californicus and M. henlei were the main species caught by gillnets with the smaller mesh sizes, the guitarfish Pseudobatos productus and Zapteryx exasperata , and the Pacific angel shark Squatina californica were the main species caught gillnets with the largest mesh sizes. Gillnet selectivity was estimated for these latter four species as well as for the horn shark Heterodontus francisci. Optimum length for these species varied widely, increasing proportionally to mesh size. These findings emphasize the difficulty of determining an optimal minimum mesh size for multi-species fishery in this area. Finally, recommendations for future directions according to the species' vulnerability to fishing are discussed, focusing on the development of effective strategies to initiate or strengthen the recovery of elasmobranchs of the northwestern coast of Mexico. Highlights • A large variety of elasmobranch species were caught by all mesh sizes. • A high richness of bycatch was observed in all mesh sizes. • Small-size sharks were mainly captured by the smallest mesh sizes. • The guitarfishes and the angel shark were mainly caught by the largest mesh sizes. • The optimum lengths of main species increased proportionally with mesh sizes. [ABSTRACT FROM AUTHOR]

Background. Elasmobranchs can play important roles in marine communities. But, relatively little is known about their diet, and movement. Sphyrna lewini (Griffith et Smith, 1834) consumes fishes, cephalopods, rays, and crustaceans. Carcharhinus falciformis (Müller et Henle, 1839) feed on fishes, cephalopods, crustaceans and sea turtles. To date, there are no studies available on the trophic ecology of sharks in Malpelo Island. The aim of this study was to describe the trophic ecology of S. lewini and C. falciformis, using stable isotope analysis of d13C and δ15N, to better understand the role of both shark species in the Malpelo Island ecosystem. Material and methods. In January, February, and November 2013, specimens of Sphyrna lewini and Carcharhinus falciformis illegally caught at Malpelo Island were confiscated at the port of Buenaventura, Colombia. For each shark specimen, total length and sex were registered. Samples of muscle tissue were taken from the nape of all specimens. Each muscle sample was lyophilized for 24 h and analysed with lipid and urea extraction and without extraction. For each shark specimen, a subsample of ~1.0 mg was used for isotopic analysis. Results. A total of 14 Sphyrna lewini (Griffith et Smith, 1834) and 12 Carcharhinus falciformis (Müller et Henle, 1839) were analysed. δ13C values were similar between S. lewini (-16.3 ± 0.1‰) and C. falciformis (-16.5 ± 0.1‰). Sphyrna lewini showed a wider trophic niche than C. falciformis, with low trophic overlap (5%) between the two species. The δ15N values of S. lewini (15.9 ± 0.11‰) were higher than those of C. falciformis (14.9 ± 0.09‰). In C. falciformis, δ13C values were similar in both sexes (-16.5 ± 0.1‰), while δ15N values were significantly different between males (14.6 ± 0.1‰) and females (15.0 ± 0.1‰). The trophic position of S. lewini was 5.25 ± 0.12, and that of C. falciformis, 5.48 ± 0.18, which suggests that both shark species occupy a high position in the marine food chain. Conclusion. Both shark species co-occur at Malpelo Island, but they do not share food resources and feeding areas, and they probably feed far from the island, using it as a resting and cleaning area. This indicates the need for more research to increase biological and ecological knowledge of both species, particularly within marine protected areas and their influence areas throughout the Colombian Pacific. [ABSTRACT FROM AUTHOR]

The aim of this study was to report the presence of the leopard electric ray Narcine leoparda in Ecuadorian waters; to date, this is the southernmost report of this species in the Tropical Eastern Pacific. Thus, the geographic distribution of N. leoparda now extends another ca., 620 km from Cauca, Colombia (previous southernmost limit of this species' distribution) to Manta and Bahía de Caráquez, Ecuador. These 4 new records of leopard electric rays in the Ecuadorian Pacific increase the species richness of cartilaginous fishes in the region to a total of 93 species, including 58 sharks, 34 batoids, and one chimera. This report also extends the geographic distribution of N. leoparda in the Tropical Eastern Pacific. [ABSTRACT FROM AUTHOR]

Total mercury (THg) concentrations were measured in muscle and liver of two placental viviparous sharks, the Pacific sharpnose shark (Rhizoprionodon longurio) and the brown smooth-hound (Mustelus henlei); as well as in the muscle, liver, and yolk of the yolk-sac viviparous speckled guitarfish (Pseudobatos glaucostigmus) in Baja California Sur. The aim was to determine which factors could be involved in maternal transfer and resultant maternal and embryonic THg concentration. Higher THg concentrations were found in pregnant females compared to embryos paired tissues. THg concentrations of embryo tissues decreased with total length (T L), except for the muscle of the Pacific sharpnose shark. THg concentrations of embryo muscle was positively related to THg concentration in the muscle of pregnant females. Embryos T L , muscle THg concentration of pregnant females, percentage of THg concentration in embryos, along with the reproductive strategy are relevant factors required to improve our understanding of THg concentration in embryo tissues. • Maternal transference of THg in elasmobranchs during gestation • Maternal transfer varies depending on the species. • Embryo T L is an important factor determining [THg] in muscle and liver. • Muscle [THg] in pregnant females is an important factor determining [THg] in embryo tissues. [ABSTRACT FROM AUTHOR]

Information on morphological abnormalities in the cephalic region of three female blue sharks' (Prionace glauca) foetuses found in Baja California Sur, Mexico, is included. In one foetus with bicephaly, the liver was shared. In the other two foetuses they do not have eyes, and part of their snout was not well-developed, with malformations in cranial cartilage and gill slits. A possible explanation for these deformities in blue shark embryos is that the blue shark is the most fecund shark worldwide with the highest number of embryos produced and not all embryos can be developed in their small uteri. [ABSTRACT FROM AUTHOR]

The capture of two Gorgona guitarfish, Rhinobatos prahli, in the Gulf of Tehuantepec represents the first record for the species in Mexican waters and its northernmost range extension in the eastern Pacific. [ABSTRACT FROM AUTHOR]

Sharks are iconic and ecologically important predators found in every ocean. Because of their ecological role as predators, some considered apex predators, and concern over the stability of their populations due to direct and indirect overfishing, there has been an increasing amount of work focussed on shark conservation, and other elasmobranchs such as skates and rays, around the world. Here we discuss many aspects of current shark science and conservation and the path to the future of shark conservation in the Northeastern and Eastern Central Pacific. We explore their roles in ecosystems as keystone species; the conservation measures and laws in place at the international, national, regional and local level; the conservation status of sharks and rays in the region, fisheries for sharks in the Northcentral Pacific specifically those that target juveniles and the implications to shark conservation; a conservation success story: the recovery of Great White Sharks in the Northeast Pacific; public perceptions of sharks and the roles zoos and aquariums play in shark conservation; and the path to the future of shark conservation that requires bold partnerships, local stakeholders and innovative measures. [ABSTRACT FROM AUTHOR]

This study reports the first record of a white shark Carcharodon carcharias off the tropical coast of Nayarit and the southernmost record in the Mexican Pacific. The specimen was a juvenile female accidentally caught by artisanal fisheries in the locality of Playa Novillero, Nayarit. Oceanographic conditions at the time of capture were also recorded, with the aim of improving the knowledge on the ecology of this vulnerable and protected species. [ABSTRACT FROM AUTHOR]

Latin American countries have a high diversity of sharks, rays, and chimaeras, yet many species are at high risk of extinction due to numerous threats. The conservation of chondrichthyans is key to achieving healthy and productive aquatic ecosystems, and countries in Latin America are increasingly recognizing the need for aligning conservation strategies across jurisdictions with similar ecological and socioeconomic challenges. Reflecting on the current state of knowledge and providing consensus expert opinion on research priorities are critical steps to ensure sound management and conservation strategies for chondrichthyans. The present study is a multinational collaboration by leading researchers in Latin America to identify the top-ten research priorities for the conservation of chondrichthyans within this region. Our results were highlighted from a total of 20 broader relevant topics including taxonomy and biology, ecological function, climate change and other stressors, contribution to local economies, and international collaboration. This constitutes the first comprehensive academic perspective on research priorities for chondrichthyans in Latin America which considers the varied perceptions and perspectives related to the management of sharks, rays, and chimaeras across the region and beyond. The main conservation implications highlighted by our study relate to the urgent need to implement, evaluate and/or improve management regulations based on scientific evidence and interdisciplinary research, especially in areas with little progress on the subject and/or where species threatened by extinction are distributed. [Display omitted] • Chondrichthyans conservation in Latin America requires regulations based on research under an interdisciplinary approach. • We provide an academic perspective on chondrichthyan research top-ten priorities in the region. • Obtaining evidence is urgently needed to develop, apply, and improve successful sustainable management. • These priorities are related to previous and novel knowledge in taxonomy, biology, fisheries, and sociology. • Conservation can be compromised by mitigable factors such as pollution and climate change. [ABSTRACT FROM AUTHOR]

Total mercury concentrations ([THg]) in muscle were determined in commercial finfish and elasmobranchs from Baja California Sur (BCS), Mexico to evaluate dietary Hg exposure for BCS communities, including the relationship of trophic ecology, length and mass with [THg] that might drive future consumption advice (e.g., recommend limited consumption of large fish for some species). The [THg] ranged from 0.06 to 528.02 μg kg−1 ww in finfish and 17.68–848.26 μg kg−1 ww in elasmobranchs. Relative to the consumption threshold set for predatory fish in Mexico, all species had a concentration below 1000 μg kg−1 ww. As expected, 16 (4.02%) and 75 (18.84%) individual fish were above advisory thresholds of 500 and 200 μg kg−1 ww, respectively. The hazard quotients (HQs) in most species were significantly <1.0, only banded guitarfish showed a significant median HQ > 1.0. Thus, the relative level of risk of high Hg exposure is low for most species. • Dietary Hg exposure was assessed through fish consumption in a Mexican coastal community. • Fish muscle [THg] varies by length, weight and trophic ecology in most species. • In all species[THg] was below the threshold set for predatory fish in Mexico. • The hazard quotients (HQs) in most species were significantly <1. • The relative level of risk of Hg toxicity is low for most fish species. [ABSTRACT FROM AUTHOR]