Retrieving records of a rare and threatened shark in a mosaic of marine-protected areas of southeastern Brazil

In this study the authors use the Fishers ecological knowledge (FEK) from the south coast of the São Paulo State, in southeastern Brazil, to recover records of Atlantic nurse shark (Ginglymostoma cirratum), a threatened with extinction species, in a mosaic of marine-protected areas (MPAs) of the south coast of São Paulo, in southeastern Brazil, in the southernmost distribution of the species in the Southwest Atlantic Ocean. For half a century, in the study area only one male of G. cirratum was officially recorded, in 1967. Retrieving records from artisanal fishers, recreational anglers, fishing guides and spearfishers added 30 more records of G. cirratum, including 2 recent captures (February/2022 and May/2022), especially around coastal islands that are covered by MPAs. Two uncommon fishing techniques, but which provided the highest number of records for the species, were documented. These are fishing nets and small longlines adapted for fishing close to the rocks, being an apparently traditional activity of a few natives of the region. As Brazil has a long history of intense catches of threatened elasmobranchs and problems with fisheries monitoring, the consideration of the FEK in the fisheries monitoring carried out by the authorities can be useful to promote improvements in data collection, especially of rare and endangered species such as G. cirratum. The strengthening of the protection of the MPAs and the articulation of research and management institutions with native people and tourists who use these areas should also be considered.

Morphological study of the oral denticles of the porbeagle shark Lamna nasus

Oral denticles of sharks are composed by a crown, dentine covered by a layer of enameloid and pulp cavity, the same structure of the dermal denticles found across the body surface of most elasmobranchs. In addition, oral papillae and taste buds are distributed among denticles within the oropharyngeal cavity, playing a fundamental role for tasting as part of the chemosensory system of fishes. Scanning electron microscopy (SEM) has been employed as an important tool for the study of dermal denticles and other structures, as well as histology and more recently computed tomography (CT) scan analysis. Herein, the authors used two methods for the study of the morphology of the oropharyngeal cavity of Lamna nasus (Lamniformes), an oceanic and pelagic shark: SEM and CT scan. The general morphology of oral denticles studied herein is related to abrasion strength as they are diamond-shaped, lack lateral cusps and have less pronounced ridges. In addition, smooth ridges and broad rounded denticles could be related to prevent abrasion during food consumption and manipulation. Oral papillae had a round shape and were observed only under SEM. The densities of papillae were estimated in 100 per cm² , whereas denticles were 1760 and 1230 cm² over the dorsal and ventral regions, respectively. The high numbers of denticles are inversely proportional to papillae density; denticles seem to restrict papillae distribution. Regarding the differences between methodologies, under SEM, only the crown was visualized, as well the papillae, allowing the estimation of size and density of both structures. Nonetheless, under CT scan, the whole components of denticles were clearly visualized: different views of the crown, peduncle, basal plate, and pulp cavity. On the contrary, oral papillae were not visualized under CT due to the tissue preparation. Furthermore, both methods are complementary and were important to extract as much information as possible from denticles and papillae.

A safe haven for potential reproductive aggregations of the critically endangered Brazilian guitarfish (Pseudobatos horkelii)

Brazilian endemic batoid elasmobranch populations have declined dramatically in the past 40 years due to anthropic activities (e.g., overfishing). The Brazilian guitarfish, Pseudobatos horkelii, included in the IUCN red list of endangered species [Critically Endangered (CR)], has been captured as by-catch by trawling fishing boats to the edge of extinction. Despite governmental conservation initiatives, the species is still caught and commercialized along the Brazilian coast. In this study, the authors report three rare aggregation events for the Brazilian coast of P. horkelii, inside the only nearshore no-entry Brazilian marine protected area. Strategies for its protection are also discussed.

Metal contamination in threatened elasmobranchs from an impacted urban coast

Guitarfishes and angelsharks are two of the most endangered elasmobranch groups. Despite this, limited knowledge exists regarding the effects of environmental contamination in these groups. For this reason, this study assessed the concentrations of metals in liver and muscle of three guitarfishes (Pseudobatos horkelii, P. percellens, and Zapteryx brevirostris) and one angelshark species (Squatina guggenheim) captured during the year of 2019 in one of the most impacted areas in South America: the São Paulo State coast, Brazil, Southwest Atlantic. Cadmium (Cd) Chromium (Cr) Cupper (Cu) Iron (Fe), Mercury (Hg), and Lead (Pb) were determined by atomic spectrometry, with samples being previously acid digested. Among the non-essential metals, Cd had the highest mean concentrations for all species, followed by Pb and Hg, whereas Fe had the highest mean levels among the essential metals analyzed, followed by Cu and Cr. Liver and muscle samples had different concentrations, with liver presenting the highest concentrations. Except for Cd, non-essential metals had relatively low concentrations when compared to other elasmobranch species reported in the literature, which could be explained by the efficiency in metabolizing these compounds or differential life history patterns among the species studied herein and other. Considering that all species analyzed herein are typically consumed, human health impacts must be considered, especially concerning Cd concentrations. Furthermore, Cd, Cr and Pb were above the safety limits, indicating potential hazard for human consumption. In conclusion, our results suggest that these species are exposed to metals and that concentrations above the safety limits observed for these species must be taken into consideration regarding human consumption.

Tropical rhodolith beds are a major and belittled reef fish habitat

Understanding habitat-level variation in community structure provides an informed basis for natural resources’ management. Reef fishes are a major component of tropical marine biodiversity, but their abundance and distribution are poorly assessed beyond conventional SCUBA diving depths. Based on a baited-video survey of fish assemblages in Southwestern Atlantic’s most biodiverse region we show that species composition responded mainly to the two major hard-bottom megahabitats (reefs and rhodolith beds) and to the amount of light reaching the bottom. Both megahabitats encompassed typical reef fish assemblages but, unexpectedly, richness in rhodolith beds and reefs was equivalent. The dissimilar fish biomass and trophic structure in reefs and rhodolith beds indicates that these systems function based on contrasting energy pathways, such as the much lower herbivory recorded in the latter. Rhodolith beds, the dominant benthic megahabitat in the tropical Southwestern Atlantic shelf, play an underrated role as fish habitats, and it is critical that they are considered in conservation planning.

Report on fetal mummification in the scalloped hammerhead shark Sphyrna lewini

This study describes the fetal mummification process in two embryos of a 310 cm total length scalloped hammerhead shark Sphyrna lewini caught in southeastern Brazil, in December 2017. Fourteen embryos were observed in total, in which two males in the left uterus presented different stages of mummification. Both mummified embryos were covered by an exudate (i.e., a mucous substance), indicating a hematic mummification process. All embryos were at the placentotrophic stage of development, indicating that they were close to parturition. An intrinsic characteristic is suggested as possible etiology for this condition, such as umbilical torsion, because both embryos were at different sizes and, therefore, at different development stages. In addition, the sample size did not allow the authors to presume any pollution effect once only one female was observed. Finally, fetal mummification and other embryonic development disorders might have populational impacts due to reduction in embryo survival and, consequently, recruitment. For this reason and considering that S. lewini is categorized as a "critically endangered species," this study's results have conservational relevance.

BRUVS reveal locally extinct shark and the way for shark monitoring in Brazilian oceanic islands

Here we present records of sharks obtained using baited remote underwater stereo-video systems (stereo-BRUVS) at two Brazilian oceanic islands. Fourteen of the 60 deployments recorded 19 sharks in Trindade Island. In Saint Peter and Saint Paul Archipelago (SPSPA), two pelagic and two demersal deployments recorded two and one shark, respectively, including the locally extinct Galapagos shark Carcharhinus galapagensis. Stereo-BRUVS should be considered as adjuncts to other non-invasive methods to monitor shark populations.

Age and growth of three endemic threatened guitarfishes Pseudobatos horkelii, P. percellens and Zapteryx brevirostris in the western South Atlantic Ocean

The age and growth of three endemic threatened guitarfish species were analysed using vertebrae of Pseudobatos horkelii, P. percellens and Zapteryx brevirostris. Edge and marginal-increment analyses were used to evaluate the periodicity of the formation of the band-pairs, suggesting deposition of one band-pair per year, from late winter to late spring. The von Bertalanffy growth model was used to describe the growth of these species with the following parameters, for pooled sexes: P. horkelii L_∞ = 126.93, k = 0.19 and t₀ = -1.51; P. percellens L_∞ = 109.31, k = 0.16 and t₀ = -1.78; Z. brevirostris L_∞ = 60.37, k = 0.24 and t₀ = -1.42. Our results are essential to understanding the resilience and vulnerability of these species to harvest, which can contribute to management and conservation actions of these species.

Use of mucus as a non-invasive sampling method for DNA barcoding of stingrays and skates (batoid elasmobranchs)

In this study we tested the use of mucus from five species of Neotropical marine batoid elasmobranchs to extract genomic DNA for barcoding and phylogenetic analysis. The DNA from all individuals sampled was successfully amplified and sequenced for molecular barcode, allowing 99-100% accuracy to the species level. This method proved to provide reliable and good-quality DNA for barcoding and phylogenetic analysis of Neotropical elasmobranchs, through rapid handling and with low disturbance to animals.

Network of small no-take marine reserves reveals greater abundance and body size of fisheries target species

No-take marine reserves (NTRs), i.e. areas with total fishing restrictions, have been established worldwide aiming to promote biodiversity and ecosystem conservation. Brazil has 3.3% of its exclusive economic zone protected by 73 different NTRs, however, most of them currently lack scientific knowledge and understanding of their ecological role, particularly regarding rocky reefs in subtropical regions. In this context, this study aimed to contrast a network of NTRs with comparable fished sites across a coastal biogeographic gradient to investigate the effect of fishing and habitat variability on the abundance and body size of rocky reef fish. We used Baited Remote Underwater stereo-Video (stereo-BRUVs) and Diver Operated stereo-Video (stereo-DOVs) systems to simultaneously sample reef fish and habitat. Model selection and results identified habitat and biogeographic variables, such as distance from shore, as important predictor variables, explaining several aspects of the fish assemblage. The effect of protection was important in determining the abundance and body size of targeted species, in particular for epinephelids and carangids. Conversely, species richness was correlated with habitat complexity but not with protection status. This is the first study using these survey methods in the Southwestern Atlantic, demonstrating how a network of NTRs can provide benchmarks for biodiversity conservation and fisheries management.

Reproductive biology of the Brazilian blind electric ray Benthobatis kreffti (Chondrichthyes: Narcinidae)

ABSTRACT This study provides information on the reproductive biology of the Brazilian blind electric ray Benthobatis kreffti, endemic to southern and southeastern Brazil. Individuals were caught by bottom trawl carried out in 2003 and 2007, at 492-501 m depth off the São Paulo State continental slope. A total of 152 females (115-299 mm) and 144 males (91-243 mm) were sampled. Maturity was first observed at 177 and 162 mm, with total length at 50% maturity of 191 and 176 mm in females and males respectively. Uterine fecundity ranged from 1-3 and was not related to female total length. Size at birth estimated from the largest near-term observed embryos and smallest free-swimming ray was 91-100 mm. The low fecundity observed is typical of deepwater elasmobranch species, as well as late maturity in comparison with costal species. The relatively large size-at-birth suggests that this species invests more in length of each embryo than in litter size, increasing the offspring’s survival chance. In this context, these parameters highlight the vulnerability of this and other deepwater species to non-natural death, mostly caused by deep-sea fisheries.

Condition analysis of the Brazilian sharpnose shark Rhizoprionodon lalandii: evidence of maternal investment for initial post-natal life

The present study analysed the condition factor (K) and the hepato-somatic index (I _H ) of the Brazilian sharpnose shark Rhizoprionodon lalandii during its entire life cycle. Discontinuity of liver growth was observed after sexual maturity. High condition values were recorded in the length classes of 300-350 mm (neonates), when the livers represented about 8% of total mass, decreasing until the length classes of 400-450 and 450-500 mm in females and males, respectively. Seasonal analysis exhibited low I _H values in the summer, while for K, low values were in spring, indicating greater investment for body growth during spring and for gonad maturation in summer. Such findings indicate that this small coastal shark species accumulates reserve substances in the liver that will be used during reproduction. The decline in I _H values in juveniles suggests that reserves provisioned by the mother to the neonate liver can be used in the first months of life.

Human introduction or natural dispersion? Atlantic Ocean occurrence of the Indo-Pacific whitetip reef shark Triaenodon obesus

Occurrence of multiple whitetip reef sharks Triaenodon obesus in the Atlantic Ocean is reported for the first time from near a sunken ferry off the Paraná coast in south-eastern Brazil. This occurrence is hypothesized to have been caused by either a human introduction or a remarkably long oceanic displacement.

Hunting tactics of the lemon shark, Negaprion brevirostris, in shallow waters of an oceanic insular area in the western equatorial Atlantic

ABSTRACT The hunting tactics of lemon sharks, Negaprion brevirostris, are described from underwater and cliff-top observations in the Fernando de Noronha Archipelago, western equatorial Atlantic, Brazil. Two main tactics were observed in the shallow waters of sandy beaches and reefs environments: (i) “substrate inspection” of crevices and holes over rocky and reef bottoms, and (ii) “sardine blitz”, which refer to striking schools of fishes (mainly sardines) in the surf zone. The first tactic was restricted to juveniles up to 2 m of total length, whereas subadult and adult sharks with total length larger than 2 m displayed the second. As lemon sharks use waters less than 5 m depth to hunt, perform social behaviours and predator avoidance, results highlight the importance of properly managing these habitats for their conservation, especially in areas where tourism has increased substantially.

Reproductive biology of the guitarfish Rhinobatos percellens (Chondrichthyes, Rhinobatidae) from the São Paulo Coast, Brazil, western South Atlantic Ocean

The reproductive biology of the guitarfish Rhinobatos percellens was studied from 751 specimens caught by bottom pair trawlers off the coast of São Paulo, Brazil, between c. 24° 00' S; 45° 15' W and c. 25° 10' S; 47° 52' W, from September 2007 to August 2009. The total length (L(T)) and total mass (M(T)) relationship for males and females combined was M(T) = 1·29E-06 L(T) (3·15) (r = 0·99, n = 751). The mean L(T) of sexually mature specimens was 548 mm for males and 583 mm for females. Clasper growth was allometric and showed three distinct phases. Most claspers were calcified in specimens of c. 550 mm L(T). The mean diameter of the largest oocyte was 29·8 mm, the mean ovarian fecundity was seven oocytes and ovulation occurred between August and November. Uterine fecundity ranged from two to 13 embryos (mean of five embryos). Larger females had higher litter sizes and larger embryos; the size-at-birth was c. 200 mm L(T). The hepato-somatic index oscillated seasonally for males and females; the gonado-somatic index had little variation in males, but varied seasonally in females. The presence of many non-pregnant adult females and of encapsulated eggs during two consecutive seasons suggests a resting period between gestations and the possibility of diapause.

Identification and characterization of polymorphic microsatellite loci in the blue shark Prionace glauca, and cross-amplification in other shark species

Two to 14 alleles were found to be segregating per locus (mean 5·2), with observed and expected heterozygosities ranging from 0·08 to 0·78 and 0·08 to 0·94, respectively. Cross-amplification of six of these microsatellite loci indicated that they are also polymorphic in three species of Carcharhiniformes and two species of Lamniformes. The newly developed primers reported here constitute a useful tool for genetic population analyses on Prionace glauca and, potentially, other related species.

Identification of the shark species Rhizoprionodon lalandii and R. porosus (Elasmobranchii, Carcharhinidae) by multiplex PCR and PCR-RFLP techniques

Rhizoprionodon lalandii and R. porosus are widely distributed along the Atlantic coast of the Americas, living close to coastal areas and therefore frequently captured by seaboard fisheries. However, morphological identification of species in this genus is very difficult, especially when sharks have their heads and fins removed, making information about fishing, trading, and the evaluation of fishery effects on species conservation very difficult. This study's main objective is to develop molecular tools to identify these species using multiplex polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism techniques. Both techniques result in good low-cost markers and may be very useful in future studies about the exploitation of these species.

Description of a new species of skate of the genus Malacoraja Stehmann, 1970: the first species from the southwestern Atlantic Ocean, with notes on generic monophyly and composition (Chondrichthyes: Rajidae)

The first report of a western South Atlantic soft skate, genus Malacoraja Stehmann, 1970, is described as Malacoraja obscura, new species, from the southeastern Brazilian continental slope off the states of Espírito Santo and Rio de Janeiro, in depths ranging from 808-1105 m. The new species is known from five specimens and is distinguished from congeners by its unique dorsal coloration with small, faded white spots on disc and pelvic fins, by retaining in larger specimens an irregular row of thorns along dorsal midline of tail (extending from tail base to two-thirds of tail length in 680 mm total length female), and by presenting a ventral tail midline devoid of small denticles only at base (naked region not extending posterior to pelvic fin rear margin). Further diagnostic characters in combination include the lack of scapular thorns in larger specimens, elevated number of tooth rows (64/62 tooth rows in subadult male of 505 mm TL, and 76/74 in large female of 680 mm TL) and vertebrae (27-28 Vtr, 68-75 Vprd), ventral disc and tail with a uniform dark brown coloration, paired postventral fenestrae on scapulocoracoid, enlarged posterior postventral fenestra, circular foramen magnum and paired internal carotid foramina on braincase floor. Adult males were unavailable for study, but an anatomical description of M. obscura, n. sp., is provided. Comparisons are made with all known material of M. kreffti, literature accounts of M. senta, and with abundant material of South African M. spinacidermis; M. obscura, n. sp., most closely resembles M. spinacidermis from the eastern South Atlantic in squamation, coloration and size. Malacoraja is monophyletic due to its unique squamation and rostral appendices, and apparently comprises two species-groups, one for M. obscura and M. spinacidermis, and the other for M. kreffti and M. senta, but clarification of species-level relationships must await more anatomical information, particularly of the latter two species.

Plastic debris collars on juvenile carcharhinid sharks (Rhizoprionodon lalandii) in southwest Atlantic

Three juvenile Brazilian sharpnose sharks (Rhizoprionodon lalandii) caught in gillnets in southeast Brazil, southwest Atlantic, were found with plastic debris rings around their gill or mouth region. The rings caused severe abrasion on the sharks' tissues as the animal grew, the collars probably hampering normal feeding and/or ventilation since two of the collared individuals were emaciated. The rings were identified as detachable lid parts from plastic bottles, likely thrown overboard by fishery and/or recreation boats. As several carcharhinid shark species dwells and reproduce in shallow waters, the impact of discarded plastic debris likely is greater on this shark type.