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Essential habitat is required for a given species to complete its lifecycle and includes habitat for breeding, feeding, and growth. Estuaries provide essential habitat for many fishes, including elasmobranchs, particularly as nurseries. Shore-based, gillnet surveys have documented ten elasmobranch species (sharks and batoids) inhabiting Texas estuaries; however, limitations in the methodology, spatial, and temporal scope employed mean the role of these estuaries as elasmobranch nurseries remains uncertain. Therefore, an alternative sampling technique was implemented to survey open water locations in two Texas estuaries during the peak time of putative elasmobranch nursery usage (May to October). Ten species of elasmobranch were observed, including a shark, Carcharhinus porosus, and batoid species, Hypanus americanus, that were not documented in previous surveys. The most commonly encountered species, Carcharhinus brevipinna, comprised 45% of individuals caught, in contrast to previous surveys of these estuaries, in which the species was less than 1% of the total elasmobranch catch. The results revealed a distinction between sharks and batoids in terms of the life history stages present, as well as the depths and distances from the tidal inlet of areas in which they were encountered. Young-of-the-year and small juvenile Carcharhinus brevipinna and Sphyrna lewini were observed across multiple years and in multiple months within years at one site, suggesting that one of the sampled estuaries functions as a nursery. Although putative nurseries for these species have been identified elsewhere in the world, estuaries serving as nursery grounds in the western Gulf of Mexico are not well described.

Isotopic values of two Caribbean sharpnose shark Rhizoprionodon porosus litters (Poey, 1861) with two and three embryos and one litter of 11 smalltail shark Carcharhinus porosus embryos showed enriched N and C compared to their mothers. In R. porosus, embryonic isotope values were 3.06 ± 0.07‰ and 0.69 ± 0.15‰ greater than their mothers' for δN and δC, respectively, whereas in C. porosus, δN and δC were 1.79 ± 0.09‰ and 1.31 ± 0.17‰ greater in embryos than their mothers., We would like to thank Edward, Darwin and Isnaldo who made collection of samples and their processing at the port possible. Financial and logistical support for this project was provided by Anadarco and the Autoridad Nacional de Acuicultura y Pesca, through Fundación Fauna Caribe Colombiana under an agreement with the Universidad de Bogotá Jorge Tadeo Lozano under the Programa de Observadores Pesqueros de Colombia.

Sharks are among the most endangered and data poor vertebrates in the world. The lack of information regarding their habitat use is especially concerning since these are crucial for the establishment of priority areas for species conservation. Investigating the trace elements present in shark vertebrae has become an interesting tool to analyze species habitat use over individuals’ lifetimes. Therefore, we applied vertebrae microchemistry to investigate habitat use of Carcharhinus porosus in Brazil’s Northern Coast (BNC). We also discuss methodological issues that must be addressed in the future to make microchemistry studies with elasmobranchs at low latitudes more robust. Vertebrae from seventeen individuals sampled in the 1980s (n = 8), and in 2017 and 2018 (n = 9) were evaluated through laser ablation inductively coupled plasma mass spectrometry. We analyzed five elements known to reflect environmental characteristics (Ba, Ca, Mg, Mn, and Sr) by sex, seasons, decades of capture, and life stages. Since Ca is the most abundant element in the vertebrae, we calculated element:Ca ratios and employed these proportions for all statistical analysis. We also used fisheries-independent catch data from the 1980s to test if the BNC is a nursery area for C. porosus. We found significant differences in element concentrations between sexes in both multi and single-element analysis, while decades differed only in the multi-element and Sr:Ca. Furthermore, seasons differed in both multi-element and Mg:Ca and Ba:Ca ratios. We did not find differences between life stages. Neonate multi-element signatures yielded three major groups, thus suggesting that the species has at least three birthing grounds in the area. Despite the occurrence of individuals of all sizes, adults show a more distinct occurrence pattern. Our results point toward the hypothesis that the BNC is an essential habitat for this species since its whole life cycle occurs in this area. Therefore, the BNC is a critical area for its conservation. We reinforce that future studies with strictly tropical species should investigate the effects of metabolism, the species’ growth rate, and the validation of other elements capable of demonstrating fine-scale changes in habitat to reduce the inherent noise in microchemistry studies.

The Gulf of California (GC) is one of the most historically important regions in Mexico for shark fisheries. However, detailed historical shark landings are not available, making it difficult to plan adequate management strategies. This study analyses historical trends in GC shark fishery landings in a data-poor environment to establish a baseline for future research and assessments. The total shark landings for the artisanal fishery from 1939 to 2014, middle-size vessel fishery landings for the 1988–2014, and species composition from 1960 to 2014 were estimated, and we assessed the uncertainty inherent in the data sources and subsequent analyses. Thirty-eight shark species were identified in the GC artisanal fishery, of which Mustelus spp., Sphyrna lewini , Rhizoprionodon longurio, Squatina californica, Carcharhinus falciformis, Sphyrna zygaena, and Carcharhinus limbatus were the taxa with the greatest landings. A noticeable decline in landings was observed for Carcharhinus leucas, Nasolamia velox, Negaprion brevirostris, Sphyrna spp. , Carcharhinus altimus, Carcharhinus obscurus, Galeocerdo cuvier, Carcharhinus porosus, Triakis semifasciata, and Carcharhinus brachyurus . Landings of the pelagic sharks Prionace glauca, Alopias pelagicus, and Isurus oxyrinchu s increased after 1986, mainly due to the development of the middle-size vessel fishery. The history of GC shark fisheries and implications for management of sustainable shark fisheries are discussed.

A fundamental challenge for both sustainable fisheries and biodiversity protection in the Neotropics is the accurate determination of species identity. The biodiversity of the coastal sharks of Guyana is poorly understood, but these species are subject to both artisanal fishing as well as harvesting by industrialized offshore fleets. To determine what species of sharks are frequently caught and consumed along the coastline of Guyana, we used DNA barcoding to identify market specimens. We sequenced the mitochondrial co1 gene for 132 samples collected from six markets, and compared our sequences to those available in the Barcode of Life Database (BOLD) and GenBank. Nearly 30% of the total sample diversity was represented by two species of Hammerhead Sharks (Sphyrna mokarran and S. lewini), both listed as Endangered by the International Union for Conservation of Nature (IUCN). Other significant portions of the samples included Sharpnose Sharks (23% - Rhizoprionodon spp.), considered Vulnerable in Brazilian waters due to unregulated gillnet fisheries, and the Smalltail Shark (17% - Carcharhinus porosus). We found that barcoding provides efficient and accurate identification of market specimens in Guyana, making this study the first in over thirty years to address Guyana’s coastal shark biodiversity. RESUMO Um desafio fundamental para a pesca sustentável e a proteção da biodiversidade nos neotrópicos é a identificação precisa das espécies. A biodiversidade dos tubarões costeiros da Guiana é pouco compreendida, porém essas espécies estão sujeitas tanto à pesca artesanal quanto à pesca industrializada não costeira. Para determinar quais espécies de tubarões são frequentemente capturadas e consumidas ao longo do litoral da Guiana, utilizamos DNA barcoding para identificar espécimes comumente encontrados e adquiridos em mercados. Nós sequenciamos o gene mitocondrial coI para 132 espécimes adquiridos de seis mercados e comparamos estas sequências com as disponíveis no Barcode of Life Database (BOLD) e GenBank. Quase 30% da diversidade total amostrada foi constituída por duas espécies de tubarões martelo (Sphyrna mokarran e S. lewini), ambas listadas como espécies ameaçadas pela UICN. Outras porções significativas da amostragem incluem Cações-Frango (23% - Rhizoprionodon spp.), considerados vulneráveis em águas brasileiras, devido a pesca de arrasto não regulamentada, e o Cação-azeiteiro (17% - Carcharhinus porosus). Descobrimos que o barcoding é uma forma identificação eficiente e precisa para espécimes de mercado na Guiana, tornando este estudo o pioneiro na documentação da biodiversidade dos tubarões costeiros da Guiana.

This study reports the first bicephalic embryo of smalltail shark Carcharhinus porosus, which was removed from a pregnant female in coastal waters of the tropical eastern Pacific Ocean. The observation suggested that although the individual's body was well formed, the malformation of the head would have affected it survival.

Marginal increment ratio (MIR) analyses were conducted as part of age and growth studies on three coastal/semi-oceanic species, the smalltail shark, Carcharhinus porosus, dagger-nose shark, Isogomphodon oxyrhynchus and the night shark C. signatus, and two ubiquitous oceanic species, blue shark, Prionace glauca, and whitetip shark, C. longimanus, collected in equatorial areas off Brazil with the aim of establishing the interspecific temporal nature of vertebral band formation. Monthly variations in marginal bands were analyzed using mean MIR on the entire sample as the standard method for all species. Reasons for the inconclusive results regarding these species are critically appraised with respect to three main sources of bias that are associated with marginal increment analysis (MIA). Bias due to insufficient sample sizes may have hampered the analysis for I. oxyrhynchus and C. longimanus due to movements from shallow waters to seamounts for the former species and to extensive migrations for the latter. Bias due to data collection over too long a period is thought to have influenced monthly mean MIR for C. porosus and P. glauca. For the latter, individuals from different age groups lay down rings at different times, making band deposition inconsistent between individuals. Finally, bias due to births occurring over too long a period was the prevalent cause for confounding MIR values among I. oxyrhynchus and C. signatus species, whose birth period lasts several months and leads to different ages within the same cohort. Other approaches used for MIA in C. signatus and P. glauca led to distinct times of band formation by age-groups when compared to MIR applied on the entire sample. For the daggernose shark, delays in events related to the reproductive cycle from one year to the next were also found to confound MIR. Requirements for the use of MIR implying a band width that displays a sinusoidal cycle when temporally plotted (month or season) were not fulfilled for any of these species. The method has been of little utility for detecting the periodicity of band deposition among sharks from the tropics. This emphasizes the need for supplying information on the temporal periodicity of pair deposition based on other methods.

C. porosus is common throughout the year in shallow waters off the Maranhão coast, northern Brazil, where it is the most abundant elasmobranch species. Of 1128 smalltail sharks collected from June 1984 to November 1987 in gill-nets from coastal waters, ~80% were juveniles. Male and female numbers did not differ from a 1:1 ratio. Modal classes were 50.0–60.0 cm (TL) for both sexes. A 120.5 cm female was the largest specimen caught and a 29.4 cm male was the smallest. Age distribution for the whole sample ranged from 0 to >12 years. The length–weight relationship did not differ significantly between the sexes. Diameter of ovarian follicles, presence of eggs/embryos and nidamental gland traits in females point to a major physiological change toward maturity at about 70.0 cm. Vitellogenesis was first observed at 63.0 cm, and the smallest of the six pregnant females was 70.0 cm. There was a significant relationship between the number of embryos and female size. From September to November, ovulation and newborns were observed in catches. Resumo. Carcharhinus porosus é comum ao longo do ano em águas rasas do norte do Brasil onde é a espécie mais abundante entre os elasmobrânquios. De 1128 exemplares coletados em águas costeiras de junho 1984 a novembro 1987 em redes de emalhar ~80% eram jovens. O número de machos e fêmeas não diferiu da razão 1:1. A classe modal foi a de 50.0–60.0 cm para ambos os sexos. Uma fêmea de 120.5 e um macho de 29.4 cm corresponderam ao maior e ao menor exemplar capturado, respectivamente. A distribuição de idades na amostra total variou de 0 a >12 anos. Arelação peso–comprimento não mostrou diferenças significativas entre os sexos. O diâmetro dos ovócitos, presença de embriões/ovos e largura da glândula nidamentária nas fêmeas indica aquisição da maturidade em 70.0 cm. Foi estabelecida uma relação significativa entre o número de embriões e o tamanho das femeas. Entre setembro e novembro ocorre a ovulação e recém nascidos foram observados nas capturas.

Age and growth of C. porosus was estimated from seasonally formed marks in vertebrae of 504 specimens (30.0–101.0 cm total length), and from length–frequency data from 1128 individuals (29.4–120.5 cm). Estimated von Bertalanffy growth parameters were: from observed length-at-age, L∞ 125.1 cm, K 0.101 year-1 and t0 –2.89 year; from back-calculated lengths, L∞ 136.4 cm, K 0.077 year-1, t0 –3.27 year; and from length–frequency analysis, L∞ 131.0, K 0.080 and t0 –3.40. Growth did not differ significantly between sexes. Males and females were mature at 71.0 and 70.0 cm, respectively, corresponding to 6 years old. The largest shark aged from vertebrae was a 12-year-old female (101.0 cm). Growth rates calculated from mean observed lengths were 7.0 cm year-1 for the first four years and 4.0 cm year-1 after maturity. Lee’s phenomenon was not apparent. The annulus forms from September to January. Parameters derived from back-calculated lengths were considered to best describe growth. Like most carcharhinids, C. porosus follows the general pattern of K-selected species, exhibiting slow growth, late maturity and low fecundity. Resumo. A idade e o crescimento de C. porosus foram estimados a partir de marcas sazonais em vértebras de 504 indivíduos (30.0–101.0 cm comprimento total) e através de distribuição de freqÜências de comprimentos de 1128 indivíduos (29.4–120.5 cm). Os parâmetros de von Bertalanffy obtidos com comprimentos observados na captura foram: L∞ 125.1 cm, K 0.101 ano –1 e t0 –2.89 anos; com comprimentos retrocalculados: L∞ 136.4 cm, K 0.077 ano-1, t0 –3.27 anos, e da distribuição de freqÜências de comprimentos obteve-se: L∞ 131.0 cm, K 0.080 ano-1 e t0 –3.40. O crescimento não difere entre sexos. Machos e fêmeas são maduras com 71 e 70 cm, respectivamente, correspondendo a idade de 6 anos. O maior espécime cuja idade foi estimada das vértebras tinha 12 anos (101.0 cm). As taxas de crescimento calculadas dos comprimentos médios observados foram 7.0 cm ano-1 para os primeiros quatro anos e 4.0 cm ano-1 após a maturidade. O fenômeno de Lee não ocorreu. O anel se forma entre setembro e janeiro. Os parâmetros obtidos do retroclculo descreveram melhor o crescimento. Como muitos carcharhinideos, C. porosus segue o padrão das espécies da seleção K, exibindo crescimento lento, maturidade tardia e baixa fecundidade.