Triakis Semifasciata Research Articles

Comparison of Physiological Stress Indices in Anesthetized and Manually Restrained Leopard Sharks, Triakis semifasciata

Background: Leopard sharks (Triakis semifasciata) are abundant, coastal, eastern Pacific, mesopredatory sharks and are frequently managed in aquariums and zoos. Medical examinations are a routine part of good husbandry practices, but the handling protocols vary greatly between facilities. In this study, we compared the physiological stress responses of T. semifasciata associated with manual restraint and sedated handling under parallel holding and handling procedures in a 10 min interval. Methods: Blood was collected and analyzed for the hematocrit (Hct), lactate, glucose, beta-hydroxybutyrate (β-HB), pH, blood gasses, 1α-hydroxycorticosterone (1α-OHB), and corticosterone (B). Results: Overall, a minimal physiological stress response was observed in both groups. However, statistically significant increases in the PCO2, β-HB and lactate occurred, while the pHTC, SO2, and BE decreased over time in the manual-restraint group. In the sedated group, the B, PCO2, and lactate increased while the pHTC, SO2, and base excess (BE) decreased over time. When comparing treatments, the sedated group had a higher B and PCO2 TC and a lower pHTC, BE, and SO2 than the manual-restraint group at the second time point. Conclusions: This study indicates that manual restraint is comparable to the described sedation in T. semifasciata for minimally invasive procedures. The overall results show that this species had low physiological stress responses to both methods.

HEMATOLOGIC AND PLASMA BIOCHEMICAL REFERENCE VALUES FOR CAPTIVE LEOPARD SHARKS (TRIAKIS SEMIFASCIATA).

Leopard sharks (Triakis semifasciata) are temperate, Eastern Pacific elasmobranchs popular in public aquariums. Blood analysis is commonly used for assessing animal health, yet reference values have not been established for this species. This study analyzed T. semifasciata population data to characterize blood reference values for a collection of T. semifasciata housed at a public aquarium. Twenty-one captive leopard sharks were sampled. Blood was collected during annual health examinations from sedated animals. After collection, blood samples were anticoagulated with lithium heparin, and hematocrit and plasma biochemistry values were analyzed. The minimum-maximum ranges were hematocrit 11-31%, buffy coat 1-2%, glucose 4.94-9.38 mM/L, sodium 244-272 mM/L, potassium 3.7-5.5 mM/L, chloride 214-246 mM/L, aspartate aminotransferase 5-31 U/L, creatine kinase 36-1,136 U/L, calcium 3.65-3.95 mM/L, phosphorus 1.13-2.23 mM/L, total protein 21-38 g/L, and total CO2 12-18 mM/L. The values identified will contribute to a better understanding of captive leopard shark physiology and to improved veterinary care for captive leopard sharks. Further research can examine the validity of machines like the Vetscan VS2, which will expand the resources available to care professionals.

Patterns of dermal denticle loss in sharks.

As they grow, sharks both replace lost denticles and proliferate the number of denticles by developing new (de novo) denticles without prior denticle shedding. The loss and replacement of denticles has potential impacts on the energetic cost of maintaining the skin surface, the biomechanical functions of shark skin, as well as our ability to predict shark abundance from fossil denticle occurrence in sediment cores. Here, we seek to better understand patterns of denticle loss and to show how denticles are being replaced in mature sharks. We illustrate shark skin surfaces with missing denticles and quantify both within-species and between-species patterns of missing denticles using images from across regions of the body for two species and images at similar body regions for 16 species of sharks. Generally, sharks are missing similar numbers of denticles (0%-6%) between species and regions. However, there are exceptions: in the smooth dogfish, the nose region is missing significantly more denticles than most posterior-body and fin regions, and the common thresher shark is missing significantly more denticles than the smooth dogfish, leopard shark, angel shark, bonnethead, and gulper shark. Denticle regrowth starts with crown development and mineralization beneath the epidermis, followed by eruption of the crown, and finally the mineralization of the root. The pulp cavity of replacement denticles is initially large and surrounded by a thin shell of enameloid upon eruption of the denticle. After eruption of the denticle, the deposition of dentine continues internally after the denticle reaches its final position. Replacement of missing denticles, representing less than 6% of the skin surface at any one time, may not compromise hydrodynamic function, but by constantly updating the skin surface throughout life, sharks may reduce surface fouling and maintain a functional complex skin surface by repairing local damage to individual denticles.

The complete mitochondrial genome of the leopard shark Triakis semifasciata (Triakidae)

ABSTRACT The leopard shark Triakis semifasciata (family Triakidae) is threatened by habitat loss and targeted by recreational and commercial fishermen in the Eastern Pacific Ocean, from Oregon, USA, to the Gulf of California, Mexico. Despite environmental issues, there are few genetic and genomic resources available for this species. This study assembled the complete mitochondrial genome of T. semifasciata from a skin metagenomic sample and described it in detail. The phylogenetic position of T. semifasciata amongst closely related species was also examined using mitochondrial protein-coding genes (PCGs). The mitochondrial genome of T. semifasciata is 16,613 bp in length and consists of 13 PCGs, two ribosomal RNA (rRNA) genes, and 22 transfer RNA (tRNA) genes. A 30 bp long region was identified as the origin of replication for the light strand (OL) between the trnN and trnC genes, and a 974 bp long putative control region (CR) contains the origin of replication for the heavy strand (OH). The gene order in T. semifasciata is identical to that of cofamilial species. An analysis of Ka/Ks ratios for all PCGs yielded values < 1, indicating that all PCGs experience strong purifying selection. All tRNAs exhibit a canonical ‘cloverleaf’ secondary structure except for tRNA-Ser1 which lacks the stem of the dihydrouridine (DHU) arm and in place possesses a simple loop. A phylomitogenomic maximum likelihood (ML) analysis did not support the monophyly of the family Trakidae and placed T. semifasciata in a sister position to Hemitriakis japanica. However, the aforementioned sister position was poorly supported by ML bootstrap values. This study represents a new genomic resource for this commercially and recreationally important species and confirms that mitochondrial genomes can be assembled from skin metagenomic samples as shown before in an unrelated shark species.

Sharkaeology: Expanding Understandings of Historical Chinese Diaspora Shark Fisheries in Monterey Bay, California, through the Genetic Species Identification of Archaeological Chondrichthyes Remains

Prior to burning down in 1906 CE, Point Alones in the Monterey Bay region of Central California was home to one of the largest Chinese fishing communities in the United States of America. Both historical records and the recovery of numerous cartilaginous fish (Chondrichthyes) vertebrae during archaeological excavations of the village indicate sharks were among the taxonomic groups being regularly harvested by its inhabitants. However, as shark vertebrae are difficult to identify past the family-level using conventional morphology-based approaches, our understanding of the Point Alones shark fishery remains incomplete. In this study, we address this issue by using ancient DNA analysis to assign species-level identifications to a sample of 54 shark vertebrae from the site. We successfully amplified a 173 bp fragment of the mitochondrial cytochrome c oxidase I gene from 47 of the 54 analyzed specimens (87.03%). Our results indicate that Tope Shark (Galeorhinus galeus; n = 39) was the primary focus of the site’s shark fishery, with Brown Smooth-Hound (Mustelus henlei; n = 7) and Leopard Shark (Triakis semifasciata; n = 1) also harvested to a lesser extent. All three of these species are found locally in the waters overlying the continental shelf, suggesting Chinese fishers were harvesting sharks from these coastal environments. While some of the sharks caught by fishers from Point Alones were likely being consumed at the village, historical records suggest a significant number of fins from harvested Tope Sharks were also likely being exported to China and other diaspora communities.

Fiskar skriker när de dör

“Fish Scream When They Die. Corall Reefs as an Example of the Interplay Between Man and Nature in Three Texts by Ian Fleming” The essay focuses on one aspect of Ian Fleming’s interest in nature and ecology: the interplay between man and nature in the novel Live and Let Die (1954), and in two short stories: ”The Hildebrand Rarity” (1960) and “Octopussy” (1962). All three texts have coral reefs at the centre of climactic scenes, in which Nature strikes back at evil and criminal individuals: the mobster Mr. Big uses a coral reef as an outré instrument of execution; he ends his life as leopard shark food when he falls into the sea at the reef. The gangster Milton Krest poisons an entire coral reef with thousands of fish just to catch one single specimen of an extremely rare fish, the Hildebrand Rarity; his murderer stuffs the Hildebrand Rarity into his mouth, and the spines of the dorsal and anal fins catch inside his cheeks, thus causing him to suffocate. The thief and murderer Dexter Smythe tries to kill a deadly scorpion fish, which he plans to feed to the cephalopod Octopussy. The fish pricks his skin with its poisonous fins. Before Smythe is paralysed, he is pulled down into the deep by Octopussy, thus dying two deaths. At a time when research on popular literature in Sweden is scarce, and the combination ecocriticism/popular literature is clearly underexploited in Swedish literary criticism, it would seem urgent to show the possibilities of this research area.

Laboratory-based measures of temperature preference and metabolic thermal sensitivity provide insight into the habitat utilisation of juvenile California horn shark (Heterodontus francisci) and leopard shark (Triakis semifasciata).

Laboratory-based studies examining fish physiological and behavioural responses to temperature can provide important insight into species-specific habitat preferences and utilisation, and are especially useful in examining vulnerable life stages that are difficult to study in the wild. This study couples shuttle box behavioural experiments with respirometry trials to determine the temperature preferences and metabolic thermal sensitivity of juvenile California horn shark (Heterodontus francisci) and leopard shark (Triakis semifasciata). As juveniles, these two species often occupy similar estuarine habitats but display contrasting behaviours and activity levels - H. francisci are relatively sedentary, whereas T. semifasciata are more active and mobile. This study shows that juvenile H. francisci and T. semifasciata have comparable thermal preferences and occupy similar temperature ranges, but H. francisci metabolism is more sensitive to acute changes in temperature as expressed through a higher Q10 (H. francisci=2.58; T. semifasciata=1.97; temperature range: 12-24°C). Underlying chronic temperature acclimation to both warm (21°C) and cool (15°C) representative seasonal temperatures did not appear to significantly affect these parameters. These results are discussed in the context of field studies examining known distributions, habitat and movement patterns of H. francisci and T. semifasciata to better understand the role of temperature in species-specific behaviour. Juvenile H. francisci likely target thermally stable environments, such as estuaries that are close to their preferred temperature, whereas juvenile T. semifasciata metabolism and behaviour appear less dependent on temperature.

Epidermal Microbiomes of Leopard Sharks (Triakis semifasciata) Are Consistent across Captive and Wild Environments.

Characterizations of shark-microbe systems in wild environments have outlined patterns of species-specific microbiomes; however, whether captivity affects these trends has yet to be determined. We used high-throughput shotgun sequencing to assess the epidermal microbiome belonging to leopard sharks (Triakis semifasciata) in captive (Birch Aquarium, La Jolla California born and held permanently in captivity), semi-captive (held in captivity for <1 year in duration and scheduled for release; Scripps Institute of Oceanography, San Diego, CA, USA) and wild environments (Moss Landing and La Jolla, CA, USA). Here, we report captive environments do not drive epidermal microbiome compositions of T. semifasciata to significantly diverge from wild counterparts as life-long captive sharks maintain a species-specific epidermal microbiome resembling those associated with semi-captive and wild populations. Major taxonomic composition shifts observed were inverse changes of top taxonomic contributors across captive duration, specifically an increase of Pseudoalteromonadaceae and consequent decrease of Pseudomonadaceae relative abundance as T. semifasciata increased duration in captive conditions. Moreover, we show captivity did not lead to significant losses in microbial α-diversity of shark epidermal communities. Finally, we present a novel association between T. semifasciata and the Muricauda genus as Metagenomes associated genomes revealed a consistent relationship across captive, semi-captive, and wild populations. Since changes in microbial communities is often associated with poor health outcomes, our report illustrates that epidermally associated microbes belonging to T. semifasciata are not suffering detrimental impacts from long or short-term captivity. Therefore, conservation programs which house sharks in aquariums are providing a healthy environment for the organisms on display. Our findings also expand on current understanding of shark epidermal microbiomes, explore the effects of ecologically different scenarios on benthic shark microbe associations, and highlight novel associations that are consistent across captive gradients.

The Relative Abundance and Occurrence of Sharks off Ocean Beaches of New South Wales, Australia.

Simple SummaryCoastal sharks are especially susceptible to anthropogenic pressures due to their use of nearshore habitats. It is therefore necessary to distinguish species-specific variation in occurrence among ocean beaches and identify key environmental drivers that may influence shark distribution patterns. For swell-influenced coastal beaches, however, information on shark abundance and occurrence is still limited. The relative abundance and occurrence of sharks off 42 ocean beaches of New South Wales (NSW), Australia, was investigated using a long-term drone-based monitoring program from 2017–2021. Overall, there were 36,384 drone flights conducted, sighting a total of 281 sharks. Shark observations occurred in <1% of drone flights, indicating that potentially dangerous sharks, and sharks in general, are rare off NSW beaches. Key environmental predictors, such as the distance to the nearest estuary, headland, and island, as well as ocean temperature and wave height, were identified for species-specific shark distribution. This study demonstrated that existing drone-based monitoring programs used to reduce shark bite incidents can also provide valuable information about the distribution of potentially dangerous, vulnerable, and endangered coastal sharks. This information will be beneficial for implementing evidence-based conservation strategies and may also assist in minimising negative human-shark interactions.There is still limited information about the diversity, distribution, and abundance of sharks in and around the surf zones of ocean beaches. We used long-term and large-scale drone surveying techniques to test hypotheses about the relative abundance and occurrence of sharks off ocean beaches of New South Wales, Australia. We quantified sharks in 36,384 drone flights across 42 ocean beaches from 2017 to 2021. Overall, there were 347 chondrichthyans recorded, comprising 281 (81.0%) sharks, with observations occurring in <1% of flights. Whaler sharks (Carcharhinus spp.) had the highest number of observations (n = 158) recorded. There were 34 individuals observed for both white sharks (Carcharodon carcharias) and critically endangered greynurse sharks (Carcharias taurus). Bull sharks (Carcharhinus leucas), leopard sharks (Stegostoma tigrinum) and hammerhead species (Sphyrna spp.) recorded 29, eight and three individuals, respectively. Generalised additive models were used to identify environmental drivers for detection probability of white, bull, greynurse, and whaler sharks. Distances to the nearest estuary, headland, and island, as well as water temperature and wave height, were significant predictors of shark occurrence; however, this varied among species. Overall, we provide valuable information for evidence-based species-specific conservation and management strategies for coastal sharks.

Global assessment of shark strandings

AbstractMarine wildlife stranding is a global phenomenon, and for some taxonomic groups, these events are well monitored and documented. Although sharks are among the most threatened vertebrates, strandings have historically been neglected, with little information on this topic currently available. To address this knowledge gap, a systematic review on scientific publications from indexed databases, multimedia material and citizen science databases was performed. A total of 3150 reports were recovered, with strandings dating back to 1880 including 89 species of sharks from 22 families. Both single/small‐scale and mass stranding events were observed. Species ranged from coastal to oceanic, with reports for small‐, medium‐ and large‐sized sharks. Leopard (Triakis semifasciata, Triakidae), brown smooth‐hound (Mustelus henlei, Triakidae) and salmon sharks (Lamna ditropis, Laminidae) were the species with most records. Females stranded significantly more than males, but juveniles and adults were affected in the same proportion. Shark strandings were reported for 47 countries, and the United States was the most representative location, highlighting the states of California and Oregon. Survival rates were extremely low, indicating that stranded sharks are more vulnerable that other taxonomic groups. Potential and putative causes were identified, being similar to those suggested for marine mammal strandings. Our results indicate that although they occur to a lesser extent when compared to mammals, shark strandings are neglected, and urgent measurements are necessary to better understand, document and to properly respond to these events.

The Epidermal Microbiome Within an Aggregation of Leopard Sharks (Triakis semifasciata) Has Taxonomic Flexibility with Gene Functional Stability Across Three Time-points

The epidermis of Chondrichthyan fishes consists of dermal denticles with production of minimal but protein-rich mucus that collectively, influence the attachment and biofilm development of microbes, facilitating a unique epidermal microbiome. Here, we use metagenomics to provide the taxonomic and functional characterization of the epidermal microbiome of the Triakis semifasciata (leopard shark) at three time-points collected across 4 years to identify links between microbial groups and host metabolism. Our aims include (1) describing the variation of microbiome taxa over time and identifying recurrent microbiome members (present across all time-points); (2) investigating the relationship between the recurrent and flexible taxa (those which are not found consistently across time-points); (3) describing the functional compositions of the microbiome which may suggest links with the host metabolism; and (4) identifying whether metabolic processes are shared across microbial genera or are unique to specific taxa. Microbial members of the microbiome showed high similarity between all individuals (Bray–Curtis similarity index = 82.7, where 0 = no overlap, 100 = total overlap) with the relative abundance of those members varying across sampling time-points, suggesting flexibility of taxa in the microbiome. One hundred and eighty-eight genera were identified as recurrent, including Pseudomonas, Erythrobacter, Alcanivorax, Marinobacter, and Sphingopxis being consistently abundant across time-points, while Limnobacter and Xyella exhibited switching patterns with high relative abundance in 2013, Sphingobium and Sphingomona in 2015, and Altermonas, Leeuwenhoekiella, Gramella, and Maribacter in 2017. Of the 188 genera identified as recurrent, the top 19 relatively abundant genera formed three recurrent groups. The microbiome also displayed high functional similarity between individuals (Bray–Curtis similarity index = 97.6) with gene function composition remaining consistent across all time-points. These results show that while the presence of microbial genera exhibits consistency across time-points, their abundances do fluctuate. Microbial functions however remain stable across time-points; thus, we suggest the leopard shark microbiomes exhibit functional redundancy. We show coexistence of microbes hosted in elasmobranch microbiomes that encode genes involved in utilizing nitrogen, but not fixing nitrogen, degrading urea, and resistant to heavy metal.

Marine resource recovery in Southern Thailand during COVID-19 and policy recommendations

COVID-19 and subsequent government health containment measures have slowed down economic activities worldwide, particularly tourism. With the number of foreign tourists entering Thailand during 2020 and 2021 greatly diminished, the number of tourists at marine and coastal attractions in Southern Thailand has declined as well. This study found evidence of a relationship between the decline of the number of tourists and marine resource recovery. This recovery appears in the form of cleaner beaches, clearer seawater and increased sighting of marine animals. Between 2020 and 2021, official reports found increased sighting of dugongs, dolphins, blacktip reef sharks, whale sharks, leopard sharks, sea turtles, green turtles, hawksbill turtles, and false killer whales at marine national parks in Southern Thailand. The study also found that, prior to the COVD-19 outbreak, the number of tourists at Patong Beach and Maya Bay exceeded their tourism carrying capacities. Finally, this study proposes eight policy measures related to tourism management for marine resource sustainability: conservation and recreation zoning, enforcing marine park closure, redesigning marine park entrance fee systems, ensuring adequate recreational facilities, stricter enforcement of the law, promoting alternative tourism sites, encouraging more inclusivity and participation in decision making processes, and enhancing public awareness.

Physiological response to capture stress in endemic Southern African catsharks (family Scyliorhinidae).

Fishing is the major threat to marine fish populations, particularly to higher trophic-level predators such as sharks. Many sharks, and other fish, are caught as commercial by-catch or for recreational purposes and then released; therefore, it is important to understand the effects of capture stress on their physiology and subsequent survival. Nonetheless, although important data have been collected for some sharks, there can be substantial interspecific differences, and the consequences of capture stress are still poorly understood for most species. In this study, the authors quantified the physiological effect of capture on four catshark species endemic to Southern Africa, which are regularly discarded as by-catch and targeted by recreational fisheries. Fifteen pyjama sharks, nine leopard sharks and nine shysharks were captured, and a blood sample was collected to measure their physiological response to capture stress. Stressed blood biochemistry was compared to samples obtained after the sharks recovered for 24 h in an underwater pen. Levels of pH and K+ were significantly lower, and lactate levels were significantly higher, in sharks immediately after capture stress compared to after the 24 h recovery period. Although the species showed a similar response to capture stress, they differed significantly in pH, K+ and lactate levels, and there was some evidence of size affecting the strength of the response to capture stress. The substantial physiological response elicited by even the relatively quick capture event in this study suggests that common fishing practices will have a stronger impact on catshark homeostasis because of longer hooking times and more disruptive fishing gear. Although the relationship between survival and physiological changes elicited by capture needs further investigation, the results provide further evidence that minimizing stress would be beneficial to maximize the survival of sharks and other fish following capture-and-release fishing practices.

Determining sexual maturity in male leopard sharks in San Francisco Bay, California

Determining sexual maturity in male leopard sharks in San Francisco Bay, California

Amino acid isotope discrimination factors for a carnivore: physiological insightsfrom leopard sharks and their diet.

Stable isotopes are important ecological tools, because the carbon and nitrogen isotopic composition of consumer tissue reflects the diet. Measurements of isotopes of individual amino acids can disentangle the effects of consumer physiology from spatiotemporal variation in dietary isotopic values. However, this approach requires knowledge of assimilation patterns of dietary amino acids. We reared leopard sharks (Triakis semifasciata) on diets of squid (Loligo opalescens; 1250days; control sharks) or squid then tilapia (Oreochromis sp.; switched at 565days; experimental sharks) to evaluate consumer-diet discrimination factors for amino acids in muscle tissue. We found that control sharks exhibited lower nitrogen isotope discrimination factors (∆15N) than most previous consumer studies, potentially because of urea recycling. Control sharks also had large carbon isotope discrimination factors (∆13C) for three essential amino acids, suggesting microbial contributions or fractionation upon assimilation. Compared to controls, experimental sharks exhibited higher ∆13C values for four amino acids and ∆15N values for seven amino acids, corresponding with differences between diets in δ13C and δ15N values. This suggests that not all amino acids in experimental sharks had reached steady state, contrary to the conclusion of a bulk isotope study of these sharks. Our results imply that (1) the magnitude of a shift in dietary δ13C and δ15N values temporarily influences the appearance of discrimination factors; (2) slow turnover of amino acid isotopes in elasmobranch muscle precludes inferences about seasonal dietary changes; (3) elasmobranch discrimination factors for amino acids may be affected by urea recycling and microbial contributions of amino acids.

METAGENOMIC NEXT-GENERATION SEQUENCING REVEALS MIAMIENSIS AVIDUS (CILIOPHORA: SCUTICOCILIATIDA) IN THE 2017 EPIZOOTIC OF LEOPARD SHARKS (TRIAKIS SEMIFASCIATA) IN SAN FRANCISCO BAY, CALIFORNIA, USA

During March to August of 2017, hundreds of leopard sharks ( Triakis semifasciata) stranded and died on the shores of San Francisco Bay, California, US. Similar mass stranding events occurred in 1967 and 2011, but analysis of those epizootics was incomplete, and no etiology was confirmed. Our investigation of the 2017 epizootic revealed severe meningoencephalitis in stranded sharks, raising suspicion for infection. We pursued a strategy for unbiased pathogen detection using metagenomic next-generation sequencing followed by orthogonal validation and further screening. We showed that the ciliated protozoan pathogen, Miamiensis avidus, was present in the central nervous system of leopard ( n=12) and other shark species ( n=2) that stranded in San Francisco Bay but was absent in leopard sharks caught elsewhere. This ciliated protozoan has been implicated in devastating outbreaks in teleost marine fish but not in wild elasmobranchs. Our results highlight the benefits of adopting unbiased metagenomic sequencing in the study of wildlife health and disease.

Using eOceans diver data to describe contemporary patterns of marine animal populations: A case study of sharks in Thailand

Many marine animals around the world are threatened by a variety of anthropogenic activities, yet there is often a paucity of data to monitor patterns in abundance and distribution or to evaluate human interventions. The new citizen science program eOceans helps to fill this gap by gathering observations of various marine animals from worldwide ocean explorers. In 2012, a dedicated Thailand-wide census of sharks, and other animals, began as a collaboration between eOceans scientists and the dive tourism industry. Using the observations from 9524 dives (9357 h underwater) logged by 169 divers on 153 sites, we describe the spatial and temporal patterns of sharks in coastal Thailand. A total of 12 shark species were encountered, most commonly (67%) as individuals, and were observed on 11% of all dives, on 59% of sites, in all months and years. The two most frequently encountered species were blacktip reef (Carcharhinus melanopterus) and leopard sharks (Stegostoma fasciatum). Many species had peak encounter rates in summer, but aggregated in various seasons in different years. Mating events and nursery sites were rarely observed, and only for blacktip reef and whitetip reef (Triaenodon obesus) sharks. These results could be of value to species- or region-specific biologists, ecologists and fisheries scientists, as well as to managers and policy makers that could use the findings to monitor future trends and prioritize conservation strategies. Moreover, this study highlights the value that collaborative citizen science projects could have in support of marine science, management and conservation efforts worldwide.

Temperature effects on the blood oxygen affinity in sharks.

In fish, regional endothermy (i.e., the capacity to significantly elevate tissue temperatures above ambient via vascular heat exchangers) in the red swimming muscles (RM) has evolved only in a few marine groups (e.g., sharks: Lamnidae, Alopiidae, and teleosts Scombridae). Within these taxa, several species have also been shown to share similar physiological adaptations to enhance oxygen delivery to the working tissues. Although the hemoglobin (Hb) of most fish has a decreased affinity for oxygen with an increase in temperature, some regionally endothermic teleosts (e.g., tunas) have evolved Hbs that have a very low or even an increased affinity for oxygen with an increase in temperature. For sharks, however, blood oxygen affinities remain largely unknown. We examined the effects of temperature on the blood oxygen affinity in two pelagic species (the regionally endothermic shortfin mako shark and the ectothermic blue shark) at 15, 20, and 25°C, and two coastal ectothermic species (the leopard shark and brown smooth-hound shark) at 10, 15, and 20°C. Relative to the effects of temperature on the blood oxygen affinity of ectothermic sharks (e.g., blue shark), shortfin mako shark blood was less affected by an increase in temperature, a scenario similar to that documented in some of the tunas. In the shortfin mako shark, this may act to prevent premature oxygen dissociation from Hb as the blood is warmed during its passage through vascular heat exchangers. Even though the shortfin mako shark and blue shark occupy a similar niche, the effects of temperature on blood oxygen affinity in the latter more closely resembled that of the blood in the two coastal shark species examined in this study. The only exception was a small, reverse temperature effect (an increase in blood oxygen affinity with temperature) observed during the warming of the leopard shark blood under simulated arterial conditions, a finding that is likely related to the estuarine ecology of this species. Taken together, we found species-specific differences in how temperature affects blood oxygen affinity in sharks, with some similarities between the regionally endothermic sharks and several regionally endothermic teleost fishes.

Historical reconstruction of Gulf of California shark fishery landings and species composition, 1939–2014, in a data-poor fishery context

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 oxyrinchus 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.

Bicarbonate-sensing soluble adenylyl cyclase is present in the cell cytoplasm and nucleus of multiple shark tissues.

The enzyme soluble adenylyl cyclase (sAC) is directly stimulated by bicarbonate (HCO3 −) to produce the signaling molecule cyclic adenosine monophosphate (cAMP). Because sAC and sAC‐related enzymes are found throughout phyla from cyanobacteria to mammals and they regulate cell physiology in response to internal and external changes in pH, CO2, and HCO3 −, sAC is deemed an evolutionarily conserved acid‐base sensor. Previously, sAC has been reported in dogfish shark and round ray gill cells, where they sense and counteract blood alkalosis by regulating the activity of V‐type H+‐ ATPase. Here, we report the presence of sAC protein in gill, rectal gland, cornea, intestine, white muscle, and heart of leopard shark Triakis semifasciata. Co‐expression of sAC with transmembrane adenylyl cyclases supports the presence of cAMP signaling microdomains. Furthermore, immunohistochemistry on tissue sections, and western blots and cAMP‐activity assays on nucleus‐enriched fractions demonstrate the presence of sAC protein in and around nuclei. These results suggest that sAC modulates multiple physiological processes in shark cells, including nuclear functions.