Prionace Research Articles

Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean.

This study used data provided by the Chinese Longline Fishery Scientific Observer Programme from the tropical eastern Atlantic Ocean to estimate the reproductive parameters of the blue shark (Prionace glauca) and crocodile shark (Pseudocarcharias kamoharai). Sizes ranged from 80 to 298 cm fork length (FL) for blue sharks and from 48 to 99 cm FL for crocodile sharks. Sexual segregation was observed during different months for both sharks. The sex ratio for blue sharks was 1.38 F:1 M, and 1 F:2.79 M for crocodile sharks. The size of adult blue sharks ranged from 144 to 280 cm for males and from 174 to 298 cm for females; and that of crocodile sharks from 63 to 97 cm for males and 78-99 cm for females. The size at 50% of maturity for blue sharks was estimated at 191.7 cm FL for females and 197.5 cm FL for males, and that of crocodile sharks was assessed at 84.9 cm FL for females and 78.5 cm FL for males. Most sexually matured females were pregnant; their means were 207.2 ± 16.4 cm FL for blue sharks and 89.4 ± 4.3 cm FL for crocodile sharks. Mature sizes for both species were significantly different among months. Embryonic sizes also varied widely among months for crocodile sharks, but a slight change was recorded for those of blue sharks. The observed mean size at birth and litter size were 34.5 cm FL and 37 ± 12 for the blue sharks, and that of the crocodile sharks, 39.5 cm FL and a dominant four embryos in the uterus. Due to the observed increasing catch trend of blue sharks and the slow reproductive cycle of crocodile sharks, this study presents the need of implementing conservation measures to ensure the sustainability of both species in their habitat.

Fisheries-Independent Evidence of Longline Fisheries Impact on the Threatened Mediterranean Blue Shark Prionace Glauca in The Waters Around the Balearic Islands (Spain)

Fisheries-Independent Evidence of Longline Fisheries Impact on the Threatened Mediterranean Blue Shark Prionace Glauca in The Waters Around the Balearic Islands (Spain)

Depredation by Killer Whales (Orcinus orca) on a Blue Shark (Prionace glauca) in Northeastern Atlantic

Depredation by Killer Whales (Orcinus orca) on a Blue Shark (Prionace glauca) in Northeastern Atlantic

Trophic interactions between shark species on the western coast of Baja California Sur: Inferences from stable isotopes

On the west coast of Baja California Sur, the shark species Mustelus henlei, Carcharhinus falciformis, Prionace glauca, Isurus oxyrinchus, and Sphyrna zygaena are of economic importance and coexist in the same ecosystem. However, the trophic role of each species in this ecosystem is poorly understood. Stable isotopes of nitrogen and carbon (δ15N, δ13C) have been used as an indicator of trophic habitat at different time scales, showing the foraging area and trophic position of sharks. The isotopic values in the muscle and blood of five shark species were analyzed on the southwest coast of Baja California Sur. The isotopic values of P. glauca, S. zygaena and C. falciformis indicated a trophic habitat in oceanic areas, which is a characteristic of these species considering that they feed mainly on mesopelagic cephalopods; whereas M. henlei and I. oxyrinchus showed a benthic diet in oceanic waters. The highest trophic position based on muscle and blood results was in S. zygaena, while the lowest trophic position was in the tissue of C. falciformis, probably because this species feeds on a higher proportion of the crustacean Pleuroncodes planipes. Some of these species share prey and forage in the same area.

Shark discards in selective and mixed-species pelagic longline fisheries.

The conservation status of several pelagic shark species is considered vulnerable with declining populations, yet data on shark fishing mortality remain limited for large ocean regions. Pelagic sharks are increasingly retained by mixed-species fisheries, or are discarded and not reported by selective fisheries for tunas (Thunnus spp.) or swordfish (Xiphias gladius). We estimated the fishing mortality of sharks (landings plus discard mortalities) in a South African-flagged pelagic longline fishery with diverse targeting and discard behaviour. A hierarchical cluster analysis was used to stratify the fleet according to the relative proportions of tunas, swordfish, blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) landed by individual vessels between 2013 and 2015. A spatial analysis of logbook data indicated that subfleets operated in distinct fishing areas, with overlap. Approximately 5% of all commercial longlines set during 2015 were sampled by a fisheries-independent observer, and the species, discard ratios and physical condition at discard of 6 019 captured sharks were recorded. Blue sharks and shortfin makos dominated observed shark catches, which were comprised of nine species and two species groups. Some 47% of observed sharks were retained and 20% were discarded in good physical condition. Only 4% of shortfin makos were discarded, compared to 68% of blue sharks. Blue shark discard mortality rates were twice as high as published at-vessel mortality rates, suggesting that onboard handling, among other factors, contributed to discard mortalities. Extrapolation to total fishing effort indicated a near 10-fold increase in blue shark and shortfin mako fishing mortality compared to an earlier study (1998-2005). Escalating shortfin mako fishing mortality was attributed to increased targeting to supply higher market demand. Discarding of blue sharks by selective fishing for tunas and swordfish had a greater impact on their fishing mortality than retention by shark-directed fleets. Higher levels of observer sampling are required to increase confidence in discard ratio estimates.

Ecological Risk Assessment with integrated genetic data for three commercially important shark species in the Mexican Pacific

Sharks are highly vulnerable species due to their biological characteristics. Productivity and Susceptibility Analysis (PSA) is a useful method to assess the vulnerability of shark populations to prioritize management strategies. Given that molecular and genetic tools have played an important role in the conservation of vulnerable populations and species, the objective of this study was to evaluate the ecological risk of Prionace glauca, Isurus oxyrinchus, and Alopias vulpinus in the Mexican Pacific by incorporating genetic information into PSA. We hypothesized that the integration of genetic variables such as genetic structure and diversity (Fst, h, and π), in a PSA will allow us to discriminate species with the same vulnerability index. The results of PSA-1 indicated that I. oxyrinchus, and A. vulpinus were at high ecological risk with identical vulnerability values (v = 2.2). Our results suggest that PSA with the combination of genetic attributes could be a useful tool for the application of conservation strategies or management policies, making easier the interpretation of results when the productivity or susceptibility attributes do not provide enough variation to prioritize between species or populations analyzed. Nevertheless, more studies that combine fishery and genetic information of commercially important sharks are needed.

Does Subunit Composition Influence the Intermolecular Crosslinking of Fish Collagen? A Study with Hake and Blue Shark Skin Collagens.

Acid-soluble collagens from European hake and Blue shark skin were isolated, characterized, and compared. As the structure of collagen determines its function, the final objective of this study was to investigate biochemical differences between both collagens to identify future potential applications. Chromatographic behavior revealed differences in collagen from both species. Increases of temperature and stirring time produced no effect on European hake collagen solubility in the mobile phase, resulting in the same chromatographic profiles. Conversely, the application of temperature and stirring-time increments showed a positive effect on Blue shark collagen solubility, resulting in different chromatographic profiles and observing higher molecular weight components when sample is incubated at 50 °C (15 min) after 48 h stirring. To test if the different chromatographic behavior exhibited by both collagens could be influenced by differences in subunit composition (alpha-chains), cation exchange chromatography was employed to separate collagen subunits. The electrophoretic patterns and gel permeation chromatography with light-scattering detection (GPC-LS) results of the obtained cation exchange peak fractions revealed differences regarding subunit composition between both species, influencing the crosslinking pattern. This is the first comparative study using GPC-LS to provide information of European hake and Blue shark collagen subunit composition.

Effect of pelagic longline bait type on species selectivity: a global synthesis of evidence

Fisheries can profoundly affect bycatch species with ‘slow’ life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait’s chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.

When prey becomes killer: does a double lethal attack on a blue shark reveal a precise defensive strategy in young swordfish?

AbstractIn this paper a rare case of a double swordfish mortal attack against an adult blue shark (Prionace glauca) is reported. A female blue shark, with a total length of 3 m, was found stranded along the southern Sicilian coast (Strait of Sicily, Mediterranean Sea) on 30 May 2018. The analysis of this carcass revealed the presence of two swordfish bill fragments, impaled in the shark head; the former on the snout, the latter near the eye. The results of anatomical and computed tomography scanning analysis on the head of the blue shark showed that the larger bill fragment (19.7 cm) probably determined the death of this animal, having been impaled in a vital point, just behind the right eye. The analysis of both these events and other similar swordfish-shark interactions reported in the literature makes possible the hypothesis that young swordfish specimens put in place a precise defensive strategy against their potential predators or competitors, aimed at hitting vulnerable and vital points and delivering a mortal blow.

Species composition of the largest shark fin retail-market in mainland China

Species-specific monitoring through large shark fin market surveys has been a valuable data source to estimate global catches and international shark fin trade dynamics. Hong Kong and Guangzhou, mainland China, are the largest shark fin markets and consumption centers in the world. We used molecular identification protocols on randomly collected processed fin trimmings (n = 2000) and non-parametric species estimators to investigate the species composition of the Guangzhou retail market and compare the species diversity between the Guangzhou and Hong Kong shark fin retail markets. Species diversity was similar between both trade hubs with a small subset of species dominating the composition. The blue shark (Prionace glauca) was the most common species overall followed by the CITES-listed silky shark (Carcharhinus falciformis), scalloped hammerhead shark (Sphyrna lewini), smooth hammerhead shark (S. zygaena) and shortfin mako shark (Isurus oxyrinchus). Our results support previous indications of high connectivity between the shark fin markets of Hong Kong and mainland China and suggest that systematic studies of other fin trade hubs within Mainland China and stronger law-enforcement protocols and capacity building are needed.

Involving stakeholders in the evaluation of management strategies for shortfin mako (Isurus oxyrinchus) and blue shark (Prionace glauca) in the Spanish longline fisheries operating in the Atlantic Ocean

Shortfin mako (Isurus oxyrinchus) and blue shark (Prionace glauca) are a relevant bycatch in the Spanish surface longline fisheries that operate in the Atlantic Ocean. Concern has been raised after the 2017 and 2019 shortfin mako evaluations for the Northern Atlantic stock. It stated the population being overfished and suffering from overfishing. Also blue shark is subject to high extraction rates in the Atlantic Ocean. Few data and uncertainty in assessment results suggest that further management strategies could be taken into account for both species. This study evaluated different fisheries management strategies for shortfin mako and blue shark in the Atlantic Ocean from the stakeholders' perspective. Personal interviews were conducted with Spanish fishermen and surveys were sent to scientists and non-governmental organizations (NGOs). Local Ecological Knowledge was considered to be useful as fishermen possess unique expertise based on their continued interaction with the species and environment. Interviews allowed understanding the fishermen's perception on variations of stock abundance, distribution patterns, size of capture and seasonal fluctuations for both species. SWOT (Strength, Weaknesses, Opportunities and Threats)-analysis was used to study the different management measures. Main management strategies proposed by all stakeholders to reduce the bycatch of both species were spatial-temporal closure, minimum size and quotas. The Sole Bank was suggested as a temporarily closed area to protect blue shark juveniles during the summer months. The participation of stakeholders enriched the knowledge available and provided a broader data set now available for decision makers in the corresponding regional fisheries management organization (RFMOs).

Can multi‐species shark longline fisheries be managed sustainably using size limits? Theoretically, yes. Realistically, no

Abstract Size limits are a common fisheries management strategy that are applied to many fisheries and species. Most size limits use a minimum legal size to protect adult fish as per the ‘reproduce at least once’ paradigm, where stock collapse becomes impossible if every adult can produce one spawner prior to harvest. These approaches can be useful in fisheries where determining catch is difficult and therefore catch limits can be ineffective and potentially cause stock decline. Shark longline fisheries can be complicated to manage due to a deficiency of species‐level reporting. Catch limits are therefore difficult to determine, creating a need for other management measures. Here, three different size‐based management approaches were tested using the shark longline fishery from Papua New Guinea as a case study. These approaches included minimum size, maximum size and harvest slot approaches. Age‐structured Leslie matrix models revealed a broad range of productivities for 12 commonly caught species, ranging from low population growth rates of 1% per year for pelagic thresher sharks Alopias pelagicus to >33% per year for blue sharks Prionace glauca. Therefore, different harvest strategies were required for each species to be fished sustainably. However, management could be applied by grouping similar and easily distinguishable groups of species together. Synthesis and applications. The most pragmatic harvest strategy for all shark species included in this study was to limit harvest to mature individuals using minimum legal sizes. This provided sufficient resilience for all species to tolerate higher levels of fishing mortality than the Papua New Guinea (PNG) longline fishery could impose. Legal minimum lengths were derived from the largest length‐at‐maturity within each species group. However, while this produced a sustainable harvest strategy, issues with selectivity, post‐release mortality, interactions with other fisheries, economic viability and illegal, underreported and unregulated fishing were challenges to restricting fishing to the correct size classes and overall management efficacy. Therefore, while theoretically viable harvest strategies were outlined, it is apparent that size limits would not ensure that these shark species are fished sustainably. Therefore, the PNG longline fishery cannot operate sustainably if it were to reopen using size limits as its sole management strategy.

Mercury concentrations in the tissues of blue shark (Prionace glauca) from Sagami Bay and cephalopods from East China Sea

The toxicity of mercury (Hg), is generally known, and around 90% of Hg exist as methylmercury (CH3Hg+) in marine organism. Mercury concentrates in sharks and whales, which are at the top of the food chain as predators to cephalopods. The concentrations of Hg in liver and muscle of blue shark, caught in Sagami Bay, and in digestive gland and mantles of Todarodes pacificus, Sepia madokai, and Uroteuthis edulis caught in East China Sea were measured and analyzed. The Hg concentrations in the sharks, squids, and cuttlefishes determined in this study were almost same as those in the other sea regions. In addition, the Hg concentration in the blue shark was higher in the muscle than in the liver. In S. madokai and U. edulis, Hg accumulated in the digestive gland but not in the mantle. Although the Hg concentration in the digestive gland of T. pacificus is lower than those of S. madkai and U edulis, Hg concentration in the mantle is critically higher. More than 90% of Hg is present as CH3Hg+ in muscle of blue shark and mantle of T. pacificus. This feature is explained due to amino acids with the thiol groups and chain genes in the muscle of blue shark as well as in the mantle of T. pacificus. Myosin in the mantle of T. pacificus and blue shark enhances the stability of CH3Hg+. The amount of Hg in the digestive gland of T. pacificus could be too large to store; thus, Hg is released to the mantle, whereas the nutrients in the digestive gland of T. pacificus are supplied to other tissues. It is considered that the muscle fiber of T. pacificus is strong; therefore, large amounts of myosin levels may be present in T. pacificus than in S. madokai and U. edulis.

Ecological responses to blue water MPAs.

Marine protected areas (MPAs) can contribute to protecting biodiversity and managing ocean activities, including fishing. There is, however, limited evidence of ecological responses to blue water MPAs. We conducted the first comprehensive evaluation of impacts on fisheries production and ecological responses to pelagic MPAs of the Pacific Remote Islands Marine National Monument. A Bayesian time series-based counterfactual modelling approach using fishery-dependent data was used to compare the temporal response in the MPAs to three reference regions for standardized catch rates, lengths, trophic level of the catch and species diversity. Catch rates of bigeye tuna, the main target species (Kingman/Palmyra MPA, causal effect probability >99% of an 84% reduction; 95% credible interval: -143%, -25%), and blue shark (Johnston MPAs, causal effect probability >95%) were significantly lower and longnose lancetfish significantly higher (Johnston MPAs, causal effect probability >95%) than predicted had the MPAs not been established, possibly from closing areas near shallow features, which aggregate pelagic predators, and from ‘fishing-the-line’. There were no apparent causal impacts of the MPAs on species diversity, lengths and trophic level of the catch, perhaps because the MPAs were young, were too small, did not contain critical habitat for specific life-history stages, had been lightly exploited or experienced fishing-the-line. We also assessed model-standardized catch rates for species of conservation concern and mean trophic level of the catch within and outside of MPAs. Displaced effort produced multi-species conflicts: MPAs protect bycatch hotspots and hotspots of bycatch-to-target catch ratios for some at-risk species, but coldspots for others. Mean trophic level of the catch was significantly higher around MPAs, likely due to the aggregating effect of the shallow features and there having been light fishing pressure within MPAs. These findings demonstrate how exploring a wide range of ecological responses supports evidence-based evaluations of blue water MPAs.

Mavi Köpekbalığı Prionace glauca (Linnaeus, 1758)'nın (Chondrichthyes: Charcharhinidae) Fethiye Açıklarında (Akdeniz) Kılıç Paraketası ile Yakalanması

On 25 December 2012, a specimen of Prionace glauca (Linnaeus, 1758) was caught by a swordfish longliner along with 9 swordfish together off Fethiye at a depth of 1200 m. The specimen caught was measured as TL and weighed (kg), and photographed. The specimen was 85 cm TL and 7 kg. According to the previous studies, blue sharks especially observed abundantly in northern Aegean Sea, and can be accepted very rare incidental catch from the Turkish coasts owing to weak presuppose of swordfish fishery. However, there is an important place of blue sharks in the global fin trade area. Therefore, population trend of this shark species is swift decreasing.

Application of DNA barcoding to detect mislabeling of fish fillet products from Jabodetabek’s market

Mislabeling of fish fillet product is one of the key issues in food safety and sustainability. Species identification is an important step of fish fillet traceability and DNA barcoding has been proved as a standard method. Fourty seven 47 fish fillet products were collected from modern and traditional markets in the Jabodetabek area. DNA barcoding was used to analyze the compliance of the product label. This research also highlighted that near threatened (NT), Vulnerable (VU), endangered (EN), and critically endangered (CR) species considered to be facing a high risk of extinction have been used as a substitution in fish fillet product. The application of DNA mini-barcoding gives better resolution in species identification for commercial species. From this research, we found that there are some mislabeled fish fillet products, including blue shark meat that is listed as Near Threatened in IUCN Red List in one of the products.

Spiral valve parasites of blue and common thresher sharks as indicators of shark feeding behaviour and ecology.

This study documented the parasite faunas of the spiral valves of blue sharks Prionace glauca (L. 1758) and common thresher sharks Alopias vulpinus (Bonnaterre, 1788) caught in the California Current Large Marine Ecosystem (CCLME) north of the Mexican border. The spiral valves of 18 blue and 19 thresher sharks caught in the CCLME from 2009 to 2013 were examined for parasites. Seven parasite taxa were found in blue sharks and nine in threshers. The tetraphyllidean cestode Anthobothrium sp. (78% prevalence) was the most common parasite in blue sharks, and the phyllobothriid cestode Paraorygmatobothrium sp. (90% prevalence) was the most common in threshers. An adult nematode of the genus Piscicapillaria was found in threshers for the first time and may be a new species. Adult individuals of Hysterothylacium sp. were found in both shark species. The adult acanthocephalan Rhadinorhynchus cololabis and remains of the parasitic copepod Pennella sp. - both parasites of Pacific saury, Cololabis saira - were found in the intestines of threshers, indicating recent feeding on saury. This study paves the way for a more comprehensive examination, including more samples and a wider variety of shark species, to provide a greater understanding of shark feeding behaviour and possibly provide information on shark population biology.

Characterization of fish collagen from blue shark skin and its application for chitosan- collagen composite coating to preserve red porgy (Pagrus major) meat.

Pepsin soluble collagen (PSC) was extracted from blue shark (Prionace glauca) skin and was used for chitosan-collagen composite coating to investigate coating effects on fresh red porgy (Pagrus major) fillet quality during storage at 4°C. Total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), pH, K value, drip loss, and sensory evaluation scores were measured as deterioration indexes. Results show that coating by 1% of chitosan solutions containing 0.0%-0.8% of PSC significantly improved most deterioration indexes. Coating by 1% of chitosan solution containing 0.8% of PSC yielded the best results for K value, drip loss, and sensory evaluation, although the other indexes show no clear PSC concentration dependence. These results indicate 1% of chitosan solution containing 0.8% of PSC as the best coating formulation examined in this study. PRACTICAL APPLICATIONS: Aquatic products have high contents of water and protein. Their qualities are likely to decline because of endogenous chemical and enzyme reactions, and also because of the role of spoilage and pathogenic microorganisms during storage. The edible collagen and chitosan coating suggested by this research is biodegradable, biocompatible, cost effective, and is able to meet the requirements for food quality and storage duration. Pepsin soluble collagen (PSC) is an aquatic product processing by-product that makes the maximum use of resources. As described herein, a composite formulation comprising collagen and chitosan improves preservation effects of different types of coatings. A more high-quality and effective edible coating formulation was obtained, thereby extending the red porgy fillet shelf life.

Assessment of trends in the Portuguese elasmobranch commercial landings over three decades (1986–2017)

Portugal plays a major role in shark, skate and ray fisheries in the European Union. With the decline of these animals raising concerns amongst scientists all over the world, we set out to provide an updated assessment on elasmobranch landings in Portugal between 1986 and 2017. The dataset analysed in this study consisted of 15,521 records, each with information concerning the species (or higher taxonomic level), port, month, year, and weight of fish landed. A non-parametric change points assessment statistical technique was used to evaluate important changes in landings throughout the time series. Principal components analysis was also performed to mean values of landings per year for the most captured species, and similar analysis was conducted using fishing ports instead of year, for the same sub-set of species / taxa. According to the data, more than 143 thousand metric tons of elasmobranchs were landed in Portuguese ports between 1986 and 2017, divided by 58 taxa of sharks, skates and rays. The most landed taxa were demersal rays and skates (Raja spp.), followed by spotted dogfishes (Scyliorhinus spp.), blue shark (Prionace glauca), Portuguese dogfish (Centroscymnus coelolepis), leafscale gulper shark (Centrophorus squamosus), gulper shark (Centrophorus granulosus) and shortfin mako (Isurus oxyrinchus). Together, these seven taxa accounted for more than 75% of all landings. Several cases of misreporting were identified and discussed. Overall, landings of elasmobranchs in Portugal show marked decreases and changes in composition, with deep-sea sharks being the most influential group during the studied period.

Mercury and arsenic in processed fins from nine of the most traded shark species in the Hong Kong and China dried seafood markets: The potential health risks of shark fin soup

Shark fin is one of Asia's most valued dried seafood products, with over 80 shark species traded in Hong Kong [HK]. We analyzed processed shark fins from mainland China and HK markets (n = 267) for mercury, methyl‑mercury, and arsenic, to inform consumers, policy makers and public health officials on the health risks of ingesting fins from nine of the most common shark species in the fin trade. Fins from all species frequently exceed Hg limits established by HK authorities. Most of the mercury found is in the form of methyl‑mercury (69.0 ± 33.5%). Five species surpass methyl‑mercury PTWIs and blue shark fins can exceed inorganic arsenic BMDL0.5. Species-of-origin was a significant predictor of heavy metal concentrations, with higher mercury concentrations associated with coastal sharks and lower arsenic levels found with increasing shark trophic level. Species-specific labeling would help consumers avoid shark fin products that pose the highest health risk.