Isurus Oxyrinchus Research Articles

New Insights Into the Seasonal Movement Patterns of Shortfin Mako Sharks in the Gulf of Mexico

Highly mobile apex predators such as the shortfin mako shark (mako shark;Isurus oxyrinchus) serve an important role in the marine ecosystem, and despite their declining populations and vulnerability to overexploitation, this species is frequently harvested in high abundance in both commercial and recreational fisheries. In 2017, the North Atlantic stock was deemed overfished and to be undergoing overfishing and was recently listed in CITES Appendix II. Effective management of this species can benefit from detailed information on their movements and habitat use, which is lacking, especially in the Gulf of Mexico, a potential mating and parturition ground. In this study, we used satellite telemetry to track the movements of mako sharks in the western Gulf of Mexico between 2016 and 2020. In contrast to previous studies that have primarily tagged juvenile mako sharks (>80% juveniles), ∼80% of sharks tagged in this study (7 of 9) were presumed to be mature based on published size-at-maturity data. Sharks were tracked for durations ranging from 10 to 887 days (mean = 359 days; median = 239 days) with three mature individuals tracked for >2 years. Mako sharks tagged in this study used more of the northwestern Gulf of Mexico than reported in previous movement studies on juveniles, suggesting potential evidence of size segregation. While one mature female remained in the Gulf of Mexico over a >2-year period, predominantly on the continental shelf, two mature males demonstrated seasonal migrations ∼2,500 km from the tagging location off the Texas coast to the Caribbean Sea and northeastern United States Atlantic coast, respectively. During these migrations, mako sharks traversed at least 12 jurisdictional boundaries, which also exposed individuals to varying levels of fishing pressure and harvest regulations. Movement ecology of this species, especially for mature individuals in the western North Atlantic, has been largely unknown until recently. These data included here supplement existing information on mako shark movement ecology and potential stock structure that could help improve management of the species.

Predation of satellite-tagged juvenile loggerhead turtles Caretta caretta in the Northwest Atlantic Ocean

We present evidence of predator interactions with 8 juvenile loggerhead sea turtles Caretta caretta equipped with pop-up satellite archival transmitting tags (PSATs) following incidental capture in the Northwest Atlantic. Ingestion of PSATs occurred up to 5 mo after tagging and was identified by an abrupt change in depth distribution, a stabilization and/or increase in ambient temperature and a marked drop in light levels to near zero, with cessation of diel light level cycling. In some cases, following expulsion from the digestive tract of predators, positively buoyant PSATs descended to the sea floor or beyond the programmed release depth threshold (1800 m), indicating that they remained tethered to the indigestible carapaces of turtles and that the entire turtle was originally consumed. PSAT data, combined with the sudden termination of satellite uplinks from 2 loggerheads also equipped with platform transmitting terminals, provided additional evidence of whole-turtle predation. PSAT data indicated that both endothermic and ectothermic sharks ingested tags. Based on PSAT-logged temperature data, dive patterns and geographic distribution, the following shark species were considered as candidate predators: white, porbeagle, shortfin mako, tiger and blue. This study represents the first analysis of data collected by loggerhead turtle PSATs inside predators. The results expand the list of shark species known to prey on large juvenile loggerheads and point to the importance of acknowledging predation as an important source of mortality for loggerhead turtles in the Northwest Atlantic Ocean.

Reproductive biology of Isurus oxyrinchus captured by the south Brazilian surface longline commercial fleet in the Southwest Atlantic Ocean, with data on CPUE and size distribution by sex

Reproductive biology of <i>Isurus oxyrinchus</i> captured by the south Brazilian surface longline commercial fleet in the Southwest Atlantic Ocean, with data on CPUE and size distribution by sex

Accessing Multiple Paternity in the Shortfin Mako Shark (Isurus oxyrinchus).

Multiple paternity has been demonstrated in a variety of sharks with different reproductive modes (i.e., viviparous, ovoviviparous, adelphophagy, oviparous), although the number of sires per litter varies considerably among species. To date, such analyses have focused mainly on coastal and nearshore shark species due to the difficulty in sampling oceanic sharks. In the present study, we observed multiple paternity in the oceanic shark Isurus oxyrinchus from seven polymorphic microsatellite loci and three litters collected from Nanfangao Fishing Port. Paternity tests showed that an average of 4.6 sires were assigned to each litter of I. oxyrinchus using COLONY software, and that the average number of sires dropped to 2.5 when using GERUD. These findings suggest that multiple paternity could be a common reproductive strategy used by the shortfin mako shark, and that this mating system should be integrated into a demographic model to make more accurate population projections and risk analyses in the future.

Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction

Inferring the size of extinct animals is fraught with danger, especially when they were much larger than their modern relatives. Such extrapolations are particularly risky when allometry is present. The extinct giant shark †Otodus megalodon is known almost exclusively from fossilised teeth. Estimates of †O. megalodon body size have been made from its teeth, using the great white shark (Carcharodon carcharias) as the only modern analogue. This can be problematic as the two species likely belong to different families, and the position of the †Otodus lineage within Lamniformes is unclear. Here, we infer †O. megalodon body dimensions based on anatomical measurements of five ecologically and physiologically similar extant lamniforms: Carcharodon carcharias, Isurus oxyrinchus, Isurus paucus, Lamna ditropis and Lamna nasus. We first assessed for allometry in all analogues using linear regressions and geometric morphometric analyses. Finding no evidence of allometry, we made morphological extrapolations to infer body dimensions of †O. megalodon at different sizes. Our results suggest that a 16 m †O. megalodon likely had a head ~ 4.65 m long, a dorsal fin ~ 1.62 m tall and a tail ~ 3.85 m high. Morphometric analyses further suggest that its dorsal and caudal fins were adapted for swift predatory locomotion and long-swimming periods.

Comparative eye and liver differentially expressed genes reveal monochromatic vision and cancer resistance in the shortfin mako shark (Isurus oxyrinchus)

The shortfin mako, Isurus oxyrinchus is an oceanic pelagic shark found worldwide in tropical and subtropical waters. However, the understanding of its biology at molecular level is still incipient. We sequenced the messenger RNA isolated from eye and liver tissues. De novo transcriptome yielded a total of 705,940 transcripts. A total of 3774 genes were differentially expressed (DEGs), with 1612 in the eye and 2162 in the liver. Most DEGs in the eye were related to structural and signaling functions, including nonocular and ocular opsin genes, whereas nine out of ten most overexpressed genes in the liver were related to tumor suppression, wound healing, and human diseases. Furthermore, DEGs findings provide insights on the monochromatic shark vision and a repertory of cancer-related genes, which may be insightful to elucidate shark resistance to cancer. Therefore, our results provide valuable sequence resources for future functional and population studies.

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.

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).

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.

Species composition and size distribution of sharks and rays caught in Bali Strait and its surrounding area and its relation to fisheries management

Muncar is one of the shark production centers in Java, where the fishing ground in Bali Strait and its surrounding area. Routine data collection was carried out from May 2018 to April 2019 at the Brak Fish Market and the Muncar Coastal Fishing Port (PPP), Banyuwangi to determine the species composition and size distribution of sharks and rays caught in Bali Strait and its surrounding area. Data collection was done by census and almost of all individuals were identified to species level and and measured. During the study, 3.551 individuals of sharks and rays were landed in this port, consisting of 75 species from 25 families (48 species of sharks, one species of ghost shark and 26 rays species). The most common types of sharks belong to Carcharhinidae and for the rays was Dasyatidae. Among these, thirteen species were listed in Appendix II CITES, i.e. Carcharhinus falciformis, Alopias pelagicus, A. superciliosus, Isurus oxyrhinchus, I. paucus, Sphyrna lewini, S. zygaena, Mobula mobular, M. tarapacana, M. thrustoni, Glaucostegus typus, Rhynchobatus australiae and Rhyna ancylostoma. Most of sharks and rays caught were juvenile to adolescent and at immature or maturing stages.

Offshore recreational fisheries of large vulnerable sharks and teleost fish in the Mediterranean Sea: first information on the species caught

Large-sized pelagic sharks and teleost fish are vulnerable to overexploitation by professional fisheries but little is known about the species caught by recreational fishing. This study presents for the first time in the Mediterranean an evaluation of the catch of pelagic sharks and teleost fish being caught by recreational fishermen by analyzing publicly available videos posted on social media. The analysis reveals that several vulnerable species, including the blue shark Prionace glauca, the shortfin mako Isurus oxyrinchus, the thresher shark Alopias vulpinus, the sixgill shark Hexanchus griseus, the swordfish Xiphias gladius, and the Mediterranean spearfish Tetrapturus belone are caught by offshore recreational fishermen, with the blue shark and the swordfish being the most commonly caught species. The majority of individuals caught are juveniles that are mostly released back to sea, issues that are in agreement with field studies. New measures related to handling practices are proposed to protect these species.

MEDLEM database, a data collection on large Elasmobranchs in the Mediterranean and Black seas

The Mediterranean Large Elasmobranchs Monitoring (MEDLEM) database contains over 3000 records (more than 4000 individuals) of large elasmobranch species from 20 different countries around the Mediterranean and Black seas, observed from 1666 to 2017. The main species included in the archive are the devil fish (1 813 individuals), the basking shark (939 individuals), the blue shark (585 individuals) and the great white shark (337 individuals).In the last decades other species such as the shortfin mako (166 individuals), the spiny butterfly ray (138) and the thresher shark (174 individuals) were reported with an increasing frequency. This was possibly due to an increased public awareness on the conservation status of sharks, and a consequent development of new monitoring programmes. MEDLEM does not have a homogeneous reporting coverage throughout the Mediterranean and Black seas and it should be considered as a database of observed species presence. Scientific monitoring efforts in the south-eastern Mediterranean and Black seas are generally lower than in the northern sectors and the absence in our database of some species does not imply their actual absence in these regions. Some considerations are made on the frequency and spatial distribution of records, size structure of the observed individuals for selected species, general area coverage and species involved as by-catch by fishing gear.

Artisanal elasmobranch fisheries of northwestern Baja California, Mexico

Elasmobranch species composition and spatiotemporal variability can often be characterized from landing surveys of local fisheries, with important management implications. In the present study, we describe the elasmobranch landing composition of 4 major artisanal fishing ports in northwestern Baja California, Mexico. Sampling was conducted opportunistically between 1995 and 2010 and included an effort of 684 fishing days. Species composition was gear-dependent and varied with the fishing area, with thresher sharks (Alopias vulpinus) and spiny dogfish (Squalus suckleyi) dominating the catches landed by coastal gill net fisheries, and blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrhinchus) dominating the catches landed by the offshore longline fishery. Size-structure analysis indicated that catches were composed primarily of juveniles for most species, although the catch of mature soupfin sharks (Galeorhinus galeus) increased in longline fisheries during the winter. The results indicate that minor regional differences in elasmobranch species composition occur along the Pacific coast of Baja California and are most likely related to regional oceanographic or habitat differences. The results of this study may form the basis for future efforts to monitor species composition changes over time, to more completely assess elasmobranch populations.

Are circle hooks effective management measures in the pelagic longline fishery for sharks in the Gulf of Gabès?

Abstract This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

Capture-induced exertional rhabdomyolysis in the Shortfin Mako Shark, Isurus oxyrinchus.

Shortfin Mako sharks (Isurus oxyrinchus) are top-order predators in oceanic food chains. They are captured worldwide by commercial and recreational fisheries, but little is known about the effects that fishing has on the homeostasis and longevity of these animals. This study aimed to assess the health of Shortfin Mako sharks captured by recreational fishers off eastern Australia. Twenty-four sharks were captured, and their gender, length, weight, reproductive maturity, and stage were recorded. After blood and urine collection, serum analytes were quantified using standard biochemical methods, whereas urine was analyzed using semi-quantitative reagent strips, microscopic examination, centrifugation, and ammonium sulfate precipitation tests. Six Makos presented with red-brown urine. The means of notable serum analytes were as follows: sodium 276mmol/L, potassium 15.6mmol/L, inorganic phosphate 10.6mmol/L, magnesium 3.3mmol/L, urea 325mmol/L, creatinine 52μmol/L, AST 2806 U/L, CK 240938 U/L, lactate 44.4mmol/L, osmolarity 1160mmol/L, and pH 7.13. These analytes differed from the respective sand tiger shark reference interval, which was used as a proxy for Makos. The red-brown urine was due to myoglobin and had a mean pH of 5.76 that, when combined with red-brown casts, led to a diagnosis of fishing-induced exertional rhabdomyolysis that occurred secondary to lactic acidosis, hypoxia, and hypovolemia. It was further exacerbated by hyperkalemia and acute renal failure, serious complications that often lead to mortality. Practitioners caring for sharks and rays should consider collecting urine from free-living or aquarium animals when they are captured for examination and/or treatment, particularly at times with maximal seawater temperatures.

Updated reproductive parameters for the shortfin mako (Isurus oxyrinchus) in the North Atlantic Ocean with inferences of distribution by sex and reproductive stage

Updated reproductive parameters for the shortfin mako (Isurus oxyrinchus) in the North Atlantic Ocean with inferences of distribution by sex and reproductive stage

Updated reproductive parameters for the shortfin mako (Isurus oxyrinchus) in the North Atlantic Ocean with inferences of distribution by sex and reproductive stage: suppl. fig. 2

Updated reproductive parameters for the shortfin mako (Isurus oxyrinchus) in the North Atlantic Ocean with inferences of distribution by sex and reproductive stage: suppl. fig. 2