Re-estimation of juvenile Isurus oxyrinchus growth in the Mexican Pacific through a multimodel inference approach and verification of growth band periodicity.

An update of the age and growth for juveniles of the short fin mako shark (I. oxyrinchus) from the Mexican Pacific is presented, based on the analysis of growth band counts from dorsal vertebrae of 198 individuals [110 females, 74-231 cm of total length (TL) and 88 males, 72-231 cm TL) caught during 2008-2018. New available information on vertebral growth band periodicity (biannual deposition in juveniles) and the convenience of using vertebrae form the dorsal region over the cervical region to count growth bands, as well as a multimodel approach, were used. The von Bertalanffy (VB) growth model, Gompertz, logistic and two parameters of VB (2-VB) were fitted to the length-at-age. Only ages ≤6 years were used for the fitting of the models and their performance was compared with the small-sample bias-corrected form of the Akaike information criterion (AICc), their differences ( ∆ i ) and weights ( w i ). Following a multimodel inference approach, the model averaged asymptotic length ( L ¯ inf ), length-at-age 0 ( L ¯ 0 ) and their unconditional standard error ( SE ¯ ), were estimated for each sex scenario using the three-parameter version of each model. The precision of growth band counts was acceptable for the different methods used and by two different readers. The centrum edge analysis (CEA) and marginal increment analysis (MIA) did not support the hypothesis of biannual band pair formation for juveniles, likewise for adults the periodicity could not be verified due to the small sample of large animals. Age was estimated assuming the formation of two pairs of growth bands per year during the first 5 years and one pair of bands per year afterwards considering direct validation information. The estimated ages in years ranged from 0-14 for females and 0-6 for males. The Kimura likelihood ratio test showed no differences in the growth curves of juveniles by sex (P > 0.05). According to the AICc, the 2-VB model better fitted the length-at-age data for combined sexes (Linf = 386.4 cm, k = 0.12 years-1 , L0 = 70 cm). The model averaged L ¯ inf and L ¯ 0 were 378.3 cm ( SE ¯ = 64.5 ) and 69.5 cm ( SE ¯ = 6.3 ), respectively. The growth parameters determined for juveniles of I. oxyrinchus are similar to those estimated in other regions, showing relatively fast growth rate as previously reported, medium longevity in comparison to other shark species and natural mortality close to that reported in the last stock assessment for the North Pacific Ocean. These life-history parameters should be considered to evaluate the population in the region and to develop better fishery management and conservation measures.

Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator.

Overfishing is a primary cause of population declines for many shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fisheries-dependent and of questionable quality for many species of commercially exploited pelagic sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory shortfin mako shark (Isurus oxyrinchus) in the western North Atlantic Ocean. Forty satellite-tagged shortfin mako sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (F = 0.19-0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015-0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates of F were greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fisheries-dependent methodology.

Virtual reconstruction of the skeletal labyrinth of two lamnid sharks (Elasmobranchii, Lamniformes).

The first virtual reconstruction of the skeletal labyrinth of the porbeagle shark Lamna nasus and the shortfin mako shark Isurus oxyrinchus is presented here using high-resolution micro-computed tomography. The results, in comparison with previously published information, suggest relationships between skeletal labyrinth morphology and locomotion mode in chondrichthyans, but also show that further studies are required to establish such connections. Nevertheless, this study adds to the knowledge of the skeletal labyrinth morphology in two apex elasmobranch species.

Intraoral Radiographic Study of the Pulp Cavity of the Shortfin Mako Shark (Isurus Oxyrinchus).

The shortfin mako shark (Isurus oxyrinchus) is a large pelagic predator that inhabits coastal and ocean waters. It has several teeth arranged in rows that run from the rostral to the lingual face. These teeth are in several stages of maturation, where the teeth closest to the rostral face are more mature and functional and the teeth closest to the lingual face are still in development. The tooth supply of the shark is unlimited throughout its life. The mechanism of tooth replacement follows that, when the front teeth are discarded physiologically, the posterior teeth replace it. This study us used a head and dental arch of I. oxyrinchus. Intraoral radiographs were obtained with the aim to show details of the pulp cavity. The study concluded that the pulp diameter varies according to the stage of dental maturation.

A shortfin mako shark circling a finless porpoise with damaged caudal fin.

Research on predator-prey interactions between sharks and cetaceans remain limited. Here, we report on a video of a shortfin mako shark circling a finless porpoise with a damaged caudal fin in the Seto Inland Sea, Japan. The finless porpoise was neither emaciated nor inactive, but unable to swim effectively due to the complete lack of a caudal fin. Some circumstantial evidence, including a bite mark on the porpoise's head, strongly suggests that the mako shark attacked it. Furthermore, the possible time difference between the two injuries the porpoise sustained may reflect the shark's hunting tactics. While mako sharks primarily feed on small fish and cephalopods, this observation suggests they also may prey on live cetaceans more often than previously thought.

Juvenile survival and movements of two threatened oceanic sharks in the North Atlantic Ocean inferred from tag-recovery data.

Understanding population dynamics, movements, and fishing mortality is critical to establish effective shark conservation measures across international boundaries in the ocean. There are few survival and dispersal estimates of juveniles of oceanic shark species in the North Atlantic despite it being one of the most fished regions in the world. Here we provide estimates of dispersal, survival, and proportion of fishing mortality in the North Atlantic for two threatened oceanic sharks: the blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus). Our results are based on multi-event models applied to tag-recovery data of 700 blue sharks and 132 shortfin makos tagged over a decade. A total of 60 blue sharks (8.57% of tagged) and 30 makos (22.73%) were recovered by the longline fishery between 2009 and 2017. Tag-reporting rate (percentage of returned information when a tagged shark was caught) was estimated to be high (0.794 ± 0.232 SE). Mean annual survival, as predicted from the models, was higher for blue shark (0.835 ± 0.040 SE) than for shortfin mako (0.618 ± 0.189 SE). Models predicted that fishing caused more than a half of total mortality in the study area for both species (0.576 ± 0.209), and more than a third of tagged individuals dispersed from the study area permanently (0.359 ± 0.073). Our findings, focused mainly on juveniles from oceanic areas, contribute to a better understanding of shark population dynamics in the North Atlantic and highlight the need for further conservation measures for both blue shark and shortfin mako, such as implementing efficient bycatch mitigation measures and static/dynamic time-area closures in the open ocean.

Three complete mitochondrial genomes of shortfin mako sharks, Isurus oxyrinchus, from the Atlantic and Pacific Oceans.

We present complete mitogenome sequences of three shortfin mako sharks (Isurus oxyrinchus) sampled from the western Pacific, and eastern and western Atlantic oceans. Mitogenome sequence lengths ranged between 16,699 bp and 16,702 bp, and all three mitogenomes contained one non-coding control region, two rRNA genes, 22 tRNA genes, and 13 protein-coding genes. Comparative assessment of five mitogenomes from globally distributed shortfin makos (the current three and two previously published mitogenomes) yielded 98.4% identity, with the protein-coding genes ATP8, ATP6, and ND5 as the most variable regions (sequence identities of 96.4%, 96.5%, and 97.6%, respectively). These mitogenome sequences contribute resources for assessing the genetic population dynamics of this endangered oceanic apex predator.

Demographic Analysis of Shortfin Mako Shark (Isurus oxyrinchus) in the South Pacific Ocean.

The shortfin mako shark (Isurus oxyrinchus) demonstrates low productivity and is thus relatively sensitive to fishing. Natural mortality (M) and fishing mortality (F) data are critical to determine their population dynamics. However, catch and fishing effort data are unavailable for this species in the South Pacific Ocean, making stock assessments difficult. Demographic quantitative methods aid in analyzing species with limited data availability. We used a two-sex stage-structured matrix population model to examine the demographic stock status of mako sharks. However, data-limited models to determine fishery management strategies have limitations. We performed Monte Carlo simulations to evaluate the effects of uncertainty on the estimated mako shark population growth rate. Under unfished conditions, the simulations demonstrated that the mako sharks showed a higher finite population growth rate in the 2-year reproductive cycle compared to the 3-year reproductive cycle. Protecting immature mako sharks led to a higher population growth rate than protecting mature mako sharks. According to the sex-specific data, protecting immature male and female sharks led to a higher population growth rate than protecting mature male and female sharks. In conclusion, sex-specific management measures can facilitate the sustainable mako shark conservation and management.

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.

Isotopic variation in blood components based on their biochemistry and physiology: A comparison between sharks and fur seals.

Research using stable isotopes analysis (SIA) of carbon (δ13 C) and nitrogen (δ15 N) in blood components is lacking, because of the challenge of sample collection, processing, and storage in remote areas. There also is a paucity of information regarding the effect of tissue biochemical composition on isotopic ratios with few comparisons among taxa. We collected blood samples from shortfin mako sharks (n = 70; 2016) and Guadalupe fur seals (n = 25; 2017). All samples were centrifuged to obtain plasma from sharks and serum from the Guadalupe fur seals, and all the samples were prepared for SIA and analyzed using a Costech 4010 elemental analyzer interfaced with a Delta V Plus isotope ratio mass spectrometer. We found significant differences between plasma δ13 C values of shortfin mako sharks (-17.6 ± 0.9‰) and serum of Guadalupe fur seals (-20.3 ± 1.2‰), but we did not find any differences for δ15 N values between the two species. The differences in δ13 C values between species are probably due to the specific blood composition and to the different biochemical characteristics and different adaptations within taxa. These findings highlight the importance of further research on the influence of biochemistry features on isotopic results, in this way a more accurate assessment will be possible for this factor, separating it from the dietary influences on stable isotopic values.

The complete mitochondrial genome of an Atlantic Ocean Shortfin Mako Shark, Isurus oxyrinchus.

We report the first complete mitochondrial genome of a shortfin mako shark from the Atlantic Ocean. The genome had 16,700 base pairs and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a non-coding D-loop. There were 81 individual differences compared to the published mitochondrial genome of a shortfin mako from the Pacific Ocean, with most variability found in protein coding genes, especially ND5, ND3, and ND1. These highly variable genes may be useful population markers in future studies, and availability of a second mitogenome will assist with future, genome-scale studies of this IUCN Endangered species.

Mercury in blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) from north-eastern Atlantic: Implication for fishery management.

Pelagic sharks (blue shark Prionace glauca and shortfin mako Isurus oxyrinchus) caught by long-line Spanish and Portuguese fleets in the NE Atlantic, were sampled at Vigo fish market (Spain) for total mercury (Hg) analysis. Hg concentration in white muscle increased with size and weight in both species, but at a higher rate in shortfin mako than in the blue shark. No difference was found with sex, year and season. Spatial variation was observed in the blue shark with higher Hg values in the North of the Azorean archipelago, but not in the shortfin mako. These high-level predators are particularly susceptible to bioaccumulate contaminants (Hg) in their tissues (muscle). However, a significant positive relationship between Hg concentration and trophic level (δ15N) of individuals was observed only in the shortfin mako. Most sharks landed were juveniles which presented Hg concentration lower than the maximum limit allowed by the European Union (1mgkg-1 wet weight) for marketing. However, concentrations above this threshold were most recorded in blue sharks larger than 250cm total length (TL) and in shortfin makos larger than 190cm TL, raising the question of the commercialization of large-sized individuals.

A Comparative Study of Intratesticular Ductules in the Spermatogenically Active Testes of Shortfin Mako and Thresher Sharks.

This comparative study of the radial testes of sexually mature thresher sharks (Alopias vulpinus) and shortfin mako sharks (Isurus oxyrinchus) describes the histology of the three-tiered network of sperm-carrying ductules in the testis and the lymphomyeloid tissue associated with it, namely the epigonal organ. In both species, a testis → epigonal gradient was evident regarding the thickness of the ductule epithelial lining and subepithelial investment of connective tissue. Ductules straddling the testis-epigonal border often displayed luminal leukocytes and various signs of regression, including the progressive thickening of the ductule epithelial lining, dissolution of the cytoplasm, and loss of normal histoarchitecture. In Isurus, large amorphous areas formed due to the fusion of neighboring regressing ductules. The epigonal organ of Alopias additionally revealed circular degenerative sperm-containing, Hassall-like bodies with either a degenerate or cellular appearance, the latter the result of cell proliferative activity (as shown by proliferating cell nuclear antigen (PCNA) immunohistochemistry) in an expanding outer border comprising cells with intensely PCNA immunoreactive slender and oblong nuclei. The latter cells exhibited a periphery-to-center transformation of their nuclei, at which stage they were PCNA-negative and most likely in a terminally differentiated state as they phagocytized the cell debris in the degenerate core. Intermediate stages of these circular bodies were a rarity. The relationship between these degenerate bodies, and the common occurrence of blind pockets in the epithelial linings and non-apoptosis-related degenerate patches in the apical cytoplasmic regions of the irregular shaped ductules in Alopias is unclear, and needs further elucidation. Anat Rec, 299:1435-1448, 2016. © 2016 Wiley Periodicals, Inc.

The complete mitochondrial genome of the shortfin mako, Isurus oxyrinchus (Chondrichthyes, Lamnidae).

The complete mitochondrial genome of the shortfin mako (Isurus oxyrinchus) was determined by using a PCR-based method. The total length of mitochondrial DNA is 16,701 bp and includes 13 protein-coding genes, 2 ribosomal RNA, 22 transfer RNA genes, 1 replication origin region, and 1 control region. The mitochondrial gene arrangement of the tiger tail seahorse is also matching the one observed in the most vertebrate creatures. Base composition of the genome is A (28.8%), T (28.0%), C (28.0%), and G (15.2%) with an A + T rich hallmark as that of other vertebrate mitochondrial genomes.

Descripción Anatómica del Esqueleto de Tiburón Mako (Isurus oxyrinchus) / Anatomical Description of Mako Shark (Isurus oxyrinchus) Skeleton

La especie Isurus oxyrinchus, conocido también como Tiburón Mako o Marrajo Común, pertenece a la familia Lamnidae, de la clase Condrictria, cuya principal característica es su esqueleto, el cual está constituido completamente por cartílago. Se considera una especie vulnerable según la UICN (Unión Internacional para la Conservación de la Naturaleza) como consecuencia de su utilización en la industria alimentaria y, en el último tiempo, a la caza deportiva, debido a su gran velocidad. Tiene una distribución cosmopolita, encontrándose en los océanos Pacífico, Atlántico, Índico, así como también en el Mar Mediterráneo y Mar Rojo. En Chile se tiene registro de su captura desde el norte hasta la región centro-sur del país. Son ejemplares de gran tamaño, llegando a medir hasta 3,5 metros y pesar alrededor de 570 kg. El presente trabajo corresponde a un estudio anatómico de un ejemplar juvenil de Tiburón Mako, obtenido por pesca incidental en las costas del Maule, Chile. La descripción del esqueleto se realizó de manera sistemática por segmentos: cráneo, columna y aletas. Se obtuvo un registro fotográfico de los resultados. De acuerdo a lo observado, podemos indicar que existe gran similitud con lo descrito en el Tiburón Espinoso y Tiburón Blanco, salvo algunas variaciones de forma en el esqueleto de esta especie, que corresponderían a las características que le confieren su aptitud para nadar a gran velocidad. La presente descripción, permite ampliar el conocimiento de la anatomía del Tiburón Mako, generando información de esta especie poco estudiada.

The species Isurus oxyrinchus, also known as Mako Shark or commonly as Shortfin Mako, belongs to the Lamnidae family, of the Condrictis class. The main anatomical feature of this class is a skeleton fully composed of cartilage. Considered to be a vulnerable species according to the IUCN (International Union for Conservation of Nature), as a result of its extensive use in food industry and hunting sports due to its high speed. It has a cosmopolitan distribution, being found in the Pacific, Atlantic and Indian Oceans, the Mediterranean Sea and the Red Sea. In Chile, a variety of this species has a distribution from the North to the Central-South regions of the country (according to industrial fishing data). Specimens are large in size, reaching 3.5 m and around 570 kg of weigh. The aim of this work was to perform a gross anatomy study of a juvenile Mako Shark, obtained by incidental fishing off the coast of Maule, Chile. The description of the skeleton was carried out in a systematic way by segments: skull, spine and fin. A photographic record of the specimen was obtained. According to the results, there is great similarity with what was described for the prickly shark and white shark, except for some shape variations in the skeleton. These differences could be explained by its ability to swim at high speed. The present description allows expanding knowledge of the anatomy of the Mako Shark, generating more information on this species.