Dolphin in lower Shark River Slough

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.

To Madagascar and back: long-distance, return migration across open ocean by a pregnant female bull shark Carcharhinus leucas

A large, pregnant, female bull shark Carcharhinus leucas was tracked migrating from Seychelles across open ocean to south-east Madagascar, c. 2000 km away, and back again. In Madagascar, the shark spent a prolonged period shallower than 5 m, consistent with entering estuarine habitat to pup, and upon return to Seychelles the shark was slender and no longer gravid. This represents an unprecedented return migration across the open ocean for a C. leucas and highlights the need for international collaboration to manage the regional C. leucas population sustainably.

To Madagascar and back: long-distance, return migration across open ocean by a pregnant female bull shark Carcharhinus leucas

A large, pregnant, female bull shark Carcharhinus leucas was tracked migrating from Seychelles across open ocean to south-east Madagascar, c. 2000 km away, and back again. In Madagascar, the shark spent a prolonged period shallower than 5 m, consistent with entering estuarine habitat to pup, and upon return to Seychelles the shark was slender and no longer gravid. This represents an unprecedented return migration across the open ocean for a C. leucas and highlights the need for international collaboration to manage the regional C. leucas population sustainably.

DNA from historical and trophy samples provides insights into white shark population origins and genetic diversity

Characterizing genetic variation by retrospective genotyping of trophy or historical artifacts from endangered species is an important conservation tool. Loss of genetic diversity in top predators such as the white shark Carcharodon carcharias remains an issue, exacerbated in this species by declining, sometimes isolated philopatric populations. We successfully sequenced mitochondrial DNA (mtDNA) D-loop from osteodentine of contemporary South African white shark teeth (from 3 jaws), and from 34 to 129 yr old dried cartilage and skin samples from 1 Pacific Ocean and 5 Mediterranean sharks. Osteodentine-derived sequences from South African fish matched those derived from an individual’s finclips, but were generally of poorer quality than those from skin and cartilage of historical samples. Three haplotypes were identified from historical Mediterranean samples (n = 5); 2 individuals had unique sequences and 3 shared the contemporary Mediterranean haplotype. Placement of previously undescribed mtDNA haplotypes from historical material within both the Mediterranean and Pacific clades fits with the accepted intra-specific phylogeny derived from contemporary material, verifying our approaches. The utility of our methodology is in its provision of additional genetic resources from osteodentine (for species lacking tooth pulp) and cartilage of rare and endangered species held in often uncurated, contemporary and historical dry collections. Such material can usefully supplement estimates of connectivity, population history, and stock viability. We confirm the depauperate haplotype diversity of historical Mediterranean sharks, consistent with founding by a small number of Pacific colonizers. The consequent lack of diversity suggests serious challenges for the maintenance of this top predator and the Mediterranean ecosystem.

DNA from historical and trophy samples provides insights into white shark population origins and genetic diversity

Characterizing genetic variation by retrospective genotyping of trophy or historical artifacts from endangered species is an important conservation tool. Loss of genetic diversity in top predators such as the white shark Carcharodon carcharias remains an issue, exacerbated in this species by declining, sometimes isolated philopatric populations. We successfully sequenced mitochondrial DNA (mtDNA) D-loop from osteodentine of contemporary South African white shark teeth (from 3 jaws), and from 34 to 129 yr old dried cartilage and skin samples from 1 Pacific Ocean and 5 Mediterranean sharks. Osteodentine-derived sequences from South African fish matched those derived from an individual’s finclips, but were generally of poorer quality than those from skin and cartilage of historical samples. Three haplotypes were identified from historical Mediterranean samples (n = 5); 2 individuals had unique sequences and 3 shared the contemporary Mediterranean haplotype. Placement of previously undescribed mtDNA haplotypes from historical material within both the Mediterranean and Pacific clades fits with the accepted intra-specific phylogeny derived from contemporary material, verifying our approaches. The utility of our methodology is in its provision of additional genetic resources from osteodentine (for species lacking tooth pulp) and cartilage of rare and endangered species held in often uncurated, contemporary and historical dry collections. Such material can usefully supplement estimates of connectivity, population history, and stock viability. We confirm the depauperate haplotype diversity of historical Mediterranean sharks, consistent with founding by a small number of Pacific colonizers. The consequent lack of diversity suggests serious challenges for the maintenance of this top predator and the Mediterranean ecosystem.

Oceans Deep: Lesson B (Shark Attack)

Teacher resources for Lesson B in the Discover Oceanography 'Scheme of Work' for use in schools.

Movement patterns and habitat use of the silver tip shark ("Carcharhinus albimarginatus") at the Revillagigedo Archipelago

[EN]The Revillegigedo Archipelago Biosphere Reserve is home to several shark species that spend at least part of their life history associated with oceanic islands associated with hotspots of pelagic biodiversity and in particular with apex predators. Silvertip sharks (Carcharhinus albimarginatus) are is commonly found in all the islands of the archipelago. However, very little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 35 silvertip sharks tagged in three islands of the archipelago (San Benedicto, Socorro and Roca Partida) and monitored for a period of between 7 and 1165 (mean ± SD: 553.7± 354.2) days.

Desk Review of Queensland shark stock assessment for Fisheries Queensland

An independent desk review of the document entitled “Stock assessment of whaler and hammerhead sharks (Carcharhinidae and Sphyrnidae) in Queensland” commissioned by the Queensland’s Department of Agriculture and Fisheries was undertaken during January 15-February 12, 2016.

Assessment of a data-limited, multi-species shark fishery in the Great Barrier Reef Marine Park and south-east Queensland

The status of five species of commercially exploited sharks within the Great Barrier Reef Marine Park (GBRMP) and south-east Queensland was assessed using a data-limited approach. Annual harvest rate, U, estimated empirically from tagging between 2011 and 2013, was compared with an analytically-derived proxy for optimal equilibrium harvest rate, UMSY Lim. Median estimates of U for three principal retained species, Australian blacktip shark, Carcharhinus tilstoni, spot-tail shark, Carcharhinus sorrah, and spinner shark, Carcharhinus brevipinna, were 0.10, 0.06 and 0.07 year-1, respectively. Median U for two retained, non-target species, pigeye shark, Carcharhinus amboinensis and Australian sharpnose shark, Rhizoprionodon taylori, were 0.27 and 0.01 year-1, respectively. For all species except the Australian blacktip the median ratio of U/UMSY Lim was <1. The high vulnerability of this species to fishing combined with life history characteristics meant UMSY Lim was low (0.04-0.07 year-1) and that U/UMSY Lim was likely to be > 1. Harvest of the Australian blacktip shark above UMSY could place this species at a greater risk of localised depletion in parts of the GBRMP. Results of the study indicated that much higher catches, and presumably higher U, during the early 2000s were likely unsustainable. The unexpectedly high level of U on the pigeye shark indicated that output-based management controls may not have been effective in reducing harvest levels on all species, particularly those caught incidentally by other fishing sectors including the recreational sector. © 2016 Elsevier B.V.

Extracting DNA from ‘jaws’: high yield and quality from archived tiger shark (Galeocerdo cuvier) skeletal material

Archived specimens are highly valuable sources of DNA for retrospective genetic/genomic analysis. However, often limited effort has been made to evaluate and optimize extraction methods, which may be crucial for downstream applications. Here, we assessed and optimized the usefulness of abundant archived skeletal material from sharks as a source of DNA for temporal genomic studies. Six different methods for DNA extraction, encompassing two different commercial kits and three different protocols, were applied to material, so-called bio-swarf, from contemporary and archived jaws and vertebrae of tiger sharks (Galeocerdo cuvier). Protocols were compared for DNA yield and quality using a qPCR approach. For jaw swarf, all methods provided relatively high DNA yield and quality, while large differences in yield between protocols were observed for vertebrae. Similar results were obtained from samples of white shark (Carcharodon carcharias). Application of the optimized methods to 38 museum and private angler trophy specimens dating back to 1912 yielded sufficient DNA for downstream genomic analysis for 68% of the samples. No clear relationships between age of samples, DNA quality and quantity were observed, likely reflecting different preparation and storage methods for the trophies. Trial sequencing of DNA capture genomic libraries using 20 000 baits revealed that a significant proportion of captured sequences were derived from tiger sharks. This study demonstrates that archived shark jaws and vertebrae are potential high-yield sources of DNA for genomic-scale analysis. It also highlights that even for similar tissue types, a careful evaluation of extraction protocols can vastly improve DNA yield.

Feeding habits of the blue shark (Prionace glauca) off the coast of Brazil

Estômagos de 222 tubarões-azuis coletados ao longo da costa brasileira foram analisados, sendo 116 da região nordeste e 106 da região sul. Um total de 51 táxons de presas foram identificados. Os itens mais importantes na região sul foram baleias Mysticeti, teleósteos, o peixe gempilídeo Ruvettus pretiosus e o nomeídeo Arioma bondi. Cefalópodes foram mais diversos, com preferência pelas espécies migradoras verticais Histioteuthis spp., Cranchiidae e o polvo epipelágico Ocythoe tuberculata. Na região nordeste, o tubarão-azul consumiu principalmente teleósteos, incluindo o peixe alepisaurídeo Alepisaurus ferox e o gempilídeo Gempylus serpens. Entre os cefalópodes, Histioteuthis spp. e o polvo epipelágico Tremoctopus violaceus foram os itens principais. Predação sobre cardumes foi ocasional, como observada para Arioma bondi. Aves também foram consumidas em ambas as regiões. Puffinus gravis foi o quinto item mais freqüente na região nordeste. Durante o ciclo migratório reprodutivo, o tubarão-azul costuma predar nas adjacências da termoclina, que é mais profunda na região nordeste e mais perto da superfície na região sul.

Record of the goblin shark Mitsukurina owstoni (Chondrichthyes: Lamniformes: Mitsukurinidae) from the south-western Atlantic.

This paper reports the first well-documented specimen of the goblin shark, Mitsukurina owstoni in the south-western Atlantic, based on a mature male measuring 3152 mm total length, caught on 27 November 2008 off the Rio de Janeiro coast, south-east Brazil.

Physicochemical and microbiological changes in dried small-spotted catshark (Scyliorhynus canicula): developing an alternative shark-based salted-dried seafood product

A relatively high proportion of harvested seafood is still wasted due to spoilage, particularly in developing countries, or because they are by-catches or have little economic value, seemingly related to inherent problems linked to unattractive color, flavor, texture, small size, and high-fat content. Thus, many fish and seafood species are still underutilized.

Conservation and management of exploited shark populations based on reproductive value

Several life history traits of sharks result in juveniles being particularly vulnerable to exploitation. However, population level impacts of harvests on juvenile sharks have not been well quantified. This paper examines a range of harvest strategies, including those targeting juveniles. Reproductive value and yield per recruit are used to compare the harvests, which are represented by Leslie matrix models with a harvest matrix. Two species are used as examples: the short-lived Rhizoprionodon taylori and the long-lived Squalus acanthias. Harvests that maintain a stationary population size cause reproductive values to change in opposing ways, but they remove equal fractions of the population's reproductive potential. A new theorem gives population growth as a function of the fraction of reproductive potential removed by a harvest, a relationship useful for comparing harvests on juveniles and adults. Stochastic projections indicate that the risk of depletion is associated with the fraction of reproductive potential removed annually, a measure which encompasses the information in both the selectivity and the rate of fishing mortality. These results indicate the value of focusing conservation efforts on preserving reproductive potential.

Age and growth of the bigeye thresher shark, Alopias superciliosus, from the pelagic longline fisheries in the tropical northeastern Atlantic Ocean, determined by vertebral band counts

The bigeye thresher, Alopias supercilious, is commonly caught as bycatch in pelagic longline fisheries targeting swordfish. Little information is yet available on the biology of this species, however. As part of an ongoing study, observers sent aboard fishing vessels have been collecting set of information that includes samples of vertebrae, with the aim of investigating age and growth of A. supercilious. A total of 117 specimens were sampled between September 2008 and October 2009 in the tropical northeastern Atlantic, with specimens ranging from 101 to 242 cm fork length (FL) (176 to 407 cm total length). The A. supercilious vertebrae were generally difficult to read, mainly because they were poorly calcified, which is typical of Lamniformes sharks. Preliminary trials were carried out to determine the most efficient band enhancement technique for this species, in which crystal violet section staining was found to be the best methodology. Estimated ages in this sample ranged from 2 to 22 years for females and 1 to 17 years for males. A version of the von Bertalanffy growth model (VBGF) re-parameterised to estimate L(0), and a modified VBGF using a fixed L(0) were fitted to the data. The Akaike information criterion (AIC) was used to compare these models. The VBGF produced the best results, with the following parameters: L(inf) = 293 cm FL, k = 0.06 y(-1) and L(0) = 111 cm FL for females; L(inf) = 206 cm FL, k = 0.18 y(-1) and L(0) = 93 cm FL for males. The estimated growth coefficients confirm that A. supercilious is a slow-growing species, highlighting its vulnerability to fishing pressure. It is therefore urgent to carry out more biological research to inform fishery managers more adequately and address conservation issues.