Small Sharks Research Articles

Concentração e retenção do selênio em peixes marinhos

Fish contains considerably higher selenium (Se) concentrations than other kinds of meats, and thus it is considered a major dietary source of this nutrient. At the same time, fish is also the major source of mercury (Hg) in the human diet, whose toxicity can be reduced by the Se through the interaction between both compounds. In consequence, the biological availability of Se is reduced. In the current study, the occurrence of Se was evaluated in commercially available Brazilian marine species, and the retention of Se in sharks (sand tiger shark) was determined. The average levels of Se found in bony fish, gutted corvina ( Micropogonias furnieri), triggerfish ( Balistes capricus), hake and sardine (Sardinella brasiliensis), 0.48 ± 0.18 µg.g –1 , and in cartilaginous fish, small shark (squantina Guggenheim), hammerhead shark, spinner shark, and sand tiger shark, 0.36 ± 0.07 µg.g –1 , did not differ from one another (p > 0.05). In fact, their occurrence was in accordance with the literature data on marine fish. The levels of Se found in the sharks (predatory species) are not enough to establish a stoichiometric relation for the interaction with Hg focusing on the desired toxic protection. The effective Se retention evaluated in the sand tiger shark, after extraction with water, was considered high (minimum of 68.81%) and important taking nutritional and toxicological aspects into account.

CARACTERIZACIÓN DE LA PESCA DEL TIBURÓN MARTILLO <i>SPHYRNA LEWINI </i>, EN LA PARTE EXTERNA DEL GOLFO DE NICOYA, COSTA RICA

En el ámbito nivel mundial, el tiburón martillo (Sphyrna lewini) es una de las especies más afectadas por la sobrepesca y el aleteo. Recientemente se incorporó a la Lista Roja de la UICN como especie en peligro de extinción. El presente estudio pretendió caracterizar la pesca y la distribución de S. lewini en la parte externa del Golfo de Nicoya. Para lograr este propósito, se realizaron muestreos entre marzo del 2006 y mayo del 2007 y se analizaron los tiburones martillo capturados por pescadores artesanales afiliados a la Cooperativa artesanales de Pescadores de Tárcoles (CoopeTárcoles R. L.), que faenan en la parte externa del Golfo de Nicoya. Para cada tiburón, se determinó la longitud total, la zona de pesca donde se capturó y el arte utilizado. En total se analizaron 273 tiburones. Se identificó un área de crianza primaria en el Peñón y se determinó que existe una relación lineal positiva entre la longitud total y la profundidad de la zona de pesca (R2 = 0.4296; p ‹ 0.0001), y la longitud total y la distancia de la zona de pesca de la desembocadura del río Grande de Tárcoles (R2 = 0.4052; p ‹ 0.0001). Los tiburones de menor tamaño (crías) se encontraron en la zona del Peñón, donde las aguas son poco profundas, turbias y productivas, ofreciendo a las crías alimento y protección de los depredadores. Por lo cual, se recomienda proteger esta zona, en particular en marzo, abril y mayo, época de nacimiento de las crías.The scalloped hammerhead shark (Sphyrna lewini) is one of the shark species most impacted by overfishing, and is currently listed by the IUCN Red List as an Endangered. This research sought to characterize the distribution of S. lewini in the external area of Gulf of Nicoya, central Pacific coast of Costa Rica, based on observations from a coastal artisanal fishery. From March 2006 to May 2007, we analyzed scalloped hammerhead shark landings by members of the Tarcoles Artisanal Fishermen's Cooperative (CoopeTárcoles R. L.), who operate in the outer part of the Gulf of Nicoya. We measured the total length of each shark, recorded the reported location of capture, and the gear used. In total, we recorded data for 273 sharks landed. We determined that total length holds a positive linear relationship with the depth of the fishing area (R2 = 0.4296, *** p <.0001) as well as with the distance from the mouth of the Tárcoles River (R2 = 0.4052, *** p <.0001). The smaller sharks (pups) were caught in a fishing site known as Peñon, slightly north of the mouth of the Tarcoles River, where the waters are shallow, turbid and highly productive, providing food and shelter for the pups. As pups mature and attain larger sizes, they move towards deeper waters away from the Tarcoles River, out of the Gulf of Nicoya. We identify Peñon as a primary nursery for scalloped hammerhead sharks, and recommend management actions that seek to reduce fishing effort between March and May, when pups are born.

Don Fawcett (1917–2009): Unlocking Nature's Closely Guarded Secrets

Don Fawcett (1917–2009): Unlocking Nature's Closely Guarded Secrets

The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae)

Sclerorhynchids (extinct sawfishes, Batoidea), pristids (extant sawfish, Batoidea) and pristiophorids (sawsharks, Squalomorphi) are the three elasmobranch families that possess an elongated rostrum with lateral teeth. Sclerorhynchids are the extinct sawfishes of the Cretaceous period, which reached maximum total lengths of 100 cm. The morphology of their rostral teeth is highly variable. Pristid sawfish occur circumtropically and can reach maximum total lengths of around 700 cm. All pristid species are globally endangered due to their restricted habitat inshore. Pristiophorid sawsharks are small sharks of maximum total lengths below 150 cm, which occur in depths of 70–900 m. Close examination of the morphology of pectoral fin basals and the internal structure of the rostrum reveals that sclerorhynchids and pristids evolved independently from rhinobatids, whereas pristiophorids are squalomorph sharks. The elongation of the rostrum may be an adaptation for feeding, as all marine vertebrate taxa that possess this structure are said to use it in the context of feeding.

Temporal variation in the artisanal elasmobranch fishery of Sonora, Mexico

Baseline, species-specific information is largely unavailable for artisanal elasmobranch fisheries, but is essential for the monitoring of exploited populations and the development of effective management plans. Seasonal surveys were conducted during 1998–1999 in Sonora, Mexico to determine the extent and activities of artisanal elasmobranch fisheries operating in the eastern Gulf of California. Nineteen fishing sites were documented, the majority of which (84.2%) targeted elasmobranchs during some part of the year. Most small demersal sharks and rays were landed in bottom set gillnet fisheries that also targeted demersal teleosts, whereas large sharks were usually taken in directed surface longline or, to a lesser extent, drift gillnet fisheries. Rays numerically dominated sampled landings in Sonora (63.4%, n = 100,136), and catch rates exceeded those of sharks during spring and summer months. The shovelnose guitarfish, Rhinobatos productus, was the primary fishery target during these seasons. During autumn, small sharks, especially mustelids ( Mustelus spp.) were numerically dominant, but rays (e.g., Dasyatis dipterura) were also caught in large numbers. Winter landings in Sonora were principally composed of mustelid sharks, which represented the greatest seasonal catch rates of all elasmobranch taxa during this study. Large sharks were of comparably minor importance, with a limited summer fishery operating in the southern part of the state. Variation in catch composition was evident in association with differential interannual environmental conditions (El Niño and La Niña) and seasonal temperature fluctuations. Size composition of landings varied greatly by species, but relatively small size classes of sharks and rays were abundant and large, often gravid females of several ray species (e.g., R. productus and Narcine entemedor) supported spring and summer fisheries in nearshore waters. Populations of many large shark species (e.g., Carcharhinus leucas, Carcharhinus limbatus, Carcharhinus obscurus and Galeocerdo cuvier) have likely been overfished, prompting a shift in effort towards coastal populations of smaller elasmobranchs.

Nursery grounds, movement patterns and growth rates of dusky sharks, Carcharhinus obscurus: a long-term tag and release study in South African waters

Knowledge of movement patterns of sharks in coastal waters is critical for the structuring of regional management plans. Through a long-term tag–recapture program, 9716 dusky sharks (Carcharhinus obscurus) were tagged and released along the east coast of South Africa. A total of 648 C. obscurus, principally small sharks (<100 cm PCL), were recaptured. Most recaptures were within 100 km of the tagging location in the nursery habitat in KwaZulu-Natal (KZN) with small scale movements occurring throughout the year. Forty-eight C. obscurus undertook movements >200 km that indicated a southerly migration between KZN and Eastern/Southern Cape (E/SC) between June and November. Seasonal northerly migrations were less well defined. The largest southerly and northerly movements were 1323 km and 1374 km, respectively. For sharks moving 1–100 km south from their tagging locality in KZN, an increase in displacement occurred between June and September identifying animals beginning their migration to the E/SC. With increasing displacement, there was also an increase in minimum swimming speed. Calculated growth rates of small sharks of 10.3–11.5 cm year–1 were in agreement with current literature values. Established tag–recapture programs provide an important tool in understanding the ecology of early life-stages of coastal shark species.

New Fossil Triakid Sharks from the Early Eocene of Prémontré, France, and Comments on Fossil Record of the Family

During the last two decades, an abundant selachian assemblage has been collected from the late Ypresian (NP12) fossiliferous sands of Premontre (Aisne, northern France) but has received little attention. Sharks of the family Triakidae (Carcharhiniformes) are particularly well represented and all are described and figured herein. Among them, two new species of the genus Galeorhinus are described: G. duchaussoisi sp. nov. and G. louisi sp. nov.; these are compared to the common Paleogene G. ypresiensis which is refigured. Another triakid taxon, the genus Gomphogaleus gen. nov., is described. Most of the triakids have been recorded elsewhere in the North Atlantic region, suggesting a wider distribution than expected for these small sharks during the Paleogene. The present paper updates the list of selachians from Premontre, bringing the number of taxa from 19 to 33 (including 22 sharks and 11 batoids) and improving our knowledge of the ancient North Atlantic Ypresian selachian fauna. Despite this vastly improved record, it is clear that fossil data are still very incomplete and insufficient for calibrating phylogenetic hypotheses of living forms. Review of the Premontre fauna shows that the Triakidae were much more diverse and broadly distributed than at present, suggesting that the limited distribution and low diversity of living forms is probably a recent phenomenon.

Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)

Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average = 1.29 km2) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length = 1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species.

Ontogenetic vertebral growth patterns in the basking shark Cetorhinus maximus

Age and growth of the basking shark Cetorhinus maximus (Gunnerus) was examined using vertebral samples from 13 females (261 to 856 cm total length (TL)), 16 males (311 to 840 cm TL) and 11 specimens of unknown sex (376 to 853 cm TL). Vertebral samples were obtained worldwide from museums and institutional and private collections. Examination of multiple vertebrae from along the vertebral column of 10 specimens indicated that vertebral morphology and band pair (alter- nating opaque and translucent bands) counts changed dramatically along an individual column. Smaller sharks had similar band pair counts along the length of the vertebral column while large sharks had a difference of up to 24 band pairs between the highest and lowest count along the col- umn. Our evidence indicates that band pair deposition may be related to growth and not time in this species and thus the basking shark cannot be directly aged using vertebral band pair counts.

Washing formaldehyde from fixed spirit specimens: a mechanism for the preservation of Megamouth III

The discovery in August 1988 of a rare and massive deep-sea dwelling shark, megachasma pelagios, or megamouth presented the Western Australian Museum with a unique opportunity to study and exhibit the massive 5.2 m, 700 kg shark. In order to ensure that the formalin-preserved specimen was safe to handle and install in a custom-made polyester and fibreglass exhibition tank, it was essential to establish how long it would take to reduce the amount of formaldehyde in the shark to a safe level. Tests on a small shark established that formaldehyde diffuses from the preserved specimen in accordance with the logarithm of the washing time. The same mechanism controlled the release of formaldehyde on Megamouth III and this facilitated a compliant installation procedure. Hazards associated with the exhibition of more than 10,000 L of 70% aqueous ethanol and methods for purification of old storage solutions are reported. The extended washing resulted in a safe amount of formaldehyde being found in the storage solution even after 13 years on exhibition. Conservation challenges and proposed new display methods are also discussed.

Acoustic monitoring of sixgill shark movements in Puget Sound: evidence for localized movement

Understanding the movements of species, particularly those that may exert strong influence on community structure or that may be susceptible to human perturbations, is critical to effectively conserve and manage populations. However, the study of movement behavior in marine fishes has been historically difficult and typically produces a limited amount of data (i.e., start and end points). We use an array of automated acoustic receivers to monitor autumn and winter movement patterns of sixgill sharks ( Hexanchus griseus (Bonnaterre, 1788)) in Puget Sound, Washington, USA. Daily movement of sharks and maximum distance moved from tagging sites varied with size, with larger sharks having shorter daily movements and maximum distances from tagging locations than smaller sharks. Sharks were detected at the same site as the previous day 76% of the time. Movement away from the shark’s tagging location increased slightly over the duration of the study, but most sharks occupied the same sites for most of the study. These relatively small and stable movement patterns could lead to localized, top-down impacts from sixgill sharks and suggest that local human perturbations, such as fishing or pollution, have the potential to negatively affect local populations of sixgill sharks.

Spatial and temporal variation in shark communities of the lower Florida Keys and evidence for historical population declines

Sharks are top predators in many marine ecosystems. Despite recent concerns over declines in shark populations, studies of shark communities in coastal habitats are limited. We used drumlines and longlines to determine shark community composition and habitat affinities in the Florida Keys, USA. Community composition varied among habitats. Catch rates of smaller sharks were highest in protected shallow waters, while large sharks were more abundant in deep channels. Overall probabilities of catching large sharks on drumlines did not vary with water temperature, while catches of small sharks on longlines increased with increasing water temperature. Individual species differed in their responsiveness to variation in water temperatures and habitat. Bait type affected catch rates of some species, suggesting that fishing methods should be considered explicitly in studies describing shark communities or temporal trends in abundance. Catch rates of large-bodied sharks were higher in a remote and protected location compared with similar habitats near inhabited Keys. Also, historical accounts of a shark fishery in the study area during the 1920s suggest substantial declines in large shark abundance and shifts in community composition. By implication, ecosystem impacts of changes in the large shark community may be dramatic and likely occurred before adequate baselines were established.

Fishermen's Lore and the Salmon-Dogfish Fable in Webster's The Duchess of Malfi

IN the third act, scene v of John Webster's The Duchess of Malfi (1623), the duchess despairs over her brother the duke's resolve to rid himself of the shame of her attachment to a commoner, by whom she has borne children. She conveys her grief—and also the folly of her brother's obsession with family honour, an obsession that would deny her a future of true love and happiness—by telling a small fable. The fable involves fishes and evidently is a story of Webster's own invention. The salmon of the fable represents the scorned duchess herself, and the dogfish her arrogant brother. In actuality, as we know, the salmon is a valuable fish that breeds in ‘shallow rivers’ (see below) before dying or returning to the sea, whereas in Webster's time, as today, the spine-finned dogfish (in truth a small shark, a nuisance to commercial fishermen who found them in their nets) remained offshore amid the ‘high … floods’ of the sea. Sad tales befit my woe: I’ll tell you one. A salmon, as she swam unto the sea, Met with a dog-fish, who encounters her With this rough language: ‘Why art thou so bold To mix thyself with our high state of floods, Being no eminent courtier, but one That for the calmest and fresh time o’ th’ year Dost live in shallow rivers, rank'st thyself With silly smelts and shrimps? And darest thou Pass by our dog-ship without reverence?’ ‘O,’ quoth the salmon, ‘sister, be at peace: Thank Jupiter we both have pass’d the net! Our value never can be truly known, Till in the fisher's basket we be shown: I’ th’ market then my price may be the higher, Even when I am nearest to the cook and fire.’ So to great men the moral may be stretched; Men oft be valu’d high, when th’ are the most wretched. … 1

Deep-diving and diel changes in vertical habitat use by Caribbean reef sharks Carcharhinus perezi

Longline sampling (83 sets) supplemented with 6 pop-off archival transmitting (PAT) tag deployments were used to characterize vertical habitat use by Caribbean reef sharks Carcharhinus perezi at Glover's Reef atoll, Belize. Longline catch-per-unit-effort (CPUE) in 2 shallow reef habitats (lagoon <18 m depth, fore-reef < 40 m depth) underwent significant nocturnal increases for sharks larger than 110 cm total length (TL), but not for smaller sharks. Nocturnal CPUE of small sharks appeared to increase in the lagoon and decrease on the fore-reef, suggestive of movements to avoid larger conspecifics. PAT tag deployments (7 to 20 d) indicate that large C. perezi generally increased the amount of time they spent in the upper 40 m of the water column during the night, and inhabited much greater depths and tolerated lower temperatures than previously described. The wide vertical (0 to 356 m) and temperature range (31 to 12.4°C) documented for this top-predator reveals ecologi- cal coupling of deep and shallow reef habitats and has implications for Marine Protected Area (MPA) design.

HOW SHARKS SENSE SMELLS

The smooth dogfish, Mustelus canis, is a small shark that feasts on lobster, squid, and other small shellfish, finding its food by tracking odour plumes. It doesn't just follow its nose, but also relies on the movement of the water and vibrations, picked up by its lateral line system, to find its meal. Jayne Gardiner and Jelle Atema wanted to know how the dogfish used their different senses – smell, mechanoreception by the lateral line and vision – to track odour plumes in a large flow tank(p. 1925).The sharks had two odour plumes to choose from: seawater or yummy squid juice. Each plume was squeezed out of a small nozzle to create a relatively smooth `oozing' odour source, which became turbulent as it flowed over a brick 15 cm downstream of the nozzle. When the lights were on, and all their senses were intact, the sharks preferred the turbulent part of the odour plume,indicating their choice by biting or nudging the brick. When the team knocked out the lateral line using streptomycin, the sharks had to search for longer,but couldn't distinguish between turbulent and oozing odour, suggesting that they couldn't tell the difference between smooth and turbulent flow without their lateral lines.When the team plunged the sharks into darkness, the intact sharks had no problems choosing the turbulent odour, however those whose lateral lines weren't working rarely found the odour plumes. The few sharks that did find them couldn't tell the seawater or squid odours apart. This shows that sharks need both their lateral line and sense of smell to track odours. If their lateral line is not working, vision can help them to find the source of the smell, but if the lights go out, the fish have big problems, and might go hungry.

The Late Cretaceous anacoracid shark, Pseudocorax laevis (Leriche), from the Niobrara Chalk of western Kansas

Abstract Eight isolated teeth of the Late Cretaceous anacoracid shark, Pseudocorax laevis (Leriche), from the Smoky Hill Chalk Member of the Niobrara Chalk in western Kansas are formally identified and described. These teeth were recovered from the bottom half of the Smoky Hill Chalk, which chronostratigraphically ranges from the Late Coniacian (ca. 87 Ma) to the late Early Santonian (ca. 85 Ma). Pseudocorax laevis was likely a small shark, measuring only about 1 m in total length. Like other anacoracids, P. laevis possibly practiced scavenging.

Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

DSC measurements on sharks

Sharks are commonly termed fish, even though they are only distantly related to the classical (bony) fish. What differentiates a shark from a bony fish? Sharks have a spinal column and are thus vertebrates. However, their skeleton is not made of bones, but of cartilage, and together with their nearest relatives the rays and the chimeras they form the class of cartilaginous fish. Since the late 1980s trade in shark fin was considered to be one of the most valuable fishery products in the world. Another valuable shark product is cartilage. Shark meat has been used as food in coastal regions for over 5000 years. Small sharks are preferred for meat in many markets. In Germany, the belly flaps of spiny dogfish ( Squalus acanthias) are smoked as “Schillerlocken”, an expensive gourmet item. The question came up to us recently if we were able to detect whether shark muscle were heat-treated as in the case of smoking or not. Different tariffs for heated and untreated fishery products make it important for processors to label their products correctly. According to customs departments this necessitates investigations into whether the declaration of goods is true or not. Looking at the relevant literature, papers dealing with thermal stability of shark muscle were very scarce. Therefore, we decided to perform DSC measurements on a variety of shark using a SETARAM MicroDSC VII and to compare the DSC patterns obtained. Beside thermal stability the colour of different shark meats were also measured instrumentally. To answer the question of whether DSC measurement can differentiate previously heat treated sharks from those lacking this treatment, the cutlets from smooth-hound ( Mustelus spp.) underwent thermal treatment in the range from 40 to 70 °C. DSC patterns of the shark muscle and the skin were used to observe the influence of heat treatment.

Biology and dental morphology of Priscusurus adruptodontus, gen. et sp. nov. (Chondrichthyes, Lamniformes) from the Albian (Early Cretaceous) of Peru

ABSTRACT A partial association of fourteen teeth from a small lamniform shark with uncertain affinities is described. The material comes from the middle? Albian of Peru and represents a new genus and species, Priscusurus adruptodontus. The new taxon is characterized by a tearing-type dentition with comparably small teeth that lack any ornamentation and lateral cusplets. Other diagnostic features include distally inclined cusps in all tooth positions, an asymmetric root, and the lack of a lingual nutritive groove. The most remarkable feature is the very distinctly shaped lingual tooth neck, which differentiates teeth of the new taxon from all known lamniforms. The total body length, which was estimated from the crown height of the tallest preserved anterior tooth and a regression equation for the dentition of the modern sand tiger shark, Carcharias taurus, is only 69 cm. The very rare finds of this taxon and the restricted occurrence may indicate that Priscusurus was probably an endemic element of the shelf areas of western South America.

Comparisons of Trawl and Longline Catches of Deepwater Elasmobranchs West and North of Ireland

A comparison was made between catches from deepwater trawl and longline surveys (1993–2000) in the Northeast Atlantic. Longline catches were dominated by elasmobranchs, particularly squalid sharks and species numbers were low. Trawl catches had higher species numbers, with more teleosts, though elasmobranchs were still an important component. Species composition of the catch was depth dependent. Comparative trawl and longline surveys of the eastern and southern slopes of the Rockall Trough (west and north of Ireland) were used to examine size-selectivity. Trawls and longlines selected for significantly different size frequency distributions of Centroscymnus coelolepis and Deania calceus, though not for Centrophorus squamosus. These data highlight some important aspects of behavior of the species studying relation to fishing gears. Smaller C. coelolepis were selected by longlines than trawls, suggesting that smaller sharks were present at a considerable height above the seabed, out of reach of trawls, but attracted to baited hooks. In the case of D. calceus, larger females were selected by hooks, but were not present in trawl catches, possibly indicating their ability to escape towed gears. Trawl selectivity ogives were constructed for D. calceus and ogives for C. coelolepis and C. squamosus were simulated, using available data. Results suggest that longlines are not as selective for C. coelolepis as trawls. Selectivity ogives for D. calceus were similar in form, but longlines selected bigger individuals. Life history studies suggest that these species cannot sustain high fishing pressures. The implications of these results for the management of fisheries taking elasmobranchs are discussed.