Large Sharks Research Articles

Trophic ecology shapes gastrointestinal helminth communities of two sympatric mesopredatory sharks in the Adriatic Sea

AbstractWe investigated and compared the structure of parasite communities in two sympatric, commercially exploited sharks. We analysed 188 gastrointestinal tracts from a crustacean feeder Mustelus punctulatus and 157 gastrointestinal tracts from a piscivorous Squalus acanthias. The overall prevalence of helminth parasites was very high (84.0%) for M. punctulatus with nematode Cucullanus micropapillatus as the most abundant species (mean abundance 13.96) and Anisakis spp. larvae as the most prevalent taxa (47.9%). In contrast, only 21.7% of S. acanthias specimens were infected, showing Anisakis spp. larvae as the most prevalent (17.8%) and abundant taxa (mean abundance 0.39). The subsample of Anisakis spp. larvae, isolated from both hosts, was molecularly identified at ITS locus as A. pegreffii. Significant variations among size classes were recorded for M. punctulatus, mainly as a consequence of higher C. micropapillatus loads in larger sharks. Seasonal patterns in prevalence and abundance of C. micropapillatus were recorded for M. punctulatus, with peaks in autumn, whereas Anisakis spp. larvae prevailed during spring, for both sharks. Sex contributed little to the observed parasite abundances, although female spiny dogfish were more prone to infections than males, and higher helminth diversity was recorded in females in both shark species. The differences in infection parameters between the two shark species likely reflect the variations in foraging strategies and availability of intermediate hosts. Our findings suggest that crustacean feeder M. punctulatus is more susceptible to helminth infections in the Adriatic Sea, which may affect the health status of local shark populations.

Distribution, body length, and abundance of blue shark and shortfin mako offshore of northeastern Japan, as determined from observed pelagic longline data, 2000–2014

AbstractLongline surveys have been conducted in the Northwest Pacific Ocean from 2000 to 2014 using chartered commercial longline vessels. Each year, two cruises were conducted offshore of northeastern Japan from mid‐April to mid‐June. For each longline set during the surveys, onboard scientists collected detailed biological information about the species caught, such as the size and sex, and recorded the catch numbers for all species. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) have eurythermal distributions, but the application of a generalized additive model (GAM) showed that the sea surface temperatures (SSTs) at catch sites positive for shortfin mako were warmer than those for blue shark. On the basis of the GAM, the probabilities of occurrence of both sharks differed by size category: small sharks had a narrower SST range than that of large sharks. Most catches of both sharks were juveniles, and the nominal catch rate of blue shark was more than 10 times that of shortfin mako. The standardized catch per unit effort (CPUE) for both species was calculated using a generalized linear model (GLM) with negative binomial errors, or a delta‐lognormal GLM. The standardized CPUE for blue shark in the second quarter of the year peaked in the mid‐2000s and then decreased, but it has been increasing since 2012. The CPUE for shortfin mako in the second quarter generally increased, with fluctuations.

The structure of a marine tropical food web, and its implications for ecosystem-based fisheries management

We reconstructed the structure of a tropical marine food web and then analyzed it to evaluate how the trophic network could respond to anthropogenic pressures such as the removal of species by fisheries. To reconstruct the presence/absence of predator-prey interactions, we assembled detailed quantitative information from the scientific literature on the stomach contents of 80 predator species (elasmobranchs, teleosts and invertebrates) collected in the Golfo de Tortugas (Colombia) between 1990 and 2009. We tested three conceptual models of network structure (random, small-world, and scale-free), characterized by different system properties and tolerance to perturbations, to evaluate which one better fitted the reconstructed food web. Our results suggest that this network has small-world structure and scale-free properties. An impact on one species may therefore spread to many species through short interaction chains; only a few nodes with high centrality values would support the network structure. However, contrary to current theory, our analysis revealed no clear relationships between species with high centrality and the large-scale structural patterns observed in the network (small-world and scale-free properties). This observation indicates that ecosystem-based fisheries management should prioritize not only high-centrality species (e.g., shrimps, which furthermore are species of high commercial value in the area), but should also consider species with unique structural properties such as those with little or no topological redundancy such as large sharks. For this reason, top predator conservation needs more attention than currently received in fisheries management.

Use of marine protected areas and exclusive economic zones in the subtropical western North Atlantic Ocean by large highly mobile sharks

AbstractStudy aim and locationMany populations of highly mobile marine fishes, including large sharks, are experiencing declines. The benefits of spatial management zones, such as marine protected areas (MPAs), for such animals are unclear. To help fill this knowledge gap, we examined core habitat use areas (CHUAs) for bull (Carcharhinus leucas), great hammerhead (Sphyrna mokarran) and tiger sharks (Galeocerdo cuvier) in relation to specific MPAs and exclusive economic zones (EEZs) in the western North Atlantic Ocean.MethodsBull, great hammerhead and tiger sharks (N = 86 total) were satellite tagged and tracked in southern Florida and the northern Bahamas between 2010 and 2013. Filtered and regularized positions from Argos locations of tag transmissions were used to generate CHUAs for these sharks. Overlaps of CHUAs with regional protected areas and exclusive economic management zones were quantified to determine the proportion of each tracked shark's CHUA under spatial protection from exploitation.ResultsA total of 0%, 17.9% and 34.7% of the regional CHUAs for tracked bull, great hammerhead and tiger sharks, respectively, were fully protected from exploitation in the study area.Main conclusionsExpansion of protected areas to include U.S. territorial waters would effectively protect 100% of the CHUAs for all tracked sharks in the study area. This finding is particularly significant for great hammerhead sharks, which are currently overfished, vulnerable to bycatch mortality and are the focus of strident regional conservation efforts. These findings also provide a means to inform decision makers and marine conservation planning efforts as to the types of management actions available and potential efficacy of spatial protections for these marine predators.

“Somewhere in Infinite Space”: John Mitchel’s Jail Journal and Oceanic Literature

“Somewhere in Infinite Space”:John Mitchel’s Jail Journal and Oceanic Literature Andrew Kincaid The mid-nineteenth century spawned a remarkable series of texts in Irish literature: epic maritime narratives, accounts of actual and vast sea journeys that had no literary precedent since the twelfth-century accounts of St. Brendan and that have had no true geographic parallel since. The aftermaths of the Young Ireland rebellion of 1848 and the Fenian Rising of 1867 produced a series of detailed transoceanic journals written by prisoners who had been convicted of treason and condemned to transportation to the Antipodes. The Fenian revolt led to sixty-two prisoners being shipped “down under” in 1867 aboard the four-masted frigate, the Hougoumont. The journey of 14,000 miles took eighty-nine days. John Casey and Denis Cashman, both members of the rebel cargo, kept diaries of this navigation around the globe. A third, John Flood, kept a notebook that contains poems, personal musings, and lessons in stenography (presumably to teach others and to help pass the time). Written solely at sea, Casey’s Journal of a Voyage from Portland to Fremantle on Board the Convict Ship Hougoumont and Cashman’s untitled chronicle recount their personal moods and reflections. Cashman, for instance, speaks of “the eternal melancholy” he feels at sea.1 Similarly, Casey remarks on “the everlasting monotony of our days.”2 In addition, their narratives also engage the ecological and sociological environments in which they find themselves. Cashman details, for example, the harsh treatment, from court-martials to floggings, doled out to the nonpolitical criminals. Both Cashman and Casey describe schools of porpoises and dolphins, the wingspan of albatrosses, the majesty of whales following the ship, and the cutting up of a large shark that the prisoners caught and hauled aboard. In these strange events Cashman finds curiosity, beauty, and even a sense of adventure, as when he records, “Then the huge monster opens his terrible jaws [End Page 19] . . . and the sport commences.”3 These moments often contrast with the stale and outworn imagery with which he describes Ireland and its loss, for example, “the green hills, the shady groves and pleasant valleys of that beautiful land far away.”4 These oceanic texts, symptomatic of postfamine Ireland and of rebellion and exile, are unique historical documents, providing us with personal accounts of deportation by prominent figures in the emerging global diaspora. But they are also unique literary documents, equal parts epic and existential lament. The Fenian Rising led to three separate accounts of the Hougoumont, but the government’s punitive reaction to the Young Ireland movement some twenty years earlier produced an even greater oceanic text: John Mitchel’s Jail Journal (1854). Initially a follower of Thomas Davis, Mitchel wrote for the Nation before proceeding to advocate for a more militant and republican form of Irish nationalism in a newspaper that he founded, the United Irishman. Charged in April 1848 for spreading seditious speeches and articles under the new and hastily drafted Treason-Felony Act (a law designed specifically to arrest him), Mitchel was sentenced to deportation “beyond the seas for the term of fourteen years.”5 Jail Journal records his transportation from Dublin to Van Diemen’s Land. His log opens with the verdict and his immediate delivery to the government steamer Shearwater: “May 27, 1848.—On this day, about four o’clock in the afternoon, I, John Mitchel, was kidnapped, and carried off from Dublin, in chains, as a convicted ‘felon.’”6 What follows is a sweeping epic. Mitchel opens his maritime saga on the day he is removed from Dublin’s Newgate prison to the steam frigate Shearwater, moored at the city’s North Wall. Sentenced to “fourteen years in transportation” (JJ 1), he has no idea as to his final destination. He speculates that it may be Gibraltar, or Bermuda, or perhaps Norfolk Island. After a short journey down the eastern coast of Ireland, he is imprisoned on Spike Island, in Cork Harbor, for four nights. Visited by a friendly doctor, he is excused, due to his bad asthma, from “being set to work” (JJ 14) on the impending journey. Mitchel is transferred in Cork to the man...

Whale shark on a white shark’s menu

As the world’s largest fish, whale sharks Rhincodon typus could be assumed to be predator-free. Juvenile whale sharks are known to be preyed upon by sharks, marlin and orcas, and, although unconfirmed, bite marks on a sub-adult whale shark were attributed to white sharks Carcharodon carcharias (Department of the Environment and Heritage, DEH 2005). Attacks on large whale sharks by other large sharks are reported, but the predator remains unidentified (Fitzpatrick et al. 2006). Here, we provide confirmation that white sharks feed on adult whale sharks. In the 1960s, a 4.5-m male white shark was caught at Cheynes Beach Whaling Station (near Albany, southwest Australia) by the Department of Fisheries. At that time, white sharks frequented this area and fed on dead whales that were tied up prior to processing for oil. The individual was dissected and two unidentified and damaged shark centra (vertebrae) were recovered from the stomach contents (Fig. 1). These centra have been held in the ichthyology collection of the Western Australian Museum (WAM) for the last 50+ years. The centra were recently re-examined and identified as belonging to a whale shark of at least 8.5 m in length (based on ~12-cm-diameter centra; Wintner 2000). Compared to other orectolobiform sharks, whale shark centra are less calcified, with an open intermedialia. The cartilages of these centra appear etched by stomach acid and distorted due to decalcification, desiccation and shrinkage. Whale sharks are generally tropical, occasionally appearing in more temperate waters, including Albany (DEH 2005). White sharks are most common in temperate Australia; however, they are known from tropical regions, including Ningaloo Reef, where sub-adult whale sharks congregate in the austral Autumn (Fitzpatrick et al. 2006). The diet of white sharks is dominated by smaller sharks, teleosts and mammals (Cortes 1999), and feeding on large cetaceans, either live or dead, is known (e.g. Dudley et al. 2000; Hussey et al. 2012) and regularly reported in the popular media. We cannot confirm whether the white shark preyed on a living whale shark or whether it scavenged on a dead carcass. We also cannot confirm whether the interaction was in tropical or temperate seas.

Ontogeny and life history of a large lamniform shark from the Early Cretaceous of North America

Due to an incomplete fossil record, little is known about lamniform shark life history from the Early Cretaceous of North America. Recent discoveries have shown that during this time, some lamniformes reached gigantic sizes (>6–8 m in total length) not seen in earlier species. Given the importance of life history to understand how organisms reach such sizes, we conducted an ontogenetic analysis on three very large shark vertebrae, representing a single individual from the Lower Cretaceous (Albian) Duck Creek Formation of Texas. Using three different techniques (computed tomography, histological sectioning, and surface texture analysis), we were able to show that this individual was born at a relatively small size and subsequently grew at rapid rate, achieving a total length of over 6.3 m in approximately 18 years; a rate not observed in any other Cretaceous species. Comparison of the different aging techniques yielded complementary results; however, surface texture analysis produced the most complete ontogenetic record for this specimen. More work is needed to determine broad patterns in the life history evolution of giant Early Cretaceous lamniform sharks.

Seasonality and Ontogenetic Habitat Partitioning of Cownose Rays in the Northern Gulf of Mexico

The seasonal and spatial heterogeneity of highly mobile mesopredators may play a large structuring role in estuarine dynamics. With a hypothesized relaxation of predation pressure from large sharks, growing populations of cownose rays (Rhinoptera bonasus) have been implicated in negatively affecting shellfish beds across multiple estuaries of the Atlantic coast; however, the pervasiveness of these potential impacts remains poorly understood elsewhere due to a lack of information on cownose ray distribution and seasonality across the species’ range. To better predict cownose ray dynamics in estuaries of the northern Gulf of Mexico, we conducted a multi-scale study using a combination of aerial and gillnet surveys. Cownose ray abundance was highly seasonal along the Mississippi-Alabama shelf, and a significant along-shelf gradient (west-east) in nearshore ray density was observed. This trend was best explained by changes in salinity, with higher abundances best correlated with more estuarine (i.e., lower salinity) conditions in nearshore areas. From north-south across the Alabama shelf, cownose rays displayed strong spatial and seasonal distributional patterns with ontogeny: adults (in particular, females) were primarily restricted to barrier islands and Gulf waters, whereas juveniles and young-of-the-year (YOY) exploited fresher waters of inshore bays protected from large predators. Among inshore locales, cownose ray catch was lowest over oyster habitats and only consisted of YOY rays, suggesting that foraging impacts may be reduced in these structurally complex substrates.

Identification of Shark Teeth (Elasmobranchii: Lamnidae) from a Historic Fishing Station on Smuttynose Island, Maine, Using Computed Tomography Imaging

Abstract - Two incomplete shark teeth were recovered during archaeological excavation of a historic fishing station on Smuttynose Island, ME. Specimens were identified to the species-level using non-destructive computed tomography (CT) imaging techniques. Their external and internal morphology is described and illustrated. Both teeth are from large sharks in the Order Lamniformes. The larger specimen is a developing tooth from the upper jaw of a Carcharodon carcharias (White Shark). The second specimen is a broken tooth from the lower jaw of a Lamna nasus (Porbeagle). The Smuttynose excavations provide an opportunity to examine faunal assemblages and the island's historic 17th-through 19th-century fisheries. Criteria for identifying teeth of common pelagic sharks of the Western North Atlantic are offered, and the role of sharks in the historic Gulf of Maine fishery is discussed.

The small-scale shark fisheries in the southern Gulf of Mexico: Understanding their heterogeneity to improve their management

Fisheries targeting sharks in the southern Gulf of Mexico are generally restricted to a few months or fish in several months but participate in other fisheries. Sharks are also part of the by-catch in most fisheries that use gill nets or longlines. The fisheries targeting sharks include the following: (1) a gill net fishery for Rhizoprionodon terraenovae and Sphyrna tiburo in April–June and August–September, respectively, off of northern Campeche; (2) a gill net fishery for Carcharhinus leucas in November–March off of central and southern Campeche; (3) a longline fishery for C. leucas, Carcharhinus plumbeus and Sphyrna lewini throughout the year off of the Tabasco state; (4) a longline fishery for C. leucas by medium-sized boats from the state of Yucatan; and (5) a fishery with gill nets for Carcharhinus limbatus off of the central coast of Tabasco in April–May. The decline in shark catches over the last two decades in Mexico prompted a series of management measures, including the restricted issuance of fishing licenses, gear regulations and closed seasons. Fishery management includes all shark species, but does not consider species-specific differences in life history, the regional seasonality of the target fisheries, or differences in the gear types that are used to target small or large sharks. We recommend the establishment of separate management measures for small and large shark fisheries because, in addition to differences in the biological productivity of the target species, these two fisheries differ in the type of gear used and the seasonality and region in which the fishing occurs. The fishery for R. terraenovae off of northern Campeche has characteristics (same period and area over many years, catch composition dominated by adults and the target species accounts for 80–90% of the catch) that enable population assessments and the evaluation of the efficacy of management measures. Further restrictions on the use of gear types that target large sharks are recommended due to the vulnerability of those species (e.g., C. leucas).

Record of <em>Carcharocles megalodon</em> in the Eastern Guadalquivir Basin (Upper Miocene, South Spain)

Tortonian diatomites of the San Felix Quarry (Porcuna), in the Eastern Guadalquivir Basin, have given isolated marine vertebrate remains that include a large shark tooth (123.96 mm from apex to the baseline of the root). The large size of the crown height (92.2 mm), the triangular shape, the broad serrated crown, the convex lingual face and flat labial face, and the robust, thick angled root determine that this specimen corresponds to Carcharocles megalodon . The symmetry with low slant shows it to be an upper anterior tooth. The total length estimated from the tooth crown height is calculated by means of different methods, and comparison is made with Carcharodon carcharias . The final inferred total length of around 11 m classifies this specimen in the upper size range of the known C. megalodon specimens. The palaeogeography of the Guadalquivir Basin close to the North Betic Strait, which connected the Atlantic Ocean to the Mediterranean Sea, favoured the interaction of the cold nutrient-rich Atlantic waters with warmer Mediterranean waters. The presence of diatomites indicates potential upwelling currents in this context, as well as high productivity favouring the presence of large vertebrates such as mysticetid whales, pinnipeds and small sharks (Isurus). These large vertebrates recorded in the Eastern Guadalquivir Basin were potential prey of C. megalodon .

Big fish (and a smallish skate) eat small fish: diet variation and trophic level of Sympterygia acuta, a medium‐sized skate high in the food web

AbstractThe bignose fanskate, Sympterygia acuta, is a small‐to‐medium‐sized species endemic to shallow coastal waters of the Southwest Atlantic. Sympterygia acuta displays a clear seasonal reproductive cycle, characterized by maximum egg‐laying activity in spring and hatching in summer. We hypothesized that diet and feeding activity change with maturity stage and season and that, given its smallish size, the trophic level is low. Using a multiple‐hypothesis modeling approach, the diet of S. acuta in relation to sex, body size, maturity stage, region (i.e. north and south) and season was analysed; and a potential relationship between feeding activity and the seasonal reproductive cycle was assessed. Sympterygia acuta fed on a broad spectrum of prey, but teleosts were more important (47.97% index of relative importance, %IRI), followed by decapods (39.84%IRI), cumaceans (8.31%IRI) and isopods (1.89%IRI). Maturity stage was a strong determinant of the ontogenetic diet shift of S. acuta, and relationships between number of prey consumed with season and region were found.. Feeding activity was higher in the cold season than in the warm season, and was less important in the south region than in the north region. Unexpectedly, the specific trophic level was high (3.87). Sympterygia acuta shifts its diet with maturity stage, possibly by a combination of an improved ability to capture prey and a change in energy demand of mature individuals. Despite being a small‐to‐medium‐sized skate, S. acuta showed a trophic level similar to that of large‐bodied marine predators. It reduces its feeding activity seasonally because in the warm season this species may experience an increased predation risk from large sharks.

Improving in-water estimates of marine turtle abundance by adjusting aerial survey counts for perception and availability biases

Aerial surveys are often used to estimate wildlife abundance. The probability of detecting an animal during a survey involves two processes: (1) availability bias when animals present in the search area are not available for detection and (2) perception bias, when some animals potentially visible to observers are missed. Estimating these two sources of bias can lead to improved abundance estimates. However, to date, no marine turtle aerial survey has quantified both biases. To improve in-water marine turtle abundance estimates from aerial counts we estimated: (1) perception bias using independent tandem observers and mark recapture models, and (2) availability bias by quantifying the effect of turtle diving behaviour and environmental conditions on the detection probability of turtles. We compared unadjusted and adjusted abundance estimates to evaluate the effects of these detection biases in aerial surveys. Adjusted data produced a substantially higher estimate of turtles than the unadjusted data. Adjusting for availability bias increased the estimates 18.7 times; adjusting for perception bias resulted in a further 5% increase. These results emphasize the need to consider availability and perception corrections to obtain robust abundance estimates. This approach has application for aerial surveys for other marine wildlife including marine mammals and large sharks.

Expanded trophic complexity among large sharks

To understand the effects of predator removal in marine ecosystems requires accurate estimates of trophic position and trophic structure that have been difficult to obtain to date. For example, most sharks are classified as diet generalists that feed around trophic position 4, but this classification contradicts observations of diverse feeding behaviour among large species, suggesting that trophic structure has been oversimplified among upper trophic level species. To test this assumption, bulk δ15N and δ13C values of 13 shark species constituting the large shark assemblage off southern Africa were integrated into (i) a hierarchical Bayesian model, accounting for body size and variable sample sizes among species, and (ii) a dietary δ15N-dependent enrichment model to quantify individual and assemblage-wide trophic position and structure. Compound specific isotopic analysis of amino acids (CSIA-AAs) for a subset of species was used to verify results. Although discrepancies occurred between methods, overall these data confirm that large sharks, including several globally threatened species, feed at markedly higher trophic positions and across a broader trophic range than is currently assumed. This identifies a lower degree of functional equivalence among the assemblage. Such complex trophic structure among large sharks suggests that cascading effects from species-specific removals in food webs may be weaker but more pervasive than currently assumed. Reassignment of the trophic structure of large marine predators has important consequences for any potential regulatory and stabilizing roles in marine food webs.

Landing profiles of Portuguese fisheries: assessing the state of stocks

Long-term trends in Portuguese fisheries landing profiles of biodiversity, assemblage composition, trophic groups and marine trophic index (1950–2009) were studied to understand the evolution of the fisheries from an ecological viewpoint and evaluate the effects of fisheries on stocks. The number of species landed has increased considerably since the 1980s. This indicates an expansion of the fisheries and also a better use of the marine biodiversity for redistributing effort. Changes in the ecological composition of fisheries catches have occurred since the 1950s, with a significant shift in the middle 1980s (anchor point). Deep-sea resources and higher trophic levels (cephalopods, large benthopelagics, flatfishes, demersal invertebrates, small-medium and large rays, medium bathydemersal, shrimps, small benthopelagics large sharks) have increased while traditional commercial species captured by nearshore fisheries (medium and small pelagics) have decreased. Despite the decreasing trend in catches since 1988, the marine trophic index (MTI = 3.04) increased by approximately 0.2 units per decade (MTI in 2009 = 3.46). The number of collapsed, overexploited and fully exploited stocks has increased considerably over the last 20 years (>50%). Overall, the data indicate that redistributing fishing effort and targeting of deep-sea resources may have been driven by depletion of inshore fishery stocks, which signals concern for the fishery. Marine biodiversity indexes and ecological structure of landings profiles should be considered by fishery managers when redefining new marine fisheries policy.

Variation in whole-, landed- and trimmed-carcass and fin-weight ratios for various sharks captured on demersal set-lines off eastern Australia

Sharks are important apex predators in marine systems but many populations have experienced large declines, which has resulted in adverse effects on marine food webs. Sharks are also economically important, as their fins are valued in Asian markets. In response to concerns about declining shark populations, a number of nations, including Australia, have developed national plans of action for their conservation and management. As part of New South Wales’ (NSW) efforts to understand the characteristics of their shark fishery, data were collected on the depth of capture, species, sex, body length and weight, fin weight, and reproductive status of individuals caught in the NSW commercial ‘large shark’ demersal set-line fishery. We created models of the relationship between fin to body weight and wastage (discarded or low value portions of the carcass) and compared the ratios of whole, landed, trimmed, and fin weight to determine the relationship between fin weight and wastage to length by species. Our results indicate that length, sex, and the interactions between length with species and sex account for differences in the relative fin weight of sharks; whereas species, length, and their interaction account for differences in the proportion of a shark carcass that is wasted. The data reveal that catching smaller sharks will increase relative fin weight and decrease wastage. Given these results, we recommend that managers consider weight ratio data information in their decision making to promote a sustainable and profitable shark fishery.

A Study of Shark Stealth Behavior in the Proximity of Divers

This study examines the approach patterns of sharks in the vicinity of human divers, focusing on the diver’s body orientation and a shark’s distance from the sea bed when approaching the diver. A standardized video method was used to record the scenario of diver(s) kneeling in the sand while being approached by sharks. This showed that sharks had a preference to move in from outside a diver’s field of vision while larger sharks stayed closer to the sea floor. This may simultaneously enhance camouflage while reducing potential escape routes for the approaching animal. This stealth behavior raises the question of how sharks may interpret humans when moving towards them.

Development of microsatellite markers for globally distributed populations of the threatened silky shark, Carcharhinus falciformis

Eighteen microsatellite loci were developed for the silky shark Carcharhinus falciformis and screened across a total of 53 individuals from the western Atlantic Ocean, Eastern Tropical Pacific Ocean, and Red Sea. The number of alleles per locus ranged from 3 to 19, observed heterozygosity ranged from 0.158 to 0.917, and the probability of identity values ranged from 0.010 to 0.460. Though believed to be one of the most abundant species of large sharks, C. falciformis were recently listed as “near threatened” globally and “vulnerable” in the Eastern Tropical Pacific by the IUCN, due to reductions in catch rates from both target and non-target fisheries (Dulvy et al. in Aquat Conserv 18:459–482, 2008). Very little information exists about the population structure and genetic diversity of C. falciformis around the world. These new loci will provide effective tools for examining the sustainability of this declining species.

When did Carcharocles megalodon become extinct? A new analysis of the fossil record.

Carcharocles megalodon (“Megalodon”) is the largest shark that ever lived. Based on its distribution, dental morphology, and associated fauna, it has been suggested that this species was a cosmopolitan apex predator that fed on marine mammals from the middle Miocene to the Pliocene (15.9–2.6 Ma). Prevailing theory suggests that the extinction of apex predators affects ecosystem dynamics. Accordingly, knowing the time of extinction of C. megalodon is a fundamental step towards understanding the effects of such an event in ancient communities. However, the time of extinction of this important species has never been quantitatively assessed. Here, we synthesize the most recent records of C. megalodon from the literature and scientific collections and infer the date of its extinction by making a novel use of the Optimal Linear Estimation (OLE) model. Our results suggest that C. megalodon went extinct around 2.6 Ma. Furthermore, when contrasting our results with known ecological and macroevolutionary trends in marine mammals, it became evident that the modern composition and function of modern gigantic filter-feeding whales was established after the extinction of C. megalodon. Consequently, the study of the time of extinction of C. megalodon provides the basis to improve our understanding of the responses of marine species to the removal of apex predators, presenting a deep-time perspective for the conservation of modern ecosystems.

Morphological scaling of body form in four shark species differing in ecology and life history

Body form can change across ontogeny, and can influence how animals of different sizes move and feed. Scaling data on live apex predatory sharks are rare and, therefore, we examined patterns of scaling in ontogenetic series of four sympatric shark species exhibiting a range of sizes, ecologies and life histories (tiger, bull, blacktip, and nurse shark). We evaluated 13 linear morphological variables and two areas (caudal and dorsal) that could influence both animal condition and locomotor performance. These measurements included dimensions of the dorsal, pectoral, and caudal fins, as well as several dimensions of body circumference, and of the head. For all four species, the body axis (eye-to-eye, lateral span, frontal span, proximal span) scaled close to isometry (expected slope of 1.0). The two largest sharks (tiger and bull sharks) also showed significant negative allometry for elements of the caudal fin. We found significant negative allometry in the lengths of the upper lobe of the caudal fin (caudal fin 1) and the overall height of the caudal fin (caudal fin 2) in tiger and bull sharks, with slopes ranging from about 0.60 to 0.73. Further, tiger sharks showed negative allometry in caudal fin area. These results suggest that in terms of overall body dimensions, small sharks are roughly geometrically similar to large sharks, at least within the species we examined. However, juvenile tiger (and to a lesser extent bull sharks) are notable in having proportionately larger caudal fins compared to adult sharks. As the caudal fin contributes to generating thrust during forward locomotion, this scaling implies differences among adult and juvenile sharks in locomotor ability. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 126–135.