Habitat,movements and environmental preferences of dusky sharks,Carcharhinus obscurus,in the northern Gulf of Mexico

The dusky shark (Carcharhinus obscurus) is the largest member of the genus Carcharhinus and inhabits coastal and pelagic ecosystems circumglobally in temperate, subtropical and tropical marine waters. In the western North Atlantic Ocean (WNA), dusky sharks are overfished and considered vulnerable by the International Union for the Conservation of Nature. As a result, retention of dusky sharks in commercial and recreational fisheries off the east coast of the United States (US) and in the northern Gulf of Mexico is prohibited. Despite the concerns regarding the status of dusky sharks in the WNA, little is known about their habitat utilization. During the summers of 2008–2009, pop-up satellite archival tags were attached to ten dusky sharks (one male, nine females) at a location where they have been observed to aggregate in the north central Gulf of Mexico southwest of the Mississippi River Delta to examine their movement patterns and habitat utilization. All tags successfully transmitted data with deployment durations ranging from 6 to 124 days. Tag data revealed shark movements in excess of 200 km from initial tagging locations, with sharks primarily utilizing offshore waters associated with the continental shelf edge from Desoto Canyon to the Texas/Mexican border. While most sharks remained in US waters, one individual moved from the northern Gulf of Mexico into the Bay of Campeche off the coast of Mexico. Sharks spent 87 % of their time between 20 and 125 m and 83 % of their time in waters between 23 and 30 °C. Since dusky sharks are among the most vulnerable shark species to fishing mortality, there is a recovery plan in place for US waters; however, since they have been shown to make long-distance migrations, a multi-national management plan within the WNA may be needed to ensure the successful recovery of this population.     

Habitat use and group size of pied cormorants (<Emphasis Type="Italic">Phalacrocorax varius</Emphasis>) in a seagrass ecosystem: possible effects of food abundance and predation risk

Both food abundance and predation risk may influence habitat use decisions. However, studies of habitat use by birds in marine environments have focused only on food abundance. I investigated the possible influences of food abundance and predation risk from tiger sharks (Galeocerdo cuvier) on habitat use by pied cormorants (Phalacrocorax varius) over two spatial scales and on cormorant group size. Cormorants were usually solitary, but group size was highest in shallow habitats during months when shark density was low. Regardless of season, cormorant density within shallow habitats was higher over seagrass than sand, and cormorants were distributed between these two microhabitats proportional to prey density. Therefore, cormorants appear to respond to prey abundance at a relatively narrow spatial scale (i.e., tens of meters). At the habitat-patch scale (~1 km), the density of cormorants and their prey (teleosts) was higher in shallow habitats than in deep ones, but the density of cormorants was influenced by an interaction between water temperature (i.e., season) and habitat. There was decreased use of shallow habitats as water temperature, and the density of tiger sharks, increased. When shark density was low, cormorants were distributed across habitats roughly in proportion to the abundance of fish, suggesting that cormorants respond to food abundance at the scale of habitat patches. However, as shark abundance increased, the relative density of cormorants dropped in the dangerous shallow habitats such that there was a greater density of cormorants relative to their food in deep habitats when sharks were abundant. This suggests that pied cormorants trade-off food and risk by accepting lower energetic returns to forage in safer habitats. This study provides the first evidence that marine habitat selection by birds may be influenced by such a trade-off, and provides further evidence that tiger sharks are important in determining habitat use of their prey and mediating indirect interactions within Shark Bay.Communicated by P. W. Sammarco, Chauvin     

Movements and swimming behaviour of white sharks (Carcharodon carcharias) in Australian waters

We used a combination of satellite telemetry, archival and conventional tags to show that white sharks made broad-scale movements consistent with mixing of the population across their entire Australasian range. The capture of one of these sharks in New Zealand, some 3,550 km from the point of tagging in South Australia, provides further confirmation that white sharks sometimes move into open ocean waters and cross deep ocean basins. However, most movements were confined to shelf waters, generally in areas of less than 100 m depth and in some cases into waters of less than 5 m depth. Sharks showed considerable plasticity in swimming patterns, which included many of the behaviours reported for other species. One of the archival-tagged sharks showed separate periods of distinct swimming behaviour as it moved into different habitats and travelled between them. The changes in swimming behaviour were abrupt and suggested rapid switching of hunting strategies for different prey types in these habitats. All tracked sharks showed both prolonged periods of directional swimming in coastal waters at swimming speeds of 2–3 km h⁻¹ as well as temporary residency in particular regions. Movements of tagged white sharks, together with data from shark control programs and bycatch records, suggest a seasonal movement northward along the east coast of Australia during the autumn–winter months and south in spring–early summer. The consistency of paths taken by white sharks in Australian waters suggests that they may follow common routes or “highways” in some areas. If so, identifying such areas may assist in reducing interactions with fishing operations and thus reduce bycatch.     

Tiger shark (Galeocerdo cuvier) abundance and growth in a subtropical embayment: evidence from 7 years of standardized fishing effort

The tiger shark (Galeocerdo cuvier Peron and Lesueur 1822) is a widely distributed predator with a broad diet and the potential to affect marine community structure, yet information on local patterns of abundance for this species is lacking. Tiger shark catch data were gathered over 7 years of tag and release research fishing (1991–2000, 2002–2004) in Shark Bay, Western Australia (25°45′S, 113°44′E). Sharks were caught using drumlines deployed in six permanent zones (~3 km² in area). Fishing effort was standardized across days and months, and catch rates on hooks were expressed as the number of sharks caught h⁻¹. A total of 449 individual tiger sharks was captured; 29 were recaptured. Tiger shark catch rate showed seasonal periodicity, being higher during the warm season (Sep–May) than during the cold season (Jun–Aug), and was marked by inter-annual variability. The most striking feature of the catch data was a consistent pattern of slow, continuous variation within each year from a peak during the height of the warm season (February) to a trough in the cold season (July). Annual growth rates of recaptured individuals were generally consistent with estimates from other regions, but exceeded those for populations elsewhere for sharks >275 cm fork length (FL), perhaps because mature sharks in the study area rely heavily on large prey. The data suggest that (1) the threat of predation faced by animals consumed by tiger sharks fluctuates dramatically within and between years, and (2) efforts to monitor large shark abundance should be extensive enough to detect inter-annual variation and sufficiently intensive to account for intra-annual trends.     

A multiple instrument approach to quantifying the movement patterns and habitat use of tiger (Galeocerdo cuvier) and Galapagos sharks (Carcharhinus galapagensis) at French Frigate Shoals, Hawaii

We equipped individual tiger (Galeocerdo cuvier Péron and Lesueur, 1822) and Galapagos (Carcharhinus galapagensis Snodgrass and Heller, 1905) sharks with both acoustic and satellite transmitters to quantify their long-term movements in the Papahanaumokuakea Marine National Monument (Northwestern Hawaiian Islands). Tiger sharks exhibited two broad patterns of behavior. Some individuals were detected at French Frigate Shoals (FFS) year round, whereas others visited FFS atoll in summer to forage on fledging albatross, then swam thousands of kilometers along the Hawaiian chain, or out into open ocean to the North Pacific transition zone chlorophyll front, before returning to FFS in subsequent years. These patterns suggest tiger sharks may use cognitive maps to navigate between distant foraging areas. Different patterns of spatial behavior may arise because cognitive maps are built up through individual exploration, and each tiger shark learns a unique combination of foraging sites. Galapagos shark detections were all associated with FFS, suggesting these sharks may be more resident around oceanic islands. Both Galapagos and tiger sharks primarily used the mixed layer (<100 m depth) and made occasional deeper dives through the thermocline down to 680 m. Results show reef-associated sharks utilize a wide variety of habitats ranging from shallow atoll lagoons to deep reefs and open ocean and may provide important trophic links between these habitats.     

The effects of shark cage-diving operations on the behaviour and movements of white sharks, Carcharodon carcharias, at the Neptune Islands, South Australia

The attraction or provisioning of sharks for the purpose of tourism is a lucrative and popular industry that remains controversial regarding its possible risks to target species and impacts on local ecosystems. The long-term impacts of such activities on the behaviour and movement patterns of sharks have typically been difficult to establish as most studies investigate contemporary behaviour concurrent with existing operations and thus have no comparative base from which to compare effects. We compared patterns of residency and behaviour of acoustic-tagged white sharks at the Neptune Islands in South Australia between periods before and after an abrupt and sustained doubling of cage-diving effort that occurred in 2007. The number of sharks reported by cage-dive operators significantly increased after 2007. Comparisons also revealed there were significant increases in sharks’ periods of residency, the periods spent within areas where shark cage-diving operations occur and changes in sharks’ diel pattern of habitat use. Changes were site-specific with no significant differences in shark behaviour revealed over the same period at an island group 12 km from regular shark cage-dive sites. The results suggest that cage-diving operations can lead to long-term changes in the site-specific behaviour of a highly vagile shark species which may need to be considered in the context of their conservation and in managing the impacts of the industry.     

Movement and environmental preferences of Greenland sharks (<Emphasis Type="Italic">Somniosus microcephalus</Emphasis>) electronically tagged in the St. Lawrence Estuary,Canada

Three Greenland sharks (Somniosus microcephalus) were tagged with electronic tags, in Baie St. Pancrace, St. Lawrence Estuary, Quebec, Canada. One shark was tagged on 23 July 2004, with an acoustic telemetry tag. Two sharks were each tagged with a pop-up satellite archival tag (PSAT) on 27 August 2004. Two of the sharks remained in or close to the bay, one for 47 days and the other for at least 66 days. The third shark left the bay immediately after tagging on 27 August 2004. This shark entered the main channel of the St. Lawrence Estuary, and had moved 114.9 km upstream by 1 November 2004 when the tag reported to ARGOS satellites. The tags provided a total of 179 days of data on the movement and environmental preferences of Greenland sharks in the St. Lawrence Estuary. Sharks that reported depth and ambient water temperature data from the bay showed significant diel differences in depth preferences and corresponding ambient temperatures. The sharks remained near the bottom of the water column during the day and displayed increased vertical movements at night. The shark that resided in the main channel did not show this pattern, but generally remained at depths between 325 and 352 m. Sharks in the bay experienced water temperatures that ranged from −1.1 to 8.6°C at depths from 0 to 67 m. In the main channel the shark experienced temperatures that ranged from 1.0 to 5.4°C at depths from 132 to 352 m. This is the first report of numerous Greenland sharks inhabiting shallow near shore bays during summer and autumn.     

Tiger shark (Galeocerdo cuvier) movement patterns and habitat use determined by satellite tagging in eastern Australian waters

Partial migration is considered ubiquitous among vertebrates, but little is known about the movements of oceanodromous apex predators such as sharks, particularly at their range extents. PAT-Mk10 and SPOT5 electronic tags were used to investigate tiger shark (Galeocerdo cuvier) spatial dynamics, site fidelity and habitat use off eastern Australia between April 2007 and May 2013. Of the 18 tags deployed, 15 recorded information on depth and/or temperature, and horizontal movements. Tracking times ranged between four and 408 days, with two recovered pop-up archival tags allowing 63 days of high-resolution archived data to be analysed. Overall mean proportions of time-at-depth revealed that G. cuvier spent the majority of time-at-depths of <20 m, but undertook dives as deep as 920 m. Tagged sharks occupied ambient water temperatures from 29.5 °C at the surface to 5.9 °C at depth. Deep dives (>500 m) occurred mostly around dawn and dusk, but no definitive daily dive patterns were observed. Horizontal movements were characterised by combinations of resident and transient behaviour that coincided with seasonal changes in water temperature. While the majority of movement activity was focused around continental slope waters, large-scale migration was evident with one individual moving from offshore Sydney, Australia, to New Caledonia (c. 1,800 km) in 48 days. Periods of tiger shark residency outside of Australia’s fisheries management zones highlight the potential vulnerability of the species to unregulated fisheries and the importance of cross-jurisdictional arrangements for species’ management and conservation.     

Habitat use and foraging behavior of tiger sharks (<Emphasis Type="Italic">Galeocerdo cuvier</Emphasis>) in a seagrass ecosystem

Understanding the foraging behavior and spatial distribution of top predators is crucial to gaining a complete understanding of communities. However, studies of top predators are often logistically difficult and it is important to develop appropriate methods for identifying factors influencing their spatial distribution. Sharks are top predators in many marine communities, yet no studies have quantified the habitat use of large predatory sharks or determined the factors that might influence shark spatial distributions. We used acoustic telemetry and animal-borne video cameras ("Crittercam") to test the hypothesis that tiger shark (Galeocerdo cuvier) habitat use is determined by the availability of their prey. We also used Crittercam to conduct the first investigation of foraging behavior of tiger sharks. To test for habitat preferences of sharks, the observed proportion of time in each habitat for each individual was compared to the predicted values for that individual based on correlated random walk and track randomization methods. Although there was individual variation in habitat use, tiger sharks preferred shallow seagrass habitats, where their prey is most abundant. Despite multiple encounters with potential prey, sharks rarely engaged in prolonged high-speed chases, and did not attack prey that were vigilant. We propose that the tiger sharks' foraging tactic is one of stealth, and sharks rely upon close approaches to prey in order to be successful. This study shows that using appropriate analysis techniques and a variety of field methods it is possible to elucidate the factors influencing habitat use and gain insights into the foraging behavior of elusive top predators.     

Diel movement patterns of the Hawaiian stingray,<Emphasis Type="Italic"> Dasyatis lata</Emphasis>: implications for ecological interactions between sympatric elasmobranch species

The Hawaiian stingray, Dasyatis lata, is a common benthic elasmobranch in nearshore Hawaiian waters. Acoustic telemetry was used to track the movements of seven rays in Kaneohe Bay, Oahu, Hawaii. Rays were tracked continuously over 31-74 h periods. Geographical movements were analyzed to determine space utilization and rate of movement. Rays were found to utilize significantly larger activity spaces at night (0.83ǂ.70 km²) (mean-SD) than during the day (0.12ǂ.15 km²). Mean total activity space for rays tracked was 1.32ǂ.75 km². Rates of movement were also significantly higher at night (0.34ǂ.30 km h^-1) than during the day (0.15ǂ.22 km h^-1). Average straight-line swimming speed was 0.64ǂ.16 km h^-1, with a maximum observed swimming speed of 1.9 km h^-1. Tidal stage had no effect on rate of movement. Comparison with previously published data on juvenile scalloped hammerhead sharks, Sphyrna lewini, in Kaneohe Bay revealed a high degree of overlap in habitat use and time of activity, suggesting possible ecological interactions between these two species.     

Short- and long-term importance of small sharks in the diet of the rare deep-sea shark Dalatias licha

Knowing the trophic ecology of marine predators is essential to develop an understanding of their ecological role in ecosystems. Research conducted on deep-sea and threatened shark species is limited. Here, by combining analyses of individual stomach contents and stable isotope values, we examined the trophic ecology (dietary composition and trophic position) of the kitefin shark Dalatias licha, a deep-sea shark considered as near threatened globally and as data deficient in the Mediterranean Sea. Results revealed the importance of small sharks in the diet of the kitefin shark at short- and long-term scales, although fin-fish, crustaceans and cephalopods were also found. Predation on sharks reveals the high trophic position of the kitefin shark within the food web of the western Mediterranean Sea. Stable isotope values from liver and muscle tissues confirmed our results from stomach content analysis and the high trophic position.     

Genetic structure of leopard shark (<Emphasis Type="Italic">Triakis semifasciata</Emphasis>) populations in California waters

The leopard shark (Triakis semifasciata) is an important predator in coastal marine ecosystems of California, targeted by recreational and commercial fishermen and of specific interest in fisheries management. From October 2003 to August 2006, 169 leopard sharks were collected from the coast of California (between 40.750°N and 32.678°N) and analyzed for mitochondrial and nuclear genetic structure. Analyses of mtDNA control region sequences revealed relatively low levels of genetic variation (five haplotypes, average pairwise divergence π = 0.0067). In contrast, leopard sharks were highly polymorphic for inter simple sequence repeats (ISSRs), which characterize a broad range of the nuclear genome. The null hypothesis of panmixia in California waters was rejected for both genetic markers, and ISSRs displayed a statistically significant pattern of isolation by distance (IBD) across the species range (P = 0.002). A variety of analyses showed that divergence is most pronounced in the northernmost population of Humboldt Bay. Natal philopatry in T. semifasciata was tested using Siegel-Tukey tests on data partitioned by breeding site status, and sex-specific philopatry was tested by comparing IBD plots between sexes. Although there was some evidence for natal philopatry in leopard sharks (P = 0.038), and population divergence may be related to the proximity of breeding sites (P = 0.064), we found no support for sex-specific philopatry. In addition to identifying a novel set of highly variable genetic markers for use in shark population studies, these results may be used to better inform management decisions for leopard sharks in California.     

Shark-inflicted injury frequencies, escape ability, and habitat use of green and loggerhead turtles

Interactions between large marine predators and their prey are difficult to observe and little is known about the risk of predation faced by sea turtles. The frequency of predator-inflicted injuries, however, has afforded insights into the predation risk faced by many taxa. We measured the frequency of shark-inflicted injuries on green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles in Shark Bay, Western Australia with a view to determining differences between species and sex-classes in the risk of predation from tiger sharks (Galeocerdo cuvier). Furthermore, we investigated how escape ability and habitat use might influence the probability of turtles being injured by sharks. Shark-inflicted injuries were more frequent on loggerhead than on green turtles, and most frequent on adult male loggerhead turtles. Species effects could not be attributed to differences in habitat use, since green turtles were found in habitats favored by tiger sharks more often than were loggerhead turtles. Green turtles, however, were faster and maneuvered better than loggerhead turtles, suggesting that escape ability is a factor in interspecific differences in injury frequency. The sex-class difference in injury frequency of loggerhead turtles suggests that males face greater predation risk than females and may take more risks. For green turtles, the lack of a sex difference in injury frequency might be due to greater escape ability lowering overall predation risk or to no differences between sexes in the benefits of risk-taking.     

Movement patterns of young Caribbean reef sharks, Carcharhinus perezi, at Fernando de Noronha Archipelago, Brazil: the potential of marine protected areas for conservation of a nursery ground

The movement patterns and long-term site-fidelity of primarily juvenile Caribbean reef sharks, Carcharhinus perezi, were investigated using tag-recapture and automated telemetry at an insular nursery area, the Fernando de Noronha Archipelago, Brazil. Of the 143 externally tagged juvenile sharks (<110 cm), 22 (15.3%) were recaptured between 0 and 5 km from the site of tagging after 5–800 days at liberty, suggesting some site-fidelity in young individuals of this species. Site-fidelity and movement patterns of ten juvenile sharks ranging from 78 to 110 cm total length (TL) and one opportunistically captured adult female (224 cm TL) were also investigated for periods of up to 2 years with an array of automated telemetry receivers. Tagging and telemetry data from both inside and outside a marine protected area (MPA) show that shark abundance and activity is greatest along the part of the archipelago’s coastline least disturbed by human activity. Telemetry tracking also showed that juvenile reef sharks demonstrated a high degree of site-fidelity and occupied specific locations along the coast throughout the year, with some evidence of an increase in activity space with ontogeny. Sharks appeared to range more widely at night and there were no seasonal variations in habitat use. Our results suggest that MPAs may be a useful conservation tool to protect young C. perezi and potentially other reef-dwelling carcharhinid sharks during their early life history.     

The effects of cage-diving activities on the fine-scale swimming behaviour and space use of white sharks

Wildlife tourism has become increasingly popular and is one of the fastest growing sectors of the tourism industry. A radio-acoustic positioning system was deployed to monitor the fine-scale movements of 21 white sharks (Carcharodon carcharias) and investigate the effects of shark cage-diving activities on their swimming behaviour and space use. This study contributes towards improving our understanding of the complex relationship between wildlife tourism and its effects on sharks, and assesses how tourism targeting sharks affects behaviour at a finer spatial scale than previously investigated. Our study demonstrated that shark cage-diving operators (SCDO) influenced the fine-scale three-dimensional spatial distribution and the rate of movement of white sharks at the Neptune Islands. White sharks stayed more than 30 m away from the SCDO on 21 % of the days detected, but spent a significant amount of time in close proximity to the SCDO on the remaining days. Individual variation was detected, with some sharks behaviourally responding to SCDO more than others. The degree of variation between individual sharks and the different levels of interaction (e.g. presence, proximity to SCDO, and consumption of tethered bait) highlights the complexity of the relationships between SCDO and the effects on sharks. To improve our understanding of these relationships, future monitoring of shark cage-diving operations requires proximity to SCDO to be recorded in addition to the presence within the area. Further work is needed to assess whether the observed behavioural changes would affect individual fitness and ultimately population viability, which are critical information to unambiguously assess the potential impacts of wildlife tourism targeting sharks.     

Australian and U.S. News Media Portrayal of Sharks and Their Conservation

Investigation of the social framing of human–shark interactions may provide useful strategies for integrating social, biological, and ecological knowledge into national and international policy discussions about shark conservation. One way to investigate social opinion and forces related to sharks and their conservation is through the media's coverage of sharks. We conducted a content analysis of 300 shark‐related articles published in 20 major Australian and U.S. newspapers from 2000 to 2010. Shark attacks were the emphasis of over half the articles analyzed, and shark conservation was the primary topic of 11% of articles. Significantly more Australian articles than U.S. articles treated shark attacks (χ² = 3.862; Australian 58% vs. U.S. 47%) and shark conservation issues (χ² = 6.856; Australian 15% vs. U.S. 11%) as the primary article topic and used politicians as the primary risk messenger (i.e., primary person or authority sourced in the article) (χ² = 7.493; Australian 8% vs. U.S. 1%). However, significantly more U.S. articles than Australian articles discussed sharks as entertainment (e.g., subjects in movies, books, and television; χ² = 15.130; U.S. 6% vs. Australian 1%) and used scientists as the primary risk messenger (χ² = 5.333; U.S. 25% vs. Australian 15%). Despite evidence that many shark species are at risk of extinction, we found that most media coverage emphasized the risks sharks pose to people. To the extent that media reflects social opinion, our results highlight problems for shark conservation. We suggest that conservation professionals purposefully and frequently engage with the media to highlight the rarity of shark attacks, discuss preventative measures water users can take to reduce their vulnerability to shark encounters, and discuss conservation issues related to local and threatened species of sharks. When integrated with biological and ecological data, social‐science data may help generate a more comprehensive perspective and inform conservation practice. Descripción de Tiburones y su Conservación por Medios Informativos Australianos y Norteamericanos     

Movements of whale sharks (Rhincodon typus) tagged at Ningaloo Reef, Western Australia

Whale sharks (Rhincodon typus Smith) aggregate seasonally (March–June) to feed in coastal waters off Ningaloo Reef, Western Australia. Pop-up archival tags were attached to 19 individuals (total lengths 4.5–11.0 m) at this location in early May of 2003 and 2004 to examine their horizontal and vertical movements. The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef. They used both inshore and offshore habitats and made extensive vertical movements, occasionally to a depth of at least 980 m. Frequent up-and-down movements, diel vertical migration, and crepuscular descents were evident in the depth records. The sharks experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.     

Predicting occurrence of juvenile shark habitat to improve conservation planning

Fishing and habitat degradation have increased the extinction risk of sharks, and conservation strategies recognize that survival of juveniles is critical for the effective management of shark populations. Despite the rapid expansion of marine protected areas (MPAs) globally, the paucity of shark‐monitoring data on large scales (100s–1000s km) means that the effectiveness of MPAs in halting shark declines remains unclear. Using data collected by baited remote underwater video systems (BRUVS) in northwestern Australia, we developed generalized linear models to elucidate the ecological drivers of habitat suitability for juvenile sharks. We assessed occurrence patterns at the order and species levels. We included all juvenile sharks sampled and the 3 most abundant species sampled separately (grey reef [Carcharhinus amblyrhynchos], sandbar [Carcharhinus plumbeus], and whitetip reef sharks [Triaenodon obesus]). We predicted the occurrence of juvenile sharks across 490,515 km² of coastal waters and quantified the representation of highly suitable habitats within MPAs. Our species‐level models had higher accuracy (? ≥ 0.69) and deviance explained (≥48%) than our order‐level model (? = 0.36 and deviance explained of 10%). Maps of predicted occurrence revealed different species‐specific patterns of highly suitable habitat. These differences likely reflect different physiological or resource requirements between individual species and validate concerns over the utility of conservation targets based on aggregate species groups as opposed to a species‐focused approach. Highly suitable habitats were poorly represented in MPAs with the most restrictions on extractive activities. This spatial mismatch possibly indicates a lack of explicit conservation targets and information on species distribution during the planning process. Non‐extractive BRUVS provided a useful platform for building the suitability models across large scales to assist conservation planning across multiple maritime jurisdictions, and our approach provides a simple for method for testing the effectiveness of MPAs.     

Science or Slaughter: Need for Lethal Sampling of Sharks

Abstract: General consensus among scientists, commercial interests, and the public regarding the status of shark populations is leading to an increasing need for the scientific community to provide information to help guide effective management and conservation actions. Experience from other marine vertebrate taxa suggests that public, political, and media pressures will play an increasingly important part in setting research, management, and conservation priorities. We examined the potential implications of nonscientific influences on shark research. In particular, we considered whether lethal research sampling of sharks is justified. Although lethal sampling comes at a cost to a population, especially for threatened species, the conservation benefits from well‐designed studies provide essential data that cannot be collected currently in any other way. Methods that enable nonlethal collection of life‐history data on sharks are being developed (e.g., use of blood samples to detect maturity), but in the near future they will not provide widespread or significant benefits. Development of these techniques needs to continue, as does the way in which scientists coordinate their use of material collected during lethal sampling. For almost half of the known shark species there are insufficient data to determine their population status; thus, there is an ongoing need for further collection of scientific data to ensure all shark populations have a future. Shark populations will benefit most when decisions about the use of lethal sampling are made on the basis of scientific evidence that is free from individual, political, public, and media pressures.     

Reproductive biology of the tiger shark (Galeocerdo cuvier) in Hawaii

The tiger shark (Galeocerdo cuvier) is the largest shark in the family Carcharhinidae and the only carcharhinid with aplacental viviparous (ovoviviparous) reproduction. Despite its size and prevalence, many details of tiger shark reproductive biology are unknown. Size at maturity and litter size have been reported by several authors, but a lack of large numbers of pregnant females has made it difficult to determine gestation period, seasonality, and timing of the female reproductive cycle. Here we analyze data from shark control program fishing and incidental catches in Hawaii (n = 318) to construct the most complete picture of tiger shark reproduction to date. Males reached maturity at approximately 292 cm total length (TL) based on clasper calcification, whereas females matured between 330 and 345 cm TL based on oviducal gland and uterus widths. Litter sizes ranged from 3 to 57 with a mean of 32.6 embryos per litter. Data from 23 litters from various months of the year indicate that tiger sharks are usually 80–90 cm TL at birth, and that the gestation period is 15–16 months. Mating scars were observed in January–February and sperm is presumably stored for 4–5 months until ovulation takes place in May–July. Gestation begins in June–July and pups are born in September–October of the following year. Our data suggest that female tiger sharks in Hawaii give birth only once every three years. This could have major implications for conservation and management of this species, as it suggests that tiger shark fecundity is 33% lower than previously thought. This could greatly reduce the ability of this species to rebound from fishing pressure.

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