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Tiger shark - Galeocerdo cuvier
Scientists used high tech ultrasound imaging to study tiger shark reproduction
Researchers performed in-water ultrasounds on tiger sharks in the wild to study their reproduction

Date: February 29, 2016
Source: University of Miami Rosenstiel School of Marine & Atmospheric Science

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Researchers use ultrasound probe to scan for pups on the abdomen of a tiger shark (Galeocerdo cuvier).
Credit: Jim Abernethy

Researchers from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and the University of New England used the same ultrasound imaging technology used by medical professionals on pregnant women to study the reproductive biology of female tiger sharks. The study offers marine biologists a new technique to investigate the reproductive organs and determine the presence of embryos in sharks without having to sacrifice the animal first, which was commonly done in the past.

In the study, the research team performed in-water ultrasounds on live tiger sharks (Galeocerdo cuvier) and took blood samples for hormone analysis to determine the reproductive status of females at Tiger Beach in the Bahamas, a site known for its year-round abundance of tiger sharks. The new method allows researchers to determine if the female sharks at Tiger Beach were mature and pregnant.

"Using the same ultrasound imaging technology used on pregnant women, we discovered Tiger Beach was important for females of different life stages, and that a high proportion of tiger sharks were pregnant during winter months," said James Sulikowski, a professor at the University of New England's Department of Marine Science.

"Our data suggests that Tiger Beach may function as a refuge habitat for females to reach maturity as well as a gestation ground where pregnant females benefit from calm, warm waters year-round that help incubate the developing embryos and speed up gestation," said study co-author Neil Hammerschlag, a research assistant professor at the UM Rosenstiel School and Abess Center for Ecosystem Science and Policy.

Populations of many migratory marine predators such as sharks are experiencing large declines across the globe and fishing aggregations of pregnant females can significantly impact the health of local and regional populations. Tiger Beach is located within the Bahamas Exclusive Economic Zone, where shark fishing has been prohibited since 2011. The relatively high abundance of tiger sharks in the Bahamas compared to the rest of the Caribbean where populations are much lower could be attributed in part to the protection of mature and gravid females in the Bahamas shark sanctuary.

"It is crucial for marine biologists to understand their behaviors to provide information for resource managers to effectively protect and manage them," said Hammerschlag.


Story Source: University of Miami Rosenstiel School of Marine & Atmospheric Science. "Scientists used high tech ultrasound imaging to study tiger shark reproduction: Researchers performed in-water ultrasounds on tiger sharks in the wild to study their reproduction." ScienceDaily. (accessed March 2, 2016).

Journal Reference:
JA Sulikowski, CR Wheeler, AJ Gallagher, BK Prohaska, JA Langan, N Hammerschlag. Seasonal and life-stage variation in the reproductive ecology of a marine apex predator, the tiger shark Galeocerdo cuvier, at a protected female-dominated site. Aquatic Biology, 2016; 24 (3): 175 DOI: 10.3354/ab00648

ABSTRACT: Advancing our knowledge of the reproductive biology and mating systems of free-ranging sharks is inherently challenging. The large size and mobility of the specimens are just a few of the problems that make such studies complicated, and in some respects, impractical. The tiger shark Galeocerdo cuvier is a large, roving, apex predator found in many oceans throughout the world. Although their nomadic nature is primarily linked to large-scale migrations, these sharks can also display site fidelity. One site where this is known to occur is at Tiger Beach, Bahamas. Unique to the waters of this area is the consistent sighting of large females. While the sex-specific use of the area remains unknown, the shallow, warm environment could represent a critical habitat for reproductive events. To investigate the reproductive biology of tiger sharks at Tiger Beach, 65 individuals were opportunistically sampled between 2011 and 2014. Reproductive status of captured females (n = 59) was assessed with ultrasonography and by measuring circulating sex steroid hormones (progesterone, testosterone and estradiol). Our results indicate that Tiger Beach is a high-use site for female tiger sharks of mixed life stages. The results also suggest that Tiger Beach may function as a refuge habitat, allowing females to reach maturity free from male mating harassment, as well as functioning as a gestation ground where gravid females can benefit from year-round calm warm waters, which may reduce the gestation period and accelerate embryo development. 
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  • Claudiu Constantin Nicolaescu
Comparative analysis reveals use patterns of deeper Caribbean coral reefs by shark species
Group spawning may drive predator habitat use for lemon sharks, may inform fisheries management

Date: May 4, 2016
Source: PLOS

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This is a a grouper spawning aggregation.
Credit: George Schellenger; CCAL

Three species of shark, tiger, lemon and Caribbean reef, all use deeper coral reefs in the Virgin Islands, but only lemon shark presence was associated with seasonal grouper spawning aggregations, according to a study published May 4, 2016 in the open-access journal PLOS ONE by Alexandria Pickard from Nova Southeastern University, Florida, Bradley Wetherbee of the University of Rhode Island and colleagues.

Groupers and other fish often spawn together in coral reefs at depths between 30 and 150 meters in the Caribbean, and these aggregations may make them easy pickings for predators. However, little is known about coral ecosystems at these depths when compared to shallow coral reefs. To quantify spatio-temporal patterns of reef use for three species of shark, the authors of this study analyzed data from acoustic transmitters placed on 18 sharks--6 lemon sharks, 10 tiger sharks, and 2 Caribbean reef sharks--that were tracked with acoustic receivers covering an area of more than 1,000 square kilometers near the island of St. Thomas.

The authors found that all three species were present year-round in deeper coral reefs, but shark use patterns differed. While only two Caribbean reef sharks were tracked, both had a small range typical of the species that was not associated with the presence of spawning groupers. The range of lemon and tiger sharks was about 100 times greater, but only the lemon sharks showed increased activity in spots where groupers were actively spawning. Though the study included only a small number of sharks monitored over varying lengths of time, the findings may suggest that fish prey location may influence movements of their shark predators, and that group spawning events may shape ecosystem dynamics in deeper coral reefs.

Bradley Wetherbee, a co-author of the study, notes, "Our study demonstrates that every member of a community has its own unique role or niche. Even though three species of sharks might be found in the same place at the same time on a reef, they are all doing different things and interact with other species in different ways."

Story Source: PLOS. "Comparative analysis reveals use patterns of deeper Caribbean coral reefs by shark species: Group spawning may drive predator habitat use for lemon sharks, may inform fisheries management." ScienceDaily. (accessed May 5, 2016).

Journal Reference:
Alexandria E. Pickard, Jeremy J. Vaudo, Bradley M. Wetherbee, Richard S. Nemeth, Jeremiah B. Blondeau, Elizabeth A. Kadison, Mahmood S. Shivji. Comparative Use of a Caribbean Mesophotic Coral Ecosystem and Association with Fish Spawning Aggregations by Three Species of Shark. PLOS ONE, 2016; 11 (5): e0151221 DOI: 10.1371/journal.pone.0151221

Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30–150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE and as upper trophic level predators they are likely involved in a range of interactions with other members of MCEs.

Attached to this post:[Image: attach.png] Comparative_Use_of_a_Caribbean_Mesophotic_Coral_Ecosystem_and_Association_with_Fish_Spawning_Aggregations_by_Three_Species_of_Shark.pdf (2.38 MB)
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  • Claudiu Constantin Nicolaescu
Tiger sharks opt for scavenging on dead and dying sea turtles as a feeding strategy
Study provides new insight into the behavior of an ocean top predator

Date: August 8, 2016
Source: University of Miami Rosenstiel School of Marine & Atmospheric Science

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A tiger shark scavenges on the carcass of a green turtle off Raine Island, Australia.
Credit: Richard Fitzpatrick, BioPixel

An international team that includes University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science researchers found behavioral evidence that tiger sharks prefer to opportunistically scavenge on dead or weakened green turtles rather than actively hunting healthy individuals despite more opportunities to do so. The study, conducted off the coast of Australia during the turtle nesting season, also found the behavior of healthy green turtles suggests that they do not perceive tiger sharks as a major threat during nesting season.

In the new study, the research team used data from satellite tagged tiger sharks and green turtles off the northern coast of Australia's Great Barrier Reef in the waters around Raine Island collected over a five-year period. During some years, up to as many as 12,000 green sea turtles aggregate around Raine Island to lay eggs on the beach, which offers scientists a natural laboratory to compare the movements and behaviours of the turtles and tiger sharks during a time when sea turtle concentrations are higher than average.

"After long nesting periods onshore, many green turtles become weakened from exhaustion. Up to as many as 80 individuals a night may die in certain years, and their bodies eventually get washed into the water during high tide," said study co-investigator Adam Barnett from BioPixel.

They researchers found surfacing of both tiger sharks and green turtles was highest where they overlapped in core home range, closest to the island, and surfacing also increased for both animals with increasing proximity to the shoreline. In other studies where green sea turtles and tiger shark home range overlap have been analyzed, scientists have observed turtles that avoid isolating themselves at the water surface when they are vulnerable to ambush from tiger sharks. Likewise, when tiger sharks are actively hunting turtles, they stalk their prey from deep below to launch a stealthy attack.

"From analyzing the behavioral data from tracked tiger sharks and green turtles, it appears that tiger sharks are patrolling the shores of Raine Island for a few opportunities to scavenge on the few dead turtles that get washed into the water or the weakened individuals that make their way in the water, instead of actively hunting the hundreds of healthy green turtles that they are encountering daily during the turtle nesting season," said the study's lead author Neil Hammerschlag, a research assistant professor at the UM Rosenstiel School and UM Abess Center for Ecosystem Science and Policy. "The sharks are probably having to go out of their way to avoid hundreds of live turtles to find the dead and weakened ones. It is energetically more advantageous and also safer for sharks to scavenge on carcasses rather than have to chase down live turtles. In this way, tiger sharks are similar to terrestrial carnivores, such as hyenas and polar bears, which will selectively scavenge when the opportunity arises."

"Raine Island is the most biologically significant island on the Great Barrier Reef. It is home to the largest sea bird nesting population on the Reef and the largest green sea turtle nesting site in the world," said study co-investigator Richard Fitzpatrick from BioPixel. "To date, lots of research has been done on the turtles and birds. This research has increased our understanding of the predators that use the Raine Island region, and in turn enhanced our understanding of the whole Raine Island ecosystem."

Story Source: University of Miami Rosenstiel School of Marine & Atmospheric Science. "Tiger sharks opt for scavenging on dead and dying sea turtles as a feeding strategy: Study provides new insight into the behavior of an ocean top predator." ScienceDaily. (accessed August 10, 2016).

Journal Reference:
Neil Hammerschlag, Ian Bell, Richard Fitzpatrick, Austin J. Gallagher, Lucy A. Hawkes, Mark G. Meekan, John D. Stevens, Michele Thums, Matthew J. Witt, Adam Barnett. Behavioral evidence suggests facultative scavenging by a marine apex predator during a food pulse. Behavioral Ecology and Sociobiology, 2016; DOI: 10.1007/s00265-016-2183-2

The ability of predators to switch between hunting and scavenging (facultative scavenging) carries both short-term survival and long-term fitness advantages. However, the mechanistic basis for facultative scavenging remains poorly understood. The co-occurrence of tiger sharks (Galeocerdo cuvier) and green turtles (Chelonia mydas) at Raine Island (Australia), provides an opportunity to examine a top marine predator’s feeding mode in response to seasonal pulses in nesting turtles that offer both hunting and scavenging opportunities. Using satellite telemetry, we evaluated home range overlap between sharks and turtles and quantified their surfacing behavior around Raine Island during the turtle nesting season. We found core home range overlap to be highest during the nesting season. Both sharks and turtles spent significantly more time at the surface in areas of greatest range overlap closest to shore, where turtle density was highest. Both sharks and turtles showed decreased surfacing with increasing distance from Raine Island. Combined with published data on turtle demography at Raine Island, we propose the following: (1) sharks patrol the surface to increase scavenging opportunities on turtle carcasses and intercept weakened individuals after nesting; (2) healthy turtles may not perceive sharks as a major threat and/or other biological factors override anti-predatory responses; and (3) sharks during the nesting season may primarily scavenge on dead turtles individuals rather than actively hunt. Our study results and approach may be applicable to other situations in which direct observations of predator-prey interactions are limited. 
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  • Claudiu Constantin Nicolaescu
How do shark teeth bite? Reciprocating saw, glue provide answers

Date: September 8, 2016
Source: University of Washington

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Shark teeth were attached to reciprocating saw blades using epoxy.
Credit: University of Washington

Sharks have a big reputation for their teeth. The ocean predators use their buzz saw mouths to efficiently dismantle prey, ranging from marine mammals and sea turtles to seabirds and -- as Hollywood likes to remind us -- an occasional human.

There are more than 400 species of sharks in the world and each has a unique tooth shape. Some are simple triangles, while others are deeply notched or spear-shaped. But despite this variety, scientists haven't detected a difference in how different shark teeth cut and poke tissue.

A recent University of Washington study sought to understand why shark teeth are shaped differently and what biological advantages various shapes have by testing their performance under realistic conditions. The results appeared in August in the journal Royal Society Open Science.

"When you have all these different tooth shapes, there should be some functional reason. That issue was fundamentally troubling to me," said senior author Adam Summers, a UW professor of biology and of aquatic and fishery sciences. "It seemed likely what we were missing is that sharks move when they eat."

Sharks shake their heads rapidly when they bite their prey, so evaluating how teeth perform while in a side-to-side motion was critical to the study tests, which took place during a summer marine biology course at the UW's Friday Harbor Laboratories on San Juan Island.

Summers and his collaborators affixed three different types of shark teeth to the blade of a reciprocating power saw, then cut through thick slices of Alaska chum salmon at a speed that mimicked the velocity of head-shaking as a shark devours its prey.

"Sure enough, when we cut through salmon, different teeth cut differently," Summers said. "We found a way to distinguish between this huge morphological difference we see among shark teeth in nature."

The researchers also noticed that some species' teeth dulled more quickly than others. Two kinds of teeth, belonging to tiger and silky sharks, dulled after only several passes of the saw blade over tissue, meaning that it's possible these sharks in the wild must replace their teeth every time they kill prey.

Teeth from the bluntnose sixgill shark didn't cut as well, but they also didn't dull as quickly as the other teeth.

"There's this tradeoff between sharpness and longevity of the tooth edge," Summers explained. "It looks like some sharks must replace their teeth more often, giving them a consistently sharp tool."

This might shed light on the feeding patterns of different sharks, the authors explain. For example, bluntnose sixgill sharks with duller, longer-lasting teeth might be swallowing their prey whole. Tiger sharks that eat a larger range of prey such as sea turtles, dugongs and seabirds usually bite their prey to pieces before eating it and would need sharper teeth to puncture a sea turtle's rigid shell, for example.

When tissue is punctured and twisted side-to-side as prey is during a shark attack, the prey's tissue doesn't always behave the same way. This is not unlike a child's Silly Putty that will stretch into a long, stringy piece when slowly pulled apart, but break in two when yanked at a much faster speed.

Biological tissues behave in the same unpredictable way when pulled, prodded or strained. It was this nuance that the research team tried to capture using experiments that involved movement. They believe it's the first study of its kind for mimicking how sharks hunt and kill.

"It is really important to test biological materials at strain rates that are high enough to mimic how the predator and prey tissues would actually behave in real life," said co-author Stacy Farina, a postdoctoral researcher at Harvard University and an adjunct lecturer at Shoals Marine Laboratory. Farina was a teaching fellow at Friday Harbor Labs when the research was conducted.

The experiments for this study were designed and carried out during an intensive five-week course at Friday Harbor Labs in summer 2014. Katherine Corn, now at the University of California, Davis, used epoxy from a local hardware store to glue shark teeth to the reciprocating saw blades. The materials worked surprisingly well.

"We asked ourselves, how do we safely and effectively move these teeth back and forth quickly? The quick and dirty way was, glue them onto a power saw," Farina said. "It was a simple solution to a complicated problem."


Story Source: University of Washington. "How do shark teeth bite? Reciprocating saw, glue provide answers." ScienceDaily. (accessed September 12, 2016).

Journal Reference:
Katherine A. Corn, Stacy C. Farina, Jeffrey Brash, Adam P. Summers. Modelling tooth–prey interactions in sharks: the importance of dynamic testing. Royal Society Open Science, 2016; 3 (8): 160141 DOI: 10.1098/rsos.160141

The shape of shark teeth varies among species, but traditional testing protocols have revealed no predictive relationship between shark tooth morphology and performance. We developed a dynamic testing device to quantify cutting performance of teeth. We mimicked head-shaking behaviour in feeding large sharks by attaching teeth to the blade of a reciprocating power saw fixed in a custom-built frame. We tested three tooth types at biologically relevant speeds and found differences in tooth cutting ability and wear. Teeth from the bluntnose sixgill (Hexanchus griseus) showed poor cutting ability compared with tiger (Galeocerdo cuvier), sandbar (Carcharhinus plumbeus) and silky (C. falciformis) sharks, but they also showed no wear with repeated use. Some shark teeth are very sharp at the expense of quickly dulling, while others are less sharp but dull more slowly. This demonstrates that dynamic testing is vital to understanding the performance of shark teeth.

Attached to this post:[Image: attach.png] Modelling_tooth___prey_interactions_in_sharks__the_importance_of_dynamic_testing.pdf (622.65 KB)
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  • Claudiu Constantin Nicolaescu
Tagged tiger shark proving unstoppable

Date: January 11, 2018
Source: Nova Southeastern University
For more than a decade, researchers have been tagging and tracking sharks in order to study their migratory patterns and more. One tiger shark - Andy - is now the longest-ever tracked tiger shark, providing years worth of data for researchers.

Not freezing temperatures or nor'easters or Hurricanes Harvey, Irma, Jose or Maria can stop "Andy," a tiger shark tagged in Bermuda by scientists from Nova Southeastern University's (NSU) Guy Harvey Research Institute (GHRI) in 2014. Travelling approximately 37,565 miles off the eastern coast of the United States and around Bermuda, the Bahamas and Turks and Caicos, Andy is now the longest tracked tiger shark on record and shows no sign of slowing down. He's been going for more than 1,240 days.

"We are delighted with how long Andy has reported data, which has tremendous value for us as researchers," said Mahmood Shivji, Ph.D., the director of NSU's GHRI and a professor in the university's Halmos College of Natural Sciences and Oceanography. " This amazing, nearly three and a half year track is revealing clear repeated patterns in the shark's migrations between summer and winter."

More than 150 sharks, including tigers, makos and oceanic whitetips, have been tagged by the GHRI in the last decade. The data collected is used to study the migration patterns of these incredible creatures. Andy and many other GHRI tagged sharks can be followed online in near real-time at

"Tracking the migration patterns of sharks, like Andy, for extended periods of time allow us to better understand their behavior and habitat utilization, resulting in better knowledge on how to manage the species," said world renowned artist and Guy Harvey Ocean Foundation (GHOF) Chairman Guy Harvey, Ph.D.

According to a paper published in the most recent ICES Journal of Marine Science by Shivji and his colleagues, tiger shark migrations are heavily influenced by a shark's physical characteristics (i.e. size, age) and environmental variations (i.e. water temperature, prey availability). This study, funded by the Guy Harvey Ocean Foundation, NSU's GHRI, the Shark Foundation (Hai Stiftung) and the Bermuda Shark Project, reveals not only the environmental factors driving these massive migrations by tiger sharks but also highlights how the different age groups behave. This information could prompt fisheries managers to reevaluate how best to protect this near-threatened species.

Story Source: Nova Southeastern University. "Tagged tiger shark proving unstoppable." ScienceDaily. (accessed January 12, 2018).

Journal Reference:
James S E Lea et al. Ontogenetic partial migration is associated with environmental drivers and influences fisheries interactions in a marine predator. ICES Journal of Marine Science, 2018 DOI: 10.1093/icesjms/fsx238

The ability to predict animal movement based on environmental change is essential for understanding the dynamic nature of their spatial ecology, and in turn the effectiveness of conservation strategies. We used a large marine predator that displays partial migration (the tiger shark Galeocerdo cuvier) as a model to test the role of oceanic conditions in predicting the space-use of different size classes. By using generalized additive mixed models (GAMMs), we revealed that environmental variables (sea surface temperature, primary productivity, thermal fronts, and bathymetry) had much greater predictive power for the movements of large, migratory tiger sharks than for small, resident individuals. We also found that coverage of tiger shark movements within “shark sanctuaries” (protected areas specifically for sharks) in the northwest Atlantic could be increased from 12 to 52% through inclusion of Bermuda’s waters. However, as large tiger sharks are migratory, over 80% of potential longline fisheries interactions would still occur outside the boundaries of even the expanded protected areas. This emphasises that management of highly migratory species needs to be dynamic and account for changing interactions with fisheries over time, which in a changing climate may rely on predicting movements based on oceanic conditions to be effective.
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  • Claudiu Constantin Nicolaescu
Tiger shark sex life fuels sustainability risk

January 17, 2018, University of Queensland

[Image: tigersharkse.jpg]
Credit: University of Queensland

Tiger sharks appear to be genetically monogamous – and it could be putting the species at risk.

University of Queensland research has found tiger sharks differ from many other sharks in that they don't use multiple paternity as a reproductive strategy.

UQ researcher Dr. Bonnie Holmes said multiple paternity occurred when a single litter of offspring was fertilised by multiple males, resulting in pups from the same brood having different fathers – which may ultimately increase the genetic diversity of a species.

Dr. Holmes said it was previously believed this was a wide-spread reproductive strategy among sharks, with half-siblings born at the same time.

"The DNA of 112 tiger shark pups from Cairns, Rainbow Beach and the Gold Coast was tested to see if they had different fathers," Dr. Holmes said.

"Surprisingly, all pups in each litter appeared to have the same father, except one."

Dr. Holmes said this provided critical information for managing the sustainability of tiger sharks globally.

"It is the first genetic assessment of the reproductive strategy of these sharks," she said.

"On the Australian east coast, the species is targeted heavily in shark control operations, recreational game fishing activities and commercial fishing operations.

"Tiger sharks in this region may have a reduced capacity to withstand significant fishing pressure, compounded by a reproductive strategy that may make them more vulnerable to loss of genetic diversity and reductions in effective population size."

Dr. Holmes said successful mating in sharks might depend on the rate of encounter between potential mates.

"Because tiger sharks roam widely, multiple mating is probably less common as they are less likely to encounter a member of the same species."

She said further studies of tiger shark litters were required to corroborate the findings.

"Although multiple paternity is widely accepted as a common reproductive strategy in elasmobranchs (sharks, rays and skates), the frequency and prevalence may vary between species and populations.

"If multiple paternity does occur in tiger sharks, it does so at extremely low frequencies within litters."

The research is published in Royal Society Open Science.

Journal Reference:
Holmes BJ, Pope LC, Williams SM, Tibbetts IR, Bennett MB, Ovenden JR. 2018 Lack of multiple paternity in the oceanodromous tiger shark (Galeocerdo cuvier). R. Soc. open sci.5: 171385.

Multiple paternity has been documented as a reproductive strategy in both viviparous and ovoviviparous elasmobranchs, leading to the assumption that multiple mating may be ubiquitous in these fishes. However, with the majority of studies conducted on coastal and nearshore elasmobranchs that often form mating aggregations, parallel studies on pelagic, semi-solitary species are lacking. The tiger shark (Galeocerdo cuvier) is a large pelagic shark that has an aplacental viviparous reproductive mode which is unique among the carcharhinids. A total of 112 pups from four pregnant sharks were genotyped at nine microsatellite loci to assess the possibility of multiple paternity or polyandrous behaviour by female tiger sharks. Only a single pup provided evidence of possible multiple paternity, but with only seven of the nine loci amplifying for this individual, results were inconclusive. In summary, it appears that the tiger sharks sampled in this study were genetically monogamous. These findings may have implications for the genetic diversity and future sustainability of this population.
Attached to this post:[Image: attach.png] Lack_of_multiple_paternity_in_the_oceanodromous_tiger_shark__Galeocerdo_cuvier_.pdf (724.9 KB)
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  • Claudiu Constantin Nicolaescu
Why sharks like it hot - but not too hot

By Helen Briggs
BBC News
4 hours ago

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The tiger shark is a formidable ocean predator

Scientists have calculated the water temperature at which tiger sharks are most active and abundant.

They say the sharks, which are second only to great whites in attacking people, prefer a balmy 22C.

Shark populations may shift range as the oceans heat up, bringing them into greater conflict with humans, according to the scientific study.

For instance, tiger sharks may move into waters off Sydney in both winter and summer months.

Dr Nicholas Payne of Queen's University Belfast and the University of Roehampton led the research.

"Our study suggests that 22 degrees is not too cold for the animals and it's not too hot for them," he said. "It's about right in terms of their optimal preference for temperature."

Cold blooded

Most sharks are cold blooded. Their body temperatures match the temperature of the water around them.

The research, reported in the journal Global Change Biology, could lead to new ways to predict when and where tiger shark attacks might happen.

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The tiger shark diet is made up of fish, crustaceans, sea turtles and seabirds

Increases in coastal water temperatures of one or two degrees could lead to a southern shift in the population of tiger sharks.

"At the same time places like Sydney might start to see more tiger sharks during winter months whereas at the moment you very rarely see tiger sharks in Sydney in winter," Dr Payne added.

In some parts of the world, governments are trying to find ways of dealing with the problem of shark attacks on surfers and swimmers.

These measures include culling programmes, which are highly controversial.

Providing more information on where sharks go and what they do at particular times of year could help in the planning of strategies to prevent shark attacks.

To find out more, the researchers studied tiger shark catches off Australia's eastern coast over several decades to get a picture of where the animals were most abundant.

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Tiger sharks have a large appetite and can eat almost anything they find in their path

They then attached cutting-edge electronic devices to the dorsal fin of tiger sharks living off Hawaii.

The tags on the sharks measure water temperature and have a motion sensor to measure the shark's activity and swimming speed.

"It was really cool because it allowed us to get an idea of how active these animals are as they swim around in the ocean and how temperature affects their activity levels," said Dr Payne.

While overall numbers of tiger sharks are unlikely to change with ocean warming, we are likely to see shifts in the distribution of the animals, he explained.

Concerns over global warming have led to studies of how animals might adapt. Marine animals appear to respond more rapidly to climate change than animals living on land.

Journal Reference:
Payne NL, Meyer CG, Smith JA, et al. Combining abundance and performance data reveals how temperature regulates coastal occurrences and activity of a roaming apex predator. Glob Change Biol. 2018;00:1–10.

The redistribution of species has emerged as one of the most pervasive impacts of anthropogenic climate warming, and presents many societal challenges. Understanding how temperature regulates species distributions is particularly important for mobile marine fauna such as sharks given their seemingly rapid responses to warming, and the socio-political implications of human encounters with some dangerous species. The predictability of species distributions can potentially be improved by accounting for temperature's influence on performance, an elusive relationship for most large animals. We combined multi-decadal catch data and bio-logging to show that coastal abundance and swimming performance of tiger sharks Galeocerdo cuvier are both highest at ~22°C, suggesting thermal constraints on performance may regulate this species' distribution. Tiger sharks are responsible for a large proportion of shark bites on humans, and a focus of controversial control measures in several countries. The combination of distribution and performance data moves towards a mechanistic understanding of tiger shark's thermal niche, and delivers a simple yet powerful indicator for predicting the location and timing of their occurrences throughout coastlines. For example, tiger sharks are mostly caught at Australia's popular New South Wales beaches (i.e. near Sydney) in the warmest months, but our data suggest similar abundances will occur in winter and summer if annual sea surface temperatures increase by a further 1–2°C. 
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  • Claudiu Constantin Nicolaescu
Why do sharks dive?

January 7, 2019 by michelle Wheeler, Particle

[Image: tigershark.jpg]
A juvenile tiger shark. Credit: Albert Kok/Wikipedia

Is it to regulate their body temperature? Conserve energy? Find food?

Tiger sharks at Ningaloo Reef are thought to search the seafloor for prey as they dive down and scan for silhouettes as they swim up to the surface.

But could there be other reasons why the sharks continuously move up and down through the water column?

That's what UWA student Sammy Andrzejaczek is hoping to find out for her Ph.D. research.

Sammy captured 24 tiger sharks at Ningaloo Reef and attached tracking devices to them for up to 48 hours.

Best described as Fitbits for sharks, the devices recorded activity rates and other data 20 times a second.

"I can even look at each individual tail beat," Sammy says.

"It helps us understand why they move the way they do, how environmental change might impact their movements and how removal of prey species from the water column may affect their movement."

Caught On Camera

The tags also contained video cameras, so Sammy could see the habitats the sharks moved through and the animals they encountered.

She watched how the sharks reacted to prey and how the prey reacted to the sharks.

Sammy and her colleagues tagged tiger sharks to find out why they dive. Credit: SAMMY ANDRZEJACZEK

Spoiler alert: Tiger sharks can be pretty lazy—Sammy says something as simple as a turtle noticing a shark and turning away could cause the shark not to bother hunting the turtle down.

"It's all the interactions that are happening on a daily basis that we don't actually usually see," Sammy says.

"Because if you put a human in the water, it's not a natural system any more."

"We get the daily life of a tiger shark without having to distract it from its normal routine."

Spam And Nails

Sammy says tiger sharks feed on just about everything.

"Stomach content analysis has found their normal prey items, such as turtles and rays and fish," she says.

"But they've also found some really interesting things, such as licence plates, cans of spam and nails."

"So they've got a very broad diet."

Tiger sharks may search for food as they move up and down through the water column, Sammy says.

See what tiger sharks do when they dive. Credit: SAMMY ANDRZEJACZEK

"On the way down, they're scanning the seabed for prey," she says.

"And then on the way, up they're searching for silhouettes of prey at the surface."

Ningaloo's top predators

Sammy says studying top predators like sharks can help us understand the ecosystem as a whole.

How tiger sharks move through Ningaloo Reef and feed can help us figure out how they might be impacting the animals beneath them in the food chain, she says.

But hours of watching tiger sharks hunt hasn't put Sammy off the animals at all.

She says her time tagging sharks at Ningaloo was the best month of her Ph.D., if not her life.

"At first, I was a bit apprehensive about it … getting that close to some very big animals," Sammy says.

"But they were very chilled once you had them restrained alongside the boat."

"They'd just sit there, you'd attach the tag, you'd take the line off and they'd just swim off really calmly, it was pretty amazing to see. They're just absolutely beautiful animals."

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  • Claudiu Constantin Nicolaescu
Baby Tiger Sharks eat songbirds
DNA analysis of shark barf tells scientists what kinds of birds the sharks scavenge

Date: May 21, 2019
Source: Field Museum

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Tiger shark. Credit: © frantisek hojdysz / Adobe Stock

Tiger sharks have a reputation for being the "garbage cans of the sea" -- they'll eat just about anything, from dolphins and sea turtles to rubber tires. But before these top predators grow to their adult size of 15 feet, young tiger sharks have an even more unusual diet. Scientists have just announced in a new paper in Ecology that baby tiger sharks eat birds. And not seabirds like gulls or pelicans -- familiar backyard birds like sparrows, woodpeckers, and doves.
"Tiger sharks will see an easy meal and snatch it up, but I was surprised to learn that the sharks were eating songbirds -- I assumed that they'd be seabirds," says Kevin Feldheim, a researcher at Chicago's Field Museum and a co-author of the study who led the DNA analysis that told the researchers what kinds of birds the sharks were eating. "It was one of the coolest projects I've been associated with using DNA to tell a story." The paper's lead author, Marcus Drymon of Mississippi State University, and his team investigated juvenile tiger sharks' diets by wrassling the three-foot-long sharks onto a boat, pumping the sharks' stomachs, and analyzing a sample of their stomach contents. (The sharks were then released unharmed.) Drymon and the team were surprised to see that of the 105 sharks they studied, 41 had bird remains in their stomachs.
But since the birds were partially digested, it was hard for the scientists to tell exactly what kinds of birds they were. To figure it out, they sent the bird remains to the Field Museum's Pritzker Laboratory for Molecular Systematics and Evolution for DNA analysis. The scientists took tiny pieces of the bird remains and used chemicals to break them down into their basic molecular components. From there, they were able to examine the DNA sequences present in the bird tissues and compared them to databases of bird DNA to see what species they were from. "None of them were seagulls, pelicans, cormorants, or any kind of marine bird," Drymon says. "They were all terrestrial birds" -- the kinds that might live in your backyard.
This isn't the first time that tiger sharks have been known to eat birds. "There's a site off Hawaii where baby albatrosses learn to fly, and adult tiger sharks pick them off," explains Feldheim. But this is the first time scientists have evidence that tiger sharks eat songbirds that primarily live on land. That's because these sharks were in the Gulf of Mexico, during migration season. "In every instance, the timing of the tiger shark eating the bird coincided with the peak sighting for that species of bird off our coast," says Drymon.
"The tiger sharks scavenge on songbirds that have trouble flying over the ocean. During migration, they're already worn out, and then they get tired or fall into the ocean during a storm," adds Feldheim. He notes that the terrestrial birds might make more attractive prey than seabirds because the seabirds can handle themselves better in and around the water than the songbirds can.
The study gives scientists a better understanding of tiger sharks, which could ultimately help us to protect them. "All sharks are in trouble," says Feldheim. "We don't know the extent of how industrialized fishing has taken a toll, but the vast majority of top predator populations have declined in recent years."
Beyond the conservation implications, though, Feldheim argues that the study shows the importance of having DNA databases available to scientists: "It shows us how much more we can still learn about sharks in general and what DNA can tell us that observation can't."
This study was contributed to by scientists from Mississippi State University Extension Service, Mississippi-Alabama Sea Grant, Field Museum, Forbes Biological Station-Bellrose Waterfowl Research Center, the National Oceanic and Atmospheric Administration National Marine Fisheries Service, and the University of South Alabama.

Story Source: Field Museum. "Baby tiger sharks eat songbirds: DNA analysis of shark barf tells scientists what kinds of birds the sharks scavenge." ScienceDaily. (accessed May 22, 2019).

Journal Reference:
  1. J. M. Drymon, K. Feldheim, A. M. V. Fournier, E. A. Seubert, A. E. Jefferson, A. M. Kroetz, S. P. Powers. Tiger sharks eat songbirds: scavenging a windfall of nutrients from the sky. Ecology, 2019; e02728 DOI: 10.1002/ecy.2728
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  • Claudiu Constantin Nicolaescu
New Irish research reveals the secret lives of tiger sharks

by Thomas Deane, Trinity College Dublin

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A tiger shark is released after tagging in the Bahamas. Credit: Diego Camejo

A team of scientists led by experts from Trinity and a US-based NGO have just returned from the Bahamas where they learned all about the secret lives of the region's tiger sharks.
Cutting-edge bio-logging devices fixed to the sharks are providing a suite of biological information that has never been collected before, which will help the team assess how the global climate crisis may impact these apex predators.
Tiger sharks are classified as 'near threatened' by the International Union for the Conservation of Nature, with commercial and artisanal fishing pressure and infrequent (once every three years) reproduction contributing to this status. Several countries continue to cull populations of tiger sharks given perceived risks to human swimmers, despite some regions having seen declines in shark abundance of ~ 75% in recent decades.
These huge (up to 5m in length) animals are found in tropical and sub-tropical oceans worldwide but have always been difficult to study given their aquatic lifestyle. The scientists involved in the current study got around this issue by using their biologging devices on the sharks—with sensors recording video, body temperature, swimming activity and orientation as the animals went about their normal routine.
By measuring how temperature influences the sharks' behaviour and swimming performance, the team will be better placed to predict how these animals will respond to future climate change.

Credit: Trinity College Dublin

Assistant Professor in Zoology in Trinity's School of Natural Sciences, Dr. Nicholas Payne, said:
"We are all really excited by the initial results. These animals can be incredibly hard to study in their natural habitat, and it's only recently that the technology is becoming available which allows us to make the kinds of observations we need.
Unlike us, these sharks don't have great physiological mechanisms for controlling their body temperature. As a result, if the temperature of their habitat changes, then so does their performance. Our new data will help us understand how tiger sharks respond to variation in temperature and that will ultimately allow us to make more accurate forecasts of what will happen to these animals if global temperatures continue to change."
CEO of non-profit Beneath The Waves, Dr. Austin Gallagher, sees this kind of research as an important step toward shark conservation. He said: "Apex marine predators like tiger sharks have a critical regulating influence on marine ecosystems, and the more we can learn about their ecology and physiology, the better equipped we'll be to manage and conserve their populations into the future. Our new data are exciting because they are helping reveal some of the secrets behind where these sharks go and what they do."
This research was funded by Science Foundation Ireland and the Irish Research Council.
Beneath The Waves is a not-for-profit shark research and conservation organisation based in the US. You can read all about their work here.
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