Maintaining Homeostasis in sharks: Gills
The sharks Gills one of the most important things on the shark. Yes it can help it breathe but it also regulates the sharks' intake of salt from the ocean. If a shark has to much salt then it can lead to death.
SHARKS NEED TO MAINTAIN THEIR SALT LEVELS
Because most sharks live in a saltwater environment, they must maintain a balance between the salt in the water and in their bodies. If the balance is off, it could lead to the shark having either too much or not enough water in its body - either imbalance can quickly lead to death.
Sharks have far more salt in their bloodstream than most vertebrates - about 250 times as much, or close to the same concentration as seawater. This allows them to stay in perfect "osmotic" balance with the surrounding seawater.
To maintain this balance, sharks secrete a salty compound called urea, which flows through their system to maintain a balance between the salt in the water and in their bodies. A shark's kidneys play an important role in this process. If sharks build up too much urea, they can excrete the salty excess from an opening below their abdomen called a "cloaca" or through their gills.
A few sharks, like bull sharks, have developed "super kidneys" that can remove large amounts of urea from the bloodstream. This allows them to enter and hunt in freshwater rivers and lakes, where salt levels are far below seawater.
How Sharks breathe
The elasmobranch traits have helped sharks rule the sea. Special adaptations have ensured that sharks are well suited to ocean life and able to survive in many different environments throughout the sea. Sharks have skin like sandpaper. Tooth-like scales, called placoid scales or denticles, are embedded in sharks' skin and in parts of their mouth linings and gill cavities. These scales are probably replaced by larger scales as a shark grows. Different shark species have different types of scales. A shark's survival depends partly on the quality of its teeth. Sharks' teeth are modifications of the placoid scales on their bodies.
Characteristic of Life: Organization
The Structural and Functional Organization of the Lateral Line System of Sharks
The lateral line sense organs of sharks include ampullae of Lorenzini and neuromasts. Each of these two classes of receptors is highly specialized and therefore can be expected to biologically respond to one specific modality of stimulus of minimal threshold intensity. Current anatomical, electro-physiological and behavioral evidence indicates that the ampullae are organized to respond to very weak DC and low frequency AC electric fields that originate from external sources in the environment and that this information is used in the detection of prey. Neuromasts consist of canal receptors and pit organs and are mechanoreceptors that are sensitive to water movements caused by external sources as well as the animal's own swimming movements. There is no convincing experimental evidence of the behavioral role that neuromasts play in the life of sharks, but they can orient toward a source that causes water displacements and perhaps use the neuromast system in the coordination of locomotor activity.
Ampullae and neuromasts are innervated by different components of the lateral line nerves that project to special terminal areas within the central nervous system. The dorsal root of the anterior lateral line nerve, which is believed to carry nerve fibers from the ampullae of Lorenzini exclusively, enters and terminates within the anterior lateral line lobe of the medulla. Neuromasts (canal and pit organs) are innervated by the ventral root of the anterior lateral line nerve and posterior lateral line nerve, which project to the posterior lateral line lobe (nucleus medialis) of the medulla and, in addition, distribute to the eminentia granularis of the cerebellum, superior and inferior lobes of the auricle, and to the spinal cord. There is no apparent overlap between those central terminal fields that receive fibers from electroreceptors and those that receive fibers from mechanoreceptors nor with the central terminal field of VIIIth nerve neurons. This supports the contention that different functional classes of lateral line receptors are specialized to perform a particular function, but the central coordinating and integrating mechanisms are unknown.
A shark's skin is rough, covered by a layer of tiny tooth-like scales. They have streamlined bodies. Shark pups are born swimmers. A shark's fins help it to balance and change direction. A shark's pectoral and pelvic fins act like aircraft wings. Gill slits are long, thin openings behind their heads. As a shark breathes, water goes into the mouth and passes over its gills. Sharks that spend time resting on the seabed have an alternative way of breathing holes called spiracles.
Sharks use their keen senses to hunt. Sharks's eyes are sensitive and can see best in dim light. In deep, dark water they use a reflective layer at the back of the eyes that acts like a mirror. An extra layer of skin closes over the eyes to protect them during hunting. Sharks that don't have the extra skin over their eyes roll them back their heads when they attack. Sharks have two nostrils on their snouts. Sharks can smell a drop of blood in ninety-five liters of seawater. They can hear a wounded animal struggling from as far away as the length of a football field. A shark's inner ears have tiny hairs that sense the slightest movements in the water.
Scientist: Tobey Curtis,NOAAFisheries Northeast Regional Office
My research focuses on shark and skate fisheries, as well as the distribution, movements, and habitat use of a variety of species. For NOAA Fisheries, I help coordinate the management of spiny dogfish and skate fisheries in the Northeast Region.
My unique area of shark expertise is electronic tagging and tracking and using GIS to analyze movements and habitat selection.
Characteristic of life:Reproduce
Collaspe and Conservation of Shark populations in the Northwest Atlantic Ocean:
We provide strong quantitative evidence to support the argument that these species have declined substantially in the past decade.
The trends for oceanic sharks have also shown decline. We estimate that thresher sharks—a group composed of the common thresher (Alopias vulpinus) and bigeye thresher (A. superciliousus)—have declined by 80% (95% CI: 76 to 86%) (Figs. 2E and 3E). Unlike the area examined for other oce- anic sharks, the area examined for thresher sharks encompasses the known distribution of their Northwest Atlantic populations (18). Observed declines suggest that these popula- tions have collapsed. The interpretation of trends in abundance for other oceanic sharks is complex because their ranges extend across the North Atlantic. Blue sharks declined by an estimated 60% (95% CI: 58 to 63%) (Fig. 2F). Conflicting patterns between the areas of highest catches (Areas 5 to 7: 90% catches) (Fig. 3F) could indicate density-dependent habitat selection, with blue sharks moving into preferential habitat (Area 7) as the pop- ulation declined. Abundance of mako sharks (mostly shortfin mako, Isurus oxyrinchus) declined moderately (Figs. 2G and 3G). The oceanic whitetip shark declined by an esti- mated 70% (95% CI: 62 to 75%) (Figs. 2H and 3H). From our data, we cannot infer reliable trends for oceanics across the entire North Atlantic Ocean. However, because other longline fleets exert intense fishing effort across the North Atlantic (7), this pattern could well be representative of the entire region.
Our results show that overfishing is threatening large coastal and oceanic sharks in the Northwest Atlantic. The large and rapid declines we document are in addition to sub- stantial historical reductions (2, 22). Overex- ploitation of elasmobranchs (sharks, skates, and rays) is known to have already nearly eliminated two skate species from much of their ranges (23, 24). The magnitude of the declines estimated here suggests that several sharks may also now be at risk of large-scale extirpation.
Shark deprived of her mate turns asexual
WHO needs males? A female shark has had babies on her own years after being separated from her long-term mate. It's a rare case of an animal switching from sexual to asexual reproduction.
Leonie the zebra shark (Stegostomafasciatum) met her male partner at an aquarium in Townsville, Australia, in 1999. They had more than two dozen offspring before he was moved to another tank in 2012. From then on, Leonie had no male contact. Then in early 2016, she had three baby sharks.
Intrigued, Christine Dudgeon at the University of Queensland in Brisbane and her colleagues began fishing for answers. One possibility was that Leonie had been storing sperm. But tests showed that the young only had DNA from their mum, so were the result of an ability some sharks are known to have: reproducing asexually (Scientific Reports, doi.org/bw97).
"In species that are capable of both reproductive modes, there are quite a few observations of switches from asexual to sexual reproduction," says Russell Bonduriansky at the University of New South Wales in Sydney. "However, it's much less common to observe switches in the other direction."
In female sharks, an egg can be fertilised by an adjacent cell known as a polar body, Dudgeon says. This contains identical genetic material, leading to "extreme inbreeding", she says. "It's not a strategy for surviving many generations because it reduces genetic diversity and adaptability."
Yet, it may be necessary at times when males are scarce. "It might be a holding-on mechanism," Dudgeon says. "Mum's genes get passed down from female to female until there are males available to mate with." It's possible that the switch from sexual to asexual reproduction is not that unusual; we just haven't known to look for it, she says.
Scientist: Jennifer V. Schmidt, Ph.D.
Dr. Jennifer Schmidt received her PhD from Northwestern University in Chicago, and did postdoctoral work at Princeton University. She is a geneticist and molecular biologist by training, with a long-standing interest in conservation genetics, and in the use of genetic tools to characterize wild populations. In 2001 she partnered with the Shark Research Institute to use genetics to understand the migration and reproduction of whale sharks. Her global whale shark genetic study includes animals from nearly 20 different countries, and has taken her to field sites in places like Mexico, Djibouti and the Philippines. In 2005 she became Director of Genetic Studies for the Shark Research Institute, and since 2016 has served as SRI Director of Science & Research.
Characteristic of life: Respond to Stimuli
Dr. Abolone-marine biology, surfing, and more: Sharks attacks are on the rise
Surfers are the most likely people to be attacked by sharks. There are among a group of victims called “surface recreationalists” by the International Shark Attack File that also includes water skiing, windsurfing, boogie boarding, rafting, or floating on inflatables that make up the largest single group of people attacked. Next in line are swimmers and bathers, then divers (mostly Scuba but also hookah and free-diving). The last group are those entering or exiting the water, such as when climbing a ladder into a boat or jumping off a platform. Of the 242 known attacks in California, for example, 28% were surfers,10% swimmers, 9% Scuba divers, 8% free divers with most of the rest were fishers, kayakers and skin divers. No one knows why surfers are the largest group of victims. But the sharks that cause most of the attacks (see below) are large, powerful predators that commonly prey on surface-based prey such as marine mammals, sea turtles and birds. Also, surfers tend to spend longer amounts of time in the water than most other groups, making them more vulnerable, and the shape of their surface profile unfortunately resembles many of their marine mammal prey
Deadly shark attacks on the rise
THE beach is off-limits. A surfer has died this week in the latest of a series of fatal shark attacks off the coast of Australia. But as police boats scour the ocean for the culprit, which attacked about 10 metres from the shore, there is no evidence that shark numbers have risen at all.
Tadashi Nakahara died after both his legs were severed at Shelly Beach in northern New South Wales. The incident occurred just a week after beaches further south were closed for a record nine days following shark sightings.
This is the third fatal attack in New South Wales in the past 12 months, and the sixth in Australia, compared with just four in 2012 and 2013 . But "there is no data to suggest that there has been an increase in shark numbers", says Christopher Neff from the University of Sydney. The rise in attacks could be random, or it could be driven by other factors that bring sharks closer to coast, such as small changes in thermal currents or bait fish movements. There may also be more people in the ocean, he says.
Woman Critical After Shark Attack on California Beach
CAMP PENDLETON, Calif. (AP) — A woman who lost part of her right leg in a shark attack while wading at a popular Southern California beach was listed in critical condition Monday at a hospital.
Leeanne Ericson was rescued Saturday by a handful of Camp Pendleton beachgoers, including one who used a tourniquet fashioned from a surfboard leash to stanch the bleeding.
She was flown to Scripps Memorial Hospital in La Jolla, where hospital spokeswoman Janice Collins said she was critical condition but declined to release further details.
"All of the back of her leg was kind of missing," Thomas Williams, one of several witnesses who pulled the woman ashore, told the Orange County Register.
He said a veteran surfer, Hunter Robinson, suggested using a surfboard leash to stanch the bleeding until Camp Pendleton Marine Corps Base emergency personnel arrived.
The shark attacked at a beach known as Church on the northern tip of the base.