Tonic immobility is a reflex that causes a temporary state of inactivity in an animal. Similar to hypnosis. It occurs in a variety of different species, including many sharks and rays...

But how is any of this possible? Well, it’s largely due to the specific species chosen for this approach. Koehler, L., Smith, L.E., Nowell, G., 2018. Recovered and Released – A novel approach to oviparous shark conservation. Ocean and Coastal Management. 154. 178-185. Instead of laying her eggs, the female will carry them inside her body. Providing extra safety from potential predators. The embryos develop within an eggcase that has a thin membrane. Once developed the baby shark will hatch inside her mother, who'll then give birth to the young. In some species the pups aren't born immediately after hatching. Instead they stay in the uterus where they'll feed off unfertilised eggs. This is known as oophagy. Sharks invest a lot of energy into producing a few, well-developed young. There are 3 main methods of reproduction: oviparity (egg-laying), ovoviviparity and vivparity (live birth). GRUESOME FACT – Sandtiger pups not only eat unfertilised eggs but their un-hatched siblings too! This is called intrauterine cannibalism.

HOW CAN YOU HELP?

All shark releases so far have been public events, with the public and various dive clubs and organisations coming along to wave the sharks off. Dive clubs have even supported the releases by providing equipment such as air tanks for the divers involved. The shark pups can be viewed for a short period of time before they are taken down to depths of around 20 metres in a suitable habitat and released by the volunteer divers. These types of tags are placed at the base of a shark’s fin to record information about the ocean environment (such as temperature, pressure, salinity, and light levels) and location of the shark. The tag is programmed to pop off the shark after a specified amount of time, float to the surface, and transmit the information to the satellite. Specialized Tags Viviparity is the most advanced method of reproduction. The baby shark develops inside their mother’s body, receiving nutrients and oxygen through an umbilical cord. This is the same method used by mammals. But, unlike mammals, when the pups are born they're immediately independent and have to fend for themselves.

Sharks primary sensory structures are the lateral line, pit organs, and ampullae of Lorenzini. Here’s how they work: PRODUCE FEW YOUNG - varying from 2 pups for the Bigeye Thresher and up to 135 for the Blue Shark. Compare this to the reproduction potential of bony-fish who release millions of eggs. Sharks are particularly vulnerable to the threats posed by humans because they reproduce slowly. They: ARE SLOW GROWING & LATE TO MATURE - as an extreme case the Greenland Shark can live ~400 years and doesn’t reach sexual maturity until ~150 years! Many are killed before they’ve produced offspring. Magnetoreception: The Ampullae of Lorenzini are like little semiconductors connected to snout pores that help to give sharks the ability to detect and orient to the Earth’s magnetic field. A Tail of Two SharksOviparity is when eggs are fertilized in the womb and then a shark lays the eggs encased in a leathery pouch, called a “mermaid’s purse.” The eggs are left unprotected and are oftentimes eaten by predators before they can hatch. The eggs hatch with no parental care after the eggs are laid. The protective capsule acts as a life-support machine, containing everything that's needed. The embryo absorbs nutrients from a yolk-sac before hatching. And emerges as a miniature version of the adult.

Today, many aquariums and research facilities use Dr. Clark’s target training and feeding method to attract sharks to a designated feeding area. The feeding method is a helpful way to ensure each shark gets the right amount and type of food, which is especially important when feeding a mix of shark species in one pool.Some sharks have homocercal tails, where the upper and lower tail lobes are the same size, or symmetrical. A symmetrical tail can propel a shark through the water at high speeds. A great example of this tail is the shortfin mako whose latin name, Isurus oxyrinchus, means “same tail, pointy snout.” The shortfin mako can have swim bursts up to 90 miles per hour! Odds A smalltooth sawfish shark with a satellite tag and yellow spaghetti tag. Fin-Mounted Smart Position and Satellite Tags Friedrich, LA, Jefferson, R, Glegg, G, 2014. Public perceptions of sharks: gathering support for shark conservation. Marine Policy 47, 1–7. For many, the Natural History Museum is a place that inspires learning, gives purpose and provides hope. People tell us they 'still get shivers walking through the front door', and thank us for inspiring the next generation of scientists. To reverse the damage we've done and protect the future, we need the knowledge that comes from scientific discovery. Understanding and protecting life on our planet is the greatest scientific challenge of our age. And you can help.