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What are elasmobranchs?
The sharks, skates and rays are elasmobranchs; a closely related group of fishes with cartilaginous skeletons and five or more gill slits on each side of their head. These characters distinguish them from the teleost fishes, such as cod, herring and tuna, which have bony skeletons and a single gill cover.
The sharks and rays are an ancient group of fishes. They have lived on earth for nearly 400 million years and evolved such complex and advanced characteristics and behaviours that they have become very successful and important components of the natural marine environment.
There are thought to be about 400 species of sharks and 600 species of rays in existence world-wide, although some of these have not yet been described and named by scientists. Over 60 different elasmobranchs are regularly recorded from European waters.
Some sharks and rays are tiny, able to fit onto the palm of your hand; others, such as the whale shark and basking shark, are enormous. Most are predatory, but some are also scavengers and the largest are plankton feeders, like the great whales. Many are highly migratory. Different species occur in different habitats, including very deep oceans, the open sea, shallow coastal areas and, in some tropical regions, a few rarities even occur in lakes and rivers.
Sharks and rays have developed reproductive strategies which are very similar to those of large mammals with few natural predators (such as the whales or elephants). They grow slowly, mature late (not until an age of 20-25 years for some species), have a relatively small number of young, and are long-lived (up to 70 years). The few young that each female produces in her life-time are born large after a long pregnancy, and have a high likelihood of surviving to adulthood -- under natural conditions.
Why are sharks and rays under threat?
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