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  Seaweek 2005 - Save Our Sharks - Student Info sheet    
 
   
Student Information Sheet 3 - The Role of Rays in the ecosystem
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Glossary
   

Manta rays can grow to have a wingspan
many metres across, but feed on small
organisms filtered from the water. They
are often accompanied by remoras
or suckerfish that ‘hitch a ride’ to the
rays using a specialised suction
mechanism on the top of their head.
(© Andrea Marshall).

Background
The fish that we call rays, stingrays and skates belong to the same group as sharks. This is because rays, skates and sharks all have a skeleton that is made of a material called cartilage. Cartilage is similar to bone but it lacks the chemical that makes bone hard. Your nose and ears are strengthened by cartilage rather than bone. This means that cartilaginous fish (sharks, rays and skates) have strong but relatively soft and flexible skeletons.

Rays and skates are the most diverse of the cartilaginous fishes. There are around 600 species worldwide. These range from the gigantic manta rays, with a ‘wingspan’ of over six metres, right down to skates the size of a person’s hand. Though they vary greatly in size and body form, a common characteristic of rays and skates is that they all have a flattened body with broad pectoral fins that form a body ‘disc’.

   

Stingrays are bottom dwelling rays and their pectoral fins are ideally adapted to burying in sand or mud. The pectoral fins of pelagic rays, such as eagle rays and mantas, are more wing-like with strong muscles for prolonged swimming. These pelagic rays seem to literally ‘fly’ through the water.

Distribution
Rays are found throughout the oceans, from the tropics to the cold waters around the Arctic and Antarctica. They are also found at all depths, from the intertidal zone down to the deep sea. While most rays live in the sea, a few also live in fresh water; some up to thousands of kilometres inland in South America.

Their wide distribution and diversity means that rays have an important role in almost all marine ecosystems, with each species having its own distinctive niche.

The ocean is a three-dimensional environment, with underwater habitats structured both vertically and horizontally. Almost all rays feed on prey living close to, on, or just underneath the bottom. They act somewhat like the vacuum cleaners of the ocean.

This means that the animals that feed on them live on the bottom as well. Rays feed mainly on invertebrates and small vertebrates, with prey ranging from quite large fish down to tiny crustaceans. All known rays are carnivorous, and as a group they are high in the food web.


A tropical whipray (Himantura sp.)
( Shane Litherland)


A typical encounter with a large ray,
swimming close to the seafloor.
(© Andrea Marshall)

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Save Our Sharks March 6 to 13, 2005