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Rays

 

Rays are present in most marine ecosystems worldwide, and have a vital role in maintaining the health and function of these ecosystems. Their ecological niche has been little-studied when compared to sharks, but their diversity, abundance and worldwide distribution testifies to their success.

 

Rays are closely related to sharks. They have flat bodies with eyes and mouths on their undersides and long slender tails. Some rays skim the ocean floor looking for food. Many rays have strong jaws that help them crush mollusks and crustaceans. Like sharks, rays don't have a swim bladder, but unlike sharks, they move their pectoral fins when they swim. They must stay in motion constantly or they will sink. 

 

Electric rays make their own electricity, with organs on either side of their heads that can deliver a shock of up to 200 volts. They use this electric shock to scare away predators and to shock prey. Stingrays, eagle rays and devil rays have spiny stingers on their tails that can inject a predator with venom.

 

As rays have few predators, their low natural death rate has allowed them to adopt a life history strategy focused on producing a few, large young. Compared to most bony fish, rays are long-lived, slow-growing, and are late to mature.  Unfortunately, this makes rays highly vulnerable to human-made pressures such as fishing, habitat degradation and pollution. 

 

Rays are a common catch within many fisheries, both inshore and offshore. Most fishing pressure occurs in waters over the continental shelves, putting the species living in this area at risk. Deep sea fisheries are still being commercially developed, and rays will increasingly be caught as bycatch in these areas. The low reproductive rate of rays means that species can be heavily reduced, even to extinction, before the targeted bony fish species shows a significant decline in catch. 

 

Habitat modification and pollution are also major issues for some inshore species. Estuarine and coastal areas are suffering increasing alteration through development, restriction of river flows, land reclamation and other pressures. The young of many inshore species spend their first few months or years in high productivity ‘nursery’ areas. Often these nursery areas are located in estuaries or shallow mangrove area ecosystems where there is plenty of food and protection from larger predators. The destruction of these nursery areas can result in a permanent reduction in the local ray population. 

 

Rays have a vital role in maintaining the health and function of the ecosystems. Their ecological niche has been little-studied when compared to sharks, but their diversity, abundance and worldwide distribution are evidence of their success. The challenge is to ensure these rays are protected, so they do not quietly disappear before we can fully understand just how important they are.

 

Sharks and rays keep our ocean balanced.