Secrets of largest fish revealed
Published: September 24, 2005
High-tech electronic tags on the whale shark, the world’s largest fish, have revealed how and where they find food.
Researchers in Belize have tracked the sharks as they dive almost a kilometre in search of food, and find shoals of spawning fish in order to eat the eggs.
The sharks grow to 20m in length, and are listed as vulnerable to extinction.
The researchers believe their findings will help to plan tourism operations around whale sharks in a way which does not harm the creatures themselves.
These new, unprecedented insights into the whale shark’s world come from the Belize Barrier Reef, the world’s second largest barrier reef system and a site given UN World Heritage status.
“Our study showed that sharks dive much deeper than previously believed, reaching depths of over 1,000m in search of food,” said Rachel Graham of the US-based Wildlife Conservation Society (WCS).
“Water this deep is only a few degrees above freezing; and this explains why tropical whale sharks have an insulating fat layer just below their skins, something which has perplexed scientists for years.”
Day or night
During the night, the sharks generally remain in shallow water, feeding off plankton, and reserving deep dives for the heat of the day.
Deep dives often end with a high-speed ascent, perhaps to deliver a burst of oxygen to their bodies after a period in deeper, less oxygenated water.
Around the time of the full moon, Cubera snappers come together near the shore to spawn, forming huge masses of writhing bodies in a soup of freshly-released eggs.
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