Great Hammerhead: a two-minute wildlife lesson

Fish and Sharks · day 7 of 7

Five facts

1. This is the biggest of all hammerhead sharks. It averages 4.6 m long and can reach 6.2 m.
2. At dawn and dusk it sweeps its wide head over the seabed like a metal detector, sensing the electric signals of stingrays hidden in the sand.
3. Stingray spines often end up stuck in its mouth, yet they do not seem to bother it. One shark had 96 of them.
4. It often swims tilted on its side, using its tall back fin for lift. It can spend up to 90% of its time like this, saving energy.
5. Yellow jacks, a kind of fish, have been seen rubbing against its sides, possibly to scrape off parasites.

The quiz

1. What is the longest a great hammerhead can grow?

• 2 m
• 12 m
• 6.2 m (correct)
• 20 m

It averages 4.6 m and reaches a maximum of 6.2 m.

2. What is it sensing when it sweeps its head over the seabed?

• Electric signals of stingrays hidden in the sand (correct)
• The noise of passing ships
• Warm water from underwater volcanoes
• Light from glowing fish

Sensors under its head pick up the electric signals of buried stingrays.

3. How many stingray spines were found in and around one great hammerhead's mouth?

• 2
• 15
• 500
• 96 (correct)

One shark caught off Florida had 96 spines, and they did not seem to bother it.

4. How does the great hammerhead save energy while swimming?

• By swimming backwards
• By swimming tilted on its side (correct)
• By resting upside down
• By riding on whales

Rolled onto its side, it cuts drag by about 10%.

5. What have yellow jacks been seen doing around great hammerheads?

• Biting their fins
• Riding on top of their heads
• Rubbing against their sides (correct)
• Laying eggs on their tails

They rub against the shark's sides, perhaps to get rid of parasites.

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