Giant Trevally: a two-minute wildlife lesson

Coral Reef · day 7 of 7

Five facts

1. Giant trevallies are clever hunters: they shadow monk seals, use sharks to ambush prey and even leap to catch birds.
2. A trevally escorts a monk seal, and if the seal disturbs prey, the trevally will try to steal it.
3. Adult giant trevallies have been seen ramming blacktip reef sharks again and again with their heads.
4. In fish over 50 cm, males turn dark grey to jet-black, while females stay a much paler silvery-grey.
5. Spawning is timed by the moon: off Hawaii and the Solomon Islands, big schools gather at certain phases of the lunar cycle.

The quiz

1. Which animals do giant trevallies shadow to pick off prey?

• Sea turtles
• Monk seals (correct)
• Dolphins
• Manta rays

They shadow monk seals, use sharks to ambush prey and leap to catch birds.

2. What does a trevally do when a monk seal disturbs some prey?

• Shares it with the seal
• Chases the seal away
• Tries to steal it (correct)
• Ignores it

It tries to snatch the prey away from the seal.

3. What do adult giant trevallies sometimes do to blacktip reef sharks?

• Herd them into shallows
• Clean their skin
• Race them across the reef
• Ram them with their heads (correct)

Adults have been seen ramming blacktip reef sharks repeatedly with their heads.

4. What colour are mature male giant trevallies over 50 cm?

• Dusky to jet-black (correct)
• Bright yellow
• Silvery-grey
• Spotted red

Above 50 cm, males are dark to jet-black, and females are a paler silvery-grey.

5. What controls when giant trevallies spawn in large schools?

• Ocean depth
• Phases of the moon (correct)
• Bird migrations
• Shark patrols

Lunar cycles control spawning, with large schools forming at specific moon phases.

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