Grouper Thumping

 

            Spiegel Grove, Key Largo, 108 feet, I think on the port stern, (it’s the downline that tees), a large vertical steel structure with four “windows” cut in it, each large enough to maybe allow a diver to swim through.  I rose up off the deck to look in the window, and I was face-to-face inches from the gigantic mouth of the largest Goliath grouper I ever saw.  I tried to measure it in imaginary yardsticks, and I came up with 11 feet.  It barely fit in the “box.”

            My buddy was videotaping, and I was looking and kind of posing with the grouper.  There was never a thought of swimming into the box.  The grouper spasmed, making a loud boom; you could feel it in your chest.  It did this often.  It did not sound happy.

            What do we know about this thumping behavior?  I had never heard it before.  Is it a technique the grouper uses to stun prey?  Is it a territorial warning sound?

Mating

They do this thumping, or booming, during the mating season, which is going on right now.  However, I'm not an expert on this, so there may be other reasons they make these sounds as well.

Allison

Warning

Hi Martin, the fish was letting you know he wasn't happy with your proximity.

Allison is also correct that these fish create these sounds during aggregation/mating as well as agonistic behavior to fend off rivals and, in your case, a diver.

ftp://ftp.floridamarine.org/users/sedar/goliath/Mann_etal09.pdf

Thank You Carlos

On several previous encounters I found Goliath groupers especially diver friendly, so it is surprising I so upset this giant, but I will be timid should it occur again.

I am deeply grateful for your input.

Thank you.

Marty

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