Officials of Haad Nopparat Tharap Mu Koh Phi Phi National Park hauled the three-metre-long trap to the surface using a specialised air-lift bag.
The shell will be analysed at the Phuket Marine Biology Centre to determine the turtle’s age.
Scuba diving teacher Paranya Phantajitr told park officials that a foreign friend had noticed the shell inside the trap and she went to confirm the grim find. She was unable to raise the trap herself.
A foreign diver had earlier posted pictures on Facebook of a dead turtle inside a fish trap on a coral reef near Koh Samed.
He posted that he’d informed park officials about it but no action was taken.