Tern dropping and retrieving its catch

Hi all

I've not been on here for a while - so it's a real tonic to get back to it, and see all your interesting posts.

I don't know if anyone knows the reason for this - seen over a river estuary. A tern caught a small fish, then kept (seemingly deliberately) dropping it in the water, and immediately retrieving it again. It was mobbed by a black headed gull, but escaped - later, dropping its catch on the marshes and returning to its fishing. 

Very odd!

Best wishes

Karen B Suffolk