They operate around cement base (9)
I believe the answer is:
sturgeons
'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps they are linked in a way I don't understand?
'operate around cement base' is the wordplay.
'operate' becomes 'surgeons' (I can't justify this - if you can you should give a lot more credence to this answer).
'around' means one lot of letters goes inside another.
'base' indicates one should take the final letters (the base of the word).
The final letter of 'cement' is 't'.
'surgeons' enclosing 't' is 'STURGEONS'.
Can you help me to learn more?
(Other definitions for sturgeons that I've seen before include "swimmers" , "Large fish valued for their roe" .)