Whale needs power, alternatively graceful bearing (8)
I believe the answer is:
porpoise
'whale' is the definition.
(porpoise is a kind of whale)
'power alternatively graceful bearing' is the wordplay.
'power' becomes 'p'.
'alternatively' becomes 'or'.
'graceful bearing' becomes 'poise' (I've seen this before).
'p'+'or'+'poise'='PORPOISE'
'needs' acts as a link.
(Other definitions for porpoise that I've seen before include "Member of dolphin family" , "Beakless whale" , "Dolphin-like beast" , "Sea beast" , "Sea creature (reported close behind by the 10 to the 9!)" .)