Whale, first of rorquals etc, jumping in somersault (9)
I believe the answer is:
cartwheel
'somersault' is the definition.
(I've seen this before)
'whale first of rorquals etc jumping' is the wordplay.
'first of rorquals' becomes 'r' (1st letter of 'rorquals').
'jumping' indicates an anagram.
'whale'+'r'+'etc'='whaleretc'
'whaleretc' anagrammed gives 'CARTWHEEL'.
'in' is the link.
(Other definitions for cartwheel that I've seen before include "Revolutionary move" , "Gymnastic feat" , "acrobatic manoeuvre" , "to go on the wagon" , "Acrobat's manoeuvre" .)