Shark vessel circles swirling fog (7)
I believe the answer is:
dogfish
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shark</span>' is the definition.<br/ ><span class="explanation-format__explanation">(dogfish is a kind of shark)</span><br/ ><br/ >'<span class="explanation-format__original">vessel circles swirling fog</span>' is the wordplay.<br/ >'<span class="explanation-format__original">vessel</span>' becomes '<span class="explanation-format__intermediate">dish</span>' <span class="explanation-format__explanation">()</span>.<br/ >'<span class="explanation-format__original">circles</span>' is an insertion indicator.<br/ >'<span class="explanation-format__original">swirling</span>' is an anagram indicator.<br/ >'<span class="explanation-format__original">fog</span>' is an anagram of '<span class="explanation-format__intermediate">ogf</span>'.<br/ >'<span class="explanation-format__intermediate">dish</span>' going around '<span class="explanation-format__intermediate">ogf</span>' is '<span class="explanation-format__answer">DOGFISH</span>'.<br/ ></span>
(Other definitions for dogfish that I've seen before include "Small, edible shark" , "Restaurants call it rock salmon" , "Nursehound" , "'Small shark, sounds canine (7)'" .)