The Icelandic cod stock has been shown to consist of two distinct behavioural types, usually referred to as frontal or coastal fish that occupy the same spawning grounds but exhibit either deep-water or shallow-water migration behaviour outside the spawning periods.
Sýnt hefur verið fram á að íslenski þorskstofninn er samsettur úr tveimur aðgreindum atferlisgerðum sem nota þó sama hrygningarsvæði.