porpoise vs herring hog

porpoise and herring hog both are nouns.

Word	Noun	Adjective	Verb	Adverb
porpoise	Yes	No	No	No
herring hog	Yes	No	No	No

As nouns, herring hog is a hyponym of porpoise; that is, herring hog is a word with a more specific, narrower meaning than porpoise:

porpoise: any of several small gregarious cetacean mammals having a blunt snout and many teeth
herring hog: the common porpoise of the northern Atlantic and Pacific

Other hyponyms of porpoise include harbor porpoise, Phocoena phocoena, Phocoena sinus, vaquita.

porpoise (noun)	herring hog (noun)
any of several small gregarious cetacean mammals having a blunt snout and many teeth	the common porpoise of the northern Atlantic and Pacific