shell collecting vs collecting

shell collecting and collecting both are nouns.

Word	Noun	Adjective	Verb	Adverb
shell collecting	Yes	No	No	No
collecting	Yes	No	No	No

As nouns, collecting is a hypernym of shell collecting; that is, collecting is a word with a broader meaning than shell collecting:

Other hypernyms of shell collecting include aggregation, assembling, collection, malacology.

shell collecting (noun)	collecting (noun)
the collection and study of mollusc shells	the act of gathering something together