The fish species most vulnerable to both overfishing and habitat problems were the anadromous species, those that migrate upstream from the ocean to freshwater to spawn.
(those; migrate; upstream from the ocean to freshwater) (The fish; species; most vulnerable to both overfishing and habitat problems; were the anadromous species)
those The fish
migrate species
upstream from the ocean to freshwater
most vulnerable to both overfishing and habitat problems were the anadromous species