How can the actions of humans both help and harm endangered species?
Humans can decrease their impact on any species, and also provide new habitats and protections for endangered ones.
People often do not realize that habitat displacement from human settlement expansions has a MUCH more devastating impact on species viability than hunting or fishing. Over-exploitation of species by humans also leads to endangerment, but that realization often makes hunters and fishermen MORE supportive of self-imposed restrictions and voluntary contributions for improved habitats!
It is the continuous movement of human populations into other species' habitats that is usually ignored, although it is the most likely way to bring about endangerment, and eventually extinction of a species.