food fish? As a shark, the dog's flesh is saturated with urea which must be leached out before it's edible.

eating baby salmon? I doubt that they could catch one.

place in the ecosystem? Like dungeness crab, they are primarily scavengers. I could live with less dogs and more crab.

good sign for fishing? That's a new one on me.

There used to be a large dogfish fishing (trawling, I believe) industry in Puget Sound. They were primarily extracting oil from the dog livers. The little beggers were fished to the brink of local extinction. Unfortunately, before this happened, synthetic substitutes were discovered.

Doggies are still long-lined by boats out of Neah Bay, probably for fish & chips.