So:
It has been demonstrated time and time again that fish farms have negative impacts on the environment around them and to wild fish populations as they are point sources for high densities of viral particles and parasites. They entangle pinnipeds which are sometimes killed, produce poor quality fish when compared to wild alternatives, are a horrible waste of marine biomass due to conversion inefficiency from fish feed, have invasive potential from escapes, among many other problems up and down marine food webs. From personal observation, they smell horrible, operate in otherwise ideal passageways for wild juvenile salmon, create intense parasite loads on surrounding wild juveniles, are prone to dangerous viral outbreaks that may at any moment decide to cause disease to wild fish, among many other negatives.
1) Yep they do entangle pinnipeds which are sometimes killed, but seine/gill nets and bottom trawling for wild fish kills most likely just as many, along with a number of dolphins, and other non target fish species that get thrown over as by-catch (dead).
2) True they farmed salmon may be of lesser quality than wild. What do you propose we do? Eliminate fish farms completely and commercially fish for wild fish to replace the production amount? Good luck with over fishing every stock to the point of extinction. It isn't doable to maintain the worlds population on wild fish at this point, or any longer for that matter. Point is farmed fish are still healthy for you.
3) Horrible waste of marine biomass? First off fish have the highest conversion efficiency when compared to any animal. Farmed fish most likely achieve a higher conversion efficiency than wild fish, and do so by using less marine biomass than wild fish do (wild fish eat all fish, farmed fish eat pellets composed of plant, fish, and other content). If a fish farmer has a conversion efficiency of over 1.0 (weight gain per amount of food fed) they get fired.
4) Atlantic's could have potential to be invasive, yes. Take into consideration however that years ago DFO released millions of Atlantics into our waters to try and establish sport fishing populations. None of these ever took. Generally Atlantic's have terrible immunity to things like IHN which is carried by 99% of pacific salmon. Therefore the chance of an Atlantic to compete with a pacific for spawning ground, spawn, hatch and make it back to the ocean is very very low.
At this point with the world's growing population, I think it is inevitable to have fish farms producing most if not all of our fish. If we were to fish on wild stocks to support our desire for fish it would be over fishing making these fish a thing of the past, and not farms. In the end we would be stuck with farms any ways and no wild fish at all. Right now they are obviously finding a way to work together with wild fish, as the runs of wild fish the past few years have been record breaking at times, and none have been pointing towards an extinction event as so many will claim.
Lastly, everyone always comes back to that parasite loading on wild salmon thing. If you read the other thread (can't remember at this point, been so many of these) I provided articles showing that wild fish are not being eliminated due to sea lice. I still have yet to see a viable paper showing that sea lice densities (of parasitic stage) are present around farms.
Lastly, sure all of a sudden some virus' are popping up. As I said before, who is to say we don't have our own strain of ISA present here and that anti-farmers are just finding it now because they are looking for a way to eliminate farms? The ocean is a big connected body of water. Isn't it a little foolish to think that if it isn't one place in the ocean it can't move around due to currents and such? This IHN thing is actually pretty sad to be honest, all pacific salmon and herring are carriers, they just don't show symptoms or die from IHN, Atlantic's do. If you guys are worried about IHN "spreading" from Atlantic's to pacific's you need to get your facts straight, because it is most likely the other way around.