That's a very good question. I would say that you look at the source as part of it. You see who's saying that and whether they're independent or working for an aquaculture company or some agency that has a vested interest in continuing with salmon aquaculture in the way it's currently practised. That's one way to look at it.
No matter what scientific question is asked, it's not uncommon for scientists to have dissenting opinions. The way science works is by a back-and-forth and a winnowing of the evidence until eventually the weight of evidence builds up strongly enough on one side that the hypothesis of interest is accepted.
I've looked at some of the testimonies given before this committee, and one of the things I don't think has come across clearly enough is that.... People have criticized the work, for example, of Dr. Krkosek. They have written commentaries saying why they think he's wrong. What has not come across clearly enough is that Krkosek and others have written counter-critiques showing why those criticisms are wrong. You never hear about that from the people who write the original criticisms.
Science is a process in which there is a lot of back-and-forth, but eventually the weight of evidence comes down on the one side or the other. This is an issue you will have to deal with when you believe the weight of evidence is strong enough to support the hypothesis that I believe to be true.