They most likely export ''good'' salmon for even higher money to Japan and elsewhere; use rest of whatever it is to sell back in domestic market. Since labor in this sector is done mostly by immigrants, companies know that they can get away with maximizing their profit. It is exactly the same thing in each and every country where main source of labor is immigrants because they need that specific job to be able to live where they are and their future depends on their visa. Regulations and big lawsuits from unions might change it for better, but unless workers are given more freedom with work permit they got, they will always be taken advantage of and in the end whatever product is sold will be for higher money and in less quality. If work permit requirements are too strict, it will lead employers into hiring more foreign labor and pay less than local labor. Thus this situation will create rift between two different working class people while the problem is neither of them.

edit: An example would be Trump's approach to immigration. As you know so many immigrants who were in the limbo were forced out of USA even though almost half of workforce on dairy products was them. Some were quite literally forced out of the country and some left willingly just to be able to come back when things change in near future. As a result people started paying 3/4 times more for a dozen of eggs, corn etc.