I think MPAs can be used to protect species, particularly those that are highly territorial or resident in particular areas. For those species that are far-ranging, such as tuna and salmon, MPAs probably will not be effective, because there is a high degree of variation in terms of how these species migrate during their adult life stages.
I think MPAs on estuaries and in rearing areas certainly could contribute to the health of salmonids. It needs to be backed up with science, and it needs to be related to the “valued ecosystem component” that you're focusing on.
I'm not sure that they have the data to drive this. I think they need to invest in the science to design areas that are effective, and they need to adapt them to conditions that change over time. This is a very complex issue that you're trying to deal with, and a simple solution of MPAs.... Well, there is no simple solution. They need to be intelligently designed.