There's some evidence that no-take areas, or areas where no extraction is allowed, can help restock places outside these, through what's called “spillover”. The evidence of that is somewhat mixed, though. If we have more fish in a place that's protected and if the fish don't move a lot—we have some that don't, like a lot of the rockfish, which are fairly sedentary—then they're going to release their young and they're going to go into the fished areas. That's one of the mechanisms: that no-take areas can exist to help fisheries. However, whether that's sufficient to offset the loss of fishing grounds within that—it happens by having an MPA closed—that's what's not clear in terms of some of the science.
The other point is that MPAs have a short-term impact, an initial impact, on fishing, because if those no-take areas are closed, those fisheries cannot fish those areas. Their benefit, however, is likely to be much longer-term into the future. It depends on the species. In many cases, it's going to take about five years. In others, such as the yelloweye rockfish I was talking about, you're talking more like 20 years for those individuals inside the boundaries to build up and provide a benefit to the outside.
There is often in the discussions a bit of a mismatch between the potential short-term impacts and the longer-term benefits that we might see from MPAs.