The sea lions have had a tremendous impact on some fisheries (especially those at the mouth of the Columbia River) and NOAA in particular keeps trying to find ways that would effectively curb the damage they do. To date, from what I've seen, those efforts have been ineffectual.
In a more perfect world, one in which man had not screwed up the balance of nature in so many ways, there would be a natural order (however cruel it may seem) that would tend to balance off the populations of fish and the pinnipeds (seals and sea lions). We (mankind) has reduced the number of fish and, for a long time, reduced the number of mammals (including pinnipeds and cetacea) that fed on them. With restrictions placed against harming seals, sea lions and whales, I imagine there is bound to be a heightened competition for the remaining fish.