they don't impact the stripers as much as the salmon/steelhead. Sure, they do grab a few but if you have seen them over on the rivers and at the dams, you can see for yourself how many they can eat. If anything, i believe seals don't pose a significant problem to striper populations. If you want to understand why we are seeing smaller populations of them, the lack of freshwater where they spawn is the main culprit.
At now it is about 300000 (may be more) sea lions around SF. Each consuming from 30 to 80 lb fish every day. It is about 5,400,000,000 lb p/yr. And numbers are growing. I think it is heavy burden on fish population. Isn't?
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.