Herring feed on shrimp, so the chain is there.
We just finished the herring spawning season right now, and definitely, fishing for that herring is not helpful in trying to rebuild the stock. That's definitely one thing to take into consideration, and the environmental conditions don't help these fish to feed and thrive either.
There are quite a few factors that should be taken into account as to why the herring is not doing great in the Pacific Ocean for now.