It is difficult not to be a pessimist about the future of the world's fish population. Global marine catches, which had increased rapidly since WWII, stalled in the late 1980's and have been declining ever since. That decline will be difficult to halt.
The rapid depletion of fish stocks is the inevitable outcome of sophisticated industrial technology being thrown at dwindling marine populations as demand rises, fueled by growth in human population and incomes. The decline has so far been masked in the developed world by seafood products that were not previously available, such as farmed salmon, and by massive fish imports from developing countries.
But over-fishing has become a severe problem in the developing world as well. So fisheries worldwide are due for wrenching changes in the near future. A clear indication of the problem is "fishing down the marine food web"-- the increasing tendency to land fish and shellfish from the bottom of marine food chains, often the prey of the larger fish that were previously targeted.
This trend provides low-quality substitutes for the high-quality fish that we were once accustomed to, and will inexorably lead us toward catching plankton, especially jellyfish. Yes, jellyfish, which were once a specialty consumed around East Asia, are now a product caught in the Atlantic as well, and exported across continents.