I have read where it could happen as early as 2035. Another big problem is the buildup of toxics, especially mercury in the edible fish and shellfish catch. It is estimated that between 10 and 20% of humanity's food comes from the oceans and polluted rivers' fish farms.
It is just one of the "key resources" that will be depleted or near depleted as to make them very expensive in a poorer world from overpopulation. The net result is skyrocketing food prices and vastly lowering food production along with scarcer pure water supplies, especially after 2040.
It is all part of what has been called a "perfect storm" of converging catastrophes: The polluted and depleted oceans, the polluted and depleted river systems, depleted aquifers, oil depletion, soil pollution and depletion, and continued increasing climate fluctuation by AGW effects.
People thought the oceans were too vast and could absorb all the pollution and the nearly endless fish stocks could not be depleted. Now we are on the last 10% of the oceans' harvest, there are over 100 ever growing estuary dead zones, and six medium or larger country sized trash gyres. The oceans are near saturation for absorbing CO2 and are increasingly acidic. The oceans are warming to the point of methane releasing slowly, at first. Right now up 1*F down to 400 meters deep and the methane, so far, is dissolving in the increasingly stinking seawater. Some areas seem as pristine as ever, hiding the facts of distant pollution coming closer. The dissolved toxics and mercury are invisible and slowly reaching out beyond the areas of heaviest coal fired power plant fallout.
People have wasted many years that could have brought about changes in numbers and ecologically negative behaviors. There is still not enough positive changes to stop the Juggernaut of various negative effects converging at 2050 or before.
](./images/smilies/eusa_wall.gif "Brick wall")
