A sustainable fish harvest is one that can continue year after year without diminishing fish stocks.
Some people may eat just a few fish. Some may eat many, Some will eat pigs that have been fed fish. Some will eat corn fertilized by fish. The total of all these harvested fish each year equals the human use of fish or "footprint." To prevent fish stock extinction, the human footprint has to be lower than the ocean's capacity to grow fish.
For 10's of thousands of years, human footprint has been below this capacity.
But today it is not. Fish stocks from harvesting diminish each year. Even with fish farming creating additional supplies, the ocean harvest diminishes stocks. If we want sustainable fisheries, or for that matter, if we want continued use of any diminishing renewable-resource or ecosystem, we must reduce our footprint. However, our increasing population increases our footprint. Even if we only replace ourselves, per capita increases in consumption increase footprint
If we capped each person's consumption at the middle class level of a developed country and let the 80% who globally have not attained this level to catch up, the human footprint would increase four times. If technology could quadruple production, allowing parity to be reached, human striving would continue to push consumption over sustainable limits.
Into this bleak view of life I propose a solution called "Dynamic Sustainability." Dynamic because the variables in the system I envision, instead of heading for fixed targets keep changing.
In my plan, footprint continues to decrease. The difference between footprint and carrying capacity continues to increase.
The difference drives technology more gently. Smaller risks need to be taken. For example, smaller demand for GM to bolster supply. My plan also requires "universal rapid increases in well-being" ( for 6 billion people) facilitating relief from social conflict.
To facilitate these never before seen trends, my solution requires, continuous and rapid decreases in population. As long as the doubling time of consumption is longer than the halving time of population then footprint will contract.
For example, if everyone had one child per family, then the population would halve each generation or 30 years. At this rate of population decline, per capita consumption could double every 30 years without creating an increase in footprint. To understand the enormity of a doubling of per capita consumption every 30 years, consider that anyone born into one house (one footprint), will own two homes (occupy two footprints) by the time they are thirty, four homes (4 FP's) by the time they are 60, and eight homes (8 FP's) by the time they are 90.
Where did all these homes (FP's) come from? Ask oneself how many parents one had (two), how many grand parents one had (four,) and how many great grand parent's one had (eight).
If all of these ancestors were only children, and each was born into one home (FP) then, through inheritance alone, these homes (the access to footprint) come into the possession of the great grand child without he or she having to take these homes (FP's) from anyone else.
Social stability comes from each individual having full knowledge of the capacity of these behavior to deliver footprint. Each individual would recognize how expensive and unnecessary it would be to hasten this rate of improvement. Sustainability is just a by product. No one can eat eight times as much fish or flush eight times as many toilets.