according to the food and agriculture organization s fao report about half of the stocks in the oceans were fully exploited and onequarter were either overexploited or depleted with no possibilities in the short or medium term of further expansion pauly and christensen the fao capture fisheries data show that the steady decline of mean trophic levels mtl of fish communities is a global phenomenon tian et al all over the world catch compositions have gone from from high trophic levels larger size and long lifespan to low trophic levels smaller size and short lifespan