Blaming it all on overpopulation seems to me to be looking at the wrong end of the problem, the consquence rather than the cause.

When people get secure, and know that their children are going to outlive them, and that there is going to be help around when they get old, the size of their families goes down, When they are insecure and think that their children are likely to die before they grow, and probably have to emigrate if they don't die, and there's going to be no help around, the size of families stays big.

That applies no matter what the religious leaders or the politicians say. The main cause of "overpopulation" is poverty and exploitation. And the main cause of overfishing and destruction of the environment is the greed and irresponsibility of rich countries, who use far far more resources per head of population - and even when the size of population in rich countries actually goes into a decline, the amount of resources we use and waste still goes up.

Overfishing is a direct result of "improved" techniques combined with a market economy driven by greed.