A world without fish?

That’s what we’ll be living in in a few decades unless we change our ways now:

The world faces the nightmare possibility of fishless oceans by 2050 without fundamental restructuring of the fishing industry, UN experts said Monday.
"If the various estimates we have received... come true, then we are in the situation where 40 years down the line we, effectively, are out of fish," Pavan Sukhdev, head of the UN Environment Program's green economy initiative, told journalists in New York.
A Green Economy report due later this year by UNEP and outside experts argues this disaster can be avoided if subsidies to fishing fleets are slashed and fish are given protected zones -- ultimately resulting in a thriving industry.
Collapse of fish stocks is not only an environmental matter.
One billion people, mostly from poorer countries, rely on fish as their main animal protein source, according to the UN.
According to the UN, 30 percent of fish stocks have already collapsed, meaning they yield less than 10 percent of their former potential, while virtually all fisheries risk running out of commercially viable catches by 2050.
The main scourge, the UNEP report says, are government subsidies encouraging ever bigger fishing fleets chasing ever fewer fish -- with little attempt to allow the fish populations to recover.
Fishing fleet capacity is "50 to 60 percent" higher than it should be, Sukhdev said.

Lifeless oceans are a very real possibility.  After all, fish eat fish.  Once a species is wiped out, whatever ate it will starve if it can’t find an alternative food source.  And on and on.
Why are we not able to live in equilibrium with our world?