In the USA there is some places that do catch and release on cats.
Dogs do not survive very well if at all, alone. However, cats do a
good job of surviving because they catch and eat bugs, frogs, birds,
rabbits, squirrels, etc. Cats are stealth hunters.
So what some humane shelters do is have the cat 'fixed' so it can't
reproduce. Then they simply let it go.
I have 3 children and at my third, I had my tubes tied. Three is
a nice size amount of children. From those, I have 5 grand children.
From those, I have 1 great grand child.
The point I am bringing out is that, it's not just about having children
or cats breeding. It's about how many 'spawn' down the line. So
of course, thousands can spawn due to two cats/two people. And
THAT is the problem.
I think they need to put birth control in the water.