This is the Atlantic Cod
It’s the most common fish in the North Atlantic. Well, it used to be - it was overfished because it’s extremely delicious.
The problem was that although there were rules about how big a cod could be before you could harvest it (smaller ones had to be thrown back) the point of the rule was to allow the female cod to get old enough to lay eggs. A female cod lays lots of eggs every year (several hundred thousand) but doesn’t do so until they’re about three years old. As such, although the fishing rules kept fishers from taking immature cod that hadn’t bred yet, because they were so good at their job a cod might, if they were lucky, breed once before being caught.
So what happened?
Smaller cod started becoming able to lay eggs. The average cod now starts breeding at the age of two. This is an incredible change because cod are long lived and examples 25 years old have been found in the wild.
By the way, the same problem is happening with Atlantic lobsters. Female lobsters are also prolific egg layers, but don’t start until they weigh over three pounds. Lobster fishers are, of course, required to release lobsters smaller than that, but again, if a female is lucky, and because the fishers are so good at what they do, they might breed once in a lifetime. Most North Atlantic lobsters are actually born in the Caribbean and float up on the Gulf Stream. By contrast, Australia, where the catch is a lot more severely limited, sees fishers regularly bringing in five pound lobsters. Again, this is a creature that can easily live for decades.