Narrator: Listen to part of a lecture in an Environmental Conservation class.
Professor: Next I want to talk about the collapse of the North American Cod population.
Let's look at Cape Cod in the northeastern United States.
The area was named Cape Cod because there was so many Cod fish in the waters just off its shores, so many that the first Europeans who fished there in the 17th century reported it was better than in New Finland, Canada.
At the time, New Finland's Cod fishery was so rich that people said it was possible just to lower a bucket in the water, pull it out and it would be full of cod.
But Cape Cod was even better, so the fishing industry there did great until after the 1940s, um, there were simply too many fishing vessels, sophisticated vessels, competing for fewer and fewer fish.
In the 1940s there were still about four hundred million pounds of fish caught at Cape Cod every year.
Just 50 years later, though, by the 1990s, commercial cod fishing there had become unprofitable.
The annual catch had gone down about 5% of its 1940s' level.
And here's what's so fascinating: as more and more fishing vessels with better and better fishing technology were competing for cod, this competition was causing changes to the biology of the fish and these changes were making it more and more difficult for the cod population to sustain itself.
Student: Changes to the biology of the fish?
Professor: Well, if a cod fish could reproduce earlier than usual, it'd have a better chance of passing on its genes to the next generation before being caught, right?
And sure enough, biologists noticed that around Cape Cod, the cod were beginning to mature at an earlier age than normal.
Prior to the population collapse, cod usually took about 8 to 10 years to fully mature, to start to reproduce, and they lived around 40 years total.
So cod had about 30 years of active reproductive life.
But now, cod were beginning to reproduce at a younger age, at 3 to 4 years old, and they were living shorter lives because they were being caught, so they had fewer years within which to reproduce.