As a sort of follow up to last week’s post about the troubles lionfish are causing for Atlantic ecosystems (and where one strategy to combat their numbers is to go after the big fish), I thought I’d share this post from Grist about shrinking numbers of cod of a certain age in the North Sea. As Philip Bump describes,
The headline in the Telegraph is startling: “Just 100 cod left in North Sea.” One hundred fish? Over a massive, 750,000-square-kilometer expanse of the Atlantic near Northern Europe?
Sort of. There are more than 100 cod in the North Sea. The problem isn’t that there are almost no cod, the problem is that there are very few cod of a certain age and size….
“There should be a lot of much-older cod in the North Sea,” [York University marine biologist Callum] Roberts said. “Cod can live for at least 25 years — or probably much older in the olden days when we fished them a lot less. It’s the big, old fish that contribute the great majority of the offspring that replenish populations. They are the anchors of reproduction. If we lose the big old fish, then the reproductive output of the population as a whole goes down steeply.”