You may be aware of the other cause of shinkage, which is slap-your-forehead obvious when you think about it:

In those places where fishermen keep the big fish and throw back the small ones, fish rapidly adapt to grow more slowly.

(It's a double-damage because the biggest females produce exponentially more eggs than small ones.)

Come on, you can't make the press blaming small fish size on fishing practices, you have to make it Al "the climate whore" Gore worthy. First thing in my mind was, why don't they quit fishing for a year and see if the fish don't grow bigger. Think Maine lobster fishery and Alaskan crab fishery management which are proven success stories in managing fisheries. mpw

Actually, the general rule in fresh water situations (not rivers) each body of water can hold x number pounds of fish - therefore if they grow bigger, there'll be less of them, when the get smaller they're more -same total pounds. The problem in many lakes is that when they stop fishing and taking out the big ones, it throws the balance off and ultimately the pond or lake becomes loaded with stunted fish, which cuts the fishing even more and it compounds the problem. Taking big fish opens up the competition for others to grow.
There are variables. I'd just as soon catch the small ones - better in the pan -less contaminates like pcbs and mercury.

DL, I'm pretty sure I'm talking about fisheries that have been reduced by fishing, and where people have wondered why they can't come back. After all the theory was "Taking big fish opens up the competition for others to grow."

This seems like hard evidence:

With the biggest fish removed from the waters with increasingly sophisticated fishing gear, the smaller fish that are able to slip through the nets take on more dominance in seeding the next generation. Some of those smaller fish are sexually maturing earlier, in turn producing some offspring that are both small and programmed to be young mothers, a potentially dangerous evolutionary trend in some cases.

Boston haddock, which once served as a backbone of New England's fishing industry, is a case in point. In the 1960s, most haddock spawned at age 3 or later. Now, even 1-year-olds are spawning. Cod are also having offspring younger. And on the West Coast, the average size of pink salmon coming back to spawn (which they always do at the same age) decreased 30 percent in 40 years.