being a biology major I find it hard to confront a big majority of people about fish conservation. You can give all the statistics you want, but its just like religion, they'll turn off their ears. You can't talk to someone that wont listen. Wait for them to start talking about how "it used to be", "how many there used to be", stuff like this. They have loaded your gun and cocked the hammer. They have admitted that their is a difference now ( less fish ). therefore admitting that you are right.
About the logging thing. Ever hear the comment " there's no difference in old growth and re growth. Show a logger a picture of two trees. One old growth, the other a spindly sapling. Then ask again if there is a difference between old growth and re growth.