I've mulled this one over before and I think it's as simple as:

by-catch = extra $$$

Netting brighter fish lower in the system makes for a more merchantable product.

my .02 cents

BD
_________________________
Bobber Down

"It makes no sense to regulate salmon habitat on land while allowing thousands of yards of gill nets to be stretched across salmon habitat in the water"

John Carlson, Gubernatorial Contender, Sept. 2000 speech at the Ballard Locks