I believe the thought process on this is very similar to why we wouldn't want to pull stock from south Texas to introduce in a much more northern climate. They are just taking this to a more specific level.
Reproductive success and growth rates have been studied in certain locations that lead them in a data driven direction of believing that by using Bass from this particular area they recruit better.
They do utilize stock from other areas for different projects but in this situation they believe a certain area's population can be enhanced with a bass that is well proven in extremely similar conditions.
There may be other, more technical reasons for this but that's what was explained to me last time I talked with one of our Bassperts about why that hatchery was going to Bass only.

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