I've been following this story in the Mail Tribune about privatizing Cole Rivers Hatchery, and it makes me think some private business ought to take it over. Maybe a private company would run it at full capacity, unlike the state. You go up there, and more than half the ponds are empty. Why aren't they all full of fish?

— D.D., email submission

So we at Since You Asked Central asked Cole Rivers Manager Dave Pease about your question, D.D., and we didn't get one-third of it out before Pease knew exactly what we were asking.

"That's a weekly question here," Pease says.

The answer is that all 87 raceways can't be used at once because not all the salmon, steelhead and trout are the same sizes, they all don't stick around the hatchery for the same amount of time, and they definitely all don't get released at the same time.

Here's an example of why.

Hatchery technicians recently transferred 1,646,200 spring chinook from the hatchery house to a concrete raceways in a process they call "ponding." Since they're all about a 1.2 inches long, they filled seven ponds.

As these fish grow, they take up more space, and fewer can be in any single raceway, Pease says. By the time they're ready for release in late summer, those chinook will have expanded into a total of 30 ponds, Pease says.

Likewise, that happens to steelhead and trout.

Other ponds are used to keep the adults that return to the hatchery. Those ponds numbers can vary dramatically depending upon the time of year, the numbers of returning fish and whether multiple species such as coho salmon and summer steelhead are returning simultaneously.

And sometimes they are empty because they need to be cleaned and prepped for the next group of fish, Pease says.

The hatchery also sports 27 smaller, circular ponds that it doesn't use very often because it recirculates water in such a way that diseases are more prevalent in them than the raceways, which have a pass-through water system, Pease says.

Occasionally, however, technicians will use the circular ponds for "show fish" that visitors can feed or for keeping a close eye on young spring chinook that were fitted with coded-wire tags in their snouts for research purposes, he says.

— Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. To see a collection of columns, go to mailtribune.com/youasked. We’re sorry, but the volume of questions received prevents us from answering all of them.