Raisin' Fish: Mid-Season Maintenance

Saturday was a gorgeous day along McAleer Creek. Relatively clear skies, temps in the high 40s, bright sunshine; a great day to play in the water alongside the creek.

I knew that by now all of the coho that were going to hatch had already done so. The guys at Issaquah Salmon Hatchery had told me that the eggs were 2-4 weeks from hatching when I got them on January 6. Now that a month has passed, only the ones that had died should be left on the trays, along with a few of the lazier alevin that hadn't made it down through the screens yet.

My nephew, Stephen, and I made our way down to the incubator and clarifier intending to pull the trays out of the incubator, clean the dead eggs off the screens and then replace one screen on top of the net bag (to keep it from rising up to the top of the barrel, which it will if left unimpeded). We found that we have had an excellent hatch this year.

You can tell how successful your hatch has been by counting the dead eggs left in the trays at the end of hatch time. Just subtract that number from the total of eggs that got put in at the beginning and you have a reasonable estimate of the number that hatched. We didn't really count the individual dead eggs, rather we estimated. I was really surprised when I pulled the first tray up as it had fewer dead eggs on it than I had seen in any previous year. I estimated that there were no more than 100 - 150 eggs there. When you consider that there had been about 23,300+ eggs on there to begin with, then you get an idea of how good the hatch rate was this year.

The next two trays held more dead eggs than the first, but even the last tray, which had the most of the three, didn't have more than 150-200 eggs on it. In all we figure that at most 500 eggs didn't hatch, which means 69,500 did. That's a 99.3% hatch rate! (99.2857% if you're looking for the significant digits). That is quite a tribute to the consistency and constancy of the water flow we've been able to acheive.

Speaking of water flow, this morning when Francis came to work we noticed that there was no water spilling out of the clarifier, which is the norm for the system. That means that there is as much water flowing through the incubator as possible and the excess is going out of the top of the clarifier barrel. While I was working on the incubator, I shut off the water flow valve at the entrance to the clarifier so that I could lower the water level in the incubator. When I opened it back up, I noticed that the flow never returned to its previous strength. My theory, supported by subsequent discoveries today, is that when you shut the valve at the lowest end of 500' of pipe with water flowing through it, that column of flowing water has a certain amount of inertia and continues to move with gravity down the pipe. This will force any small air pockets in the pipe to 'migrate' up stream and collect in the high spots. If there's enough air in the high spots, the flow of water is restricted at that point unless you bleed the system.

This morning, Francis and Stephen bled the system and found several 'angry' air pockets, ones that hissed very loudly when a stainless steel screw holding the pipes together was removed. This confirmed my moving air pocket theory pretty well. We always bleed the system from the upper end to the lower, getting rid of air pockets all the way down and not encouraging them to migrate further up.

When they got to the bottom of the system, they found that two 10' sections of pipe close to the clarifier had 6' long cracks in them and were leaking significant amounts of water. They did not appear to be leaking on Saturday. I think I would have noticed that quantity of water. We had a really hard freeze in December. I'm guessing that the ice in the lines expanded enough to start the cracks and then increased pressure of shutting the valve/bleeding the system was enough to open them up. They replaced both sections and the water flow has returned to its previous level, flowing over the edge of the clarifier barrel.

When I was cleaning out the trays on Saturday, I noticed a couple of alevin that were pretty far along in their growth. Their bodies were beginning to develop and they had almost entirely absorbed their yolk sac. Other alevin were much closer to the beginning of their process, looking as though they had just recently hatched. I think that through a bit of luck and some experience with the process we chose the best weekend to clean the trays.

So, 69,000+ coho salmon alevin reside in the incubator barrel along McAleer Creek. They will probably be there until some time in April when we let them go.

I haven't done anything with the videos Gwynedd shot of loading up the incubator. I'll try to get them posted. If anyone is anxiously awaiting them, I'd appreciate you posting a comment letting me know. That will provide me with some extra motivation.