Saturday, September 28, 2013

Used and abused

     Hi folks, and sorry for the long break. Summer just becomes a wave of activity that builds and builds and doesn't really crest until kokanee spawn is over with. I have every intention of continuing this blog; there just hasn't been time over the summer.
     I had a great summer, but it ended too soon as always. Every summer I wish I made it to more high lakes, although I did squeeze in one last pack trip at the end of August. 
     We ran our annual population survey of the Blue tailwater below Dillon on Friday the 16th and Monday the 19th of August. It's two days of work because we use a mark-recapture survey. I like surveying this section during the second half of August because I feel that we're getting a relatively clear picture of the resident fish population. If we wait until September or October, it's always hard to know how much the data is influenced by seasonal movements of browns getting ready to spawn. And when you're working on a section of river immediately below a dam, if there's a seasonal upstream concentration of adult browns, then all your data will really tell you is that the browns are getting ready to spawn.
     In higher-water years, if there is at least 150 CFS coming out of the dam after August 15, we put the electrofishing raft on the river and run the survey starting at the power plant bridge and end it at 7-Eleven, which is 0.7 mile. If it's a low-water year, such as 2012 and 2013, we wade electrofish a smaller reach, starting at the USGS gauge and working upstream to the power plant bridge. So, the low-water station is a portion of the high-water station. 
     This summer was a weird time for the Blue tailwater, because releases were pegged at minimum flows for a very long time. For August, 58 CFS is about half of the 25th percentile of flow. On December 10, 2011, flows dropped to near the minimum release of 50 CFS and stayed there until just the past couple of weeks. There had been brief periods of marginally higher releases, but the river never exceeded 200 CFS during that time, and in 2012 and 2013 there were no flows that ever resembled a "runoff" period. The last time the river exceeded 200 CFS was August 15, 2011.
     I want to be clear up front here and point out that I'm not trying to run down the Blue tailwater or be insulting. It gets a huge amount of fishing pressure and generates a lot of economic activity. It is the most accessible, visible, and urban of all our gold-medal trout rivers. But during such a long period of constant flow, the Blue tailwater resembles an aquarium more than any river I've ever spent time on. We know that the forage base is very sparse, and my belief (I don't have solid data to back this up, but we're moving in the direction of doing a study on this) is that at those low flows there are very few mysis - maybe even none - getting entrained in the tailrace. It's also really cold during the growing season. So between the cold temperatures, lack of food, and insanely high fishing pressure, growth rates in the fish are extremely slow. I stock brood culls from the Glenwood Springs hatchery there, and unfortunately that's really the only thing that maintains a large-fish component to the fishery there. 
     During this year's survey, I thought the rainbows were in particularly rough shape. So much so, that on the recapture day I designated an official photographer to document the condition of the fish. So here's a "rogues' gallery" of rainbows from the blue. I'm dead serious when I say that these fish have it pretty rough. Be sure to click on the pictures themselves so you can see close up the full gnarliness of the situation.

     There is literally not a single fish in that reach with a clean jaw. The other thing going on, that I hadn't really seen before, is shown in the pictures below. Massive abrasion starting from the upper jaw and sometimes extending all the way back nearly to the dorsal fin. I really have no idea what causes this. It's only on the brood cull rainbows, and not at all on the browns. The only thing I can think of, is that they have such a hard time finding anything to eat, that they're rolling rocks looking for food, causing the abrasions. Maybe that's a stretch, but it really baffles me. I'd  be interested in hearing anyone else's ideas.