Thursday, January 16, 2014

Good times at Radium & State Bridge

     Happy data season to all. I've been warmly ensconced in my office figuring out what I learned last field season. 
     My Glenwood counterpart, Kendall Bakich, and I did a bunch of survey work on four stations on the Colorado downstream of Gore Canyon last spring. I showed some pictures from those stations previously, but I've got that data processed now and thought I'd share some cool stuff. The Radium reach is exactly two miles of river, and the downstream end is the Radium bridge itself. The beginning of the station is up near that old cabin with the historical sign. Here is the table with some population estimates from the past four years on that section:

     As far as the rainbow numbers go, I don't get too worked up about the variation there. I think that in 2011 the timing of the spawning aggregations may have been different, causing us to pick up more fish. I don't know why numbers were down this year, but it was probably by chance too. I would describe the rainbow population in this reach of river as "incidental," sustained by whatever finds its way down there that was stocked upstream, either in reservoirs or on private water. Also, there is some low level of successful reproduction that does seem to take place, but never enough to really get the numbers going. At some point in the future I will probably start stocking HXC fry on this reach, but it will take a lot of them, and I'm doing that up above now which takes up about all of the HXC's I can get. Once they're well-established around Parshall, I'll probably switch the stocking effort downstream.
     The big news here is in the brown trout population trend. And the news is certainly good. We've seen steady and significant increases in just about every parameter of the brown trout population. I don't know exactly why it is, but I've got a theory or two.
     In 2012, you can see that the fish took a big jump up in body condition. Remember that these are spring surveys, so the body condition reflects how the fish came through that previous winter, as well as the summer before. 2011 was the giant flow year, in which the river hit 10,000 CFS at the Kremmling gauge. Often, when you look at body condition of trout after a big flow period, they lose weight during that time. But the opposite happened here. However, it's also true that the winter of 2011/2012 was not particularly cold, and it may be the case that conditions were mild enough that the fish were able to put on weight over the winter. At any rate, when you see average body condition so high, you can expect fast growth, good survival, and good fecundity (high numbers of eggs per female). 
     Our researcher Dan Kowalski has set up a monitoring program to track trends in abundance of the giant stonefly, pteronarcys californica, that we know is so critically important on that reach of river. Every year right after the hatch, he gathers a crew and we go down and count exoskeletons along an established reach of riverbank. Our site is 100 feet long. Below are the counts for that site:

     Again, this is the number of exoskeletons that we counted right after the hatch, on 100 feet of river bank. If you extrapolate this out to 1 mile on both banks of river, it yields an estimate for 2013 of about 1.8 million adult stoneflies per mile hatching in 2013. These stoneflies live for 3-4 years as nymphs before hatching as adults, so if you assume that there are 2-3 year classes in the river that did not hatch in 2013, we're talking about a population somewhere in the neighborhood of 6 million nymphs per mile. This is a very thumbnail sketch of what the numbers might be, but the point is, there is a huge number of them and we're pretty confident in saying that they are the single most important food item in sustaining that fishery. 
     I suspect that the big increase in stonefly numbers that we saw in 2013 plays a large role in the increased quality of the brown trout fishery in the past couple of years. I think it's possible that the huge runoff year of 2011 triggered a positive response in stonefly numbers, and now we're seeing the benefit of that. However, one could also argue that the drought year of 2012, in which we didn't see much in the way of high flows, allowed higher survival of stonefly larvae and that is the reason we saw the big number in 2013. Hard to say at this point, but these are the relationships that we're trying to nail down with a better understanding.  Unfortunately, we missed getting a count right after the hatch in 2012, hence the missing year in the data. 
     Those of you that fish there are aware that Eagle County built a new boat ramp just downstream of Bond, called Two Bridges, and this has created a new float that folks are taking advantage of, from State Bridge to Two Bridges. It's about six miles of river. The existence of that new ramp has changed traffic patterns on the river dramatically, because now float anglers can segregate themselves from the whitewater floaters upstream. There isn't much in the way of rapids on this new float, so the whitewater folks aren't using it much. But the fishing is good. So, we saw the need to add a new survey station in that reach.  I was really stoked to get a new survey station established there.  It is an exciting thing to do a fish survey in a spot where you know that you're the first people to ever scientifically document what the fish population there is. We started our station right at the highway bridge itself, and surveyed downstream for exactly two miles of river. This gives us a good, direct comparison to the radium reach. The results are in the table below:

     So the State Bridge survey revealed a fishery that is just slightly lower quality than Radium, but still pretty good. 
     Be sure to comment or email with any questions.


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