Sunday, March 24, 2013

Fraser River: Kaibab Park

     The third and final installment of our discussion of the Fraser will highlight Kaibab Park, in the town of Granby. This is the public reach of river adjacent to the baseball fields. I've been surveying a 650-foot reach of river there since 2009.  The upstream terminus of the station is the town's big rock diversion structure immediately downstream of the Highway 40 bridge. 
     The adult trout habitat on this reach is not great, and this portion of the river definitely experiences low flow/high temperature issues in late summer some years. There is not much of a rainbow component here, so the whole story of this reach is what's going on with the browns. Below are the population estimates for the four years I've electrofished it.

     Things were pretty consistent here until 2012, when a couple population parameters went somewhat haywire. First of all, the density of quality dish plummeted. I think that this has to be a response to drought conditions in 2012. During the periods of time last summer when there was as little as 17 CFS of water being recorded at the Northern gauge, it didn't take an expert to look at the stream and quickly determine that there was very little adult trout habitat available. There are some private reaches downstream that are a little better off physically, with undercut banks, etc. I suspect that the larger browns moved down into that area to weather the drought conditions.
      The next big difference in 2012 was the 243% increase in number of fish per mile greater than 6". To see what happened there, look at the length-frequency histograms below:

         At the same time that the adult brown trout population was declining drastically, we had a huge year class show up in 2011. Normally we don't associate giant water years with strong year classes of browns, but things behaved differently in this location. Due to the fact that this reach is toward the downstream end of the river, I think what happened in 2011 is that this part of the river received fry that were displaced by the high flows from several miles of river upstream, including probably all of the canyon. That 2011 year class stuck around and we saw them again in 2012 as a big age-1 year class. The abundance of this group of fish is what caused the fish-per-mile estimate to increase so much. 
     The third big difference in the 2012 sample is the huge number of sculpin we picked up. This is the most dense sculpin population I've seen to date. I think the reason for this increase is the same reason that I just described above, with the small brown trout. Also, the 2012 low water in this reach probably benefitted the sculpin to the extent that there were not as many predators (in the form of adult brown trout) around.
     A lot of people spend years fishing these waters and never see firsthand the species that is the most numerically common fish here. They're surprisingly elusive critters, especially when you realize how many there are in certain areas. So I'll finish up this week's post with a couple shots of sculpin - definitely one of my favorite fish.


1 comment:

  1. Thanks, Jon, for posting up these surveys- I've found each of them interesting. As someone who passes through this area only a few times a summer, I didn't even know there was public access in the Granby area. Hopefully, some of the pending water agreements can ease some of the burden on this creek.