Sunday, March 10, 2013

Fraser River: Confluence Park

     I get asked a lot about the Fraser River and the status of its fish populations. That's always a difficult question to answer, because the Fraser is an extremely dynamic stream, in which there are hardly two miles of river that resemble each other. This is a stream that undergoes many transitions in its relatively short run from its Berthoud Pass headwaters to its confluence with the Colorado at Windy Gap. To call it a river (at least in its modern state) is a little bit of a misnomer, as it's really more of a large creek. There are certainly more extreme examples in this state though -- the Swan River near Breckenridge is the one that always comes to mind.  
     So, I thought maybe I'd do a series of posts based around each of the electrofishing stations that I survey regularly on the Fraser. I've got two locations that I've been hitting anually, one that I get to less often than that but still regularly, and a number of places I've surveyed one time. The single-visit sites are mostly on private land and have served to fill in information gaps and give us a better big-picture overview of the Fraser. However, because those sites are on private land I won't comment on them here.
     The farthest upstream station that I survey regularly is called Confluence Park, and is located in the town of Winter Park. The station is 570 feet long and the upstream end is the pool where Vasquez Creek joins the Fraser. I have electrofished that reach in 2007, 2009, and 2012. We were astounded at the changes we found on this reach in 2012. 
     This reach of river is still a pretty cold, montane type of a stream with a bit more gradient than what is found below. It's heavily shaded with spruce-fir and willow stands along the banks. Brown trout are rare on this reach. It's always been more of a brook trout stream, producing some fish beyond the 13" mark in recent years. 
     I have been telling you about the successes we have seen planting small (1.5-2") Hofer x Colorado River Rainbows (HXC) down in the mainstem Colorado. We have also been planting them in this reach of the Fraser since 2008. Obviously, we don't float a raft down in July on the Fraser to stock, like we do on the Colorado. We have been stocking them by hand in a handful of locations.
     Here is the length-frequency histogram for brook trout and rainbows when we surveyed the reach in 2009:

       As you can see, brook trout were the dominant trout species. Both of the size-groups of rainbows can be traced to two different plants we made in 2008, one of CRR brood culls (the larger fish) and the first batch of HXC fingerlings (the 4" fish) to be stocked. I was surprised that those HXC's were still sitting at only 4"; that is the size they had gone in 11 months before this survey, and didn't appear to have grown at all. Beginning in 2010, we shifted to the smaller HXC's, stocked earlier in the summer. I didn't have a lot of high hopes to make this reach of the Fraser into a wild rainbow fishery, but it was a unique location as far as where we had been trying the HXC's, and I just wanted to see what they would do.
     I finally managed to get back to survey Confluence park this past year. Here is what we found in 2012:
     There were two very strong year-classes of HXC's (at 6" and at 9"), and adult brook trout were almost nonexistent. The HXC's at 2" were just stocked 2 months prior to this survey. The bar at 2" for those fish actually extends up to about 600 but it's cut off here.
     Here is a picture of the three size groups of rainbows present:

     Here's what a typical dipnet full looked like:

     It appears that what we have seen at Confluence Park is a conversion of the trout population from being brook-trout dominated to being overwhelmingly dominated by these HXC's. We know that this strain is an aggressively-feeding, fast-growing strain, but as far as I know, this is the only example to date where we have converted a brook trout stream to a rainbow trout stream with them.
     I'm not making any value judgements here that it's better to have this reach of stream be rainbow-dominated rather than brook trout-dominated; in fact, those 13" brookies were definitely special fish. I'm just saying that I was caught completely by surprise at the success of these plants at this location. These HXC's have picked up the ball and run quite a bit further with it than I expected them to in this situation.
     Just to elaborate on the point, here is the table of population estimates from the two surveys:
  2009 2012
RBT lbs/acre 13 123
RBT >14"/acre 3 0
BRK lbs/acre 48 4
Total trout lbs/acre 65 127
# Sculpin captured 38 211
Date of survey 3-Sep 7-Sep
     Forgive the shoddiness here; I haven't figured out how to make tables look nice in this blogger format. But the point is to look at what the biomass estimates did: the RBT biomass exploded by approximately 10X, while the BRK biomass has reduced to approximately 1/10th. 
     I want to go back again in 2013 to verify that the 2012 survey wasn't some weird fluke. I would also like to do some prospecting for wild rainbow fry before we stock the HXC's. After another year or so I'll probably back off a bit on the HXC stocking and see if we can arrive at some kind of a nice balance, where we have the twin luxuries of a wild rainbow fishery as well as the occasional brook trout larger than 12 inches. 

     On another note, don't forget about our State of the Fish meetings coming up: this Wednesday, the 13th, at the Granby library at 6:30 PM, and next Monday, the 18th, at the Silverthorne library at 6:30 PM. Hope to see you there!


  1. Was the Fraser historically a rainbow fishery prior to WD?


  2. Dan, good question. During the heyday of stocking catchable rainbows in streams in the '70's and '80's, a lot of 10" rainbows were stocked in the Fraser on a put-and-take basis. However, folks I've talked to about what the wild fishery was like have told me that it was principally a brook trout stream (and large brook trout at that) all the way down to Tabernash, if not farther. Unfortunately, we don't have any population survey data that goes back that far, but I've heard similar information from multiple sources. My impression is that the Fraser has undergone a lot of change over the past three decades or so.

  3. It's interesting to see the increase in biomass with the rainbows versus brook trout. I am not aware of any logical explanations for something that dramatic. So it will be interesting to see if 2012 was an anomaly, or if it is part of an ongoing trend.

    Oh, and I'm very interested to hear about the extent to which the HxCs are successfully reproducing.

    1. Well, the only explanation I can think of is simple competition.

  4. Any thoughts on the increase in sculpin. Is the increase due to population fluctuation, variation in sampling, or has the changes in the river made it more hospitable for Sculpins?

    1. Keith, I didn't include 2006 and 2007 in that table above, and the sculpin numbers in those two years were 80 and 188, respectively. In a site like this, which is close to the upstream end of their range, I think their numbers fluctuate somewhat widely from year to year, based on the kind of year it was. Big-water years at this site probably displace a lot of sculpin to downstream locations.