Henry’s Fork Rainbow Trout migrating to spawn in the Buffalo River have to pass through the fish ladder at the Buffalo River hydroelectric facility to access upstream spawning habitat. At the end of the fish ladder we, HFF, operate a fish trap from early February through the middle of June. Three times a week we check the Buffalo River fish trap and collect data on species, length, sex, and life histories via passive integrated transponders (PIT) tags if one is present. This data allows us to quantify run size, run timing, number of spawners, number of return spawners, and other valuable information needed to monitor and understand the Henry’s Fork Rainbow Trout population. Here is a quick summary of the 2017 Buffalo River fish ladder as we approach the historic median fish passage date of May 6. 

 

 

Notable Numbers

 

325 fish captured (February 17 through April 24)

  • Rainbow Trout
    • 85 spawning sized fish (greater than 12 inches)
      • 16 inches – median size
      • 21.6 inches – largest fish
    • 155 juvenile fish (less than 12 inches)
      • 5.3 inches – median size
  • Brook Trout
    • ​84 captured
      • 5.8 inches – median size
      • 9.3 inches – largest fish
  • Sculpin
    • 1 captured

Figure 1. Rainbow Trout spawning run for fish migrating from the Henry’s Fork River up the Buffalo River, February 15 through June 1, 2006-2017.

 

Summary

The 2017 Buffalo River spawning run is tracking above average relative to past spawning runs (Figure 1). Rainbow Trout run timing is often positively correlated to temperature1 and discharge2 so the unseasonably cool April weather may actually be delaying the Buffalo River spawning run. If this is the case, 2017 median run timing may be later than average and we could see upwards of 200 migrating Rainbow Trout in 2017. The physical characteristics of adult and juvenile Rainbow Trout are similar to that of migrating fish from previous years. In February and March we were capturing above average numbers of Brook Trout in the fish ladder (6-8 Brook Trout per day) but these numbers have dropped to historic averages for April (3-5 Brook Trout per day). 

 

PIT Tagged Rainbow Trout

Passive integrated transponder (PIT) tags are passively operating tags commonly used to track migratory fish. These 12mm tags have a unique 13 digit number that can be read when a tagged fish passes an electromagnetic reader such as a tag array or a handheld scanner.  From 2013 to 2016, Rainbow Trout captured in the Buffalo River fish trap were injected with PIT tags in an effort to understand survival rates and habitat utilization of juvenile and adult Rainbow Trout migrating between the Buffalo River and the Henry’s Fork. A summary of this migratory data can be found in a decadal report written last year by former research assistant, Christina Morrisett (email me at Bryce@henrysfork.org if you would like a copy of the .pdf) . We no longer PIT tag fish but we continue to infrequently capture fish tagged in prior years.

Last week we recaptured a PIT tagged Rainbow Trout that was returning to spawn in the Buffalo River for the third consecutive year. The trout was originally captured and tagged at the Buffalo River fish ladder March 30, 2015 when it was 17.1 inches. After spawning, the fish migrated back out of the Buffalo River and was detected at the Buffalo River tag array on April 21, 2015. The following year this fish was recaptured again migrating up the Buffalo River fish ladder on April 4, 2016, and measured 18.6 inches. This year the fish was recaptured at the Buffalo Fish ladder April 17. Unfortunately, there was a miscommunication or error recording the length data but this fish was estimated to be around 20 inches long. Even though one fish doesn’t represent an entire spawning run, the later than normal migration time for this fish supports the hypothesis that the entire 2017 run timing might be delayed and there are a lot more fish to come!

 

Additional information

Expect another Buffalo River fish ladder update at the end of May and a final 2017 Buffalo River fish ladder summary at the end of June.

If you have questions, comments, or concerns, feel free to contact me at Bryce@henrysfork.org or 208-652-3567

 

Citations

1Lucas, M., & Baras, E. (2008). Migration of freshwater fishes. John Wiley & Sons.

2Salinger, D. H., & Anderson, J. J. (2006). Effects of water temperature and flow on adult salmon migration swim speed and delay. Transactions of the American Fisheries Society, 135(1), 188-199.