Fall River Wild Trout Monitoring – over 2600 fish tagged so far!

Updated: April 27, 2020

Working closely with UC Davis, our PIT wild trout monitoring program, which began in 2013, continued into 2019. During the program’s life, we have tagged some 3,000 fish. The science developed clearly benefits our efforts to preserve and protect the river, as noted above in our comment letter to the CDFW on its regulatory revision project. Here are a few notable facts we have developed:

  • Genetic data shows that there are two distinct sub-populations of rainbow trout in the river – One which spawns in the spring-fed reaches of the system (Thousand Springsand Ja She) and another which spawns in the Bear Creek habitat.
  • There is very little apparent gene flow between the two populations even though the populations intermingle in the main stem of the river.
  • The spawning period is relatively extended for the spring-fed population (October-July) while the Bear Creek population has a more typical limited period.
  • Although the drought of 2012-2015 led to some loss through stranding’s in Bear Creek, the population appears to have endured.

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FRC has been working with UC Davis Center for Watershed Sciences and California Trout to monitor the wild trout in the Fall River since 2013. Fish caught by the California Department of Fish and Wildlife have been tagged with Passive Integrated Transponders (PIT tags) and had genetic samples taken. When tagged fish swim through the antenna arrays located at Thousand Springs and Bear Creek, data on that individual fish is recorded. Thus far, in ten tagging events (Spring and Fall of each year), we have tagged over 2600 fish and learned quite a bit about this amazing wild trout population.

Our partners at UC Davis provided a great update on the Fall River PIT Program in April of this year, just before our most recent tagging event, in which more fish were caught than we had tags for! Highlights from their findings include:

  • 22% (496) of the tagged fish have been seen again either by physical recapture (n=29) or at the PIT tag antenna arrays
  • Genetic data from fin clips has shown two distinct sub populations of rainbow trout living together in the Fall RIver
  • The two sub-populations are divided into spring-fed spawning and snowmelt source spawning groups which use spring fed (Thousand Springs, Spring Creek, Ja She) and Bear Creek spawning habitats, respectively
  • There is very little apparent gene flow between populations despite intermingling in the main stem Fall River during non-spawning times
  • The antenna detection data shows an extended spawning period (October-July) for spring-fed spawning fish and a more traditional spawning timing in the snowmelt system of Bear Creek
  • The stable flow and cool water temperatures year-round provide a buffer to annual climatic variability for the Fall River, while the snowmelt system is highly dependent on precipitation and resulting snowmelt
  • Although the historic multi-year drought from 2012-2015 led to some strandings and mortalities of the Bear Creek population, it does appear that a portion of the population was able to persist through the drought
  • Preliminary PIT antenna data from March 2018 shows that 23 tagged fish were seen migrating through Bear Creek Meadow
Photo Credit: Val Atkinson

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