Trout Reduction Efforts

Findings from the Natal Origins Project (NO) Project There is a low probability for an individual rainbow trout to move large distances. Abundance is a key factor: the more rainbow trout upstream in the Lees Ferry reach = more trout will move downstream to the LCR reach in search of unoccupied habitat Condition may be a secondary factor: when food resources become limited, rainbow trout will move downstream in search of food Recruitment in the reach below the LCR can be accounted for solely by immigrants from upstream sources Food limitation led to the collapse in the trout population, and by extension also likely happened in the downstream reaches. Inflow hydrology and reservoir limnology likely govern the quality and quantity of nutrients supplied to the downstream river segments. Nutrient limitation is hypothesized as being the “BIG HAMMER” to the riverine ecosystem, which needs to be evaluated in greater detail in future research. [1]

--	--	--

Updates Coggins et al. 2011. Our results suggest that removal efforts were successful in rapidly shifting the fish community from one dominated numerically by nonnative species to one dominated by native species. Additionally, increases in juvenile native fish abundance within the removal reach suggest that removal efforts may have promoted greater survival and recruitment. However, drought-induced increases in river water temperature and a systemwide decrease in rainbow trout abundance concurrent with our experiment made it difficult to determine the cause of the apparent increase in juvenile native fish survival and recruitment.

Links and Information Rainbow Trout Page Brown Trout Page Natal Origins Project (NO) Projects Bright Angel Creek Non-Native Trout Reduction Project Brown trout control at the mouth of Bright Angel Creek Mainstem trout removal at the LCR Trout Management Flows Presentations and Papers 2017 Is Rainbow Trout Control Necessary, and if so, What is the Most cost-effective approach? 2016 Bright Angel Creek Non-Native Trout Reduction, Grand Canyon National Park 2015 Bright Angel Creek Non-Native Trout Reduction Grand Canyon National Park 2013 Humpback Chub and Non-native Fish Control Update Non-native Fish Control in Tributaries: Grand Canyon National Park Nonnative fish control in GCNP tributaries 2012 Non-native fish Control Implementation PPT 2011 Coggins et al. 2011. Nonnative Fish Control in the Colorado River in Grand Canyon, Arizona: An Effective Program or Serendipitous Timing? Transactions of the American Fisheries Society, 140: 2, 456 — 470 LTEMP BiOp Triggers for Trout Removals at the LCR (LTEMP BA Appendix D) Tier 1 Trigger – Early Intervention Through Conservation Actions: 1a. If the combined point estimate for adult HBC (adults defined ≥200 mm) in the Colorado River mainstem LCR aggregation; RM 57-65.9) and Little Colorado River (LCR) falls below 9,000 as estimated by the currently accepted HBC population model (e.g., ASMR, multi-state). -OR- 1b. If recruitment of sub-adult HBC (150-199mm) does not equal or exceed estimated adult mortality such that: Sub-adult abundance falls below a three-year running average of 1,250 fish in the spring LCR population estimates, or Sub-adult abundance falls below a three-year running average of 810 fish in the mainstem Juvenile Chub Monitoring reach (JCM annual fall population estimate; RM 63.45-65.2). Tier 1 Trigger Response: Tier 1 conservation actions listed below will be immediately implemented either in the LCR or in the adjacent mainstem. Conservation actions will focus on increasing growth, survival and distribution of HBC in the LCR & LCR mainstem aggregation area. Tier 2 Trigger - Reduce threat using mechanical removal if conservation actions in Tier 1 are insufficient to arrest a population decline: Mechanical removal of nonnative aquatic predator will ensue: If the point abundance estimate of adult HBC decline to <7,000, as estimated by the currently accepted HBC population model. Mechanical removal will terminate if: Predator index (described below) is depleted to less than 60 RBT/km for at least two years in the JCM reach and immigration rate is low (the long term feasibility of using immigration rates as a metric still needs to be assessed), -OR- Adult HBC population estimates exceed 7,500 and recruitment of sub-adult chub exceed adult mortality for at least two years. If immigration rate of predators into JCM reach is high, mechanical removal may need to continue. These triggers are intended to be adaptive based on ongoing and future research (e.g., Lees Ferry recruitment and emigration dynamics, effects of trout suppression flows, effects of Paria River turbidity inputs on predator survival and immigration rates, interactions between humpback chub and rainbow trout, other predation studies). Other Stuff