1 / 19

Brian Hodge Peggy Wilzbach Walt Duffy James Hobbs

This study examines the life history structure of Oncorhynchus mykiss (steelhead) in the Lower Klamath River Basin, determining influencing factors and consequences of individual life history trajectories. The results suggest that growth, origin, and migratory history play significant roles in the probability of residentization in the population.

yvettes
Download Presentation

Brian Hodge Peggy Wilzbach Walt Duffy James Hobbs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Partial Migration in Wild Oncorhynchus mykissfrom the Lower Klamath River Basin • Brian Hodge • Peggy Wilzbach • Walt Duffy • James Hobbs USGS California Cooperative Fish and Wildlife Research Unit, Humboldt State University

  2. Lower Klamath River Basin Supports the largest and most popular steelhead fishery in California Steelhead exhibit the rare “half-pounder” life history One study has addressed O. mykiss life history on a basin scale

  3. Objectives: To determine the current life history structure of O. mykiss from the lower Klamath River Basin To determine influencing factors and consequences of individual life history trajectories

  4. Methods Photo by Matt Peterson

  5. To sea or not to sea? Resident: FL > 95th quantile for smolt length OR age > max smolt age

  6. Method I: Analysis of OtolithSr Isotope Ratios ( )

  7. Migratory History and Maternal Origin 0.7047 0.7038 0.7042 0.7067 0.7075 0.7092 0.7052 0.7066 0.7083 0.7057 0.7058 0.7072 0.7066 0.7064 *Source: Quiñones et al. 0.7062

  8. Migratory History • Tracked movement between • freshwater and marine • environments Steelhead: Mean otolith Sr isotope ratio exceeded upper bounds of known in-stream values Rainbow trout: Mean otolith Sr isotope ratio never exceeded upper bounds of known in-stream values

  9. Maternal Origin • Compared in the • core and freshwater regions • (1 tailed t-test, α=0.05) Anadromous:Core ratio significantly greater than freshwater ratio Nonanadromous:Core ratio not significantly greater than freshwater ratio

  10. Method II: Qualitative Scale Analysis • Determined age, growth, • and life history

  11. Results:Maternal Origin vs. Migratory History

  12. Maternal Origin vs. Migratory History cont’d n=63 • Maternal origin was indeterminable for 11 fish (9 STH and 2 RBT,) either because the laser transect missed the core, or because the Sr isotope ratio in the freshwater region exceeded the global marine value.

  13. Results:Scale Analysis • Observed 32 life history categories (30 spawning trajectories) • 5 nonanadromous • 27 anadromous FL: 268-508 mm FL: 256-800 mm

  14. Scale Analysis cont’d • 43 of 655 fish sampled were residents (M:F = 1.0:1.3)

  15. Scale Analysis cont’d Error bars represent ± 1 SE

  16. Conclusions • Anadromous and nonanadromous forms of O. mykiss occurr sympatrically in the lower Klamath River Basin • Steelhead and rainbow trout may give rise to the alternative life history form • Origin (likely migratory difficulty) and growth appear to influence the probability of residualization • Apparent costs of a resident life history are reduced size and fecundity at age. However, a presumed benefit is increased survival relative to an anadromous life history

  17. Management Implications • Will resident rainbow trout contribute towards recovery of steelhead in the Klamath Basin following dam removal?

  18. Acknowledgements California Department of Fish and Game, Steelhead Report Card Program

More Related