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Spatial and temporal structure in a sympatric steelhead and resident rainbow trout mating system

Spatial and temporal structure in a sympatric steelhead and resident rainbow trout mating system. John McMillan Oregon State University Steve Katz & George Pess NWFSC. Objective. Do anadromous and resident O. mykiss overlap during spawning season?

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Spatial and temporal structure in a sympatric steelhead and resident rainbow trout mating system

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  1. Spatial and temporal structure in a sympatric steelhead and resident rainbow trout mating system John McMillan Oregon State University Steve Katz & George Pess NWFSC

  2. Objective • Do anadromous and resident O. mykiss overlap during spawning season? • Is there spatial and temporal structure to their spawn time and location? • Do periods of overlap result in attempted matings? • What male mating behaviors are associated with attempted mating events?

  3. Study sites

  4. Calawah River

  5. Methods (1999 – 2003) • Co-existence & spatial - temporal structure • Arrival timing • Monthly snorkel survey • Spawn timing • Monthly or bi-monthly redd survey • Mating behavior • Mating event observations • One per redd survey • 30 minutes & 2 hours • Male tactics • Guard or sneak

  6. Surveys

  7. Classification of forms • Anadromous • > 50 cm in length • Sex • Female – blunt nose, short maxillary, silvery coloration • Male – long nose, long maxillary, kype, darker coloration • Resident • 25 – 50 cm in length (Pearsons et al. 1998; Narum et al. 2004) • Morphology (red stripe, dense spotting) • Could not determine sex during snorkel surveys

  8. Female steelhead

  9. Male steelhead

  10. Resident rainbow

  11. Steelhead pair mating & “sneaker male”

  12. Median arrival time - Denotes 50% time of arrival

  13. Monthly population composition

  14. Timing of redd excavation

  15. Spawn timing variation

  16. Spatial comp. of mating events

  17. Temporal comp. of mating events by male tactic

  18. Conclusions • Co-existence • Yes! Most of spawning season • Distribution patterns • Strong temporal structure • Male steelhead arrive earlier than females • Sex ratio shift across spawning season • Rainbow arrival skewed to end of season • Weaker spatial structure • Steelhead arrival earlier at upper-most sites • Greatest proportion of rainbow in upper-most sites

  19. Conclusions • Co-existence • Yes! Most of spawning season • Distribution patterns • Strong temporal structure • Male steelhead arrive earlier than females • Sex ratio shift across spawning season • Rainbow arrival skewed to end of season • Weaker spatial structure • Steelhead arrival earlier at upper-most sites • Greatest proportion of rainbow in upper-most sites

  20. Conclusions • Co-existence • Yes! Most of spawning season • Distribution patterns • Strong temporal structure • Male steelhead arrive earlier than females • Sex ratio shift across spawning season • Rainbow arrival skewed to end of season • Weaker spatial structure • Steelhead arrival earlier at upper-most sites • Greatest proportion of rainbow in upper-most sites

  21. Conclusions • Mating events • Steelhead x rainbow trout • Only male trout attempting to mate with female steelhead • Most common at end of season and upper-most sites • Male trout sometimes lone mate source • What tactics did males use? • Male steelhead relied equally on guard and sneak tactics • Male trout relied heavily on sneak tactic, but also egalitarian

  22. Conclusions • Mating events • Steelhead x rainbow trout • Only male trout attempting to mate with female steelhead • Most common at end of season and upper-most sites • Male trout sometimes lone mate source • What tactics did males use? • Male steelhead relied equally on guard and sneak tactics • Male trout relied heavily on sneak tactic, but also egalitarian

  23. Next steps? • Research • What are the factors influencing the distribution of the different forms? • What is the relative success of stlhd x stlhd mating v. stlhd x trout mating? • Management and monitoring • More information on populations of resident O. mykiss

  24. Genetic analysis Confirm parentage Examine reproductive success Temporal and spatial influence Mating structure Structure variability (e.g., male trout x female steelhead success vs. male steelhead vs. female steelhead) Next steps

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