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

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

5. Calawah River

7. 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

8. Surveys

9. 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

10. Female steelhead

11. Male steelhead

12. Resident rainbow

14. Steelhead pair mating & “sneaker male”

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

16. Monthly population composition

17. Timing of redd excavation

18. Spawn timing variation

19. Spatial comp. of mating events

20. Temporal comp. of mating events by male tactic

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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