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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 John McMillan Oregon State University Steve Katz & George Pess NWFSC
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?
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
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
Median arrival time - Denotes 50% time of arrival
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
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
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
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
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
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
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