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 1.Do anadromous and resident O. mykiss overlap during spawning season? 2.Is there spatial and temporal structure to their spawn time and location? 3.Do periods of overlap result in attempted matings? 4.What male mating behaviors are associated with attempted mating events? Study sites Stream Survey location (km) Stream order Gradient (%) Calawah NF Calawah Lower Sol Duc Middle Sol Duc Upper Sol Duc Calawah River 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 Surveys Stream SnorkelReddBehavior #km# #hours Calawah NF Calawah Lower Sol Duc Middle Sol Duc Upper Sol Duc 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 Female steelhead Male steelhead Resident rainbow Steelhead pair mating & sneaker male Median arrival time - Denotes 50% time of arrival Monthly population composition Timing of redd excavation Spawn timing variation Spatial comp. of mating events Temporal comp. of mating events by male tactic 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 Next steps 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)