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)