Steelhead trout life history SDP/DSV models meet data W. Satterthwaite & M. Mangel - UCSC, D. Swank, S. Sogard, & M. Beakes - NOAA J. Merz - EBMUD, Cramer Fish Sciences R. Titus & E. Collins - CDFG

Thinking about steelhead life history Why mature as resident? –Avoid ocean mortality –Potentially easier iteroparity Why smolt and emigrate? –Much larger size > higher reproductive success Why take action when young? –Less cumulative risk of mortality in stream Why take action when older? –Larger size at spawning = higher reproduction –Larger size at emigration = higher survival

Model algorithm Postulates existence of “decision windows” Assess current size and potential for future growth as parr Assess expected fitness if smolt/mature at current size Compare with expected fitness of growing to a larger size and making an optimal decision in the future (discount for mortality) For now, concentrate on females Tradeoff between future growth, further mortality risk

Age 4Age 3Age 2Age 1Age 0Age 5 rainbow Birth smolt freshwater parr smolt-1 smolt-2 rainbow smolt mature resident parr immature ocean maturity decision mature ocean smolt decision ? Timing is everything… (thanks to D. Swank) 3.3

Age 4Age 3Age 2Age 1Age 0Age 5 rainbow steelhead Birth smolt freshwater parr smolt-1 smolt-2 rainbow smolt-3 mature resident parr ocean steelhead maturity decision smolt decision Timing is everything… (thanks to D. Swank) steelhead rainbow smolt-4 steelhead

Age 4Age 3Age 2Age 1Age 0Age 5 rainbow steelhead Birth smolt freshwater parr smolt-1 smolt-2 rainbow smolt-3 mature resident parr ocean steelhead maturity decision smolt decision X Timing is everything… (thanks to D. Swank) steelhead rainbow smolt-4 steelhead

Age 4Age 3Age 2Age 1Age 0Age 5 rainbow steelhead Birth smolt freshwater parr smolt-1 smolt-2 rainbow smolt-3 mature resident parr ocean steelhead maturity decision smolt decision Timing is everything… (thanks to D. Swank) steelhead rainbow smolt-4 steelhead

Age 4Age 3Age 2Age 1Age 0Age 5 rainbow steelhead Birth smolt freshwater parr smolt-1 smolt-2 rainbow mature resident parr ocean steelhead maturity decision smolt decision Timing is everything… (thanks to D. Swank) steelhead smolt-4 steelhead smolt-3 steelhead

Dynamic State Variable model F(l,g,e,t) –F: expected lifetime fitness –l: size –g: developmental switch, maturity –e: developmental switch, smolting –t: time G(l,g,e,t) - future size at time t+1 s(t) - survival to time t+1

Dynamic State Variable model F(l,b,g,e,t) –F: fitness –l: size at t = end of window –b: size at start of window –g: developmental switch, maturity –e: developmental switch, smolting –t: time G’(l,b,g,e,t) - updated future size

Terminal reward - Spawning Latest possible spawning: F(l,g,e,T sf ) =  (l) if g=1, F(l,g,e,T sf ) = 0 otherwise

Terminal reward - Spawning Latest possible spawning: F(l,g,e,T sf ) =  (l) if g=1, F(l,g,e,T sf ) = 0 otherwise Earlier spawnings: F(l,g,e,t s ) =  (l)+ s(t)F(G(l,g,e,t s ),g,e,t s +1) if g=1, F(l,g,e,t s ) = s(t)F(G(l,g,e,t s ),g,e,t s +1) otherwise

Terminal reward - Emigrating F(l,g,e,t e ) =  (l)  if e=1, F(l,g,e,t e ) = s(t)F(G(l,g,e,t e ),g,e,t e +1) otherwise F(l,g,e,t) = s(t) F(G(l,g,e,t),g,e,t+1) Updating - Outside Windows

Terminal reward - Emigrating F(l,g,e,t e ) =  (l)  if e=1, F(l,g,e,t e ) = s(t)F(G(l,g,e,t e ),g,e,t e +1) otherwise F(l,g,e,t) = s(t) F(G(l,g,e,t),g,e,t+1) Updating - Outside Windows

Maturity Decision Window F(l,b,g,e,t dg ) = s(t) max g ( F(G’(l,b,g,0,t dg ),g,e,t dg +1)) if g=e=0, F(l,g,e,t dg ) = s(t) F(G’(l,b,g,e,t dg ),g,e,t dg +1) otherwise.

Maturity Decision Window F(l,b,g,e,t dg ) = s(t) max g ( F(G’(l,b,g,0,t dg ),g,e,t dg +1)) if g=e=0, F(l,g,e,t dg ) = s(t) F(G’(l,b,g,e,t dg ),g,e,t dg +1) otherwise. F(l,b,g,e,t de ) = s(t) max e ( F(G’(l,b,0,e,t de ),g,e,t de +1)) if g=e=0, F(l,g,e,t de ) = s(t) F(G’(l,b,g,e,t de ),g,e,t de +1) otherwise. Smolting Decision Window

Inputs: Survival and Growth Survival: CJS MARK-recapture model –Pit tagged fish recapture rates Separate analysis of YOY vs older fish –Seasonal but not yearly variation –Biased low - confounded with emigration

Inputs: Survival and Growth Survival: CJS MARK-recapture model –Pit tagged fish recapture rates Separate analysis of YOY vs older fish –Seasonal but not yearly variation –Biased low - confounded with emigration Growth –Energy balance, optimal foraging –Temperature dependencies and allometries from literature, gut capacity and BMR from lab fits

Coastal Growth Valley Growth

Coastal Growth Model Comparison with Data

Life History Predictions - Coast smolt mature wait

Life History Predictions - Coast “No” residents

Life History Predictions - Coast Many age 1 smolts > age 2 emigrants, a few older

Hayes et al TAFS Coastal Growth - Estuary Effects

Life History Predictions - Coast Threshold size of ~110mm in late December

Evidence for smolt threshold? Length<100>100maxp Scottrecap not23791 Soquelrecap not22361 GSFrecap not8113 BDG Srecap not14139 ASBRYrecap not2518

Evidence for smolt threshold? Length<100>100maxp Scottrecap not23791 Soquelrecap not22361 GSFrecap not7913 BDG Srecap not12030 ASBRYrecap not2418

Life History Predictions - American “All” smolt as YOY and emigrate age 1 Threshold size of ~150mm in late December –(higher threshold than coast) smolt mature wait

Predictions - Mokelumne Most smolt as YOY and emigrate age 1 Potential for slow growers to mature as parr smolt mature wait

Effects of changing environment Short term: compare new growth vs. old thresholds (no response to survival changes) –Coast: much faster growth could yield mature parr. Easy to change average age at smolting.

Effects of changing environment Short term: compare new growth vs. old thresholds (no response to survival changes) –Coast: much faster growth could yield mature parr. Easy to change average age at smolting. –Valley: slow growth might yield mature parr. Need to preserve good growth environment in late summer.

Effects of changing environment Short term: compare new growth vs. old thresholds (no response to survival changes) –Coast: much faster growth could yield mature parr. Easy to change average age at smolting. –Valley: slow growth might yield mature parr. Need to preserve good growth environment in late summer. Long term: –Both: Most sensitive to emigration survival Importance of estuaries, passage through delta

Future directions Bet-hedging Explicit estuarine state and decisions Refine functional relationship between temperature, flow, and growth Males

time of emigration Time Size Too small to stand much chance of survival Decent chance of survival. Extra benefit from another year’s growth outweighed by river mortality, generation time. smolting decision window

Time Size Too small to stand much chance of survival smolting decision window time of emigration Decent chance of survival. Extra benefit from another year’s growth outweighed by river mortality, generation time.

Time Size Too small to stand much chance of survival smolting decision window time of emigration Decent chance of survival. Extra benefit from another year’s growth outweighed by river mortality, generation time.

coast valley Beakes et al. in prep