Evaluation of lake sturgeon stocking strategies using an individual-based model

Amy M. Schueller and Daniel B. Hayes Michigan State University Overview • Stocking even small numbers can greatly improve population success • Greater number of parents reduces inbreeding • Stocking strategies should vary depending upon population size Introduction

• Once abundant in Great Lakes Basin • Reduced to 1% of historic levels • Restoration Plans • Stocking is a component of many plans Concerns • If habitat is limited, stocking may be only feasible method for maintaining abundance • However, concerns exist about how stocking practices may influence genetic integrity • Studies suggest that genetic integrity has not yet been compromised Objectives

• Determine stocking strategies for lake sturgeon that maintain population growth across a range of initial population sizes

• Determine implications of stocking strategies on the accrual of inbreeding Methods

• Individual based modeling approach

– Southern bluefin tuna – White sturgeon

• Represents demographics and genetics of lake sturgeon Methods

• Age specific mortality rates Methods

• Polygamous mating system mimicking natural reproductive cycle Methods

• Markers have Mendelian modes of inheritance

AA aa

Aa Methods

• Inbreeding coefficient was tracked using INBREED procedure in SAS:

n P ⎡1⎤ f x = ∑ ⎢ ⎥ + f A )1( i−1 ⎣2⎦ Model Parameters

Age at first breeding(years) Males: 15 Females: 20

Probability of spawning Males: 0.50 Females: 0.33

YOY Mortality Varied

Adult Mortality 5% per year

Number of batches per Negative exponential with spawning season per adult mean=2.5 and std=1.9 Number of young produced Negative exponential with per batch mean=0.55 and std=0.9 Methods

• Range of initial population sizes • Varied YOY mortality rate • Tested stocking strategies • Looked at: -% extant -% increasing population -mean inbreeding -% genes retained Extant populations Relative YOY 100 mortality rates 0.24 80 0.27 0.3 60 0.33 40 0.36

% extant 0.39 20 0.42 0.45 0 0.48 0 50 100 150 200

Initial population size Percent of increasing populations Relative YOY mortality rates 100 0.24 80 0.27 0.3 60 0.33 0.36 40 0.39 20 0.42 0.45 % populations increasing % populations 0 0.48 0 50 100 150 200 Initial population size Inbreeding for extant populations Relative YOY mortality rates 0.25 0.24 0.20 0.27 0.3 0.15 0.33 0.36 0.10 0.39

Mean inbreeding Mean inbreeding 0.05 0.42 0.45 0.00 0.48

0 50 100 150 200 Initial population size Retention of genes in extant

populations Relative YOY mortality rates 30 0.24 25 0.27 0.3 20 0.33 15 0.36 10 0.39 0.42 % genes retained 5 0.45 0 0.48 0 50 100 150 200 Initial population size Stocking Strategies

• Stocking strategies: – Double – Triple – PulseD – PulseT • All stocking strategies tested at a YOY mortality=0.48 – basically a situation where populations would tend to decline without intervention Extant populations 120 100

80 No stocking Double 60 Triple 40 PulseD % extant% PulseT 20 0 0 50 100 150 200 Initial population size Percent of increasing populations 120 100

80 No stocking 60 Double Triple 40 PulseD PulseT 20 % populations% increasing 0 0 50 100 150 200 Initial population size Inbreeding for extant populations 0.25

0.2 No stocking 0.15 Double Triple 0.1 PulseD PulseT

Mean inbreedingMean 0.05

0 0 50 100 150 200 Initial population size Retention of genes in extant 60 populations 50

40 No stocking Double 30 Triple 20 PulseD PulseT

% genes retained% 10 0 0 50 100 150 200 Initial population size Implications

• Stocking even small numbers can improve population success • Greater number of parents reduces inbreeding • Stocking strategies should reflect individual population needs • Stocking strategies should differ between small and large populations Acknowledgments

• Dr. Kim Scribner • Dr. Mike Jones • Dr. Andrew McAdam Questions?