Some basic tools for using population ecology as a management tool – A Primer

1. Some basic tools for using population ecology as a management tool – A Primer • GROWTH • RECRUITMENT • MORTALITY • COMPENSATION

2. Lake Pend Oreille An On-the-Ground Application of Population Ecology

3. LPO Fishery - Desired Outcomes • Ross Hall photos

4. Drawdowns to 2051 ft became routine beginning in 1966 Shrimp established in 1975 Albeni Falls Dam Built Adult Kokanee Abundance in Lake Pend Oreille

6. KOKANEE SURVIVAL • Declined in 2007; low for all ages • Survival less than 50% is a concern • Predation limiting survival to spawning

8. Indices of LT Abundance, Lake Pend Oreille

9. LPO Kokanee • Primarily lake spawners, some tributary spawners, hatchery supplementation • Longevity – 4 to 5 years (die after spawning) • Relatively low fecundity, but high plasticity (compensatory ability) • Planktivores • Key prey item for BLT, RBT, LT as well as avian and terrestrial predators • Principle threats: • Predation • Habitat impacts

10. LPO Lake trout • Lake spawners (fall) • Longevity – 30+ years, mature at 7 years • Highly piscivorous, but can survive on Mysis • Slow growth • Relatively low fecundity • Principle threat: • Directed harvest

11. Lake TroutFishery Management • Lake trout are late maturing and long lived, so are vulnerable to over-fishing. • The largest lake trout populations were over-fished in the Great Lakes before sea lamprey became a problem. • Most lake trout populations in Ontario inland lakes are considered over-fished. • Lake Pend Oreille is a field test of over-fishing of lake trout!

12. Lake TroutSize Structure IDFG 2007

13. Lake TroutGrowth McKee et al. 2004 Burnham-Curtis and Bronte 1996

14. Lake TroutMaturity IDFG 2007

15. Lake TroutFuture Prognosis? This? Which is better for Lake Pend Oreille? Or, this? IDFG 2007

16. Or This  Kokanee Biomass,Production and Yield This

17. Lake TroutFishery Management IDFG 2007

18. Lake TroutMortality • Natural (LPO2006 = 15.1% estimate): • Average = 18% (much higher if lampreys). • Range = 10–36% (much higher if lampreys). • Fishing (LPO2006 > 44.5%; 0.58kg/ha): • Highest = 45% (Superior prior to lamprey). • Populations decline if harvest > 0.50 kg/ha. • Total (LPO2006 > 59.6%): • Populations are sustainable if A < 50%. • Most populations decline if A > 50%! Healey 1978

19. Can it work? • Lake trout exploitation (angling & commercial nets) ~50% • Exploitation rates of ~ 40% collapsed Great Lakes fisheries • Rainbow trout exploitation still low • Predation still too high Lake Michigan lake trout

20. Lake TroutDistribution Great Bear Lake (31,153 km2) (452 m) Great Slave Lake (27,195 km2) (625 m) Lake Huron (59,596 km2) (220 m) Lake Pend Oreille (383 km2) (351 m) Lake Superior (82,414 km2) (405 m) Lake Ontario (19,529 km2) (237 m) Lake Michigan (58,016 km2) (285 m) Lake Erie (25,745 km2) (64 m)

21. Probability of Kokanee CollapseWith Different Mortality Rates for RBT and LT

22. Bottom Line for Success on LPO: • We need to reduce predation on kokanee by 50 tons annually to begin kokanee recovery • RBT and LT are the two primary predators • Current needs – harvest LT and RBT to reduce predation and slow growth of LT population • LT will need to be managed at a suppressed level for the long term • The public will need to support programs

23. Some Take-Away Points For F&W Population Management: • If R>M populations grow, and vice versa • More fecund animal populations apt to grow more rapidly in good, unoccupied habitat • Many species “compensate” at low densities by increasing growth rates, lowering age of reproduction & increasing fecundity • Late maturing, lower fecundity populations more susceptible to mortality agents • “Predator pits” more likely to occur when predator species has abundant supply of alternative prey • Habitat conditions affect R & M, but so also can external forces (Exploitation, Predation, Competition, Disease, etc)

24. Information and slides for this presentation were contributed by Melo Maiolie, Mike Hansen and Ned Horner.