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

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

LPO Fishery - Desired Outcomes Ross Hall photos

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

KOKANEE SURVIVAL KOKANEE SURVIVAL Declined in 2007; low for all agesDeclined in 2007; low for all ages Survival less than 50% is a concernSurvival less than 50% is a concern Predation limiting survival to spawningPredation limiting survival to spawning

Indices of LT Abundance, Lake Pend Oreille

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

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

Lake Trout Fishery 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!

Lake Trout Size Structure IDFG 2007

Lake Trout Growth McKee et al Burnham-Curtis and Bronte 1996

Lake Trout Maturity IDFG 2007

Lake Trout Future Prognosis? This? Or, this? Which is better for Lake Pend Oreille? IDFG 2007

Kokanee Biomass, Production and Yield  This Or This 

Lake Trout Fishery Management IDFG 2007

Lake Trout Mortality Natural (LPO 2006 = 15.1% estimate): –Average = 18% (much higher if lampreys). –Range = 10–36% (much higher if lampreys). Fishing (LPO 2006 > 44.5%; 0.58kg/ha): –Highest = 45% (Superior prior to lamprey). –Populations decline if harvest > 0.50 kg/ha. Total (LPO 2006 > 59.6%): –Populations are sustainable if A < 50%. –Most populations decline if A > 50%! Healey 1978

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

Lake Trout Distribution Great Slave Lake (27,195 km 2 ) (625 m) Great Bear Lake (31,153 km 2 ) (452 m) Lake Superior (82,414 km 2 ) (405 m) Lake Michigan (58,016 km 2 ) (285 m) Lake Huron (59,596 km 2 ) (220 m) Lake Erie (25,745 km 2 ) (64 m) Lake Ontario (19,529 km 2 ) (237 m) Lake Pend Oreille (383 km 2 ) (351 m)

Probability of Kokanee Collapse With Different Mortality Rates for RBT and LT

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

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)

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