Harvest Management in an Integrated Framework Michael C. Runge USGS Patuxent Wildlife Research Center
Outline • Harvest Management • Integrating Harvest & Habitat Management • Multiple Objectives
Harvest Management Oh no, Not Yield Curves Again!
Additional mortality due to hunting Natural mortality K Neq Carrying Capacity & Harvest Recruitment Recruitment or Mortality Continental Population Size
12 1.4 “K” 1.2 10 1 8 Neq* 0.8 Annual Harvest Equilibrium N 6 0.6 4 0.4 2 0.2 0 0 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 Harvest rate Harvest rate Sustainable Harvest 5
Yield Curve h = rmax/2 rmaxK/4 Sustainable Annual Harvest h = rmax h = 0 0 N* = K/2 K 0 Equilibrium Population Size (N)
Harvest Management • At least implicitly, since 1995, the dynamics captured by yield curves have been at the heart of our harvest assessments • The focus on K makes it clear that harvest dynamics really cannot be understood without the context of habitat management
Coherent Models • If we had a common modeling framework for harvest and habitat management: • We could understand how habitat management is affecting continental demographics, including harvest potential • We could understand how harvest management affects the continental population size, and hence, the use of available habitat • Continental carrying capacity (K) is a useful metric that links harvest and habitat management • Yield curves are, in fact, an extremely valuable way to look at habitat management
1000 L3 800 L2 L1 600 R1, SIS 400 R1 200 0 0 2 4 6 8 10 12 Pintail Harvest Potential Pre-1975 (53.6) Annual Harvest (thousands) Post-1975 (55.6) Latitude-adjusted BPOP (millions)
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 2 4 6 8 10 12 14 Yield Curves for Habitat Management Increase productivity on existing parcels Increase capacity on the landscape Sustained Annual Harvest Current Equilibrium BPOP
Integrated Modeling • Benefits • Track changes in habitat (positive or negative) and account for their effects on harvest potential • Evaluate effects of habitat management on continental demography • Understand how waterfowl objectives are affected jointly by harvest and habitat management • Challenges • Understanding how JV actions affect continental K • Do we have the institutional structure in place to build integrated models?
Current AHM Objective Function • This is a composite of several objectives, with an implicit method of weighting: • Maximize annual harvest of MCM • Maintain sustainable harvest of MCM • Discourage population size < NAWMP goal • Don’t allow closure above 5.5M MCM
Multiple Harvest Objectives • But the current AHM objective function leaves out many other possible objectives • Sustainable harvest of other species • Avoid partial seasons or closure for other spp. • Encourage hunter participation • Provide widespread hunting opportunity • Motivate habitat conservation • Maintain historical distributions during winter • And many others… • Turning Point question
What are your top TWO objectives for waterfowl harvest management? • maximize harvest • keep harvest sustainable for all species • avoid closed or partial seasons • maximize the frequency of long seasons • have relatively stable regulations • have relatively simple regulations • keep populations near the NAWMP goals • motivate hunter participation • motivate habitat conservation • other
Multiple Waterfowl Objectives • And the larger endeavor adds even more objectives: • Achieve NAWMP population objectives • What fundamental goals drive these? • Minimize costs of habitat conservation • Engage partners • Maintain and motivate a traditional hunting culture • Generate broad public support for wetland habitat conservation • Etc.
Trade-offs • Harvest management is embedded in a broader context with a complex set of objectives • There are trade-offs among these objectives • They cannot all be achieved perfectly • How do we evaluate and balance the trade-offs in setting harvest regulations? • Do we currently have a framework for this sort of deliberation?
NA goal Worse Coherent Objectives Desired Harvest Policy Desired Habitat Sustainable Annual Harvest Current Condition 19 Equilibrium BPOP
Summary • Harvest Management • Yield curves are a valuable tool • Integrating Harvest & Habitat Management • Continental K is a valuable common metric • Coherent models would allow us to understand how harvest potential is changing due to NAWMP activities and other factors • Multiple Objectives • Harvest management, let alone integrated management, is a complex multiple-objective problem • We need a framework to understand and balance the trade-offs among objectives • Coherent monitoring could arise out of such an integrated framework