Adaptive harvest is a framework for making objective decisions in the face of incomplete knowledge – like all things in wildlife management, it’s not an exact science.
At its best it seeks to smooth out variables such as environment, population dynamics, harvest and regulatory impacts and deliver game seasons underpinned by a process where the politics take a back seat (although, ultimately, the politics will always be there in the background). It has been described as “Management in the face of uncertainty” to embrace adaptive harvest is to, in effect, accept and embrace uncertainty.
The concept of adaptive management is well known and is applied for a wide range of uses including business operations, fisheries, whaling and the management of big game like Caribou and, perhaps best known amongst hunters, for waterfowl in North America.
In regulating game harvests, managers face four fundamental sources of uncertainty:
- Environmental variation - the temporal and spatial variation in weather conditions and other key features of habitat.
- Partial controllability - the ability of managers to control harvest only within limits; the harvest resulting from a particular set of hunting regulations cannot be predicted with certainty because of variation in weather conditions, timing of migration, hunter effort, and other factors;
- Partial observability - the ability to estimate key population attributes (e.g., population size, reproductive rate, harvest) only within the precision afforded by existing monitoring programs; and
- Structural uncertainty - an incomplete understanding of biological processes; a familiar example is the long-standing debate about whether harvest is additive to other sources of mortality or whether populations compensate for hunting losses through reduced natural mortality. Structural uncertainty increases contentiousness in the decision-making process and decreases the extent to which managers can meet long-term conservation goals.
Adaptive harvest involves a cycle of monitoring, assessment and decision making.
In an Australian context adaptive harvest has been used for forestry, macropods and fishery but never before for game management on a broad scale.
It was determined a decade ago that an adaptive harvest model, dubbed the “Waterfowl Conservation Harvest Model” (WCHM), should be adopted to manage waterfowl hunting in Victoria.
The WCHM is a mathematical expression of how a panel of experts believed that waterfowl populations in eastern Australia respond to key environmental drivers (such as wetland availability) and harvest.
The WCHM incorporates long-range movements of some waterfowl species in response to local and regional changes in wetland area by linking major patches of waterfowl habitat inside and outside Victoria.
The WCHM would use species-specific parameters, with each species’ model capturing the key features of that species’ dynamics (e.g. potential for long-range movements in response to changes in wetland area). The WCHM explicitly recognises the importance of wetland area for waterfowl populations in eastern Australia and hence the impacts of major changes in that variable on the abundances and distributions of the various species: it is for this reason that ‘conservation’ features in the name of the model. The WCHM would be used to investigate how different harvest strategies affect the sustainability (defined as projected future abundances) of each waterfowl species. An important feature of the WCHM is its application to the sustainability of non-game waterfowl species and the panel recommends that, if implemented, non-game species (including Freckled Duck) be included.
The WCHM is ‘adaptive’ because it would be updated annually based on: (i) estimated harvest in the previous hunting season, (ii) estimated wetland area, (iii) estimated waterfowl abundance, and (iv) projected rainfall.
The key benefits of the WCHM were stated as being:
- Transparency in how the annual harvest regulations (i.e. season length and bag size for each species) are recommended to the Minister, leading to reduced conflict among stakeholders
- Assurance that harvesting in Victoria is unlikely to adversely affect the sustainability of waterfowl populations in eastern Australia
- Increased understanding of the key drivers of waterfowl dynamics in eastern Australia, particularly the relative importance of wetland area and harvesting
- Development and maintenance of waterfowl research, management and monitoring expertise in Victoria.
A key requirement of the proposed approach is that stakeholders (including Ministers) must have confidence in the approach and its recommendations about season lengths and bag sizes; accept that the process is adaptive such that uncertainties should reduce with time; provide sufficient resources to operate the WCHM; and recognise its reliance on the skills of a small number of scientific staff that may not be able to be quickly replaced if they cease their current employment.
At the last election, the Victorian Government committed to reviewing and implementing the WCHM – our expectation is that we will begin to see this being implemented over the next two years.