Framework-date extensions for duck hunting in the United States: projected impacts & coping with uncertainty

              Executive Summary: On August 3, 2000, Regulations Consultants representing the four Flyway Councils
requested that the U.S. Fish and Wildlife Service (Service) conduct another assessment of the projected
impacts of extended framework dates for duck hunting. To better assess the potential impact, the Service
asked the Flyway Councils to survey their respective States concerning their interests in extended
framework dates in each of their duck-hunting zones. Based on this survey, which assumed no penalties
in season length or bag limit, only 13 of the 48 contiguous States would not take advantage of extended
opening dates, closing dates, or both in at least a portion of the State. The predicted increase in annual
harvest associated with extended framework dates in the moderate and liberal regulatory alternatives was
approximately 15 percent and 5 percent for midcontinent and eastern mallards, respectively. Assuming
these projected increases in harvest are accurate, we would expect a reduction in the frequency of liberal
regulations, with a concurrent increase in the frequency of moderate regulations, in the Pacific, Central,
and Mississippi Flyways. There was no discernable change in the expected frequency of liberal regulations
in the Atlantic Flyway. Despite repeated assessments of this nature, however, the Service remains
profoundly uncertain about the impacts of widespread framework-date extensions, and regulatory measures
necessary to offset potential increases in harvests. Therefore, we propose a management approach that
accounts for this uncertainty, and permits future modification of regulatory strategies as experience with
framework-date extensions is accumulated.
Framework-date Extensions
for Duck Hunting in the United States:
Projected Impacts & Coping With Uncertainty
January 24, 2001
Division of Migratory Bird Management
Washington, D.C.
Prepared Pursuant To:
A Request by the Flyway Regulations Consultants
August 3, 2000
1Current framework dates in the Atlantic Flyway are fixed dates of October 1 to January
20.
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Framework-date Extensions for Duck Hunting in the United States:
Projected Impacts & Coping With Uncertainty
Fred A. Johnson and James A. Dubovsky, U.S. Fish and Wildlife Service
Background
On August 3, 2000, Regulations Consultants representing the four Flyway Councils requested
that the U.S. Fish and Wildlife Service (Service) conduct another assessment of the projected
impacts of extended framework dates for duck hunting. The regulatory measure to be evaluated
involves changing the earliest opening date for duck-hunting seasons from the Saturday nearest
October 1 to the Saturday nearest September 24. The measure also involves changing the latest
closing date from the Sunday nearest January 20 to the last Sunday in January.1 The extended
framework dates would apply only to the “moderate” and “liberal” regulatory alternatives during
the 2001-05 hunting seasons. The Regulations Consultants also requested that the Service
determine the reduction in bag limit or season length necessary to offset any projected increase in
harvest.
To better assess the potential impact, the Service asked the Flyway Councils to survey their
respective States concerning their interests in extended framework dates. On August 29, 2000,
the Service provided guidelines to the Flyway Council Chairmen for soliciting input. Of interest
was whether States would use an extended opening date, an extended closing date, or both in
each of the currently recognized duck-hunting zones, assuming that no season-length or bag-limit
reduction would be imposed. Also of interest was whether States would use extended framework
dates in any portion of a State if it were necessary to reduce the season length or bag limit
statewide. Responses from all States were compiled by the Flyway Councils and forwarded to the
Service by September 20, 2000.
Nature of this Assessment
Previous assessments of the projected impacts of extended framework dates were provided by the
Service in two reports to the U.S. Congress:
U.S. Fish and Wildlife Service. 1998. Framework-date extensions for duck
hunting in the United States. U.S. Dept. Inter., Washington, D.C. 43pp.
U.S. Fish and Wildlife Service. 1999. Framework-date extensions for duck
hunting in the United States: Supplemental assessment. U.S. Dept. Inter.,
Washington, D.C. 15pp.
2
These assessments relied on experience with framework-date extensions in Iowa (1979-87, 1995)
and Mississippi (1979-84) to estimate the relative size of duck harvests associated with extended
and traditional framework dates. For mallards, the proportional increases in harvest associated
with framework extensions were assumed to be representative of the changes that could be
expected in other States. This assumption permitted us to estimate the cumulative increase in
nationwide mallard harvest that might be expected with widespread application of extended
framework dates. Once the cumulative increase in harvest was estimated, we assumed that
increases in harvest rate would be proportional to increases in harvest, and derived a projected
optimal regulatory strategy for mallards based on established procedures for Adaptive Harvest
Management (AHM) (U.S. Fish and Wildlife Service. 2000. Adaptive Harvest Management:
2000 Duck Hunting Season. U.S. Dept. Inter. 43pp.).
This assessment is similar to the one conducted in 1999, but differs in several important respects.
First, in the 1999 assessment, we assumed that all States that held hunting seasons as early or late
as possible during the 1997-98 hunting season would take advantage of extended frameworks
dates if they were offered. We recognized that some States might not take advantage of extended
framework dates, or would use them only with some regulatory alternatives or in some zones, but
the Service had no basis for predicting such scenarios. Therefore, the 1999 assessment
represented a worst-case scenario in terms of large-scale impacts. In this assessment, we used the
declared intentions of each State for specifying which duck-hunting zones would take advantage
of extended framework dates. Secondly, the 1999 assessment provided projected impacts only
for midcontinent mallards because, at the time, their status was the basis for hunting regulations in
all four Flyways. This assessment also provides projected impacts on eastern mallards, and
describes how those impacts may affect future duck-hunting regulations in the Atlantic Flyway.
Perhaps more importantly, this assessment is concerned with the uncertainty associated with
projected impacts of widespread framework-date extensions, and provides a suggested approach
for coping with that uncertainty. In particular, we examine the critical assumption that historic
experience with framework extensions in Iowa and Mississippi provides reliable inference about
the changes in duck harvests that would be expected in other States using framework extensions
for the first time. This assumption is common to all analyses of projected impacts conducted to
date, including those described in this report. Because the validity of this assumption cannot be
tested empirically, we propose a management approach that accounts for current uncertainty
about harvest impacts, and permits future modification of regulatory strategies as experience with
framework-date extensions is accumulated.
Finally, we emphasize that this assessment is restricted to the cumulative harvest impact on
midcontinent and eastern mallards, and on Flyway regulatory strategies. We currently have no
basis for quantifying regulatory impacts on segments of these populations, on other populations of
mallards, or on other species. We also have no empirical basis to assess indirect impacts of
framework-date extensions on mortality or reproductive rates arising from associated alterations
in duck behavior.
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Interest in Extended Framework Dates
Based on information provided by the Flyway Councils, only 13 of the 48 contiguous States
would not take advantage of extended framework dates in at least a portion of the State (Fig. 1).
Interest in an extended closing date was more widespread than in an extended opening date, and
was manifest throughout southern and coastal States. Only Idaho expressed an interest in using
both extended opening and closing dates in the same area. When States were asked whether they
would use extended framework dates in any portion of the State if season length or bag limit were
reduced statewide, there were only 16 positive responses. Of these 16 responses, 12 were from
States that were interested in using extended framework dates statewide.
Projected Impacts on Mallard Harvests and Flyway Regulations
This assessment relies on the proportional increase in mallard harvest associated with framework
extensions in Iowa and Mississippi, as described in the Service’s second report to Congress.
Thus, for harvest areas intending to use an extended opening date, we assumed that mallard
harvest would increase by 32.0 percent (SE = 14.2) compared with the current framework date of
approximately October 1. For areas using an extended closing date, we assumed that mallard
harvest would increase by 18.0 percent (SE = 11.3) compared with a closing date of
approximately January 20. Areas intending to use both extended opening and closing dates were
assessed both rates of increase, suggesting an increase in these areas of 55.8 percent (SE = 22.5).
No change (SE = 0) in harvest from current levels was assumed for areas not expected to use
extended framework dates.
The overall increase in mallard harvest was calculated by averaging the predicted change in
harvest for individual duck-hunting zones within States, using the proportion of band recoveries
of mallards occurring in each zone as weights. Zones were defined on the basis of county
boundaries, and most accurately reflect zones in effect during the 1996-2000 hunting seasons.
Band recoveries were adjusted for known sources of variation in reporting rate. The predicted
ratio of harvests with and without extended framework dates was 1.154 (SE = 0.039) for
midcontinent mallards, suggesting a cumulative increase in harvest of 15 percent under the
moderate and liberal regulatory alternatives. This increase is slightly less than the 23 percent (SE
= 4) projected when the expected use of extended framework dates was examined on a State,
rather than a zone, basis. The increase in harvest was projected to be less for eastern mallards.
The predicted ratio of harvests was 1.051 (SE = 0.103) if the moderate or liberal regulatory
alternatives are in effect nationwide, 1.040 (SE = 0.103) if moderate or liberal regulations are in
effect only in the Pacific, Central, and Mississippi Flyways, and 1.025 (SE = 0.103) if moderate or
liberal regulations are in effect only in the Atlantic Flyway.
Harvest rates of midcontinent and eastern mallards associated with framework extensions in the
moderate and liberal alternatives were calculated by assuming that projected increases in harvest
are proportional to increases in harvest rate (Table 1). We also assumed that the regulatory
Extended opening date
Extended closing date
Both extended opening and closing dates
Fig. 1. Geographic extent of States' interest in extended framework dates, as based on a survey by Flyway Councils in September, 2000.
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choice in the Atlantic Flyway has a negligible effect on the harvest rate of midcontinent mallards
(see U.S. Fish and Wildlife Service. 2000. Adaptive Harvest Management: 2000 Duck Hunting
Season. U.S. Dept. Inter. 43pp.). However, the regulatory choice in the western three Flyways
does have a discernable effect on the harvest rate of eastern mallards. Therefore, we estimated
eastern-mallards harvest rates associated with regulations in the Atlantic Flyway by taking a
weighted average of the estimated harvest rates associated with each regulatory choice in the
western Flyways, for each possible regulatory choice in the Atlantic Flyway. The weights were
derived using simulations of the midcontinent-mallard strategy to determine the expected
frequency of regulatory choices in the western Flyways.
Optimal regulatory strategies for mallards were derived using standard AHM methods. For
midcontinent mallards, we used an objective function to maximize long-term cumulative harvest,
with a proportional devaluation of harvest when the size of the mallard population is expected to
fall below the goal of the North American Waterfowl Management Plan. We also used current
probabilities associated with the four competing models of mallard population dynamics. For
eastern mallards, we used an objective to maximize long-term cumulative harvest, and eight
alternative models of population dynamics, equally weighted. We investigated the application of
optimal strategies using Monte Carlo simulations, and evaluated expected performance using the
mean of annual harvest and population size, and the frequency with which each of the four
regulatory alternatives was used.
Table 1. Estimated harvest rates of midcontinent and eastern mallards with and without extended
framework dates.
Flyway
regulation
Framework
extensions
Harvest rates (SE)
Midcontinent mallards Eastern mallards
Closed
without 0.0088 (0.0030) 0.1100 (0.0135)
with 0.0088 (0.0030) 0.1100 (0.0178)
Very
Restrictive
without 0.0526 (0.0106) 0.1382 (0.0205)
with 0.0526 (0.0106) 0.1388 (0.0249)
Restrictive
without 0.0665 (0.0142) 0.1488 (0.0223)
with 0.0665 (0.0142) 0.1501 (0.0271)
Moderate
without 0.1114 (0.0266) 0.1661 (0.0258)
with 0.1286 (0.0309) 0.1715 (0.0322)
Liberal
without 0.1305 (0.0323) 0.1756 (0.0278)
with 0.1506 (0.0376) 0.1820 (0.0355)
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Based on the projected harvest rates provided in Table 1, the optimal regulatory strategy for the
three western Flyways would be more conservative with widespread use of framework-date
extensions (Table 2). Most differences in hunting regulations between strategies with and without
extended framework dates occurred at population sizes of midcontinent mallards from five to
eight million, and tended to be associated with above-average pond numbers. Assuming the
projected increases in harvest rates are accurate, we would expect a reduction in the frequency of
liberal regulations, with a concurrent increase in the frequency of moderate regulations (Table 2).
We would expect no discernable change in the average size of the midcontinent mallard
population or its associated harvest.
For the Atlantic Flyway, the only difference in optimal regulatory choices between a strategy with
and without extended framework dates occurs when there are 500-550 thousand eastern mallards.
Although the regulatory strategy was slightly more conservative with extended framework dates,
there was no discernable change in the expected frequency of liberal regulations (99.7% vs.
99.9%). We also would expect no significant change in average population size or harvest of
eastern mallards. This lack of regulatory effect in the Atlantic Flyway is due to the fact that most
States interested in framework-date extensions in the Flyway do not contribute significantly to the
overall harvests of eastern or midcontinent mallards. Therefore, mallards, and hunting regulations
based on their status, likely do not provide a sufficient basis for projecting the impact of
framework-date extensions in the Atlantic Flyway. We also reiterate that projected changes in
optimal regulatory strategies for both populations of mallards are based on current probabilities
associated with the alternative models of mallard population dynamics, and these probabilities will
change over time.
Table 2. Projected changes in the frequency of regulatory choices in the Mississippi, Central, and
Pacific Flyways associated with extended framework dates.
Regulatory alternative
Projected frequency (%)
Without
extensions
With
extensions
Closed 0.0 0.0
Very restrictive 0.1 0.1
Restrictive 2.2 9.0
Moderate 17.3 47.4
Liberal 80.4 43.5
Contrary to the impression conveyed by these analyses, we remain profoundly uncertain about the
increase in mallard harvests that might be expected with widespread use of extended framework
dates. First, the strength of inferences about the impacts of framework-date extensions in Iowa
2 Alternatively, these hypotheses might be described and weighted based on the impact
analyses provided in this report.
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and Mississippi are limited due to the lack of experimental designs (see discussion in the Service’s
reports to Congress). Perhaps more importantly, we have no basis to determine whether the
experience with extensions in Iowa and Mississippi is representative. In fact, there is every reason
to believe otherwise because of differences among Flyways in duck populations, environmental
conditions, and hunter activity. Additionally, we have documented Flyway-specific effects of other
regulatory tools (e.g., season length, bag limit), suggesting that there are likely differences among
Flyways in the effects of framework-date extensions as well. It is our judgement, then, that we
have neither sufficient information or experience to reliably project regulatory impacts, nor to
estimate the reduction in season length or bag limit that might be required to offset increases in
harvest. To do otherwise would falsely portray the Service’s ability to predict the consequences of
its regulatory actions.
Coping With Uncertainty
Fortunately, there is a decision-making framework in place that can account for fundamental
uncertainties in management outcomes, and that can modify future decisions based on accumulated
management experience. AHM has proven to be effective tool for making decisions in the face of
uncertainty, at least when there is broad-based agreement on management objectives (i.e., how to
value harvests, and how those values should be shared). In this light, the decision to use
framework-date extensions has been problematic not because of any shortcoming of AHM, but
because of tacit disagreement over desirable distributions of harvest or harvest opportunity.
Unfortunately, the lack of an effective process or protocol for organizing debate, as well as a
paucity of information on hunter satisfaction, continue to be formidable obstacles to attaining
agreement on “fairness” in harvest distribution.
In the absence of such agreement, however, it is still possible to formulate an adaptive approach to
the use of framework-date extensions, provided that the Flyway Councils are prepared to accept
the changes in harvest distribution that might occur. The approach would involve embracing two
or more alternative hypotheses about the change in mallard harvests that would be associated with
widespread application of extended framework dates. Initially, these alternative hypotheses might
be considered equally likely, reflecting a high degree of uncertainty about harvest impacts.2 Based
on these alternative hypotheses and their associated probabilities, an optimal regulatory strategy
including framework-date extensions would be derived. Once the appropriate regulatory decision
had been made, mallard harvest rates would be estimated from band-recovery data and compared
with the predictions made under the alternative hypotheses. The hypothesis predicting a harvest
rate in closest agreement with that observed in the monitoring program would gain credence (i.e.,
probability mass) and, thus, be more influential in the determination of an optimal regulatory
strategy prior to setting the next annual hunting regulations. Over time, this iterative process
should identify which impact hypothesis is the most accurate among the alternatives, while
ensuring that uncertainty as to harvest impacts is properly accounted for in each regulatory
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decision. An adaptive approach to framework-date extensions was first suggested by the inter-agency
AHM Working Group, and is considered by that group as the only approach consistent
with the goals, theory, and practice of AHM.
Essential to the successful application of this adaptive approach is a reliable monitoring program
for estimating realized harvest rates of mallards. Such a program does not exist at this time
because of continuing uncertainty about the rate at which hunters report band recoveries. This
uncertainty resulted from the introduction of a toll-free phone number for reporting band
recoveries, which is the key feature of a campaign designed to increase band-reporting rates. The
Service currently is developing plans to estimate current band-reporting rates using a comparison
of standard and reward bands.