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We investigated the utility of adaptive management (AM) in wildlife management, reviewing our experiences in applying AM to overabundant sika deer (Cervus nippon) populations in Hokkaido, Japan. The management goals of our program were: (1) to maintain the population at moderate density levels preventing population irruption, (2) to reduce damage to crops and forests, and (3) to sustain a moderate yield of hunting without endangering the population. Because of significant uncertainty in biological and environmental parameters, we designed a “feedback” management program based on controlling hunting pressure. Three threshold levels of relative population size and four levels of hunting pressure were configured, with a choice of four corresponding management actions. Under this program, the Hokkaido Government has been promoting aggressive female culling to reduce the sika deer population since 1998. We devised a harvest-based estimation for population size using relative population size and the number of deer harvested, and found that the 1993 population size (originally estimated by extrapolation of aerial surveys) had been underestimated. To reduce observation errors, a harvest-based Bayesian estimation was developed and the 1993 population estimate was again revised. Analyses of population trends and harvest data demonstrate that hunting is an important large-scale experiment to obtain reliable estimation of population size. A serious side effect of hunting on sika deer was inadvertent lead poisoning of large birds of prey. The prohibition of the use of lead bullets by the Hokkaido Government was successful in reducing the lead poisoning, but the problem still remains. Two case studies on sika population irruption show that the densities set by maximum sustainable yield may be too high to prevent damage to agriculture, forestry, and/or ecosystems. Threshold management based on feedback control is better for ecosystem management. Since volunteer hunters favor higher hunting efficiency in resource management (e.g., venison), it is necessary to support the development of professional hunters for culling operations for ecosystem management, where lower densities of deer should be set for target areas. Hunting as resource management and culling for ecosystem management should be synergistically combined under AM. Keywords Cervus nippon -Density dependence-Feedback management-Maximum sustainable yield-Population dynamics
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SPECIAL FEATURE: REVIEW Adaptive Management
Adaptive management of sika deer populations in Hokkaido,
Japan: theory and practice
Koichi Kaji Takashi Saitoh Hiroyuki Uno
Hiroyuki Matsuda Kohji Yamamura
Received: 5 March 2010 / Accepted: 9 May 2010 / Published online: 1 June 2010
ÓThe Society of Population Ecology and Springer 2010
Abstract We investigated the utility of adaptive man-
agement (AM) in wildlife management, reviewing our
experiences in applying AM to overabundant sika deer
(Cervus nippon) populations in Hokkaido, Japan. The
management goals of our program were: (1) to maintain
the population at moderate density levels preventing
population irruption, (2) to reduce damage to crops and
forests, and (3) to sustain a moderate yield of hunting
without endangering the population. Because of signifi-
cant uncertainty in biological and environmental param-
eters, we designed a ‘‘feedback’’ management program
based on controlling hunting pressure. Three threshold
levels of relative population size and four levels of
hunting pressure were configured, with a choice of four
corresponding management actions. Under this program,
the Hokkaido Government has been promoting aggressive
female culling to reduce the sika deer population since
1998. We devised a harvest-based estimation for popu-
lation size using relative population size and the number
of deer harvested, and found that the 1993 population size
(originally estimated by extrapolation of aerial surveys)
had been underestimated. To reduce observation errors, a
harvest-based Bayesian estimation was developed and the
1993 population estimate was again revised. Analyses of
population trends and harvest data demonstrate that
hunting is an important large-scale experiment to obtain
reliable estimation of population size. A serious side
effect of hunting on sika deer was inadvertent lead poi-
soning of large birds of prey. The prohibition of the use
of lead bullets by the Hokkaido Government was suc-
cessful in reducing the lead poisoning, but the problem
still remains. Two case studies on sika population irrup-
tion show that the densities set by maximum sustainable
yield may be too high to prevent damage to agriculture,
forestry, and/or ecosystems. Threshold management based
on feedback control is better for ecosystem management.
Since volunteer hunters favor higher hunting efficiency in
resource management (e.g., venison), it is necessary to
support the development of professional hunters for
culling operations for ecosystem management, where
lower densities of deer should be set for target areas.
Hunting as resource management and culling for ecosys-
tem management should be synergistically combined
under AM.
Keywords Cervus nippon Density dependence
Feedback management Maximum sustainable yield
Population dynamics
K. Kaji (&)
Faculty of Agriculture,
Tokyo University of Agriculture and Technology,
3-5-8 Saiwaicho, Fuchu 183-8509, Japan
e-mail: kkaji@cc.tuat.ac.jp
T. Saitoh
Field Science Center, Hokkaido University,
Sapporo 060-0811, Japan
H. Uno
Institute of Environmental Sciences,
Hokkaido Research Organization,
Sapporo 060-0819, Japan
H. Matsuda
Department of Environmental Management,
Yokohama National University,
Yokohama 239-8501, Japan
K. Yamamura
Laboratory of Population Ecology,
National Institute for Agro-Environmental Sciences,
Tsukuba 305-8604, Japan
123
Popul Ecol (2010) 52:373–387
DOI 10.1007/s10144-010-0219-4
Introduction
Adaptive management (AM) is a management system for
natural resources through continually improving manage-
ment policies and practices, including both approaches of
adaptive learning and feedback control (Walters 1986).
Feedback management or feedback control is a manage-
ment policy for sustainable use of natural resources at an
optimal level under uncertain information of resources,
which was proposed by Tanaka (1982). Taking in its broad
sense, feedback management is almost the same as AM. To
put it concisely, AM is a scientific way of ‘‘learning by
doing’’, changing management tactics according to the
results of management action and improving a program
when new knowledge is gained and/or an error of past
knowledge is found (Christensen et al. 1996). It could work
efficiently to manage populations or resources with
uncertainties under insufficient information. Although the
essence of adaptive management is rather simple, it
requires many efforts to accomplish its processes: setting
the objectives of the management, estimating ecological
parameters, planning the management based on the pre-
dicted dynamics, and monitoring of the results. Often,
specific survey protocols and new statistical methods for
estimation and prediction are needed.
Although the AM approach has been considered the best
way for resolving both the biological and political dilem-
mas surrounding deer management in the US National
Parks (Porter and Underwood 1999), applying AM to deer
management has been very limited. A sort of adaptive
management is employed in France for managing the roe
deer (Capreolus capreolus) using indicators of ecological
change to monitor populations at a local scale (Morellet
et al. 2007). The AM approach, however, has never been
applied at a wide spatial scale, because the indicators of
ecological change have been validated only in well-defined
populations at a small scale (Morellet et al. 2007).
Hokkaido is the northernmost island of Japan and covers
78,073 km
2
. It was relatively recently (the late nineteenth
century) industrialized by the Japanese Government. Sika
deer (Cervus nippon) populations in Hokkaido are char-
acterized by a relatively simple life history (Hokkaido
Institute of Environmental Sciences 1997). The mean life
span of males (2.1–3.1 years) was shorter than for females
(3.6–3.9 years). First ovulation and/or pregnancy occurs
during the breading season at yearling age. Pregnancy rate
of adult female sika deer (2 years and older) is higher than
90%, which is maintained throughout their life. Litter size
is typically one and twinning is rare.
The history of sika deer populations in Hokkaido is
characterized by overexploitation and protection (see
‘‘ Historical background of sika deer management’’ for
details). The overharvest by commercial hunting in the late
1800s and a heavy snow in 1879 resulted in a dramatic
decline in deer abundance, while the distribution range
shrank into limited areas. Due to long-term legislated
protection such as bans on hunting (1890–1900 and 1920–
1952), and bucks-only hunting from 1955, the sika deer
population gradually recovered its distribution, becoming
well established in eastern Hokkaido by the mid-1970s, and
had spread to potential habitats all over Hokkaido by the
1990s (Kaji et al. 2000). Abundance has also greatly
recovered, causing severe damage in agricultural and for-
estry during the last three decades (Fig. 1).
In 1998, in response to this damage, the Government of
Hokkaido implemented the Conservation and Management
Plan for Sika deer (CMPS) in eastern Hokkaido and pro-
moted aggressive population control based on AM (Hok-
kaido Government 1998; Matsuda et al. 1999). During
preparation for the CMPS, we faced a lot of uncertainties in
estimating the population size and demographic parameters
because of insufficient information. Because of these large
uncertainties, we have been exploring how to apply AM to
deer management practices since 1998. This paper will
0
1,000
2,000
3,000
4,000
5,000
6,000
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Dama
g
e incurred (million
y
en)
Number of harvest
Ye ar
males (nuisance control)
males (hunting)
females (nuisance control)
females (hunting)
damage
Fig. 1 Changes in sika deer
(Cervus nippon) harvest and
agriculture/forestry damage
occurring between 1957 and
2008 in Hokkaido (Hokkaido
Government, unpublished data)
374 Popul Ecol (2010) 52:373–387
123
show the usefulness of AM in wildlife management,
reviewing our experiences in applying AM to the sika deer
population in Hokkaido.
In this review paper, we first describe the historical
background of sika deer management in Hokkaido since
the late nineteenth century, and then introduce theory and
practices of AM for sika deer populations in Hokkaido.
Through the practices, we have learned the importance of
the following points: (1) monitoring systems to recognize
dynamics of deer populations, conflict with human activi-
ties, and their impacts on ecosystems; (2) statistical tech-
niques to estimate ecological parameters and to predict
dynamics of deer populations for making a management
program; and (3) adaptive learning to solve unpredictable
problems that were brought about by management treat-
ments. Finally, based on our long-term study of two sika
deer populations, we argue a problem with maximum
sustainable yield (MSY) theory for the application to sika
deer management concerning the protection of vegetation.
In ‘Conclusion: hunting as resource management and
culling for ecosystem management’, we emphasis the
importance of hunting as resource management and of
culling for ecosystem management.
Historical background of sika deer management
Overexploitation in the second half of the nineteenth cen-
tury resulted in major declines in both deer numbers and
range worldwide. Especially in Europe and North America,
subsequent protection of deer (hunting regulation and
reduction of natural predators), habitat changes due to
agricultural and silvicultural activities and moderate cli-
mates then caused rapid population increases (McShea
et al. 1997; Linnell et al. 1998;Co
ˆte
´et al. 2004).
The history of sika deer populations in Hokkaido
(Table 1) is in some respects similar to that of deer pop-
ulations in North America. Prior to the Japanese coloni-
zation of Hokkaido in the late nineteenth century, sika deer
had occurred throughout Hokkaido. Several factors such as
overexploitation, habitat loss due to agricultural develop-
ment and timber extraction in lowland forests, and heavy
snowfalls contributed to the rapid decline in deer numbers
around 1900 (Inukai 1952). Between 1873 and 1878, the
annual harvest ranged from 60,938 to 110,002 deer. In
1876, in an effort to control hunting, the Hokkaido Gov-
ernment established a modern hunting law (Table 1;
Tawara 1979), while establishing a deer meat cannery and
encouraging exports of deer products (meat, hide and
antlers) in 1878 (Inukai 1952). The new hunting regula-
tions were based on the recommendations of Horace
Capron, a technical advisor from the US, who was familiar
with the legislation proposed to prevent the extirpation of
the North American bison (Bison bison). However, regu-
lation was not able to prevent a drastic decrease of the sika
deer populations; overharvesting and heavy snow in 1879
led to a great winter mortality, and it is thought that pop-
ulations declined to a threatened level. Three major pop-
ulations survived this bottleneck, in the Akan, Hidaka, and
Daisetsu mountain regions (Fig. 2).
To conserve the sika deer populations, hunting was
banned twice, in 1890–1900 and 1920–1952 (Table 1).
During the Second World War, deer populations gradually
recovered, such that bucks-only hunting was allowed in
parts of the Hidaka district in 1955–1956, and the hunting
areas expanded more widely in 1957. Extirpation of wolves
by 1890 (Inukai 1933), hunting regulation (prohibition of
hunting and bucks-only hunting), replacement of native
mixed-hardwood forests with conifer plantations, and
increased pasture acreage may have contributed to the
recovery of deer distribution and abundance (Kaneko et al.
1998). By the mid-1970s, sika deer occupied most avail-
able habitats in the eastern half of Hokkaido and had spread
to the south and northwestern parts of the island and had
occupied their entire potential habitats by the 1990s (Kaji
et al. 2000).
Legislated protection such as bucks-only hunting and
large game reserves (required, when setting hunting areas,
to cover areas being equivalent to 1/3 of the hunting area)
greatly contributed to the recovery of the populations and
to the maintenance of the hunting system. However, the
success of the protection measures turned out to be a cause
of overabundance. As the range of sika deer expanded,
agricultural and forest damage increased. Damage to
agricultural crops and forests by sika deer remained at low
levels from the mid-1950s through the mid-1970s, but had
increased dramatically to nearly 2 billion Japanese yen
(JPY) by 1990 and to over 5 billion JPY by 1996 (Fig. 1).
In Nature Reserves, such as the Akan National Park and
Shiretoko National Park, elm trees (Ulmus laciniata and
U. davidiana) were seriously debarked by deer and the
increase in standing dead trees became obvious. Road kills
and rail accidents also increased and human injury caused
by road accidents, animal welfare (e.g., road kills) and
economic impacts became serious.
In response to the damage, hunting regulations were
relaxed, but female hunting was not allowed until 1994
(Table 1; Fig. 1). The total harvest fluctuated between
2,000 and 3,000 animals during 1970–1989 and increased
to 16,134 animals in 1990 and to 46,634 animals in 1996.
One of causes of the problem was that no goal was ever set
for the protection of the deer.
In 1990, experts of bear and deer biology (who took part
in the 5th International Ecological Congress held in
Yokohama, Japan) from European and North American
countries were invited to Hokkaido. Through the ‘‘Deer
Popul Ecol (2010) 52:373–387 375
123
and Bear Forum Hokkaido 1990’’ held in Sapporo, they
proposed a modern wildlife management system for the
Hokkaido Government referring to those in their countries
(Ohtaishi et al. 1990). They recommended that the
Hokkaido Government establish a wildlife management
agency and promote integrated management systems for
wildlife.
The Hokkaido Government responded promptly to their
proposal and established the Hokkaido Institute of Envi-
ronmental Sciences (HIES) in 1991. Monitoring of sika
deer populations was started using population indices such
as spotlight counts, aerial surveys, catch per unit effort
(CPUE; number of deer harvested per hunter-day), sighting
per unit effort (SPUE; number of deer sighted per hunter-
day), and damage to agriculture and forestry. This was the
beginning of a more scientific approach to managing sika
deer populations in Japan. Intensive studies on seasonal
migration, age structure and reproductive condition were
also begun on model study sites. In response to the increase
in damage by sika deer, female hunting was allowed from
1994 in restricted areas and periods. Due to the strong
social pressure against female hunting from citizens and
even from some wildlife biologists who were concerned
about a marked decrease of sika deer populations, we were
not able to promote aggressive female hunting at this stage.
Although the Hokkaido Government extended female
hunting areas to 63 municipalities in 1997 (about 30% of
Hokkaido as of 1997) and the hunting period (increasing it
by about 20-fold compared to those in 1994–1996;
Table 1), the number of harvested females in this year
increased only by a factor of 1.4 under the hunting regu-
lation of one female or one male per day. This experience
revealed that hunters still favored males, and thus a sex-
specific hunting regulation was the key to increasing the
female harvest (Matsuda et al. 1999).
Lesson 1. The success of one management action could
turn out to be the cause of another problem (e.g., over-
abundance). Clear goals for management programs and
monitoring the effect of the program are essential to avoid
generating new problems.
Table 1 Status of sika deer (Cervus nippon) population and government control on hunting in Hokkaido
Year Status of deer population Government control on hunting
1873 Population begun to decrease Extensive market hunting
1876 The number of hunters, period and season were regulated
and the use of aconitum-tipped poison arrows was
prohibited
1878 A deer meat cannery was established
1879 Drastic decrease by overharvest and heavy snow
1890–1900 Near extinction Ban on hunting
1920–1952 Threatened level Ban on hunting
1955 Gradually recovered Bucks-only hunting started
1991 Gradually increased Monitoring started by HIES
1994–1996 Damage income of agriculture and forestry by
deer reached 5 billion JPY in 1996
Female hunting started in restricted areas
(8–10 municipalities) for 10 days each year.
Allowable harvest was 1 deer (1 male or 1 female) per day
1997 Female hunting areas extended to 63 municipalities
and the hunting period to 30 days
1998 Population reached a peak in eastern HK Aggressive female harvesting started based on CMPS.
Allowable harvest increased to 2 deer (2 females or 1
male ?1 female) per day, and the hunting season
extended to 3 months
2000 Population decreased in eastern HK,
while increased in western
and northern HK from 1998 to 2000
Management area extended to include central part of HK.
Hunting seasons was extended to 4 months.
Banned the use of lead bullets in rifles
2001 Population increased in eastern HK Banned the use of lead bullets in shot guns. Allowable
harvest extended to 3 deer (3 females or 1 male ?2 females)
2002 Population increased all over HK Management areas extended all over HK
2004 Unlimited female hunting started
2005 Population recovered to almost the same
level as 1993 in eastern HK
2008 Population irrupted all over HK Encouraging sustainable resource management
of deer as venison
JPY Japanese yen, HK Hokkaido, HIES Hokkaido Institute of Environmental Sciences
376 Popul Ecol (2010) 52:373–387
123
Theory and monitoring for adaptive management
of sika deer in Hokkaido
Spatial distribution, population structure
and monitoring unit
To obtain information about deer distribution, the Hokka-
ido Government conducted personal interviews or sys-
tematic mail surveys in all municipalities of Hokkaido in
1978, 1984, 1991, and 1997 with a supplementary survey
in 2005 (Kaji et al. 2000,2006; Fig. 2). These surveys
revealed the recovery process of deer from threatened
levels around 1900. At least three populations of sika deer
survived the bottleneck and expanded from a few natural
refuges in the mountainous areas of Akan, Hidaka, and
Daisetsu districts (Nagata et al. 1998; Kaji et al. 2000,
2006; Fig. 2).
Logistic regression analyses of the effect of environ-
mental conditions on deer occurrence based on GIS data
suggested that snow depth and bamboo grass (Sasa spp.)
variation were important in the regulation of sika deer
distribution, and that deer had occupied almost all the
potential range by 1990 (Kaji et al. 2000). Part of the recent
expansion resulted from experimental reintroductions in
1980 (6 females and 2 males) and in 1981 (6 females and 3
males) on Oshima, Hokkaido’s southernmost peninsula
(Fig. 2; Kaji et al. 2000).
The distribution ranges have been further expanding in
western and northern Hokkaido (Fig. 2) where there is
normally heavy snow accumulation. This range expansion
may be caused by recent warm winter climate conditions.
Based on these distribution maps, we set up 12 monitoring
units in Hokkaido (Fig. 3) and assessed population status in
each (Hokkaido Institute of Environmental Sciences 1994).
These ‘‘monitoring units’’ were not purely population-
based, but also relied on both geographical features and
District office boundaries. Each District office is composed
of several ‘‘municipalities’’. Since most sika deer in eastern
Hokkaido make large-scale seasonal migrations (Sakuragi
et al. 2003; Igota et al. 2004), 4 monitoring units (units
9–12) located in eastern Hokkaido were combined as the
area for management of the target population (the Akan
population; Fig. 3). The Akan population was the largest,
and caused the most serious damage associated with rapid
range expansion and population increase during the 1980s
and 1990s, so we focused on management of the Akan
population.
The main wintering grounds of the Akan population
were the Akan National Park and neighboring Shiranuka
Hills (Uno et al. 2009). Deer showed strong site fidelity to
their seasonal ranges (Uno and Kaji 2000; Igota et al.
2004). The summering areas are extensive and contiguous
in eastern Hokkaido (Kaneko et al. 1998), while potential
wintering areas are restricted to a few limited areas because
of heavy snow and availability of coniferous forests for
shelter (Kaneko et al. 1998; Sakuragi et al. 2003). Of 57
radio-collared female deer captured in the Shiranuka Hills
(a wintering site), 21% were non-migrants and 69% were
migrants (Igota et al. 2004).
Monitoring by population indices
Since complete counts across an entire sampling frame or
study area are rarely possible, index methods using sample
counts are a practical way to monitor the change in the size
of a target population and to evaluate the estimation error
(Thompson et al. 1998). There are, however, many prob-
lems with index methods that result in a lack of rigor and
validity (White 2001). We compared the rigor and validity
of the following population size indices; spotlight counts
19911974
19541925
1997 (supplementary survey in 2005)
1980: 6 Females, 2 Males
1981: 6 Females, 3 Males
Hidaka
Daisetsu
Akan
Fig. 2 Sika deer range expansion from 1925 to 2005 in Hokkaido,
Japan, estimated from observations reported in personal interviews
and mail surveys. Arrows at the southern end of Oshima Peninsula
indicate sites where deer were released in 1980 and 1981. Deer
populations expanded from the Hidaka, Daisetsu and Akan mountain
regions. The historical distribution map was modified from Kaji et al.
(2000,2006)
Popul Ecol (2010) 52:373–387 377
123
on farmland, aerial survey on wintering ground from a
helicopter, CPUE, SPUE, and the value of damage to
agriculture and forestry (Uno et al. 2006).
The index of aerial surveys was available only for spe-
cific ranges (Akan National Park and Shiranuka Hills) and
limited years (February–March 1993, 1994, 1997–2002).
The index based on the aerial surveys did not show a clear
correlation with any other indices. Hunters’ reports and the
resulting CPUE index were affected by changes in hunting
regulations. While, on the other hand, changes in the
hunting regulation do not seem to have affected the SPUE
index, the SPUE index varied among years and did not
show a consistent trend. In addition, there was a 2-year
time lag until the SPUE index became available, because
data processing was time consuming work. Thus, the SPUE
index was inferior to the spotlight count index which had a
shorter time lag of 1 year, although the spotlight count
index showed large annual variation. The index based on
damage by deer is influenced by agricultural practice and
has been decreasing recently due to the construction of
deer-proof fences. The spotlight survey index (Fig. 4)
appeared to track estimated population changes (Figs. 5
and 6); it increased from 1992 to 1998, and decreased
thereafter, which coincided with a period of aggressive
EPC culling during which more than 27,000 female deer
were killed annually (Figs. 5and 6). In addition, a recon-
structed sika population by cohort analysis showed a con-
sistent trend with the population index by spotlight survey
(Ueno et al. 2010). Furthermore, its estimate error is rela-
tively small (Uno et al. 2006). In conclusion, the index
based on spotlight surveys is the most useful of the five
indices in looking at the population trend (Uno et al. 2006).
However, spotlight surveys did show unrealistic low
abundance in some specific years (e.g., in 1994), and thus
the validity of the spotlight count index should be checked
by using another index (e.g., SPUE).
0 100 200
km
1
2
3
7
8
912
11
10
5
4
6
N
Fig. 3 Monitoring units for sika deer in Hokkaido. Each unit is
identified by a number (Hokkaido Institute of Environmental Sciences
1994). The shaded area indicates the management area for the Akan
population (monitoring units 9–12, comprising 40 municipalities, the
dark shaded area was where the aerial survey was conducted) In dark
shaded and middling shaded areas, we could use the spotlight counts,
CPUE and SPUE data (25 municipalities, two spotlight counts data
were excluded for analysis because of net fences). In light shaded
areas, we could use only spotlight count data (15 municipalities). We
did aerial surveys in the dark shaded area (3 municipalities) (Uno
et al. 2006)
0
50
100
150
200
250
300
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Population index
Year
Eastern Hokkaido
Western Hokkaido
Fig. 4 Population index estimated by spotlight count in eastern and
western Hokkaido. The indices were standardized by the value of
1993 in eastern Hokkaido, and 2000 in western Hokkaido (Hokkaido
Government, unpublished data)
0
20
40
60
80
100
120
140
160
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
Population Index
Number of harvest
males (nuisance control)
males (hunting)
females (nuisance control)
females (hunting)
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Year
Fig. 5 Harvest-based estimates of population indices (Matsuda et al.
2002) and number of deer harvested from 1993 to 2005 in eastern
Hokkaido. Bold line the estimates of population index, dotted lines SE
378 Popul Ecol (2010) 52:373–387
123
Feedback management based on population dynamics
model in eastern Hokkaido
Population dynamics model is essential for scientific
management planning because we need to predict popula-
tion dynamics, to determine harvest numbers, and to
evaluate management implementation by comparing the
prediction with the results. Sika deer populations in Hok-
kaido are characterized by (1) a high intrinsic rate of
increase (r
m
=0.15–0.19; Kaji et al. 2004), (2) no signif-
icant density effects on population growth until just before
a population crash (Kaji et al. 1988,2004), and (3) a rel-
atively simple life history (see ‘Introduction’). Sika deer
populations have fluctuated greatly due to heavy snow,
overharvest, and bans on hunting in Hokkaido (Inukai
1952). Because of the large number of uncertain biological,
environmental, and game-hunting parameters, the Hokka-
ido Government designed a ‘‘feedback’’ management
program which is the control of hunting pressure based on
the prediction of the dynamical model.
In 1998, the Hokkaido Government implemented the
CMPS in eastern Hokkaido. In the CMPS, population
indices were obtained from spotlight counts, hunting sta-
tistics, and the extent of damage of crops and forests that
had been monitored every year. In fiscal year 1993, the
population size in eastern Hokkaido was estimated at
120,000 ±46,000 (90% CI) deer as of March 1994 based
on aerial surveys (Hokkaido Institute of Environmental
Sciences 1995). However, since its accuracy was uncertain,
we used a relative population size index where the value
for 1993 was 100%.
Population control without setting a goal is like setting
off on a voyage without a compass, so the management
goals were carefully identified: (1) to maintain moderate
population levels to prevent irruptive behavior of the
populations, (2) to reduce damages to crops and forests,
and (3) to sustain a moderate yield without endangering the
population. Dynamics of the target population were pre-
dicted by a simple stage-structured model, considering the
effects of uncertain population parameters and severe
winters. Management actions based on population indices
estimated by the model analyses and the prediction
have been implemented by controlling hunting pressure
(Matsuda et al. 1999).
A standard feedback program determines harvest rate by
a dynamic equation (Tanaka 1982). If the estimate of
population is larger (or smaller) than an optimal size,
hunting pressure is increased (or decreased) in proportion
to the difference between the estimate and the optimal size.
Under this program, the dynamics of deer population and
hunting pressure are similar to prey–predator dynamics in
Lotka–Volterra systems (Lotka 1925; Volterra 1926). If the
population has strong density effects, the feedback system
has a stable equilibrium, although the population fluctuates
in the process of approaching the equilibrium. Thus, stan-
dard feedback management is effective when the current
population size is relatively close to the target level and/or
the population has a strong density effect (Tanaka 1982).
The current population size of sika deer, however, greatly
exceeded the target level and no significant density effect
on population growth rate was expected. Thus, a model
analysis showed that the applying standard feedback
management program to the population dynamic model for
the target population generated large fluctuations at inter-
vals of 100 years, and the target population size could
never be realized (Matsuda et al. 1999).
As an alternative, we developed a model involving three
threshold levels of relative population size, four levels of
hunting pressure, and a choice of one of four actions, based
on the estimates of relative population size (Table 2;
Fig. 7; Matsuda et al. 1999). The three thresholds were
0
20
40
60
80
100
120
140
160
0
20,000
40,000
60,000
80,000
100,000 a Eastern Hokkaido
Po
p
ulation Index
Number of harvest
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2008
2007
0
50
100
150
200
250
300
350
0
10,000
20,000
30,000
40,000
50,000
60,000
b Western Hokkaido
males (nuisance control)
males (hunting)
females (nuisance control)
females (hunting)
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2008
2007
Year
Po
p
ulation Index
Number of harvest
Fig. 6 Bayesian estimates of population indices that were obtained
from the state-space model based on the stage-structured model
(Yamamura et al. 2008) and number of deer harvested from 1993 to
2008. Bold line the estimates of population indices, dotted lines SE.
Since spotlight surveys were not sufficient in number in western
Hokkaido until 1999, the population indices were obtained using the
data between 2000 and 2008 for relative abundance, with the value
for 2000 as 100%
Popul Ecol (2010) 52:373–387 379
123
determined using risk assessment under 4 scenarios
(Matsuda et al. 1999): (1) a Critical threshold (%P
-
)
where the probability [the number of adults is smaller than
1,000 within the next 100 years] must be smaller than 1%,
(2) an Optimal level (%P*) where the probability [the
estimate of population index (%P) is smaller than %P
-
in
the next 100 years] must be smaller than 2.5%, and (3) an
Irruption threshold (%P
?
) where the probability [the
estimates of relative population index (%P) is larger than
%P
?
in the next 100 years after %Pis less than %P
?
] must
be smaller than 2.5%.
The four potential scenarios are as follows (Table 2). If
the current deer population index [%P(t)] were above the
irruption threshold (%P
?
=50% of the population indices
in 1993), emergency population control (EPC) would be
adopted; i.e., maximizing the harvest of female deer by
hunting and control kill. If %P(t) were larger than the
optimal level (%P* =25%) but smaller than %P
?
, hunt-
ing for males and females would be allowed by gradually
decreased action (GDA). If %P(t) were larger than the
critical threshold (%P
-
=5%) but smaller than the opti-
mal level (%P*), bucks-only hunting would be allowed by
gradually increased action (GIA). If %P(t) were smaller
than %P
-
, a total ban on hunting (BH) is implemented.
Sex-specific hunting is a key to maintaining a considerable
amount of harvest.
Hokkaido Government decided to adopt EPC in 1998–
1999; hunting area and period of hunting season for
females were extended to sixfold and threefold larger than
those in 1994–1996, respectively. Because of uncertainty
of actual increment of hunting effort and population
abundance, the Hokkaido Government relaxed hunting
regulations to maximize harvest of female deer step by step
according to the basic concept of feedback management
(Table 1).
Lesson 2. Since information about wildlife populations
has uncertainties, investigators should monitor populations
using several independent population indices, cross-check
them, and confirm the consistency.
Practice of adaptive management: learning by doing,
through emergency population control, 1998–2008
In 1998, since population indices exceeded the irruption
threshold (Fig. 5), the Hokkaido Government implemented
EPC (Table 2). The allowable harvest per day and the
hunting season were gradually extended thereafter
(Table 1). In fiscal year 1998, 37,800 females and 34,700
males were harvested or culled in eastern Hokkaido
(Fig. 5). The doubling of allowable harvest per day and
extending the hunting periods for females were very
effective in promoting the female harvest.
In 2000, the CMPS was revised as an authorized plan by
the Environmental Agency of the Japanese Government,
and target management areas were extended to central
Hokkaido, which consisted of monitoring units 4–7 and the
south parts of units 2 and 3; see Fig. 3) along with the
expansion of deer distribution and the increase of popula-
tion size in western and northern Hokkaido (Figs. 2and 6;
Hokkaido Government 2000). At the same time, the Hok-
kaido Government extended the hunting season to
4 months (November–February) in eastern Hokkaido. The
extension of the hunting season to the end of February was
very effective in increasing the female harvest in eastern
Hokkaido, where 3,658 more females were harvested
compared to the previous year. The extension of the
Table 2 Four management programs based on relative population size index
Program Population size index Action
Emergent population control (EPC) %P
?
\%P(t) Maximum harvest of females
Gradually decreased action (GDA) %P* \%P(t)\%P
?
Hunting for males and females
Gradually increased action (GIA) %P
-
\%P(t)\%P* Bucks-only hunting
Ban on hunting (BH) %P(t)\%P
-
Ban on hunting
%P(t) Population size index observed, %P
1
the irruption level, %P* the optimal leve, %P
-
the critical level (Matsuda et al. 1999)
%P+
%P*
%P-
EPC
GDA
GIA
BH
Year
Population size index
%P(t)
Fig. 7 Schematic diagram illustrating a framework of feedback
management for the sika deer population in eastern Hokkaido; %P(t)
population size index observed; %P
?
the Irruption threshold, %P* the
Optimal level, %P
-
the Critical threshold, EPC emergency popula-
tion control, GDA gradually decreased action, GIA gradually
increased action, BH ban on hunting (Hokkaido Government 1998)
380 Popul Ecol (2010) 52:373–387
123
hunting season to the end of February was reversed after
2000, to avoid disturbing the breeding of large birds of prey.
The relative population size indices decreased from
123% in 1998 to 79% in 2000, but it did not show further
decline thereafter (Fig. 6). Although target management
areas were extended to cover all of Hokkaido in 2002, and
unlimited female hunting started from 2004 in eastern
Hokkaido (Table 1), the female harvest did not increase
correspondingly. By 2005, the population size indices had
recovered to almost the same level as in 1993 (Fig. 6).
Although EPC with aggressive female hunting has been
continuing over 10 years since 1998, the population size
has still been far beyond the irruption threshold.
Improvement of population estimation for sika deer
Harvest-based estimation
The deer population in eastern Hokkaido for the 1993 fiscal
year was first estimated to be between 74,000 and 166,000
individuals (90% CI; Hokkaido Institute of Environmental
Sciences 1995). For this estimate, we conducted aerial
counts by helicopter at 43 survey units on wintering
grounds (Fig. 3; total area was 406.5 km
2
) between late
February and early May in 1993 and 1994, and extrapo-
lated the average density in the survey units into potential
wintering grounds in 4 districts of eastern Hokkaido.
The harvest exceeded the estimated natural population
increase during the first several years under EPC, assuming
an annual rate of increase of 16–21% (Kaji et al. 2004).
The population size indices were, however, higher than
expected, although the population size indices decreased
from 1998 to 2000. Moreover, the indices increased again
thereafter, and an analysis of population structure, using a
population dynamic model, suggested that males should
have become extirpated under the culling rates observed in
EPC. Because of these contradictions, we suspected that
the 1993 population size had been underestimated. The
aerial survey might have resulted in under-counting due to
the low visibility of deer in dense mixed coniferous–
deciduous forests, even though the count was useful in
assessing population trends as a population index. Several
studies show that ground counts of ungulates also have low
precision and often underestimate the population size (e.g.,
Largo et al. 2008). To solve the inconsistencies among
population parameters, Matsuda et al. (2002) proposed a
new method to estimate the population size by harvest-
based estimation, which requires information about actual
trends in relative population size, the rate of natural pop-
ulation increase, and the number of animals harvested
(Fig. 5). In this method, the total number of individuals is
estimated by examining the response of the population
index to the known number of individuals that have been
artificially removed. Thus, hunting is considered as an
important large-scale experiment to obtain reliable esti-
mation of population size. Using the feasible sets of
parameter values in the resultant simulations for the sika
deer population, we re-estimated the 1993 population size
to be between 170,000 and 330,000 deer. The lower limit
was given by the persistence of males and the upper limit
was given by the fact that the population had not contin-
uously decreased in size. In the 2000 CMPS, the Hokkaido
Government announced that the 1993 population size had
indeed been underestimated.
Lesson 3. Population size estimation has large uncer-
tainties. When unpredicted results are obtained, the esti-
mate of the population size should be re-examined first.
Hunting can be considered as an important large-scale
experiment to obtain reliable estimation of population size.
Harvest-based Bayesian estimation
Using harvest-based estimation, we were able to obtain
more reliable estimates of the population size. Uncertainty
in the estimation of absolute population size was, however,
still large. It is well known that estimates using indices
suffer from large observation errors when the probability of
observation fluctuates widely; therefore, we applied state–
space modeling to the harvest-based estimation combining
a generalized linear mixed model (GLMM) with a Bayes-
ian statistical model based on the population dynamic
model. We first obtained GLMM estimates of population
index by assuming two errors: (1) a lognormal error that
was yielded by the ‘local’ random fluctuation of the
expected number of observation, and (2) a Poisson error
under the given expected number of observations
(Yamamura et al. 2008). The GLMM estimates obtained of
population index still contain large errors that are caused
by the ‘global’ random fluctuation of the probability of
observation, that is, the fluctuation of the probability of
observation which is synchronous over the whole area.
Then, the state–space modeling of harvest-based estimation
was applied to the GLMM estimates to remove the influ-
ence of such global errors. Bayesian estimation was used
for obtaining the maximum likelihood estimates of the
state–space model approximately. Then, the dynamics of
the index estimated by the state–space modeling (Fig. 6a)
became less erratic than that of the index estimated by the
simple harvest-based estimation (Fig. 5). This indicates
that the state–space modeling that we call the ‘harvest-
based Bayesian estimation’ successfully removed the glo-
bal errors caused by the fluctuation of the probability of
observation.
Using the model, the 1993 population size ±SE was
estimated at 171,000 ±32,000 in eastern Hokkaido and at
Popul Ecol (2010) 52:373–387 381
123
111,000 ±63,000 in western Hokkaido. In eastern Hok-
kaido, the new population estimates showed a decrease
from 1998 to 2001, but an increase from around 2002 and
eventual recovery to the same population level as the his-
toric peak of 1998 (Fig. 6a). In contrast, the population
estimate in western Hokkaido consistently increased even
though the number of harvested deer was increasing
(Fig. 6b).
Lesson 4. Statistical techniques are essential to estimate
various variables for populations. A different management
purpose may request estimation for a different set of
variables or the different level of accuracy for variables to
make a management program. It is, therefore, best to
customize statistical techniques to each management
purpose.
Prevention of lead poisoning in sea eagles
A serious side effect of hunting on the sika deer is inad-
vertent lead poisoning of large birds of prey: Steller’s sea
eagles (Haliaeetus pelagicus) and white-tailed sea eagles
(H. albicilla). They migrate seasonally between Hokkaido
Island and the Kamchatka Peninsula and Sakhalin Island,
Russia (Working Group of White-tailed Eagles and Stell-
er’s Sea Eagles 1996; McGrady et al. 2000) and are des-
ignated as Japanese natural monuments and listed in the
Act on Conservation of Endangered Species of Wild Fauna
and Flora in Japan. After lead poisoning in these species
was first confirmed in February 1996, incidents increased
in association with expanding hunting areas and relaxing
hunting regulations. In the 1997 hunting season, a total of
18 sea eagles were found dead (69.2% of total found dead,
which were reported by citizens and volunteers, n=26)
and lead bullet fragments were recovered from eagle giz-
zards in most cases (Uno et al. 2009). It is evident that
eagles ingested lead from deer remains in the field
(Kurosawa 2000). In 1998, when the CMPS started, the
Hokkaido Government established carcass disposal stations
and promoted the use of copper bullets. In the 1998 hunting
season, however, a total of 26 eagles were found dead from
lead poisoning (78.8% of total found dead, n=33). To
prevent further lead poisoning of sea eagles, the Hokkaido
Government banned the use of lead bullets in rifles for sika
deer hunting from 2000 and in shotguns from 2001, and in
rifles for both sika deer and brown bears (Ursus arctos
yesoensis) from 2004. Thereafter, the number of sea eagles
dying from lead poisoning decreased from 11 (57.9% of
total found dead, n=19) in the winter of 2001/2002 to 2
(8.3% of total found dead, n=24) in the winter of 2007/
2008, though one goshawk (Accipiter gentilis) and 2
mountain hawk-eagles (Spizaetus nipalensis) were found
dead due to lead poisoning in the winters of 2002/2003 and
2003/2004, respectively. In addition, one mountain hawk-
eagle died from lead poisoning in 2007/2008. Although the
Hokkaido Government has banned use of the lead bullets
for all hunting since 2004, lead bullets are still legally used
and available in other parts of Japan, which may contribute
to illegal deer hunting using lead bullets in Hokkaido.
Another possibility is the presence of wounded deer, which
had already been shot using lead bullets.
Lesson 5. The influence of a management program may
go beyond the target species (or problem). Unpredicted
problems could be invited by the implementation of the
program. Accountability for improving the program is
essential, when new knowledge is gained and/or an error of
past knowledge is found.
Problems with MSY theory for the application
to sika deer management
Lessons from two sika deer population irruptions:
Nakanoshima Island and Cape Shiretoko herds
Ungulate populations, when densities are low in favorable
habitats or when released from hunting, sometimes
increase rapidly to a peak and then crash because of
overexploitation of their key food sources (Caughley
1970). Irruptive behavior is common in ungulate popula-
tions but is a complex and still poorly documented phe-
nomenon (McCullough 1997). Forsyth and Caley (2006)
developed mathematical models to better describe irruptive
dynamics of large-herbivore populations and evaluated the
dynamics of seven ungulate populations either introduced
to new ranges or released from harvesting. A recent study
on the population dynamics of the pronghorn (Antilocapra
americana) in Yellowstone National Park of the western
US also supported the paradigm that irruption is a funda-
mental pattern in large herbivores with high fecundity and
delayed density-dependent effects on recruitments (White
et al. 2007).
We have observed the irruption processes of two popu-
lations of sika deer in detail; an introduced population on
Nakanoshima Island (NKI population; Kaji et al. 1988) and
a naturally colonized population on Cape Shiretoko (CS
population; Kaji et al. 2004; Fig. 8). Both populations built
up to peak abundance followed by population crash
resulting in significant effects on the vegetation. There
were, however, marked differences in post-crash behavior
between the two populations. Following the crash in 1984,
the NKI herd increased again with a lower growth rate
(r
m
=0.15 for the period between 1964 and 1984 vs
r
m
=0.07 for the period between 1986 and 2000; Fig. 8a)
and reached a higher peak of the population size in 2001
than the first irruption, while the CS herd showed oscillating
382 Popul Ecol (2010) 52:373–387
123
behavior without decline in the peak abundance (1986 vs
2003; Fig. 8b). The intrinsic rates of natural increase (r
m
)of
the two populations ranged between 0.15 and 0.19 (dou-
bling time is about 4 years). Because the two populations
did not show evident density effects on population growth
rate just before the populations crashed, natural regulation
cannot be expected to prevent damage to natural vegetation.
Although density-dependent resource limitation through
harsh conditions in winter was the common limiting factor
in peak densities for both populations, the carrying capacity
differences and resource gaps between summer and winter
might generate the difference in fluctuation patterns
between the two populations (Kaji et al. 2009).
On Nakanoshima Island and Cape Shiretoko, associated
with population irruption, a series of vegetation changes
were observed as follows; bark-stripping to large elm trees,
increasing of bark peeling, elimination of tall plants, for-
mation of browsing line, decreasing of dwarf bamboo,
elimination of dwarf bamboo, and invasion of unpalatable
plants such as the Aleutian ragwort (Senecio cannabifolius)
and an exotic plant, the Bull thistle (Cirsium vulgare) (Kaji
et al. 2009). Such a series of vegetation changes associated
with high deer density has also been observed widely in
eastern Hokkaido (Kaji et al. 2006).
Lesson 6. Natural regulation cannot be expected for sika
deer where there is a weak density dependence on popu-
lation growth. Population control is necessary to avoid
habitat destruction.
Maximum sustainable yields harvest and damages
to vegetation
Density dependence has been an important theoretical
base for deer management, because the MSY model that
harvest is compensated by recruits assumes a feedback
mechanism based on density dependence (White and
Bartmann 1997). The idea of managing a deer population
at the density that provides the MSY has been a pre-
vailing influence in the management of European and
North American populations, particularly where manage-
ment goals stress production for hunting. In other parts of
the USA and Europe there may be less tolerance to the
MSY approach now because of concerns about over-
abundance in deer (McShea et al. 1997; Linnell et al.
1998;Co
ˆte
´et al. 2004). Ecological carrying capacity,
defined as the maximum population that an environment
can support without detrimental effects (Caughley and
Sinclair 1994), is one of the equilibrium points as repre-
sented by Kof the logistic equation. MSY is the maxi-
mum number of deer that can be harvested from the
population on a continual basis. The population level that
produces the MSY is 50% of Kand has been referred
to as Economic Carrying Capacity (Caughley 1979), or
I-Carrying Capacity (Macnab 1985), where I-Carrying
Capacity equates to the inflection point on the sigmoid
curve and is the density where the number of recruits is
maximum. McCullough (1984) stated that desirable goals
between MSY and Kare inherently self-correcting. If
overharvest or a severe winter reduces a population below
a goal, the smaller population would produce a larger
number of recruits and therefore would quickly return to
the goal. Conversely, goals below MSY may make a
population unstable because the population size is likely
to suffer higher demographic stochasticity owing to small
population size (McCullough 1984). Since MSY (50%
of K) is far below ecological carrying capacity (K), MSY
would at first seem to satisfy the conditions that prevent
negative impacts on vegetation.
0
100
200
300
400
500
1950 1960 1970 1980 1990 2000 2010
Number of deer
Year
100
200
300
400
500
600
700
Number of deer
Year
b Cape Shiretoko
a Nakanoshima Is.
1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
0
Fig. 8 a Population changes of the sika deer population on Nakano-
shima Island, Hokkaido, Japan, 1957–2006. Black bar the removal,
open circles estimated population sizes, black circles minimum
population ground count, and arrows population crashes following
peaks (Kaji et al. 1988, updated with unpublished data). bChanges in
the sika deer population on Cape Shiretoko, Hokkaido, during 1986–
2005, based on aerial photographic censuses (Kaji et al. 2004, updated
with unpublished data)
Popul Ecol (2010) 52:373–387 383
123
Cervid species have expanded their range and increased
dramatically in abundance particularly in the developed
world in recent decades, and they have caused not only
major economic losses in agriculture and forestry but also
serious negative impact on ecosystems (McShea et al.
1997;Co
ˆte
´et al. 2004). This might be caused by any of the
following reasons; (1) deer populations are close to Kdue
to insufficient population management, (2) K/2 may be too
high to prevent damage (deCalesta and Stout 1997), and/or
(3) MSY theory lacks reality because forest fragmentation
and croplands in the developed world may have increased
the landscape’s ability to support deer, as explained by the
‘fragmentation–nutrition hypothesis’’ (Sinclair 1997).
The problem with MSY theory is that it assumes density
dependence. We are not able to determine Kif a population
shows no significant density dependence. Even if a popu-
lation showed density dependence, if it is weak, density
effects on population parameters would be observed only
when the population increased to a high density that is
close to K. Measuring Khas, therefore, proven extremely
difficult, because we usually do not want the population to
ever reach K(Mysterud 2006). It is known that sika deer do
not exhibit clear density-dependent effects at relatively low
densities (Putman and Clifton-Bligh 1997). Using a sika
deer population reconstructed by cohort analysis, Ueno
et al. (2010) demonstrated a density-dependent decrease in
recruitment through its negative effect on fawn survival.
The density effect was, however, not strong enough to
achieve population regulation. Ungulate species in North
America occupying high productivity areas with relatively
stable climates (e.g., the white tailed deer, Odocoileus
virginianus) tend to conform to the logistic model, whereas
the species living in moderately productive environments
(e.g., the mule deer, O. hemionus and the elk, C. elaphus),
or living in low productivity environments (e.g., the big-
horn sheep, Ovis canadensis nelson and the desert mule
deer, O. h. crooki) show continuous population growth at
relatively constant rates and most density-dependent
responses become detectable only when Ngrows to be as
high as K(McCullough 1999). Thus, the MSY point is
located above 50% of Kin many ungulate species of which
population growth rate shows a convex curve against their
density.
We demonstrate, in the two case studies on population
irruption of sika deer, that negative impacts on vegetation
occur before density dependence becomes observable. In
other words, habitat destruction may have progressed up to
an undesired level by the time we get enough demographic
data to measure K. To prevent habitat destruction, there-
fore, we have to set a target density for management
without information about K.
Relative deer density (RDD, based on deer density rel-
ative to K) was introduced as a concept to integrate white-
tailed deer management with ecosystem management
(deCalesta and Stout 1997). We evaluated RDD (DD/
K)9100 and its effect on natural vegetation on Nakano-
shima Island and Cape Shiretoko. Kon NKI was estimated
based on the relationship between the rate of population
change [(N
t?1
-N
t
)/N
t?1
] and estimated population size
during the winter 1980–1984 in the form
Y¼0:0021Xþ0:6381 R2¼0:9221;P\0:05

;
where Yis the rate of population change as a function of
population size X. The rate of population change decreased
as population size increased. We obtained K=304 deer
(61/km
2
) when the rate of population change was 0. NKI
population reached the first peak of 299 deer (57.5/km
2
)in
the autumn 1983, which was close to K, and crashed in the
following winter. The CS herd irrupted and reached peaks
three times during 1986–2005. These estimated peak
population sizes were 592 deer in 1998, 626 in 2003, and
603 in 2005. Thus, we estimated averaging Kis 121/km
2
(range 118–125/km
2
) on CS.
On NKI, the pasture at the central part of the island
consisted of forbs, grasses and tall plants over 100 cm in
height, and there were no obvious effect of grazing on the
vegetation in 1980 when deer density was 31.5/km
2
(54%K) in 1980 (Kaji et al. 1988). On CS, woody vege-
tation showed signs of overbrowsing when deer density was
[15/km
2
(13%K) in 1987, and considerable overbrowsing
of dwarf bamboo and woody plants occurred when esti-
mated deer density was 62/km
2
(51%K) in 1995 (Kaji et al.
2004). Both populations showed that signs of overbrowsing
appeared when the deer population over 50%K(Table 3).
Thus, the two irruptive populations of sika deer (NKI and
CS herds) show that the density level of MSY management
(50%K) may allow deer to have significant negative
impacts on natural vegetation.
Much lower deer density (e.g., \25% of K) is needed to
maintain viable populations of certain sensitive plant spe-
cies (Alverson et al. 1988; deCalesta and Stout 1997;
Sinclair 1997) or to keep deer populations within a socio-
logical carrying capacity—a socially tolerable density level
(Sinclair 1997). Our lower limit (%P
-
) is set based on a
critical population size, which should be larger than the
vulnerable size (\1,000) in criterion D1 of red list cate-
gories (IUCN 1994).
Threshold harvesting strategies to avoid damage
to vegetation
From the above considerations, it is clear that MSY the-
ory is incompatible with many management goals and K/2
is too high for ecosystem management of cervid popula-
tions with weak density dependence. Instead of the MSY
approach, we developed a threshold harvesting approach
384 Popul Ecol (2010) 52:373–387
123
(Lande et al. 1995,1997) as feedback management; when
the number above some threshold population is harvested
while below the threshold there is no harvest. Feedback
management for the sika deer population set three popu-
lation thresholds and four options of different hunting
pressures which are adopted according to relative popu-
lation size (Table 2; Fig. 7). Associated with the increase
of relative population size (Fig. 7), in addition to agri-
culture and forestry, the damage of natural forests became
significant in various places of Hokkaido. Road and
railway kill of deer have also increased. On the analogy
of the relationship between population abundance and
habitat in NK and CP, these conditions indicate that
population density levels in eastern Hokkaido have nearly
equaled or exceeded 50%K. Thus, our upper limit (%P
?
)
and our target level (%P*) are considered as well below
the MSY level (K/2).
Another important point that should be considered for
ecosystem management of sika deer in Hokkaido is the
large gap between summer and winter range carrying
capacity as previously described. Sika deer in eastern
Hokkaido have a large-scale seasonal migration and large
numbers of deer concentrated in limited wintering ranges,
where significant habitat deterioration occurs. Since den-
sity-dependent resource limitation with winter weather
conditions determine the population size of sika deer in
Hokkaido (Kaji et al. 2009), the management goal should
be set based on the winter range condition.
Lesson 7. MSY theory is unrealistic for cervid popula-
tions with weak density dependence because of the diffi-
culty of measuring K, and the fact that the density level set
by MSY may be too high to prevent damage to agriculture
and/or the ecosystem. More intensive management of a
deer population at lower densities is required for ecosystem
management based on different threshold harvesting
strategies.
Conclusion: hunting as resource management
and culling for ecosystem management
The greatest change in deer management during the last
decade is the one from sport hunting to damage control.
The Hokkaido Government has been promoting aggressive
female culling through EPC to reduce damage caused by
high density deer populations. The program once suc-
ceeded in reducing the size of the deer population and
amount of agriculture/forestry damage incurred between
1998 and 2000 in eastern Hokkaido, but deer abundance is
still high (about 200,000 deer) due to reductions in the
harvest, despite the relaxation of hunting regulations. In
2008, the relative population index in eastern Hokkaido is
130 (about 260,000 deer), which is roughly equivalent to
the value in 1998 when the population reached a peak.
Thus, at least 38,000 female deer, which is the actual result
in 1998, should be harvested to reduce the population
again. We could not expect this implementation problem
(the difficulty of harvest) when we originally designed the
CMPS plan in 1998.
In 2000, a total of 10,000 registered hunters in Hokkaido
(6% of hunters in Japan) harvested 70,000 deer ([50% of
the total harvest); each hunter harvested an average of 7
deer. Although the hunting pressure on deer in Hokkaido is
the highest in Japan, sika deer populations have expanded to
cover nearly all their potential range, and occur in natural
reserves, including alpine meadows, where natural vegeta-
tion is negatively affected. In national parks and nature
reserves, where conservation of the natural environment is
the highest priority, overabundance of deer is a pressing and
major concern with regard to conserving vulnerable rare
plant species. Another concern is that, while much deer
management has been focused on damage control in rural
areas, deer have recently been invading urban areas. What
we are trying to achieve now is landscape scale
Table 3 Relationship between relative deer density (RDD) and its effects on vegetation on Nakanoshima Island and Cape Shiretoko, Hokkaido,
Japan
RDD Nakanoshima Island Cape Shiretoko
Low \20%KNo data Impacts are minor to moderate: small trees
disappeared and browsing line appeared
Low-moderate 20–39%KNo data No data
Moderate-high 40–59%KImpacts are obvious: saplings disappeared,
dwarf bamboos and small trees declined
on wintering grounds
Impacts are obvious: dwarf bamboo and tall
plants disappeared, unpalatable plants
increased
High C60%KGreat impacts: tall grass disappeared,
browsing line appeared, dwarf bamboos
disappeared, large trees were barked,
and unpalatable plants increased
Great impacts: large oak trees were barked
Classification of RDD (low, moderate, high) based on deCalesta and Stout (1997)
Popul Ecol (2010) 52:373–387 385
123
management (at the scale of the deer populations) which
can be part of an ecosystems-based approach to natural
resources management. At the same time, it is clear that
different management challenges may be faced by different
elements within a landscape (for example, a nature reserve
as opposed to an agricultural or peri-urban area). Since the
hunter population is decreasing, encouragement for utili-
zation of sika deer as a natural resource, and hunter training
and support, are urgently required to maintain hunting
systems. A new community-based management trial,
combining recreational hunting and hunter education for
rural areas, has been underway in Nishiokoppe Village,
Hokkaido, from 2004 (Igota and Suzuki 2008).
In the CMPS (third period: 2008–2011), to encourage
harvesting, sika deer are regarded as a valuable natural
resource as venison, and sustainable resource management
must be considered: (http://www.pref.hokkaido.lg.jp/NR/
rdonlyres/1B7408C3-2E60-43E4-9423-3079F8517AE6/0/
3rd_plan.pdf.). In managing deer as a resource, hunters
may be required to have relatively high levels of hunting
efficiency or the resulting densities would be too high for
ecosystem management. To avoid negative impacts on
natural vegetation in national parks, and to conserve bio-
diversity, much lower densities of deer should be set for
target areas. Since hunting efficiency would be too low for
volunteer hunters in those areas, it is important to support
the development of professional hunters for culling oper-
ations. Hunting as resource management and culling for
ecosystem management should be synergistically com-
bined under adaptive management.
Acknowledgments We are very grateful to T. Akasaka, T. Fujim-
oto, K. Tamada, T. Kurumada and H. Hirakawa for supporting our
work and stimulating discussion, while over the years, N. Ohtaishi
and D. R. McCullough have consistently encouraged us to develop
sika deer management in Hokkaido. We also thank Ed Dyson, the
editor and anonymous referees who gave us valuable comments and
corrected English on the manuscript, and T. Suzuki for drawing fig-
ures. This work was supported in part by a Grant-in-Aid for Scientific
Research (A) No. 21248019 from the Ministry of Education, Culture,
Sports, Science and Technology to K.K.
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Preface. Basic Concepts. Sampling Designs and Related Topics. Enumeration Methods. Community Surveys. Detection of a Trend in Population Estimates. Guidelines for Planning Surveys. Fish. Amphibians and Reptiles. Birds. Mammals. Glossary of Terms. Glossary of Notation. Sampling Estimators. Common and Scientific Names of Cited Vertebrates. Subject Index.