Letter to the Editor of Journal of Wildlife Management – declined by the Editor and therefore uploaded to
Research Gate on 2 December 2015 for public dissemination.
DOI: 10.13140/RG.2.1.4612.2327
Is Nevada Overharvesting Black Bears?
STEPHEN F. STRINGHAM. WildWatch. 39200 Alma Avenue.,
Soldotna, AK 99669 USA. 15 April 2015
Lackey et al. (2011, 2013) analyzed capture-mark-recapture (CMR) data for the Nevada black bear
population using Cormak-Jolly-Seber (CJS) and Pradel software within Program MARK. They estimated
that as of 2008 – prior to being hunted – the population grew at 16%/yr (λ = 1.16 + 0.04) and current size
N2008 = 262 + 31. Growth at 16%/yr to 262 in 2008 corresponds to N2000 ≈ 80 -- < 50% of Beckmann
and Berger’s (2003a,b) estimate N2000 = 180 + 117. Yet it is the 180 estimate that Lackey et al. (2011,
2013) cite for 2000. My calculation for mean growth from 180 to 262 over 8 years (SD = 0.04) is 4.8%/yr [λ
= 1.048 = 262/180^(1/8)]. These discrepancies between estimates for population size versus growth rate
were not explained by Lackey et al.
These discrepancies are likely artifacts of the small number of bears captured and the even smaller
number of recaptures. Most captures were of nuisance bears on schedules governed by management
objectives, rather by a strategic research design. Captures peaked in 2007 (Figure 1), when an historic
drought drove large numbers of bears out of normal home ranges. There were few sources of water except
Lake Tahoe, the Truckee River, and residential suburbs. There was little food except along those water
bodies and in suburbs (Bryant and Stringham unpubl. data). Given that the period covered by Lackey et
al. ended in 2008, there was not time enough for recaptures of the “new” 2007 bears to determine how
many permanently remained in Nevada. However, none of the “new” bears seen on the California side of
Lake Tahoe during 2007 remained there in 2008 (Bryant and Stringham unpubl.). So it is likely that both
the 2008 size estimate and growth rate for Nevada were exaggerated by a temporary influx of bears from
California to Nevada – an hypothesis that Lackey et al. did not report testing even after it was
communicated to them by me.
Lackey et al. (2011, 2013) claim that while the Nevada population was growing at 16%/yr, the biologically
contiguous California population “increased by about 15.7%” per year. However, the California rate was 10-
fold slower: 1.57%/yr from N1992 ≈ 24,500 to N2008 ≈ 31,500 (Ypema and Garcia 2015:Fig. 7). Given
that habitat in Nevada tends to be some of the most arid in North America (Lackey et al. 2013), whereas
California has some of the best, Nevada’s endogenous growth was presumably λ < 1.0157.
The Nevada Board of Wildlife Commissioners set their black bear harvest quota at ~ 50% of the estimated
growth rate. Based on an apparent rate of 16%/yr, the quota was set at ~ 8%/yr (Lackey et al. 2011:52). If
the annual growth rate were actually no higher than in California, overharvest would be less likely if the
harvest quota were set at < 0.8%/yr. Lackey et al. acknowledge that immigration from California occurs, but
have not measured it.
Note that Lackey et al. calculated survival rates after excluding 161 bears that were dead when first
censused – an average of 15/yr (=161/11 yrs) between 1997-2008. Most of those died of non-hunting
anthropogenic causes, especially in conflict situations and vehicle collisions (Beckmann and Lackey 2008).
If such losses could be minimized, harvest quota could be increased accordingly, so long as net growth rate
is still > 0 %/yr.
Beckmann and Berger (2003a,b) report that <20% of all bear locations and 26% of all captures were in
wildland habitat – where reproductive rate is lower than in suburbs, and where ~100% of the sport harvest
occurs. So it is in wildlands that risk of overharvest would be highest unless there is compensatory
immigration from the Nevada suburbs – opposite to the direction of net migration reported by Beckmann
and Berger (2003a,b)– or from California.
To be sure that over-harvest is not occurring, Lackey et al. would be well advised to test the hypothesis
that estimates of population size and growth rate as of 2008 were exaggerated by a transient influx of bears
during 2007. Testing could be done by (a) calculating N and λ for just 2000-2006, and (b) by bringing N
and λ fully up to date by incorporating data through 2014. Data on immigration rate from California, and
how it varies with drought, would also be enlightening.
ACKNOWLEDGMENTS
In response to a Freedom of Information Act request, C. Lackey provided a copy of his raw data on
captures. His invitation to share our questions and concerns with the scientific community through journal
publication is appreciated. This critique was funded by grants from Mike and Cathy Smith and by the No
Bear Hunt Nevada organization.
LITERATURE CITED
Beckmann, J. P., and J. Berger. 2003a. Rapid ecological and behavioural changes in carnivores: the
responses of black bears (Ursus americanus) to altered food. Journal of Zoology (London) 261:207–212.
Beckmann, J. P., and J. Berger. 2003b. Using black bears (Ursus americanus) to test ideal-free distribution
models experimentally. Journal of Mammalogy 84:594–606.
Beckmann, J. P. and C. Lackey. 2008. Carnivores, urban landscapes and longitudinal studies: a case
history of black bears. Human–Wildlife Conflicts 2:79-83.
Lackey, C. W., J. P. Beckmann, and J. Sedinger. 2011. Black bear population status - informational
report- Board of Wildlife Commissioners, September 23, 2011. Nevada Department of Wildlife.
Lackey, C. W., J. P. Beckmann, and J. Sedinger. 2013. Bear historical ranges revisited: documenting the
increase of a once-extirpated population in Nevada. Journal of Wildlife Management 77:812–820.
Ypema, R., and J. Garcia. 2015. California black bear take report. State of California, Natural Resources
Agency, Department of Fish and Wildlife. 13pp.
Research Gate on 2 December 2015 for public dissemination.
DOI: 10.13140/RG.2.1.4612.2327
Is Nevada Overharvesting Black Bears?
STEPHEN F. STRINGHAM. WildWatch. 39200 Alma Avenue.,
Soldotna, AK 99669 USA. 15 April 2015
Lackey et al. (2011, 2013) analyzed capture-mark-recapture (CMR) data for the Nevada black bear
population using Cormak-Jolly-Seber (CJS) and Pradel software within Program MARK. They estimated
that as of 2008 – prior to being hunted – the population grew at 16%/yr (λ = 1.16 + 0.04) and current size
N2008 = 262 + 31. Growth at 16%/yr to 262 in 2008 corresponds to N2000 ≈ 80 -- < 50% of Beckmann
and Berger’s (2003a,b) estimate N2000 = 180 + 117. Yet it is the 180 estimate that Lackey et al. (2011,
2013) cite for 2000. My calculation for mean growth from 180 to 262 over 8 years (SD = 0.04) is 4.8%/yr [λ
= 1.048 = 262/180^(1/8)]. These discrepancies between estimates for population size versus growth rate
were not explained by Lackey et al.
These discrepancies are likely artifacts of the small number of bears captured and the even smaller
number of recaptures. Most captures were of nuisance bears on schedules governed by management
objectives, rather by a strategic research design. Captures peaked in 2007 (Figure 1), when an historic
drought drove large numbers of bears out of normal home ranges. There were few sources of water except
Lake Tahoe, the Truckee River, and residential suburbs. There was little food except along those water
bodies and in suburbs (Bryant and Stringham unpubl. data). Given that the period covered by Lackey et
al. ended in 2008, there was not time enough for recaptures of the “new” 2007 bears to determine how
many permanently remained in Nevada. However, none of the “new” bears seen on the California side of
Lake Tahoe during 2007 remained there in 2008 (Bryant and Stringham unpubl.). So it is likely that both
the 2008 size estimate and growth rate for Nevada were exaggerated by a temporary influx of bears from
California to Nevada – an hypothesis that Lackey et al. did not report testing even after it was
communicated to them by me.
Lackey et al. (2011, 2013) claim that while the Nevada population was growing at 16%/yr, the biologically
contiguous California population “increased by about 15.7%” per year. However, the California rate was 10-
fold slower: 1.57%/yr from N1992 ≈ 24,500 to N2008 ≈ 31,500 (Ypema and Garcia 2015:Fig. 7). Given
that habitat in Nevada tends to be some of the most arid in North America (Lackey et al. 2013), whereas
California has some of the best, Nevada’s endogenous growth was presumably λ < 1.0157.
The Nevada Board of Wildlife Commissioners set their black bear harvest quota at ~ 50% of the estimated
growth rate. Based on an apparent rate of 16%/yr, the quota was set at ~ 8%/yr (Lackey et al. 2011:52). If
the annual growth rate were actually no higher than in California, overharvest would be less likely if the
harvest quota were set at < 0.8%/yr. Lackey et al. acknowledge that immigration from California occurs, but
have not measured it.
Note that Lackey et al. calculated survival rates after excluding 161 bears that were dead when first
censused – an average of 15/yr (=161/11 yrs) between 1997-2008. Most of those died of non-hunting
anthropogenic causes, especially in conflict situations and vehicle collisions (Beckmann and Lackey 2008).
If such losses could be minimized, harvest quota could be increased accordingly, so long as net growth rate
is still > 0 %/yr.
Beckmann and Berger (2003a,b) report that <20% of all bear locations and 26% of all captures were in
wildland habitat – where reproductive rate is lower than in suburbs, and where ~100% of the sport harvest
occurs. So it is in wildlands that risk of overharvest would be highest unless there is compensatory
immigration from the Nevada suburbs – opposite to the direction of net migration reported by Beckmann
and Berger (2003a,b)– or from California.
To be sure that over-harvest is not occurring, Lackey et al. would be well advised to test the hypothesis
that estimates of population size and growth rate as of 2008 were exaggerated by a transient influx of bears
during 2007. Testing could be done by (a) calculating N and λ for just 2000-2006, and (b) by bringing N
and λ fully up to date by incorporating data through 2014. Data on immigration rate from California, and
how it varies with drought, would also be enlightening.
ACKNOWLEDGMENTS
In response to a Freedom of Information Act request, C. Lackey provided a copy of his raw data on
captures. His invitation to share our questions and concerns with the scientific community through journal
publication is appreciated. This critique was funded by grants from Mike and Cathy Smith and by the No
Bear Hunt Nevada organization.
LITERATURE CITED
Beckmann, J. P., and J. Berger. 2003a. Rapid ecological and behavioural changes in carnivores: the
responses of black bears (Ursus americanus) to altered food. Journal of Zoology (London) 261:207–212.
Beckmann, J. P., and J. Berger. 2003b. Using black bears (Ursus americanus) to test ideal-free distribution
models experimentally. Journal of Mammalogy 84:594–606.
Beckmann, J. P. and C. Lackey. 2008. Carnivores, urban landscapes and longitudinal studies: a case
history of black bears. Human–Wildlife Conflicts 2:79-83.
Lackey, C. W., J. P. Beckmann, and J. Sedinger. 2011. Black bear population status - informational
report- Board of Wildlife Commissioners, September 23, 2011. Nevada Department of Wildlife.
Lackey, C. W., J. P. Beckmann, and J. Sedinger. 2013. Bear historical ranges revisited: documenting the
increase of a once-extirpated population in Nevada. Journal of Wildlife Management 77:812–820.
Ypema, R., and J. Garcia. 2015. California black bear take report. State of California, Natural Resources
Agency, Department of Fish and Wildlife. 13pp.
Figure 1. Numbers of live bears captured for the first time in Nevada (Lackey unpubl. FOIA data).
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