Printer Friendly


Between 1997-2005, moose (Alces alces) in Alaska Game Management Unit 20A (Unit 20A, Fig. 1) exhibited the lowest nutritional status documented for noninsular, wild moose in North America, including 14 other Alaskan populations. Boertje et al. (2007) based the low nutritional status on relatively low reproductive rates, low body weights of short-yearlings, and high browse utilization.

Unit 20A moose have been intensively managed and studied resulting in 12 publications and largely focused on management, biology, ecology, and demography. Early and summary research described factors limiting moose during 1963-1997 (Gasaway et al. 1983, Boertje et al. 1996, Keech et al. 2000), as well as hunter access, moose seasons, and bag limits from the 1960s through early 2000s, moose population status from 1997 to 2003, and the use of calf hunts to increase yield (Young and Boertje 2004). Further, Young et al. (2006) detailed the regulatory and biological history of Unit 20A moose from the 1960s through the early 2000s, describing impediments, achievements, and recommendations for managing high-density moose. Boertje et al. (2007) described relevant signals to begin liberal antlerless hunts to halt population growth, and Boertje et al. (2009) later described how relatively low predation allows continued increase in moose density despite low nutrition. These data helped convince stakeholders to elevate harvest beginning in 2004 through selective harvest strategies that led to eventual recovery of low bull:cow ratios (Young and Boertje 2008). Concerning habitat relationships, Seaton et al. (2011) reported on correlations between proportional browse use in late winter and nutritional condition, and Paragi et al. (2015) described browse removal, plant condition, and twinning rates before and after short-term changes in moose density. Unit 20A has served as an example of when decadesold (1970s), and at times, imprudent moose management, had an overwhelming influence on attempts to implement more recent (2000s) management strategies (Young and Boertje 2011).

The role of long-term, low nutritional status on age-specific antler development was not previously investigated in Unit 20A. However, a comparative study of age-related antler spread was conducted in our study area in the early 1970s when moose density was lower and twinning rates were more moderate than during this study m 2007-2010 (Gasaway, 1975 Alaska Department of Fish and Game [ADFG] brochure). Given the lower nutritional status of moose during this study, we hypothesized that bulls would delay reaching average 50-inch (127-cm) antler spreads compared to the 1970s.

A potential delay in entering the 50-inch (127 cm) antler class was an important consideration because reduced annual recruitment would undesirably restrict bull harvest when objectives were to maximize harvest to reduce browse degradation and meet harvest objectives set by the Board of Game under the Intensive Management regulation (Young et al. 2006, Boertje et al. 2009). A selective bull harvest strategy was implemented in Unit 20A beginning in 2002 and was eventually successful in recovering the low and declining bull:cow ratios (Young and Boertje 2008); low bullxow ratios in 1999-2001 resulted from any-bull and no cow harvests. The selective harvest strategy implemented in Unit 20A is hereafter referred to as the spike-fork/50-inch antler restriction, which restricted harvest to bull moose with: 1) spike-fork antlers, 2) antlers [greater than or equal to]50 inches wide, or 3) [greater than or equal to]3 brow tines on [greater than or equal to]1 antler (Fig. 2; Schwartz et al. 1992).

We had two primary objectives: 1) to investigate the potential for a nutrition-mediated delay in bulls reaching 50-inch antler spreads by comparing age-related antler spreads from the early 1970s to 2007-2010, and 2) to characterize antler development of young bulls of known-age that were captured and radio-collared at 10 months (Boertje et al. 2007). The purpose of the latter objective was to correct, as necessary, misclassifications of yearling and 2-year-old bulls during early winter aerial surveys (Gasaway et al. 1986, Kellie and DeLong 2006).


The Unit 20A study area is in interior Alaska immediately south of Fairbanks centered on 64[degrees] 10' N latitude and 147[degrees] 45' W longitude (Fig. 1). It encompasses 17,601 [km.sup.2], but only 13,044 [km.sup.2] contains topography and vegetation characteristically used by moose. The study area was described in detail by Gasaway et al. (1983), Boertje et al. (1996), and Keech et al. (2000). The northern portion consists of poorly drained lowlands (Tanana Flats) with elevations ranging from 130 to 300 m. The southern portion consists of the northern foothills and mountains of the Alaska Range with elevations up to 4,000 m. Lowland vegetation is a mosaic of shrub and young forest dominated by seres, climax bogs, and mature black spruce (Picea mariana) and eastern larch (Larix laricina) forest. Vegetation in the hills, foothills, and mountains grades from taiga at lower elevations to shrub-dominated communities with alpine tundra at higher elevations. The climate is typical of Interior Alaska where temperatures frequently reach 25 [degrees]C in summer and -10 to -40 [degrees]C in winter. Snow depths are generally <80 cm.


Age-Related Antler Spread

To collect antler spread data from a range of classes, we required that successful hunters from a limited, any-bull draw hunt (2007-2010) provide antlers and lower front incisors to ADFG personnel who measured antler spread (Fig. 2; Gasway et al. 1987). We used counts of cementum annuli from incisors to estimate age, but the methodology for counting annuli differed between the 1970s and this study. Fortunately, an average correction factor to true age was available from each study, given respective comparisons with known-age teeth. Gasaway et al. (1978) found that subtraction of 0.5 years from the average estimated age was required to best approximate average true age with the 1970s aging techniques. Boertje et al. (2015) found that an addition of 0.2 years from the average estimated age was required to approximate average true age, given more recent aging techniques (Matson's Laboratory, Milltown, Montana, USA). We did not have correction factors for individual teeth in either study.

To determine the average age at which bulls attained an antler spread of 50 inches (127 cm), we regressed antler width with estimated age (n = 599 bulls) to derive a trend line (2nd order polynomial) using Microsoft[R]Excel Windows[R]07 software (Redmond, Washington, USA). We compared our trend line with that derived in the 1970s (Gasaway, 1975 ADFG brochure). We had no raw data on age-related antler spreads from the 1970s for further comparisons.

Antler Development

We conducted low-level aerial inspection of known-age, 1 and 2 year-old radio-collared bulls in late August to estimate the proportion that might be misclassified during standard surveys. We hypothesized that observers would not identify antlers [less than or equal to]3 inches (7.6 cm) in length during standard aerial surveys. Criteria used to distinguish between yearling and 2 year-olds during standard aerial surveys included brow and main palm development, antler spread, and antler length (S. DuBois, W. Gasaway, and D. Roby, ADFG, unpublished report). During standard aerial surveys, we distinguished between yearling and 2-year-olds primarily with brow/main palm separation, secondarily on antler width, and lastly on antler length (Fig. 2). Antler characteristics of yearlings were; 1) no brow/main palm separation, 2) antler spread [less than or equal to]3.0 x head width ([less than or equal to]30 inches [76.1 cm]), and 3) antler length <1.2 x head width ([less than or equal to]12 inches [30.5 cm]). Antler characteristics of bulls [greater than or equal to]2-years old were: 1) brow/main palm separation, 2) antler spread >3.0 x head width (>30 inches), and 3) antler length [greater than or equal to]2.0 x head width ([greater than or equal to]20 inches [50.8 cm]). Aerial survey techniques were described by Gasaway et al. (1986) and Kellie and DeLong (2006).


Age-Antler Spread

We collected antler width data and a tooth (I1) for aging from 106 bulls in 2007, 154 in 2008, 174 in 2009, and 165 in 2010 (n = 599). A significant relationship was found between antler spread (inches, Y) and age (years, X):

Y = -0.3479[X.sup.2] + 6.9342X + 20.753; [R.sup.2]= 0.66, P< 0.001. (1)

Bulls first reached an average antler spread of 50 inches at 6.0 years of estimated age and 6.2 years of true age. We observed wide variation in antler spread in each age class with substantial overlap among age classes; antler spread of 50 inches occurred at 3 years and older (Fig. 3).

Antler Development/Composition

We classified antler characteristics of 15 month-old and 27 month-old bulls on 27 August 2007 (n = 6 and 14), 22-23 August 2008 (n = 5 and 17), and 17-19 August 2009 (n = 0 and 12). Twenty-two percent (11/51) of known-age, yearling bulls had spiked antlers <3 inches (7.6 cm) that were likely undetected during standard surveys. Nineteen percent (8/43) of known-age, 2 year-old bulls were probably misclassified as yearlings based on brow/palm separation alone - the primary antler characteristic used to differentiate between the age classes during aerial surveys. Conversely, when using antler spread and antler length as primary classification criteria, we correctly classified all known-age, 2 year-old radio-collared bulls (n = 43) during aerial inspection.


Age-Antler Spread

We surmised that the estimated delay in reaching a 50-inch antler spread associated with reduced nutritional status was too small to have meaningful biological or management significance, particularly given the wide variation in antler spread in each age class (Fig. 3). After correcting estimated ages to true ages, we concluded that, on average, bulls in populations affected by elevated density and unusually low nutrition delayed reaching 50-inch antler spread by 0.6 years. Our comparison was made with the Gasaway et al. (1987) sample (n = 91) from all of Unit 20 (i.e., Units 12, 20A, 20B, 20C, 20D, 20E, and 20F in Interior Alaska; Fig. 1), where antler spreads reached an average of 50 inches at 5.6 years of true age (6.1 years estimated age) in the early 1970s. Moose densities in Unit 20 in the early 1970s were lower than densities during this study; for example, density in Unit 20A in the early 1970s (ca. 500 moose/1,000 [km.sup.2]) was about half that in this study (1,060 moose/1,000 [km.sup.2]) (Gasaway et al. 1983, Young 2012). Further, the average twinning rate in northcentral Unit 20A during the early 1970s (16%, range =12-18%) was >2x higher than in this study (7%, range = 3-10%) (Boertje et al. 2007, Young 2012).

It is possible that a negative lag effect on nutritional condition of the population was realized in the early 1970s due to elevated moose densities in the 1960s. For example, moose numbers were declining substantially in the late 1960s and early 1970s in Interior Alaska primarily due to periodic deep snow, excessive harvest, and increased wolf predation (Gasaway et al. 1983). Twinning rates were twice as high in the 1960s, averaging 14%) (n = 9 years, range = 4-21%) versus 7% (n = 4 years, range = 3-10%) during this study (Boertje et al. 2007, Young 2012). Nutritional condition appeared to peak in the study area during 1977-1982 when twinning rates averaged 37%) (n = 6 years, range = 30-47%; Boertje et al. 2007). Clearly, our data comparisons between 2007-2010 and the early 1970s were between time periods of low versus moderate moose condition/nutrition. We speculate that a longer delay (i.e., >0.6 years) in reaching the 50-inch antler spread might be evident when comparing data between periods of low and high moose nutrition.

Given that a large percentage of the yearling and 2 year-old bulls in Unit 20A had retarded antler development during this study, it is not surprising that bulls delayed reaching 50-inch antler spreads. Keech et al. (1999) reported that neonate moose with low birth weight remained among the smallest individuals in their cohort during the first 10 months of life. Similar results are known for young of other ungulate species under natural conditions (Schwartz et al. 1994, Schultz and Johnson 1995, Pelabon 1997).

Antler Development/Composition

Presumably, bull:cow ratios were biased low for several years prior to this study because some yearling bulls were misclassified as cows during standard surveys. We estimated that the initial bullxow ratios were 2.5 bulls: 100 cows lower than corrected ratios. For example, during standard aerial surveys in 2010, we reported there were 2,311 bulls (including 639 yearling bulls) and 7,325 cows, or 31.6 bulls: 100 cows (Young 2012). Assuming 22% of the yearling bulls were misclassified as cows, the corrected estimate would be 2,452 bulls (including 780 yearling bulls) and 7,184 cows, or 34.1 bulls: 100 cows.

Yearling bull:cow ratios, a measure of annual survival from 6 to 18 months of age, would also have been biased low. In 2010, we estimated that the initial yearling bull:cow ratio was 2.2 yearling bulls: 100 cows lower than the corrected ratio (8.7 versus 10.9 yearling bulls: 100 cows). Misclassifying yearling bulls as cows would also bias the calf:cow ratio lower, but the difference was minimal (<1 calf: 100 cows) because of the high proportion of cow moose in the population.


Although unusually low nutritional condition had a measureable effect on delaying recruitment into the harvestable 50-inch antler class, we considered this delay (< 1 year) too small to warrant a change in our selective harvest strategy. We also felt encouraged to retain the selective harvest strategy because of the high annual survival rate of bulls in the 2- through 6-year age classes - 97-98% when excluding human causes of mortality (R. Boertje, unpublished data). In high-density, nutritionally stressed moose populations, sub-adult moose should be highly scrutinized for antler spread and length during aerial composition surveys to reduce the likelihood of misclassifying yearling and 2-year-old bulls.


Many individuals contributed to the work reported in this manuscript and we thank them. In particular, we wish to thank the wildlife technicians in the Fairbanks and Anchorage ADFG offices that took the time to measure antlers and pull teeth from lower jaws of hundreds of bull moose over the course of this study. We also would like to thank all the hunters that submitted specimens for this study. Finally, we wish to thank Publications Specialist L. McCarthy for her timely and much appreciated technical assistance. This study was funded by ADFG and Federal Aid in Wildlife Restoration.


BOERTJE, R. D., M. M. ELLIS, and K. A. KELLIE. 2015. Accuracy of moose age determinations from canine and incisor cementum annuli. Wildlife Society Bulletin 39: 383-389.

__, M. A. KEECH, D. D. YOUNG, K. A. KELLIE, and C. T. SEATON. 2009. Managing for elevated yield of moose in Interior Alaska. Journal of Wildlife Management 73: 314-327.

__, K. A. KELLIE, C. T. SEATON, M. A. KEECH, D. D. YOUNG, B. W. DALE, L. G. ADAMS, and A. R. ADERMAN. 2007. Ranking Alaska moose nutrition: signals to begin liberal antlerless harvests. Journal of Wildlife Management 71: 1494-1506.

__, R VALKENBURG, and M. MCNAY. 1996. Increases in moose, caribou, and wolves following wolf control in Alaska. Journal of Wildlife Management 60: 474-489.

GASAWAY, W. C, S. D. DUBOIS, D. J. REED, and S. J. HARBO. 1986. Estimating moose population parameters from aerial surveys. Institute of Arctic Biology, Biological Papers of the University of Alaska, No. 22, Fairbanks, Alaska, USA.

__, D. B. HARKNESS, and R. A. RAUSCH. 1978. Accuracy of moose age determinations from incisor cementum layers. Journal of Wildlife Management 42: 558-563.

__, D. J. PRESTON, D. J. REED, and D. D. ROSY. 1987. Comparative antler morphology and size of North American moose. Swedish Wildlife Research Supplement 1:311-325.

__, R. O. STEPHENSON, J. L. DAVIS, P. E. K. SHEPHERD, and O. E. BURRIS. 1983. Interrelationships of wolves, prey, and man in Interior Alaska. Wildlife Monographs 84.

KEECH, M. A., R. D. BOERTJE, R. T. BOWYER, and B. W. DALE. 1999. Effects of birth weight on growth of young moose: do low-weight neonates compensate? Alces 35:51-57.

__, R. T. BOWYER, J. M. VER HOEF, R. D. BOERTJE, B. W. DALE, and T. R. STEPHENSON. 2000. Life-history consequences of maternal condition in Alaskan moose. Journal of Wildlife Management 64: 450-462.

KELLIE, K. A., and R. A. DELONG. 2006. Geospatial survey operations manual. Alaska Department of Fish and Game, Division of Wildlife Conservation, Fairbanks, Alaska, USA.

PARAGI, T. F., C. T. SEATON, K. A. KELLIE, R. D. BOERTJE, K. KIELLAND, D. D. YOUNG JR., M. A. KEECH, and S. D. DUBOIS. 2015. Browse removal, plant condition, and twinning rates before and after short-term changes in moose density. Alces 51: 1-21.

PELABON, C. 1997. Is weight at birth a good indicator of weight in winter for fallow deer. Journal of Mammalogy 78: 48-54.

SCHULTZ, S. R., and M. K. JOHNSON. 1995. Effects of birth date and body mass at birth on adult body mass of male white-tailed deer. Journal of Mammalogy 76: 575-579.

SCHWARTZ, C. C, K. J. HUNDERTMARK, and E. F. BECKER. 1994. Growth of moose calves conceived during the first versus second estrus. Alces 30: 91-100.

__, __, and T. H. SPRAKER. 1992. An evaluation of selective bull moose harvest on the Kenai Peninsula. Alces 28: 1-13.

SEATON, C. T., T. F. PARAGI, R. D. BOERTJE, K. KIELLAND, S. DUBOIS, and C. L. FLEENER. 2011. Browse biomass removal and nutritional condition of moose, Alces alces. Wildlife Biology 17: 55-66.

YOUNG, D. D. 2012. Unit 20A moose. Pages 319-355 in P. Harper, editor. Moose management report of survey-inventory activities, 1 July 2009-30 June 2011. Alaska Department of Fish and Game, Species Management Report ADFG/DWC/SMR-2012-5, Juneau, Alaska, USA.

__, and R. D. Boertje. 2004. Initial use of moose calf hunts to increase yield, Alaska. Alces 40: 1-6.

__, and __. 2008. Recovery of low bull:cow ratios of moose in Interior Alaska. Alces 44: 65-71.

__, and __. 2011. Prudent and imprudent use of antlerless moose harvests in Interior Alaska. Alces 47: 91-100.

__, __, C. T. SEATON, and K. A. KELLIE. 2006. Intensive management of moose at high density: impediments, achievements, and recommendations. Alces 42:41-48.

Donald D. Young, Jr. (1) and Rodney D. Boertje (2)

(1) Retired; Present address: 550 Kentshire Drive, Fairbanks, Alaska 99709-0245, USA;

(2) Retired; Present address: 52 Edgemont Circle, Durango, Colorado 81301, USA
COPYRIGHT 2018 Alces
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2018 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Young, Donald D., Jr.; Boertje, Rodney D.
Article Type:Report
Geographic Code:1U9AK
Date:Jan 1, 2018

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters