Ranking Alaska Moose Nutrition: Signals to Begin Liberal Antlerless Harvests

Abstract

We focused on describing low nutritional status in an increasing moose (Alces alces gigas) population with reduced predation in Game Management Unit (GMU) 20A near Fairbanks, Alaska, USA. A skeptical public disallowed liberal antlerless harvests of this moose population until we provided convincing data on low nutritional status. We ranked nutritional status in 15 Alaska moose populations (in boreal forests and coastal tundra) based on multiyear twinning rates. Data on age‐of‐first‐reproduction and parturition rates provided a ranking consistent with twinning rates in the 6 areas where comparative data were available. Also, short‐yearling mass provided a ranking consistent with twinning rates in 5 of the 6 areas where data were available. Data from 5 areas implied an inverse relationship between twinning rate and browse removal rate. Only in GMU 20A did nutritional indices reach low levels where justification for halting population growth was apparent, which supports prior findings that nutrition is a minor factor limiting most Alaska moose populations compared to predation. With predator reductions, the GMU 20A moose population increased from 1976 until liberal antlerless harvests in 2004. During 1997‐2005, GMU 20A moose exhibited the lowest nutritional status reported to date for wild, noninsular, North American populations, including 1) delayed reproduction until moose reached 36 months of age and the lowest parturition rate among 36‐month‐old moose (29%, n = 147); 2) the lowest average multiyear twinning rates from late‐May aerial surveys (x = 7%, SE = 0.9%, n = 9 yr, range = 3‐10%) and delayed twinning until moose reached 60 months of age; 3) the lowest average mass of female short‐yearlings in Alaska (x̄ = 155 ± 1.6 [SE] kg in the Tanana Flats subpopulation, up to 58 kg below average masses found elsewhere); and 4) high removal (42%) of current annual browse biomass compared to 9‐26% elsewhere in boreal forests. When average multiyear twinning rates in GMU 20A (sampled during 1960‐2005) declined to <10% in the mid‐ to late 1990s, we began encouraging liberal antlerless harvests, but only conservative annual harvests of 61‐76 antlerless moose were achieved during 1996‐2001. Using data in the context of our broader ranking system, we convinced skeptical citizen advisory committees to allow liberal antlerless harvests of 600‐690 moose in 2004 and 2005, with the objective of halting population growth of the 16,000‐17,000 moose; total harvests were 7‐8% of total prehunt numbers. The resulting liberal antlerless harvests served to protect the moose population's health and habitat and to fulfill a mandate for elevated yield. Liberal antlerless harvests appear justified to halt population growth when multiyear twinning rates average ≤10% and ≥1 of the following signals substantiate low nutritional status: <50% of 36‐month‐old moose are parturient, average multiyear short‐yearling mass is <175 kg, or >35% of annual browse biomass is removed by moose.

Acceleration of vegetation turnover and element cycling by mammalian herbivory in riparian ecosystems

“…For example, there is ample demographic evidence showing that moose are food‐limited in the high‐density areas in the Tanana Flats (i.e. delayed age of first reproduction, very low twinning rates, low yearling and adult body weights; Boertje et al . 2007).…”

Persistent effects of fire severity on early successional forests in interior Alaska

“…Moose are one of the main subsistence resources in interior Alaska (Scott et al, 2001), and their populations are managed to optimize sustainable harvest densities (Boertje et al, 2009). Forage availability is an important factor in determining moose demography (Van Ballenberghe and Ballard, 1998;Boertje et al, 2007), and consequently could be important in driving population densities. Deciduous stands present higher quality forage than do coniferous stands, and have been found to support higher moose population densities than mature conifer stands (Spencer and Hakala, 1964;Cederlund and Okarma, 1988).…”

Summer dietary nitrogen availability as a potential bottom‐up constraint on moose in south‐central Alaska

“…Moose in Denali had relatively high twinning rates (44% of adult females; see Plate 1) and the age of first parturition in females was low (24 months) (Boertje et al 2007;L. These regions were chosen because the productivity of moose on the two ranges was distinctly different in the years immediately preceding this study.…”