Session One - Population Dynamics

Twentythree Authors
2000 Rangifer  
We examined the reproductive performance of female barrenground caribou (Rangifer tarandus), in relation to age, physical condition and reproductive experience for 9 consecutive years at Denali National Park, Alaska, during a period of wide variation in winter snowfall. Caribou in Denali differed from other populations where reproductive performance has been investigated in that they occur at low densities (<0.3/km z ) and experience high losses of young to predation. Average annual natality
more » ... es increased from 27% for 2-year-olds to 100% for 7 year-olds, remained high for 7-13-year-olds (98%), then declined for females >14. Females >2 years old that failed to reproduce were primarily sexually immature (76%). Reproductive pauses of sexually mature females were rare (6%) and occurred predominantly to young (3-6 years old) and old (>14 years old) females. Natality increased significantly (P<0.05) with body mass of 10-month-old females weighed 6 months prior to the autumn breeding season, and of females > 1 year old weighed during autumn (late September-early November). Natality for 2-, 3-, 4-, and 6-year-olds declined significantly with increasing late winter snowfall (February-May) during the winter prior to breeding. Because influences of weather on productivity were limited to young age-classes and adverse weather also decreased recruitment, population productivity was affected more by changes in population age-structure, than by age-specific productivity. Abstract: We compare the sex, age, and condition of caribou killed by wolves with caribou killed by hunters, and estimates of herd composition. These comparisons provide insight into selectivity and predation characteristics of wolves on barren-ground caribou. We investigated 205 kills after wolves had left the kill site and examined 65 hunter killed caribou. Of 124 known-sex kills, males comprised 45% of caribou killed by wolves. Ageclass could be determined for 171 caribou kills, of which calves comprised 17% of wolf-killed caribou. Herd composition surveys indicated available proportions of 57% cows, 14% calves, and 29% bulls. Although confidence intervals were wide, selection by wolves for calves and adult males was suggested. Sex of wolf-kills did not vary by season (March vs. November) in this study, although the test was weak due to small sample sizes. Hunters killed primarily adult females and the hunter kill may therefore reasonably approximate the availability of full-grown (>3) adult females. Wolves killed proportionally more old (ages >8) caribou than in the hunter-killed sample (2X2 Chi-square = 6.58, P = 0.010). While the old vs. young categorization is arbitrary, chi-square analyses were still significant if the cut off age was moved one year in either direction. This pattern of selectivity is consistent with that reported for other species. The comparison of physical characteristics by cause of death was limited to adult females because sample sizes for bulls and calves were insufficient. Sample sizes for wolf-killed adult females ranged from 10-12 resulting in low power of statistical comparisons. Only mean diastema length varied significantly by cause of death (P=0.031). However, means for all parameters were consistently lower for wolf-killed caribou suggesting increased vulnerability of small individuals to wolves. Trends were identical for full-grown females (>3 years of age). Wolf-killed adult female caribou had significantly lower marrow fat {x=Gl%, r=0.319, n=\2) than hunter-killed adult females (x=90%, J = 0.048, « = 52). Three of the wolf-kills had very low marrow fat (<25%) that likely had a strong influence on means. None of the 52 hunter-killed adult females had less than 30% marrow fat. Sample sizes are small and controls only roughly reflect availability. Nonetheless, this analysis suggests that selectivity by wolves among caribou sex and age classes is similar to that shown for other ungulates. SfcX, A BY ^l\J£S Abstract: As of July 1996, the Western Arctic herd numbered approximately 463 000 caribou (Rangifer tarandus). This herd last peaked at 243 000 caribou in 1970, then declined to about 75 000 by 1976. From 1976 to 1990, this herd grew approximately 13% annually. Since 1990, growth has been about 2% annually. Annual indices of recruitment and adult cow mortality collected since the early 1980s appear consistent with this population trend. Since 1990, annual subsistence and sport harvests have been roughly 20 000 and 1000-3000 caribou, respectively. Biological issues cur¬ rently facing the Western Arctic herd include: 1) body condition and its relationship to instances of sevete, localized fall and winter mortality; 2) potential effects of disease and environmental contamination on caribou and people who subsist on them; and 3) potential range deterioration. Social issues include: 1) mutual trust and exchange of information between managers and users; 2) diverse, complex and sometimes competing demands among subsistence users, sporr hunters, commercial operators and nonconsumptive users of Western Arctic caribou; 3) expansion of caribou into reindeer ranges; 4) conflicts with muskoxen management; and 5) antler sales and a proposed commercial harvest of caribou for meat. Technical issues center on monitoring a population this large over its expansive range. The political issue of dual state-federal management of wildlife in Alaska overlays all biological and social considerations. Comanagement is currently being explored to meld biological, social and political aspects of managing the Western Arctic herd.
doi:10.7557/ fatcat:6lzr435y6vcptk4gezn57ejloe