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High female mortality resulting in herd collapse in free-ranging domesticated reindeer (Rangifer tarandus tarandus) in Sweden.

Åhman B, Svensson K, Rönnegård L - PLoS ONE (2014)

Bottom Line: Lower calving success in herd B compared to A indicated differences in winter foraging conditions.We found no evidence that a lower autumn body mass generally increased the risk for a female of dying from one autumn to the next.We conclude that the prime driver of the on-going collapse of herd B is not high animal density or poor body condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.

ABSTRACT
Reindeer herding in Sweden is a form of pastoralism practised by the indigenous Sámi population. The economy is mainly based on meat production. Herd size is generally regulated by harvest in order not to overuse grazing ranges and keep a productive herd. Nonetheless, herd growth and room for harvest is currently small in many areas. Negative herd growth and low harvest rate were observed in one of two herds in a reindeer herding community in Central Sweden. The herds (A and B) used the same ranges from April until the autumn gathering in October-December, but were separated on different ranges over winter. Analyses of capture-recapture for 723 adult female reindeer over five years (2007-2012) revealed high annual losses (7.1% and 18.4%, for herd A and B respectively). A continuing decline in the total reindeer number in herd B demonstrated an inability to maintain the herd size in spite of a very small harvest. An estimated breakpoint for when herd size cannot be kept stable confirmed that the observed female mortality rate in herd B represented a state of herd collapse. Lower calving success in herd B compared to A indicated differences in winter foraging conditions. However, we found only minor differences in animal body condition between the herds in autumn. We found no evidence that a lower autumn body mass generally increased the risk for a female of dying from one autumn to the next. We conclude that the prime driver of the on-going collapse of herd B is not high animal density or poor body condition. Accidents or disease seem unlikely as major causes of mortality. Predation, primarily by lynx and wolverine, appears to be the most plausible reason for the high female mortality and state of collapse in the studied reindeer herding community.

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Accumulated survival rate of females in Herd A and B from autumn 2007 until autumn 2011, calculated using estimates from capture-recapture analysis shown in Table 3 (showing also the confidence intervals for the estimates).
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pone-0111509-g003: Accumulated survival rate of females in Herd A and B from autumn 2007 until autumn 2011, calculated using estimates from capture-recapture analysis shown in Table 3 (showing also the confidence intervals for the estimates).

Mentions: Out of the females originally marked in 2007, 231 in herd A and 130 in herd B were shown to still remain in the autumn of 2011, after four years (Table 1). Recapture rates for the different sampling occasions (Table 2) varied between 0.50 and 0.84 for herd A and between 0.38 and 0.76 for herd B, except for the last recapture in autumn 2012 when it was lower (0.39 and 0.28, respectively). The estimated yearly survival rate from one autumn to the next (based on survival rates shown in Table 3, with the last year excluded) was, on average, 92.9% for herd A, and considerably lower, 81.6%, for herd B. In the autumn of 2011, after four years, 74% of the females in herd A and only 43% of those in herd B, that had not been culled, were estimated to still be present in the herd (Fig. 3).


High female mortality resulting in herd collapse in free-ranging domesticated reindeer (Rangifer tarandus tarandus) in Sweden.

Åhman B, Svensson K, Rönnegård L - PLoS ONE (2014)

Accumulated survival rate of females in Herd A and B from autumn 2007 until autumn 2011, calculated using estimates from capture-recapture analysis shown in Table 3 (showing also the confidence intervals for the estimates).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214728&req=5

pone-0111509-g003: Accumulated survival rate of females in Herd A and B from autumn 2007 until autumn 2011, calculated using estimates from capture-recapture analysis shown in Table 3 (showing also the confidence intervals for the estimates).
Mentions: Out of the females originally marked in 2007, 231 in herd A and 130 in herd B were shown to still remain in the autumn of 2011, after four years (Table 1). Recapture rates for the different sampling occasions (Table 2) varied between 0.50 and 0.84 for herd A and between 0.38 and 0.76 for herd B, except for the last recapture in autumn 2012 when it was lower (0.39 and 0.28, respectively). The estimated yearly survival rate from one autumn to the next (based on survival rates shown in Table 3, with the last year excluded) was, on average, 92.9% for herd A, and considerably lower, 81.6%, for herd B. In the autumn of 2011, after four years, 74% of the females in herd A and only 43% of those in herd B, that had not been culled, were estimated to still be present in the herd (Fig. 3).

Bottom Line: Lower calving success in herd B compared to A indicated differences in winter foraging conditions.We found no evidence that a lower autumn body mass generally increased the risk for a female of dying from one autumn to the next.We conclude that the prime driver of the on-going collapse of herd B is not high animal density or poor body condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.

ABSTRACT
Reindeer herding in Sweden is a form of pastoralism practised by the indigenous Sámi population. The economy is mainly based on meat production. Herd size is generally regulated by harvest in order not to overuse grazing ranges and keep a productive herd. Nonetheless, herd growth and room for harvest is currently small in many areas. Negative herd growth and low harvest rate were observed in one of two herds in a reindeer herding community in Central Sweden. The herds (A and B) used the same ranges from April until the autumn gathering in October-December, but were separated on different ranges over winter. Analyses of capture-recapture for 723 adult female reindeer over five years (2007-2012) revealed high annual losses (7.1% and 18.4%, for herd A and B respectively). A continuing decline in the total reindeer number in herd B demonstrated an inability to maintain the herd size in spite of a very small harvest. An estimated breakpoint for when herd size cannot be kept stable confirmed that the observed female mortality rate in herd B represented a state of herd collapse. Lower calving success in herd B compared to A indicated differences in winter foraging conditions. However, we found only minor differences in animal body condition between the herds in autumn. We found no evidence that a lower autumn body mass generally increased the risk for a female of dying from one autumn to the next. We conclude that the prime driver of the on-going collapse of herd B is not high animal density or poor body condition. Accidents or disease seem unlikely as major causes of mortality. Predation, primarily by lynx and wolverine, appears to be the most plausible reason for the high female mortality and state of collapse in the studied reindeer herding community.

Show MeSH
Related in: MedlinePlus