Post by warsaw on May 3, 2012 2:10:23 GMT -9
www.federalregister.gov/articles/2007/01/09/06-9962/endangered-and-threatened-wildlife-and-plants-12-month-petition-finding-and-proposed-rule-to-list#p-96
"Hudson Bay in Canada typifies change in the Arctic due to its southern location and occurrence on a divide between a warming and a cooling region (AMAP 2003, p. 22). It is therefore an ideal area to study the impacts of climate change. In addition, Hudson Bay has the most significant long-term time series of data on the ecology of polar bears and is the site of the first documented evidence of major and ongoing impacts to polar bears from sea ice changes. Many researchers over the past 40 years have predicted an array of impacts to polar bears from climatic change that include adverse effects on denning, food chain disruption, and prey availability (Budyko 1966; Vibe 1967, cited in Derocher et al. 2004, p. 164; Lentfer 1972, p. 169; Tynan and DeMaster 1997, p. 315; Stirling and Derocher 1993, pp. 241-244). Stirling and Derocher (1993, p. 240) first noted changes in polar bears in Western Hudson Bay such as declining body condition, lowered reproductive rates, and reduced cub survival; they attributed these changes to a changing ice environment. Subsequently, Stirling et al. (1999, p. 303) established a statistically significant link between climate warming in Western Hudson Bay, reduced ice presence, and observed declines in polar bear physical and reproductive parameters, including body condition (weight) and natality.Show citation box.
Recent studies indicate that polar bear distributions are changing and that these changes are strongly correlated to similar changes in sea ice and the ocean-ice system. Specifically, in Western Hudson Bay, breakup of the annual sea ice now occurs approximately 2.5 weeks earlier than it did 30 years ago (Stirling et al. 1999, p. 299). The earlier spring breakup was highly correlated with dates that female polar bears came ashore (Stirling et al. 1999, p. 299). Declining reproductive rates, subadult survival, and body mass (weights) have resulted from longer periods of fasting on land as a result of the progressively earlier breakup of the sea ice caused by an increase in spring temperatures (Stirling et al. 1999, p. 304; Derocher et al. 2004, p. 165).Show citation box
Stirling et al. (1999, p. 304) reported a significant decline in the condition (weights) of both male and female adult polar bears since the 1980s in Western Hudson Bay, as well as lower natality rates. A positive relationship between body mass of females with cubs and survival of cubs was also established; survival of cubs of mothers in better condition (heavier) was greater than survival of cubs from lighter mothers (Derocher and Stirling 1996, p. 1248).Show citation box
Physical condition of polar bears has been shown to determine the welfare of individuals, and ultimately, through their reproduction and survival, the welfare of populations (Stirling et al. 1999, p. 304; Regehr et al. in prep). Declines in fat reserves during critical times in the polar bear life cycle are likely to lead to an array of impacts including a delay in the age of first reproduction, decrease in the proportion of females with adequate fat stores to complete successful denning, decline in litter sizes with more single cub litters and fewer cubs overall, as well as lower cub body weights and lower survival rates (Derocher et al. 2004, p. 170). Derocher and Stirling (1998, pp. 255-256) demonstrated that body mass of adult females is correlated with cub mass at den emergence, with heavier females producing heavier cubs and lighter females producing lighter cubs. Heavier cubs have a higher rate of survival (Derocher and Stirling 1996, p. 1249). Females in poor condition will result in a higher proportion that do not initiate denning or are likely to abandon their den and cub(s) mid-winter (Derocher et al. 2004, p. 170). Females with insufficient fat stores or in poor hunting condition in the early spring after den emergence could lead to increased cub mortality (Derocher et al. 2004, p. 170). In the southern Beaufort Sea, Regehr et al. (2006, p. 20) recently found that survival rates for cubs were significantly lower than estimates from earlier studies. The lower survival rate of cubs coincided with warming temperatures and altered atmospheric circulation starting in the winter of 1989-1990 that caused an abrupt change in sea ice conditions in the Arctic basin. In addition, sea ice conditions that include broken or more fragmented ice may require young cubs to enter water more frequently and for more prolonged periods of time, thus increasing mortality from hypothermia. Blix and Lenter (1979, p. 72) and Larsen (1985, p. 325) indicate that cubs are unable to survive immersion in icy water for more than approximately 10 minutes. This is due to cubs having little insulating fat, their fur losing its insulating ability when wet (though the fur of adults sheds water and recovers its insulating properties quickly), and the core body temperature dropping rapidly when they are immersed in icy water (Blix and Lenter 1979, p. 72).
Reductions in sea ice, as discussed above, will alter ringed seal distribution, abundance, and availability for polar bears. Such reductions will, in turn, decrease polar bear body condition (Derocher et al. 2004, p. 165). Derocher et al. (2004, p. 165) projected that most females in the Western Hudson Bay population may be unable to reach the minimum 189 kg (417 lbs) body mass required to successfully reproduce by the year 2012."
"Hudson Bay in Canada typifies change in the Arctic due to its southern location and occurrence on a divide between a warming and a cooling region (AMAP 2003, p. 22). It is therefore an ideal area to study the impacts of climate change. In addition, Hudson Bay has the most significant long-term time series of data on the ecology of polar bears and is the site of the first documented evidence of major and ongoing impacts to polar bears from sea ice changes. Many researchers over the past 40 years have predicted an array of impacts to polar bears from climatic change that include adverse effects on denning, food chain disruption, and prey availability (Budyko 1966; Vibe 1967, cited in Derocher et al. 2004, p. 164; Lentfer 1972, p. 169; Tynan and DeMaster 1997, p. 315; Stirling and Derocher 1993, pp. 241-244). Stirling and Derocher (1993, p. 240) first noted changes in polar bears in Western Hudson Bay such as declining body condition, lowered reproductive rates, and reduced cub survival; they attributed these changes to a changing ice environment. Subsequently, Stirling et al. (1999, p. 303) established a statistically significant link between climate warming in Western Hudson Bay, reduced ice presence, and observed declines in polar bear physical and reproductive parameters, including body condition (weight) and natality.Show citation box.
Recent studies indicate that polar bear distributions are changing and that these changes are strongly correlated to similar changes in sea ice and the ocean-ice system. Specifically, in Western Hudson Bay, breakup of the annual sea ice now occurs approximately 2.5 weeks earlier than it did 30 years ago (Stirling et al. 1999, p. 299). The earlier spring breakup was highly correlated with dates that female polar bears came ashore (Stirling et al. 1999, p. 299). Declining reproductive rates, subadult survival, and body mass (weights) have resulted from longer periods of fasting on land as a result of the progressively earlier breakup of the sea ice caused by an increase in spring temperatures (Stirling et al. 1999, p. 304; Derocher et al. 2004, p. 165).Show citation box
Stirling et al. (1999, p. 304) reported a significant decline in the condition (weights) of both male and female adult polar bears since the 1980s in Western Hudson Bay, as well as lower natality rates. A positive relationship between body mass of females with cubs and survival of cubs was also established; survival of cubs of mothers in better condition (heavier) was greater than survival of cubs from lighter mothers (Derocher and Stirling 1996, p. 1248).Show citation box
Physical condition of polar bears has been shown to determine the welfare of individuals, and ultimately, through their reproduction and survival, the welfare of populations (Stirling et al. 1999, p. 304; Regehr et al. in prep). Declines in fat reserves during critical times in the polar bear life cycle are likely to lead to an array of impacts including a delay in the age of first reproduction, decrease in the proportion of females with adequate fat stores to complete successful denning, decline in litter sizes with more single cub litters and fewer cubs overall, as well as lower cub body weights and lower survival rates (Derocher et al. 2004, p. 170). Derocher and Stirling (1998, pp. 255-256) demonstrated that body mass of adult females is correlated with cub mass at den emergence, with heavier females producing heavier cubs and lighter females producing lighter cubs. Heavier cubs have a higher rate of survival (Derocher and Stirling 1996, p. 1249). Females in poor condition will result in a higher proportion that do not initiate denning or are likely to abandon their den and cub(s) mid-winter (Derocher et al. 2004, p. 170). Females with insufficient fat stores or in poor hunting condition in the early spring after den emergence could lead to increased cub mortality (Derocher et al. 2004, p. 170). In the southern Beaufort Sea, Regehr et al. (2006, p. 20) recently found that survival rates for cubs were significantly lower than estimates from earlier studies. The lower survival rate of cubs coincided with warming temperatures and altered atmospheric circulation starting in the winter of 1989-1990 that caused an abrupt change in sea ice conditions in the Arctic basin. In addition, sea ice conditions that include broken or more fragmented ice may require young cubs to enter water more frequently and for more prolonged periods of time, thus increasing mortality from hypothermia. Blix and Lenter (1979, p. 72) and Larsen (1985, p. 325) indicate that cubs are unable to survive immersion in icy water for more than approximately 10 minutes. This is due to cubs having little insulating fat, their fur losing its insulating ability when wet (though the fur of adults sheds water and recovers its insulating properties quickly), and the core body temperature dropping rapidly when they are immersed in icy water (Blix and Lenter 1979, p. 72).
Reductions in sea ice, as discussed above, will alter ringed seal distribution, abundance, and availability for polar bears. Such reductions will, in turn, decrease polar bear body condition (Derocher et al. 2004, p. 165). Derocher et al. (2004, p. 165) projected that most females in the Western Hudson Bay population may be unable to reach the minimum 189 kg (417 lbs) body mass required to successfully reproduce by the year 2012."