Polar bears in Alaska's Beaufort Sea: what we know



by LORENZO CIOTTI

Polar bears in Alaska's Beaufort Sea: what we know

Polar bear is the largest terrestrial carnivore currently in existence. The specimens of adult male of white bears weigh on average from 350 to 700 kg and measure from 2.4 to 3 meters in length. It appears that in rare cases males can reach 1000 kg and 3.5 m in length, the largest polar bear known weighed 1 002 kg, a male killed in Kotzebue Sound in northwest Alaska in 1960 This gigantic specimen, when assembled, stood a whopping 3.39m tall standing on its hind limbs.

Females are about half the size of males and normally weigh between 150 and 250 kg and are about 133 cm long, but when pregnant they can weigh up to 500 kg. At birth, puppies weigh less than 1 kg. The longevity of the polar bear in nature is 25-30 years, while in captivity it can even exceed 35.

Despite its size, this animal is able to run at almost 50 km / h for short distances. Polar bears, when biting, can exert a pressure of 1235 psi, or about 560 kg. Survival and abundance of polar bears in Alaska's Beaufort Sea, 2001-2016, published on the Ecology and evolution, explained: "The Arctic Ocean is undergoing rapid transformation toward a seasonally ice-free ecosystem.

As ice-adapted apex predators, polar bears (Ursus maritimus) are challenged to cope with ongoing habitat degradation and changes in their prey base driven by food-web response to climate warming. Knowledge of polar bear response to environmental change is necessary to understand ecosystem dynamics and inform conservation decisions.

In the southern Beaufort Sea (SBS) of Alaska and western Canada, sea ice extent has declined since satellite observations began in 1979 and available evidence suggests that the carrying capacity of the SBS for polar bears has trended lower for nearly two decades.

In this study, we investigated the population dynamics of polar bears in Alaska's SBS from 2001 to 2016 using a multistate Cormack-Jolly-Seber mark-recapture model States were defined as geographic regions, and we used location data from mark-recapture observations and satellite-telemetered bears to model t ransitions between states and thereby explain heterogeneity in recapture probabilities.

Our results corroborate prior findings that the SBS subpopulation experienced low survival from 2003 to 2006. Survival improved modestly from 2006 to 2008 and afterward rebounded to comparatively high levels for the remainder of the study, except in 2012.

Abundance moved in concert with survival throughout the study period, declining substantially from 2003 and 2006 and afterward fluctuating with lower variation around an average of 565 bears (95% Bayesian credible interval [340, 920]) through 2015.

Even though abundance was comparatively stable and without sustained trend from 2006 to 2015, polar bears in the Alaska SBS were less abundant over that period than at any time since passage of the U.S. Marine Mammal Protection Act.

The potential for recovery is likely limited by the degree of habitat degradation the subpopulation has experienced, and future reductions in carrying capacity are expected given current projections for continued climate warming."