No abstract

Observations from 38 bottom‐moored Current and Pressure Recording Inverted Echo Sounders (CPIES) deployed in Drake Passage during the 2007–2008 International Polar Year provide unprecedented coverage of near‐bottom currents and pressures spanning the entire Antarctic Circumpolar Current. Year‐long‐mean currents exceed 10 cm s−1 north of the Polar Front, and mean directions are not, in general, aligned with the surface fronts. Topographic steering is most evident at the continental margins. Deep eddy kinetic energy (EKE) is maximum at about 200 cm2 s−2 between the Subantarctic and Polar Fronts, coinciding with the location but about one quarter of the value of a maximum in surface EKE. Multiple high‐speed current events, with peak speeds of 60–70 cm s−1 and lasting 30 to 70 days, are coherent across sites separated by 45 km. The observed spinup of eddies coinciding with meanders in the surface fronts is consistent with deep cyclogenesis.

Anthropogenic global warming is occurring more rapidly in the Arctic than elsewhere, and has already caused significant negative effects on sea icedependent species such as polar bears. Although observed effects have thus far been gradual, the large amount of annual variation in the climate system may cause habitat changes in individual years that exceed the long-term trend. Such years may be below critical thresholds necessary for feeding and result in unprecedented reductions in survival, reproduction, and abundance in some populations. Here, in anticipation of sudden negative population-level effects, we provide an overview of proactive conservation and management options. Preplanning, consultation, and coordination of management responses will be necessary to reduce the risks to human safety and other effects of catastrophic declines in habitat. Advance consideration of the costs, legality, logistical difficulties, likelihood of success, and invasiveness of potential responses will be critical to minimizing short-term negative effects while laying the groundwork for longer-term conservation objectives.

Ursids are the largest mammals to retain a plantigrade posture. This primitive posture has been proposed to result in reduced locomotor speed and economy relative to digitigrade and unguligrade species, particularly at high speeds. Previous energetics research on polar bears () found locomotor costs were more than double predictions for similarly sized quadrupedal mammals, which could be a result of their plantigrade posture or due to adaptations to their Arctic marine existence. To evaluate whether polar bears are representative of terrestrial ursids or distinctly uneconomical walkers, this study measured the mass-specific metabolism, overall dynamic body acceleration, and gait kinematics of polar bears and grizzly bears () trained to rest and walk on a treadmill. At routine walking speeds, we found polar bears and grizzly bears exhibited similar costs of locomotion and gait kinematics, but differing measures of overall dynamic body acceleration. Minimum cost of transport while walking in the two species (2.21 J kg m) was comparable to predictions for similarly sized quadrupedal mammals, but these costs doubled (4.42 J kg m) at speeds ≥5.4 km h Similar to humans, another large plantigrade mammal, bears appear to exhibit a greater economy while moving at slow speeds.

There has been considerable emphasis on understanding isotopic discrimination for diet estimation in omnivores. However, discrimination may differ for carnivores, particularly species that consume lipid-rich diets. Here, we examined the potential implications of several factors when using stable isotopes to estimate the diets of bears, which can consume lipid-rich diets and, alternatively, fast for weeks to months. We conducted feeding trials with captive brown bears (Ursus arctos) and polar bears (Ursus maritimus). As dietary lipid content increased to ∼90%, we observed increasing differences between blood plasma and diets that had not been lipid extracted (∆(13)Ctissue-bulk diet) and slightly decreasing differences between plasma δ(13)C and lipid-extracted diet. Plasma Δ(15)Ntissue-bulk diet increased with increasing protein content for the four polar bears in this study and data for other mammals from previous studies that were fed purely carnivorous diets. Four adult and four yearling brown bears that fasted 120 d had plasma δ(15)N values that changed by <±2‰. Fasting bears exhibited no trend in plasma δ(13)C. Isotopic incorporation in red blood cells and whole blood was ≥6 mo in subadult and adult bears, which is considerably longer than previously measured in younger and smaller black bears (Ursus americanus). Our results suggest that short-term fasting in carnivores has minimal effects on δ(13)C and δ(15)N discrimination between predators and their prey but that dietary lipid content is an important factor directly affecting δ(13)C discrimination and indirectly affecting δ(15)N discrimination via the inverse relationship with dietary protein content.