Cardiac Physiology of Polar Bears in Winter Dens

Results of winter 1967-68 and 1968-69 measurements by radio-capsules implanted in two polar bears indicate that this species is capable of reducing circulatory activity in dormancy in the same way as the grizzly and black bear. Sleeping heart rates of initially 60 beats/min changed slowly week by week to 27/min

Bradycardia of the Polar Bear

For several years two male polar bears have been studied by long-life implanted physiological radio capsules at the Naval Arctic Research Laboratory, at Point Barrow. One of the siblings has consistently been larger than the other. A regular measurement has been the resting heart rate; for this we used the lowest heart rate obtained during night-time sleep. Night-time sleep is used because different heart rate levels are obtained during day-time sleep and night-time sleep. The two bears, during the continuous light of the summer, sleep regularly from about 11 PM until 9:00 AM; occasionally short bouts of sleep occur around early afternoon. Sleeping heart rates have been obtained throughout the lifetime of these two individuals. For example, during the summer of 1971, the larger polar bear, Irish (310 kg), had mean resting heart rates of 54 ±2 SD b/m (N=12); in 1972 at 332 kg his rate was 48 ±5 SD b/m (N=12); the smaller bear in 1971, at 286 kg, had a lower sleeping heart rate (50 ±5 SD b/m). ... A technique for demonstrating bradycardia (rapid slowing of heartbeat) in marine mammals was developed by Irving and Scholander, namely instrumenting the animal and training it to place its head under water. We decided to try this technique with the larger of the polar bears (Irish). The bear was separated from its companion, deprived of food and water overnight, and then recorded during three routine situations: 1) during high activity time; 2) during the filling of the water tub (approximately 300 litres) and 3) during feeding time. Heart rates were taken by the stopwatch every 15 seconds. ... Head immersion and diving bradycardia were evident for periods lasting up to 2 minutes; during that time the animal appeared to be searching for food at the bottom of the tub. Although diving bradycardia was evident (rate reduced 10 per cent to 72 b/m), it is apparent that there was much more bradycardia during the period of eating (reduced 20 per cent to 60 b/m). This slow rate during eating was remarkably close to the sleeping heart rate. One might have expected the heart rate to go up during the excitement of feeding. Also, competition for the food was not entirely lacking; the companion polar bear in the adjoining cage was constantly reaching through the bars as it attempted to obtain some of the food. One might have expected this activity to increase the excitement. We have found no other reference to bradycardia during feeding

Response of a Lake Michigan coastal lake to anthropogenic catchment disturbance

A paleolimnological investigation of post-European sediments in a Lake Michigan coastal lake was used to examine the response of Lower Herring Lake to anthropogenic impacts and its role as a processor of watershed inputs. We also compare the timing of this response with that of Lake Michigan to examine the role of marginal lakes as ‘early warning’ indicators of potential changes in the larger connected system and their role in buffering Lake Michigan against anthropogenic changes through biotic interactions and material trapping. Sediment geochemistry, siliceous microfossils and nutrient-related morphological changes in diatoms, identified three major trophic periods in the recent history of the lake. During deforestation and early settlement (pre-1845–1920), lake response to catchment disturbances results in localized increases in diatom abundances with minor changes in existing communities. In this early phase of disturbance, Lower Herring Lake acts as a sediment sink and a biological processor of nutrient inputs. During low-lake levels of the 1930s, the lake goes through a transitional period characterized by increased primary productivity and a major shift in diatom communities. Post-World War II (late 1940s–1989) anthropogenic disturbances push Lower Herring Lake to a new state and a permanent change in diatom community structure dominated by Cyclotella comensis . The dominance of planktonic summer diatom species associated with the deep chlorophyll maximum (DCM) is attributed to epilimnetic nutrient depletion. Declining Si:P ratios are inferred from increased sediment storage of biogenic silica and morphological changes in the silica content of Aulacoseira ambigua and Stephanodiscus niagarae . Beginning in the late 1940s, Lower Herring Lake functions as a biogeochemical processor of catchment inputs and a carbon, nutrient and silica sink. Microfossil response to increased nutrients and increased storage of biogenic silica in Lower Herring Lake and other regional embayments occur approximately 20–25 years earlier than in a nearby Lake Michigan site. Results from this study provide evidence for the role of marginal lakes and bays as nutrient buffering systems, delaying the impact of anthropogenic activities on the larger Lake Michigan system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43091/1/10933_2004_Article_1688.pd

Cardiac Physiology of Polar Bears in Winter Dens

Results of winter 1967-68 and 1968-69 measurements by radio-capsules implanted in two polar bears indicate that this species is capable of reducing circulatory activity in dormancy in the same way as the grizzly and black bear. Sleeping heart rates of initially 60 beats/min changed slowly week by week to 27/min