SURVIVAL RATES OF SEA OTTER PUPS IN ALASKA AND CALIFORNIA

Adult female sea otters ( Enhydra lutris ) were instrumented with implanted radio-transmitters in Prince William Sound (PWS), Alaska, and survival rates were estimated for their dependent pups. Overall, 94 of 141 (67%) of the pups studied survived to a minimum age of 120 d and were assumed to have successfully weaned. Survival of pups in six cohorts ranged from 53% to 88%. The mean interval between successive visual observations was 12.5 d. For these calculations, the assumption was made that pups were successfully weaned if they accompanied mothers for at least 120 d. Estimated survival rates were different when this assumption was changed to either 90 d or 150 d (73% and 52%, respectively).
Females were palpated for pregnancy when instrumented. Of 19 believed to be pregnant, 17 were subsequently seen with young pups giving a detection rate for births of 89.5%. When the above observed survival rate of pups was adjusted for undetected births, the estimated overall survival rate for the study population was 60% (120 d minimum dependency).
Survival rates of pups in PWS and a population at Kodiak Archipelago (KOD) (Monson and DeGange 1995) were compared with that of pups in the population in California (CA, four studies). These data did not support the hypothesis that survival rates were lower in California (CA: 103/160, P_surv. 0.64; PWS: 94/141, P_surv. = 0.67; KOD: 19/23, P_surv. = 0.83; pairwise comparisons, X², P > 0.05). Comparison of pup survival rates among studies was hindered by small sample sizes, methodological differences, and lack of detail about assumptions underlying estimates.     

Observations of mortality associated with extended open-water swimming by polar bears in the Alaskan Beaufort Sea

During aerial surveys in September 1987–2003, a total of 315 live polar bears were observed with 12 (3.8%) animals in open water, defined for purposes of this analysis as marine waters >2 km north of the Alaska Beaufort Sea coastline or associated barrier islands. No polar bear carcasses were observed. During aerial surveys in early September, 2004, 55 polar bears (Ursus maritimus) were seen, 51 were alive and of those 10 (19.9%) were in open water. In addition, four polar bear carcasses were seen floating in open water and had, presumably, drowned. Average distance from land and pack ice edge for live polar bears swimming in open water in 2004 (n=10) were 8.3±3.0 and 177.4±5.1 km, respectively. We speculate that mortalities due to offshore swimming during late-ice (or mild ice) years may be an important and unaccounted source of natural mortality given energetic demands placed on individual bears engaged in long-distance swimming. We further suggest that drowning-related deaths of polar bears may increase in the future if the observed trend of regression of pack ice and/or longer open water periods continues.     

LENGTH-MASS AND TOTAL BODY LENGTH OF ADULT FEMALE SEA OTTERS IN PRINCE WILLIAM SOUND BEFORE AND AFTER THE EXXON VALDEZ OIL SPILL

After the 1989 T/V Exxon Valdez oil spill (EVOS), the body condition of non-pregnant female sea otters ( Enhydra lutris ) ages 4 yr and older in the EVOS-affected region of western Prince William Sound, Alaska (WPWS), was significantly poorer than that of individuals captured in the same or adjacent habitat in WPWS approximately a decade earlier, and than that of individuals inhabiting unoiled habitat in eastern PWS (EPWS) between 1984 and 1990. However, the body condition of females of this age category captured in WPWS prior to EVOS was not significantly different from that of pre-and postspill EPWS females. The mean total body length (TBL) of non-pregnant females captured prespill in WPWS was significantly less than that of pre-and postspill EPWS and postspill WPWS females. Evidence from this and other studies suggests that the body condition of at least some classes of sea otters was negatively affected by one or more EVOS-related factors.