LONG-TERM TRENDS IN HARBOR SEAL NUMBERS AT TUGIDAK ISLAND AND NANVAK BAY, ALASKA

We conducted land‐based counts of harbor seals (Phoca vitulina richardii) and collected related environmental data at Tugidak Island (Gulf of Alaska, 1994–2000) and Nanvak Bay (Bristol Bay, 1990–2000) to estimate population trends and identify factors influencing counts. At Tugidak Island, the seal population declined substantially during molting from 1976 through the 1980s, stabilized in the early 1990s, and increased at a moderate rate (3.4%/yr, CI: 1.0%–5.8%) from 1994 to 2000. Pups and all seals ashore during pupping increased at higher annual rates of 5.4% (CI: 2.2%–8.8%) and 8.3% (CI: 4.5%–12.3%) from 1994 to 2000 at Tugidak Island. At Nanvak Bay seals declined in abundance between 1975 and 1990 but increased during the 1990s at 9.2%/yr (CI: 7.2%–11.3%) during pupping and 2.1%/yr (CI: 0.6%–3.6%) during molting. Date and time‐of‐day were significant covariates in all analyses. Factors that led to declines at Tugidak Island and Nanvak Bay have seemingly abated sufficiently such that these populations are currently increasing, though still greatly reduced from the 1970s. Index sites are useful adjuncts to aerial surveys, providing survey‐related information not always available from aerial counts, which is useful in survey design and data analysis.     

SPRING HAUL-OUT BEHAVIOR OF RINGED SEALS (PUSA HISPIDA) IN KONGSFJORDEN, SVALBARD

Haul‐out behavior of ringed seals (Pusa hispida) was investigated during the spring molting period of 2003 (May–July) in Kongsfjorden, Svalbard, Norway. Hourly counts were conducted on the land‐fast ice in six spatially defined sectors in the inner fjord, from an elevated land‐based vantage point from early May through until the ice began to break up in June, from 0600 to 2200 daily (total counts n= 478). Concomitantly, measurements were made of a variety of weather parameters. Multiple regression analyses revealed that time of day (P < 0.001) and date (P < 0.001) significantly affected the number of ringed seals hauled out on the ice surface. Other factors influencing the number of seals counted on the ice were air temperature (P= 0.011) and wind speed (P < 0.001). Daily peaks occurred in the early afternoon between 1300 and 1400 and the seasonal high (n= 385) was registered during the first week in June, after which the number of seals on the ice in the fjord declined. In addition to the visual counts, 24 ringed seals were equipped with VHF transmitters, and the haul‐out behavior of individuals was monitored from May through July via an automatic recording station. The VHF‐tagged seals exhibited the same diurnal pattern seen in the total counts, with haul‐out most frequent from 1300 to 1400. Pups exhibited short and frequent haul‐outs, whereas longer haul‐out periods were seen in the older age classes; adult females had the greatest number of haul‐out periods that exceeded 24 h. The seasonal peak of haul‐out for the tagged seals preceded the peak seasonal counts by approximately 3 wk. This may reflect significant out‐ and influx of seals from and to the area, a phenomenon warranting further attention because of its implications for assessment studies.     

FEEDING METHOD AFFECTS OTOLITH DIGESTION IN CAPTIVE GRAY SEALS: IMPLICATIONS FOR DIET COMPOSITION ESTIMATION

Analysis of prey structures from scats has become widely used for assessing the diet of free-ranging seals. Captive feeding experiments have played an important role in the development of scat analysis but methodology has varied. We investigated whether using an experimental otolith-carrier species or in situ otolith experimental prey to feed haddock, plaice, and sand eel otoliths to two captive gray seals affected the amount of otolith digestion, and therefore our ability to estimate fish size and diet composition. Otolith recovery rates varied among the three prey species, but were not affected by feeding method. Otoliths were more digested in carrier experiments; resulting digestion coefficients were greater than those from in situ experiments. As a result, while the lengths of whole fish fed experimentally could be accurately predicted by applying in situ digestion coefficients, the lengths of these fish could not be accurately predicted using carrier digestion coefficients. Consequently, the estimated proportion by weight of each species in the diet can change markedly when carrier, as opposed to in situ , digestion coefficients are used. The implications for diet composition estimation are significant.     

CHANGES IN ABUNDANCE OF HARBOR SEALS IN MAINE, 1981–2001

Aerial counts of harbor seals ( Pboca vitulina concolor ) on ledges along the Maine coast were conducted during the pupping season in 1981, 1986, 1993, 1997, and 2001. Between 1981 and 2001, the uncorrected counts of seals increased from 10,543 to 38,014, an annual rate of 6.6 percent. In 2001 30 harbor seals were captured and radio-tagged prior to aerial counts. Of these, 19 harbor seals (six adult males, two adult females, seven juvenile males, and four juvenile females) were available during the survey to develop a correction factor for the fraction of seals not observed. The corrected 2001 abundance estimate was 99,340 harbor seals. Productivity in this population has increased since 1981 from 6.4% pups to 24.4% pups. The number of gray seals ( Halichoerus grypus ) counted during the harbor seal surveys increased from zero in both 1981 and 1986 to 1,731 animals in 2001.     

EFFECTS OF AN OFFSHORE OIL DEVELOPMENT ON LOCAL ABUNDANCE AND DISTRIBUTION OF RINGED SEALS (PHOCA HISPIDA) OF THE ALASKAN BEAUFORT SEA1

This study investigates how densities of ringed seals were affected by construction and oil production activities at Northstar, an artificial island built in the nearshore Alaskan Beaufort Sea. Intensive and replicated aerial surveys of seals on landfast ice were conducted during six spring seasons: for three seasons before island construction began (1997–1999); after a winter of intensive island construction (2000); and after more limited construction plus drilling (2001) and drilling plus oil production (2002). A Poisson regression model was used to examine seal densities relative to distance from Northstar after allowance for environmental covariates. Post hoc power analysis indicated that the study design and Poisson regression approach had high power to detect small‐scale changes in seal densities near Northstar if such changes had occurred. However, seal densities during spring were not significantly affected by proximity to Northstar in 2000–2002. Habitat, temporal, and weather factors did have significant effects on seal densities. This study shows that effects of the Northstar oil development on local distribution of basking ringed seals are no more than slight, and are small relative to the effects of natural environmental factors. An understanding of environmental effects is essential when assessing potential impacts of industrial activity on ringed seals.     

Cloning and sequence analysis of porcine myoglobin cDNA

Porcine myoglobin cDNA clones have been isolated from a cDNA library prepared from enriched heart-myoglobin mRNA. Sequence analysis revealed 59 nucleotides (nt) in the 5'-untranslated, 462 nt in the amino acid (aa)-coding, and 590 nt in the 3'-untranslated regions. The myoglobin cDNA showed a high G + C content (60%). When the nt sequence of the porcine myoglobin cDNA is compared with those of seal and human myoglobin cDNAs deduced from the corresponding genomic myoglobin genes [Blanchetot et al., Nature 301 (1983) 732-734; Weller et al., EMBO J. 3 (1984) 439-446; Akaboshi, Gene 33 (1985) 241-249], a high degree of homology is observed in the 5'-untranslated region and in parts of the 3'-untranslated region, as well as in the coding region.     

DIVING BEHAVIOR OF THE SAIMAA RINGED SEAL (PHOCA HISPIDA SAIMENSIS NORDQ.)

The activity and diving patterns of four adult Saimaa ringed seals ( Phoca hispida saimensis , a landlocked subspecies living in Lake Saimaa, Finland) were examined during spring, summer, and autumn by the use of VHF-transmitters. Over 17,000 dives were registered. The duration of the dives and diving patterns differed among individuals. The mean duration of dives increased from spring to autumn; e.g. , in one individual the mean dive duration increased from 6 min in June to 10.5 min in October. The haul-out periods of one individual in May to early June made up 46.2% of its total activity budget, but in another individual in July to August the haul-out periods made up only 11% of the budget and the seal was submerged for 80% of the time. Periods of successive long duration dives (>10 min) were observed in three individuals in summer and autumn. The longest dive measured was 23 min. The duration of the periods containing long dives was often over three hours (maximum six hours) and the mean duration of the dives about 15 min. These long duration dives are assumed to be aerobic resting dives. Generally, the dives of the Saimaa ringed seal appear to be of longer duration than previously assumed.     

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

1. 1.|Oil caused a substantial decrease in the insulative value of polar bear (Ursus maritimus) pelts measured in vitro.

2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%.

3. 3.|Conductance through oil-covered furs remained high at winter temperatures (T_a = 0.6°C) but decreased with time at summer temperatures (T_a = 24.7°C).

4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

HAUL-OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISK

The potential for non-aquatic predators to influence habitat use by harbor seals ( Phoca vitulina ) in a nearshore marine environment was studied by examining haul-out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul-out areas were quantified for each haul-out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul-out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul-out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores.     

INVESTIGATING THE BIASES IN THE USE OF HARD PREY REMAINS TO IDENTIFY DIET COMPOSITION USING ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA) IN CAPTIVE FEEDING TRIALS

The analysis of pinniped scats has been used to quantify their diet, using prey remains to identify species and to estimate the numbers and sizes of prey consumed. There are, however, potential biases involved with scat analysis and, for this method to be used successfully, these biases need to be quantified. Thirty-six Antarctic fur seals ( Arctocephalus gazella ) were fed meals of exclusively either fish, squid, or krill and their scats were collected and analyzed. The major sources of error in the analysis of prey remains from scats were the differential erosion and passage rate of items in relation to their size. However, using simple correction functions, such as those which model otolith erosion, it is possible to reduce these errors. Using plastic beads as dietary markers showed recovery rates were negatively related to their size. Larger squid beaks had lower recovery rates than smaller beaks, but there was no size-related bias in the recovery rates of krill carapaces. Only 33% of the squid beaks and 27% of the otoliths originally fed were recovered from the scats. Recovery rates were greater for squid (77%) and fish (50%) eye lenses and these structures gave a better estimate of numbers eaten. Differences found between experimentally derived and published regression equations (used to calculate prey sizes eaten from prey remains) highlights the need for regression equations based on local prey characteristics, if these are to be used with any success to describe the prey eaten.