PUPPING PHENOLOGY AND DEMOGRAPHY OF HARBOR SEALS (PHOCA VITULINA RICHARDSI)ON TUGIDAK ISLAND, ALASKA

The number of seals on shore at Tugidak Island (Gulf of Alaska) declined 72%–85% between 1976 and 1988 and increased during the 1990s. We compared pupping phenology and the ratio of pupping-period counts to molting-period counts between declining (1976–1979) and increasing (1994–1998) years, and examined the sex/age structure of seals ashore during the 1990s. In the 1970s the onset and peak of pupping occurred 6–18 d later than in the 1990s. Rate of pup abandonment was higher in 1978 than in the 1990s. Between 1994 and 1995, the maximum and mean number of seals ashore increased >50%, largely due to an increase in non-pups. From 1995 to 1998, the sex/age structure of seals ashore was similar among years. We observed three to four times as many seals during the molting period than during the pupping period in the 1970s, whereas similar numbers were ashore during these periods in the 1990s, perhaps reflecting changes in demography and/or haul-out behavior. Changes in pupping phenology and demography may reflect environmental changes, such as food availability, and when monitored in conjunction with population counts, may help us better interpret changes in the number of seals ashore.     

Harbor seal use of glacier ice and terrestrial haul‐outs in the Kenai Fjords,Alaska

Harbor seals, Phoca vitulina, use diverse haul‐out substrates including ice calved by tidewater glaciers. Numbers of seals at glacial and terrestrial haul‐outs on the southeastern Kenai Peninsula, Alaska, were assessed using aerial, vessel, and video surveys. Mean annual abundance at glacial and terrestrial haul‐outs differed temporally. From 2004 to 2011, numbers of seals counted during the molt increased 5.4%/yr at glacial haul‐outs and 9%/yr at terrestrial haul‐outs while numbers of pups increased 5.0%/yr at glacial sites and 1.5%/yr at terrestrial sites. Numbers of seals without pups counted during pupping increased 7.96%/yr at glacial sites and 5.1%/yr at terrestrial sites. Results indicate that pupping and molting locations are not equivalent and population monitoring during the molt does not necessarily reflect habitat association of pupping seals. Ratios of pups to total seals counted during pupping and the subsequent molt were used to contrast habitat use. Low proportions of pups at terrestrial haul‐outs, relative to most glacial haul‐outs, indicate an overall preference for pupping in glacial haul‐outs. High proportions of pups at most glacial sites (during pupping and molting) suggest reduced use of tidewater glacier habitats by nonbreeders and molting seals. Results suggest more seals associate with glacial haul‐outs than currently estimated.     

STABILITY IN THE PROPORTION OF HARBOR SEALS HAULED OUT UNDER LOCALLY IDEAL CONDITIONS

We monitored the haul-out behavior of 68 radio-tagged harbor seals ( Phoca vitulina ) during the molt season at two Alaskan haul-out sites (Grand Island, August-September 1994; Nanvak Bay, August-September 2000). For each site, we created a statistical model of the proportion of seals hauled out as a function of date, time of day, tide, and weather covariates. Using these models, we identified the conditions that would result in the greatest proportion of seals hauled out. Although those "ideal conditions" differed between sites, the proportion of seals predicted to be hauled out under those conditions was very similar (81.3% for Grand Island and 85.7% for Nanvak Bay). The similar estimates for both sites suggest that haul-out proportions under locally ideal conditions may be constant between years and geographic regions, at least during the molt season.     

MOLTING PHENOLOGY OF HARBOR SEALS ON TUGIDAK ISLAND, ALASKA

We documented the progression and timing of the annual molt of harbor seals on Tugidak Island, Alaska, from 1997 to 1999. In all years the timing of molting differed among age-sex classes. Yearlings molted first, subadults second, adult females third, and lastly adult males. Timing of molting was nearly identical in 1997–1998, whereas in 1999 molting occurred three to six days later for all age-sex classes except yearlings. Estimated dates when peak proportions of each age-sex class were molting ranged from 2 August (yearlings) to 2 September (adult males). The number of seals hauled out was positively related to the proportion of seals in the molt and negatively related to the proportion of seals in the postmolt. Population trend estimates, based on aerial counts conducted during a narrow window within the molting period, are likely biased toward certain age-sex classes. Statistical models used to estimate trend include covariates to help account for within-year variation in seal numbers, but do not account for compositional changes that occur during molting. Population modeling may elucidate the effects of within-year population structure on trend estimates. Monitoring molting phenology at additional sites is necessary to determine the extent of geographic variation in molting.     

DECLINES IN HARBOR SEAL (PHOCA VITULINA) NUMBERS IN GLACIER BAY NATIONAL PARK, ALASKA, 1992–2002

Glacier Bay National Park had one of the largest breeding aggregations of harbor seals in Alaska, and it is functionally the only marine reserve for harbor seals in Alaska; yet, numbers of seals in the Bay are declining rapidly. Understanding why seals in Glacier Bay are declining may clarify their minimal habitat needs. We estimated population trends using models that controlled for environmental and observer‐related factors. In 1992, 6,200 seals were counted on icebergs in a tidewater glacial fjord and at terrestrial sites; by 2002 only 2,550 seals were counted at these same haul‐outs. Numbers of non‐pups in the glacial fjord declined by 6.6%/yr (?39%/8 yr) in June and by 9.6%/yr (?63%/11 yr) in August and at all other haul‐outs by 14.5%/yr (?75%/10 yr) during August. In the glacial fjord the number of pups remained steady from 1994 to 1999 and made up an increasing proportion of seals counted (5.4%/yr), and the proportion of pups peaked at 34%–36%. The rapid declines do not appear to be due to changes in seal behavior or redistribution. The declines reinforce genetic evidence that harbor seals in Glacier Bay are demographically isolated from other populations and indicate that current management stocks need to be redefined. Changes in Glacier Bay's ecosystem and population demographic data from the glacial fjord suggest that interspecific competition and predation are likely factors in the declines.     

Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island,Southern Ocean

Recent pup population estimates of sympatric Subantarctic (Arctocephalus tropicalis) and Antarctic fur seals (A. gazella) at Marion Island are presented. Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007–2015) were analyzed using a hierarchical Bayesian model. The pup population declined by 46% (95% credible interval CI: 43%–48%) between 2004 (mean = 15,260, CI: 14,447–16,169 pups) and 2013 (mean = 8,312, CI: 7,983–8,697), mirrored by a 58%–60% decline at rookeries counted annually (2007–2015). Population decline was highest at high‐density west and north coast rookeries, despite negligible change in female attendance patterns, pup mortality or median pupping date over the previous 25 yr. A better understanding of foraging behavior and its effects on reproductive success and survival in this A. tropicalis population is needed before we can attribute population decline to any external factors. In contrast, total island counts of A. gazella pups in 2007, 2010, and 2013, suggest that this population is still increasing although the annual intrinsic rate of population growth decreased from 17.0% (1995–2004, 744 pups) to 4.0% (2010–2013, 1,553 pups). The slowed growth of A. gazella is likely the result of saturation at the main rookery.     

Harbor seal population decline in the Aleutian Archipelago

Populations of Steller sea lions, northern fur seals, and northern sea otters declined substantially during recent decades in the Bering Sea and Aleutian Islands region, yet the population status of harbor seals has not been assessed adequately. We determined that counts obtained during skiff‐based surveys conducted in 1977–1982 represent the earliest estimate of harbor seal abundance throughout the Aleutian Islands. By comparing counts from 106 islands surveyed in 1977–1982 (8,601 seals) with counts from the same islands during a 1999 aerial survey (2,859 seals), we observed a 67% decline over the ～20‐yr period. Regionally, the largest decline of 86% was in the western Aleutians (n= 7 islands), followed by 66% in the central Aleutians (n= 64 islands), and 45% in the eastern Aleutians (n= 35 islands). Harbor seal counts decreased at the majority of islands in each region, the number of islands with >100 seals decreased ～70%, and the number of islands with no seals counted increased ～80%, indicating that harbor seal abundance throughout the Aleutian Islands was substantially lower in the late 1990s than in the 1970s and 1980s.     

ABUNDANCE OF RINGED SEALS (PUSA HISPIDA) IN THE FJORDS OF SPITSBERGEN, SVALBARD, DURING THE PEAK MOLTING PERIOD

Ringed seal (Pusa hispida) abundance in Spitsbergen, Svalbard, was estimated during the peak molting period via aerial, digital photographic surveys. A total of 9,145 images, covering 41.7%–100% of the total fast‐ice cover (1,496 km²) of 18 different fjords and bays, were inspected for the presence of ringed seals. A total of 1,708 seals were counted, and when accounting for ice areas that were not covered by images, a total of 3,254 (95% CI: 3,071–3,449) ringed seals were estimated to be hauled out during the surveys. Extensive behavioral data from radio‐tagged ringed seals (collected in a companion study) from one of the highest density fjords during the molting period were used to create a model that predicts the proportion of seals hauled out on any given date, time of day, and under various meteorological conditions. Applying this model to the count data from each fjord, we estimated that a total of 7,585 (95% CI: 6,332–9,085) ringed seals were present in the surveyed area during the peak molting period. Data on interannual variability in ringed seal abundance suggested higher numbers of seals in Van Keulenfjorden in 2002 compared to 2003, while other fjords with very stable ice cover showed no statistical differences. Poor ice conditions in general in 2002 probably resulted in seals from a wide area coming to Van Keulenfjorden (a large fjord with stable ice in 2002). The total estimated number of ringed seals present in the study area at the time of the survey must be regarded as a population index, or at least a minimum estimate for the area, because it does not account for individuals leaving and arriving, which might account for a considerable number of animals. The same situation is likely the case for many other studies reporting aerial census data for ringed seals. To achieve accurate estimates of population sizes from aerial surveys, more extensive knowledge of ringed seal behavior will be required.     

Survival probabilities and movements of harbor seals in central California

Harbor seal numbers and population trajectories differ by location in central California. Within San Francisco Bay (SFB) counts have been relatively stable since the 1972 Marine Mammal Protection Act, but in coastal areas like Tomales Bay (TB), counts increased before stabilizing in the 1990s. Emigration, poor survival, and environmental effects have been hypothesized as contributors to differences between trajectories; however, basic demographic data were not available to evaluate these hypotheses. We monitored 32 radio‐tagged adult females (SFB n = 17, TB n = 15) for 20 mo (2011–2013), and estimated survival, resight, and movement probabilities using mark‐resight analyses and multistate mark‐resight models. Annual survival probability for both sites was 0.90 (95% CI = 0.18–0.99). Six seals were observed moving between locations resulting in an estimated probability of 0.042 (95% CI = 0.023–0.076) per month equal movement between sites. Resight probability was less in SFB relative to TB, likely due to differential haul‐out access, area surveyed, visibility, and resight effort. Because of wide confidence intervals and low precision of these first estimates of adult female harbor seal survival in California, this demographic must be further examined to dismiss its contribution to differing population trajectories. Using aerial survey data, we estimated 950 harbor seals in SFB (95% CI = 715–1,184) confirming numbers are still stable.     

CORRECTING AERIAL SURVEY COUNTS OF HARBOR SEALS (PHOCA VITULINA RICHARDSI) IN WASHINGTON AND OREGON

Aerial surveys of harbor seals on land produce only a minimum assessment of the population; a correction factor to account for the missing animals is necessary to estimate total abundance. In 1991 and 1992, VHF radio tags were deployed on harbor seals ( n = 124) at six sites in Washington and Oregon. During aerial surveys a correction factor to account for seals in the water was determined from the proportion of radio-tagged seals on shore during the pupping season. This proportion ranged from 0.54 to 0.74. Among the six sites there was no significant difference in the proportion of animals on shore nor was there a difference in age/sex categories of seals on shore between sites. The pooled correction factor for determining total population abundance was 1.53. An additional 32 seals were radio tagged in 1993 at one of the sites used in 1991. Comparing data from the two years, we found no interannual variation. Aerial surveys of all known harbor seal haul-out sites in Washington ( n = 319) and Oregon ( n = 68) were flown during the peak of the pupping season, 1991–1993. The Washington and Oregon harbor seal population was divided into two stocks based on pupping phenology, morphometics, and genetics. Mean counts for the Washington inland stock were 8,710 in 1991, 9,018 in 1992, and 10,092 in 1993. Oregon and Washington coastal stock mean counts were 18,363 in 1991, 18,556 in 1992, and 17,762 in 1993. Multiplying the annual count by the correction factor yielded estimates of harbor seal abundance in the Washington inland stock of 13,326 (95% CI = 11,637–15,259) for 1991, 13,798 (95% CI = 11,980–15,890) for 1992, and 15,440 (95% CI = 13,382–17,814) for 1993. In the Oregon and Washington coastal stock the corrected estimate of harbor seal abundance was 28,094 (95% CI = 24,697–31,960) in 1991, 28,391 (95% CI = 24,847–32,440) for 1992, and 27,175 (95% CI = 23,879–30,926) for 1993.     

Natural and human effects on harbor seal abundance and spatial distribution in an Alaskan glacial fjord

Tidewater glacial fjords support the largest populations of harbor seals (Phoca vitulina richardii) in Alaska and are a prime destination for tour ships. Chronic disturbance from ships, however subtle, could impact long‐term population stability. We examined variation in abundance and distribution of harbor seals on floating ice in Disenchantment Bay, Alaska, a tour ship destination for over a century with near daily visitation by ships in the spring/summer over the last decade. Counts of seals by aerial transect showed a sharp decline in May, prior to pupping and the first ships arriving; counts rebounded by the end of June remaining high until August. Seal distribution and abundance peaked in 5–7 tenths ice cover; total area of ice cover showed no effect. Despite regular flushing of seals by ships, we found no broad‐scale patterns in seal abundance and distribution that could be explained by ship presence. We cannot rule out mechanisms of long‐term disturbance, difficult to detect and that might explain notable differences with other, similar sites. Population declines at disturbed glacial sites and the still rising popularity of vessel‐based tourism indicate a need for individual‐based studies on how seals respond to the dynamics of glacial ice environments and human‐caused stresses.     

Trends in bowhead whales in West Greenland: Aerial surveys vs. genetic capture‐recapture analyses

We contrast two methods for estimating the trends of bowhead whales (Balaena mysticetus) in West Greenland: (1) double platform visual aerial survey, corrected for missed sightings and the time the whales are available at the surface; and (2) a genetic capture‐recapture approach based on a 14‐yr‐long biopsy sampling program in Disko Bay. The aerial survey covered 39,000 km² and resulted in 58 sightings, yielding an abundance estimate of 744 whales (CV = 0.34, 95% CI: 357–1,461). The genetic method relied on determining sex, mitochondrial haplotypes and genotypes of nine microsatellite markers. Based on samples from a total of 427 individuals, with 11 recaptures from previous years in 2013, this resulted in an estimate of 1,538 whales (CV = 0.24, 95% CI: 827–2,249). While the aerial survey is considered a snapshot of the local spring aggregation in Disko Bay, the genetic approach estimates the abundance of the source of this aggregation. As the whales in Disko Bay primarily are adult females that do not visit the bay annually, the genetic method would presumably yield higher estimates. The studies indicate that an increase in abundance observed between 1998 and 2006 has leveled off.     

TRENDS IN ABUNDANCE OF ALASKA HARBOR SEALS, 1983–2001

We estimated trends in abundance of harbor seals ( Phoca vitulina richardsii ) using over dispersed, multinomial models and counts obtained during aerial surveys conducted during 1983–2001 in the Ketchikan, Sitka, Kodiak, and Bristol Bay areas of Alaska. Harbor seal numbers increased significantly at 7.4%/yr during 1983–1998 and 5.6%/yr during 1994–1998 in the Ketchikan area, and 6.6%/yr during 1993–2001 in the Kodiak area. Counts were stable (trends not significant) during 1984–2001 (0.7%/yr) and 1995–2001 (-0.4%/yr) in Sitka, and during 1998–2001 (-1.3%/yr) in Bristol Bay. The influence of covariates ( e.g. , survey date, tide height) on trend estimates was significant and varied among areas and across years, demonstrating the need to include covariates in statistical analyses to accurately estimate trend. Our increasing trend estimate for Kodiak represents the first documented increase in harbor seal numbers over a relatively expansive area in the Gulf of Alaska. However, the trend for the Gulf of Alaska stock is equivocal due to the continued decline in Prince William Sound. Similarly, the trend for the Southeast Alaska stock is equivocal based on our increasing (Ketchikan) and stable (Sitka) trend estimates, and a recent decline reported for Glacier Bay. The Bering Sea stock appears stable after a period of possible decline.     

The elimination of raccoon rabies from Wolfe Island, Ontario: animal density and movements

During 1996 to 1998, an average of 52% to 55% of the raccoon (Procyon lotor) population on Wolfe Island, Ontario was vaccinated against rabies during proactive trap-vaccinate-release (TVR) operations. However, during 1999, the percent of the population vaccinated declined to 39% and an outbreak (6 cases) of raccoon rabies occurred on the island from December 1999 to January 2000. The raccoon population on Wolfe Island declined dramatically (71% reduction) from 1,067 raccoons (mean density = 8.4/km(2) [6.4-12.4, 95% CI]) during 1999 to 305 raccoons (mean density = 2.4/km(2) [0.87-4.1, 95% CI]) in the spring of 2000. Raccoon density immediately following the outbreak was significantly lower in cells with rabies cases, suggesting that rabies had a negative effect on population size. However, raccoon density had doubled by 1 yr following the outbreak. Movement of raccoons on Wolfe Island was as great as 24 km. Male raccoons moved greater distances than females. Movements to surrounding islands were also noted for raccoons ear tagged on Wolfe Island which indicates the island could serve as a focus for greater geographic rabies spread. Point infection control (PIC) during 2000, TVR during 2001-02, and the aerial distribution of Vaccinia-Rabies Glycoprotein (V-RG) baits during 2000 and 2003-05 were used to eliminate rabies from Wolfe Island. No cases have been detected since late January 2000 (to February 2007).     

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.     

An apparent population decrease,or change in distribution,of Weddell seals along the Victoria Land coast

Ground counts during 1959–1968 compared with counts using high resolution (0.6 m²) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet‐Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto‐Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite‐derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large‐scale seal monitoring program is required to increase understanding of seal population changes.     

The role of Steller sea lions in a large population decline of harbor seals

We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines.     

Distribution and abundance of spotted seals Phoca largha and ribbon seals Phoca fasciata in the southern Sea of Okhotsk

The distribution and abundance of spotted seals (Phoca largha) and ribbon seals (Phoca fasciata) were assessed in March and April, 2000, by aerial line-transect surveys along the southern edge of the pack ice off the coast of Hokkaido (southern Sea of Okhotsk), Japan. Five hundred and seventeen spotted seals and 107 ribbon seals were found on the total 2944 km survey line. Total abundance was estimated to be 13 653 spotted (95% CI = 6167–30 252) and 2260 ribbon seals (95% CI = 783–6607) in March, and 6545 spotted (95% CI = 3284–815 644) and 3134 ribbon seals (95% CI = 1247–17 802 512) in April. The pack ice area off Hokkaido had higher densities (0.54 seals km^–2 and 0.58 seals km^–2 in March and April, respectively) of spotted seals than those reported in eastern Sakhalin, whereas densities (0.09 seals km^–2 in March and 0.28 seals km^–2 in April) of ribbon seals were lower than those in eastern Sakhalin. The large number of spotted seal pups suggests that the study area is an important breeding center. A greater number of female spotted seals with pups tended to be found in the center of larger and rougher floes than in other categories, and they were more abundant in stable pack ice areas. Observations of ribbon seals were limited because the survey period preceded the peak of pupping season. Ribbon seal surveys were also hampered by the inability to fly over the main breeding area between the Shiretoko Peninsula and Kunashiri Island.     

MAJOR DECLINE IN NUMBER OF HARBOR SEALS, PHOCA VITULINA RICHARDSI, ON TUGIDAK ISLAND, GULF OF ALASKA

Tugidak Island, located in the Gulf of Alaska, was once the site of one of largest local concentrations of harbor seals ( Phoca vitulina richardsi ) in the world. This population, which probably consisted of about 20,500 animals in the mid-1960s declined by about 85% between 1976 and 1988. The population appeared to decline more rapidly during the late 1970s than during the 1980s. Causes for the decline are not apparent. There appear to be both similarities and dissimilarities between this decline and recent declines in abundance of northern fur seals ( Callorhinus ursinus ) and Steller sea lions ( Eumetopias jubatus ) in the Bering Sea and Gulf of Alaska.     

ANNUAL REPRODUCTIVE CYCLE OF THE FEMALE HAWAIIAN MONK SEAL (MONACHUS SCHAUINSLANDI)

Abstract: The annual reproductive cycle is described for the adult female Hawaiian monk seal ( Monachus schauinslandi ) from data collected at Laysan Island (1982–1991) and Lisianski Island (1982–1983) in the Northwestern Hawaiian Islands. Pupping, lactation, weaning, and molting were directly observed, while mating was rarely observed and was, therefore, inferred from the occurrence of mounting injuries and from adult male and female association patterns. Pooled birth rates during the study period were 0.544 for all adult-sized females and 0.675 for females parous in earlier years. For parturient females, pupping peaked in late March and early April, weaning in May, mounting injuries in May and June, and molting in July. For non-parturient females, the median mounting injury and molting dates occurred 17 and 28 days earlier, respectively. Pupping date set the timing of subsequent events in the annual cycle, but the timing of those events was adjusted by loss of the pup or poor physical condition of the female. Individual pupping patterns varied widely. The mean interval for births in consecutive years was 381 days; females that pupped in consecutive years gave birth later each season. Conversely, females who skipped a year or more gave birth earlier their next pupping season.