Home range,survival, and dispersal of endangered Saimaa ringed seal pups: Implications for conservation

Lake Saimaa in eastern Finland is inhabited by a critically endangered ringed seal subspecies Pusa hispida saimensis. Since accidental mortality in gill nets, resulting in reduced pup survival, is considered to be the main factor contributing to the decline in its population, fishing restriction areas have been established. In this study, 10 pups were located daily using very high frequency (VHF) telemetry to estimate their home ranges, movements, and survival. The pups dispersed after weaning at the age of ca. 3 mo and moved up to 15 km a day between consecutive locations and up to 25 km away from their birth sites. The home ranges of the pups at the age of 3–4 mo were variable in size, from 3 to 162 km². The pups preferred the same shallow water areas (<6 m) that were used for gill net fishing. The annual fishing restrictions covered an average of 83% of the pups’ home ranges. Four of the pups were nevertheless killed in fishing gear. The results have implications for Saimaa ringed seal management and conservation. For instance, large home ranges of pups and the long distances movements should be taken into account when zoning shore use and imposing fishing restrictions.     

Grooming and resting of otters Lutra lutra in a marine habitat

The weight gain in lactating harbour seal pups and sex-specific growth curves are described. The relationship between body length, body weight and age were derived by regression analysis based on length and age data from 365 seals, and weight values from 136 seals. The asymptotic values of the curves describing body length were 148.0 cm and 147.2 cm in females and 153.9 cm and 155.5 cm in males using Gompertz and von Bertalanffy, respectively. The corresponding body weight values were 72.8 kg and 76.7 kg in females and 90.7 kg and 88.4 kg in males.     

IMPROVED BODY CONDITION OF WEANED HAWAIIAN MONK SEAL PUPS ASSOCIATED WITH EL Niño EVENTS: POTENTIAL BENEFITS TO AN ENDANGERED SPECIES

Efforts to enhance recovery of endangered Hawaiian monk seals ( Monachus schauinslandi ) require an understanding of factors influencing population dynamics. This study examines relationships between body condition and survival of monk seal pups at French Frigate Shoals and Laysan Island and El Niño events. Girth measurements and mass estimates were used as indicators of pup body condition, and survival was evaluated from weaning to age 2. Linear models and logistic regression analysis were used to evaluate El Niño effects. Temporal trends in mean girth, mass, and survival were identified at both study sites. After accounting for temporal trends, girths were 3.7 cm and 2.7 cm greater during El Niño years at French Frigate Shoals and Laysan Island, respectively. Average mass estimates were significantly greater during El Niño years at French Frigate Shoals (2.6 kg increase), but were not significantly different at Laysan Island (1.8 kg increase). Weaned pups born at French Frigate Shoals during El Niño years survived significantly better, but this effect was not detected at Laysan Island. El Niño events probably affect pup condition and survival, but these parameters need to be monitored during future El Niño events to clarify these relationships.     

Age and sex composition of seals killed by polar bears in the eastern Beaufort Sea

Background

Polar bears (Ursus maritimus) of the Beaufort Sea enter hyperphagia in spring and gain fat reserves to survive periods of low prey availability. We collected information on seals killed by polar bears (n = 650) and hunting attempts on ringed seal (Pusa hispida) lairs (n = 1396) observed from a helicopter during polar bear mark-recapture studies in the eastern Beaufort Sea in spring in 1985–2011. We investigated how temporal shifts in ringed seal reproduction affect kill composition and the intraspecific vulnerabilities of ringed seals to polar bear predation.

Principal Findings

Polar bears primarily preyed on ringed seals (90.2%) while bearded seals (Erignathus barbatus) only comprised 9.8% of the kills, but 33% of the biomass. Adults comprised 43.6% (150/344) of the ringed seals killed, while their pups comprised 38.4% (132/344). Juvenile ringed seals were killed at the lowest proportion, comprising 18.0% (62/344) of the ringed seal kills. The proportion of ringed seal pups was highest between 2007–2011, in association with high ringed seal productivity. Half of the adult ringed seal kills were ≥21 years (60/121), and kill rates of adults increased following the peak of parturition. Determination of sex from DNA revealed that polar bears killed adult male and adult female ringed seals equally (0.50, n = 78). The number of hunting attempts at ringed seal subnivean lair sites was positively correlated with the number of pup kills (r² = 0.30, P = 0.04), but was not correlated with the number of adult kills (P = 0.37).

Conclusions/Significance

Results are consistent with decadal trends in ringed seal productivity, with low numbers of pups killed by polar bears in spring in years of low pup productivity, and conversely when pup productivity was high. Vulnerability of adult ringed seals to predation increased in relation to reproductive activities and age, but not gender.     

A missing piece in the Arctic food web puzzle? Stomach contents of Greenland sharks sampled in Svalbard, Norway

Harbour seals in Svalbard have short longevity, despite being protected from human hunting and having limited terrestrial predation at their haulout sites, low contaminant burdens and no fishery by-catch issues. This led us to explore the diet of Greenland sharks (Somniosus microcephalus) in this region as a potential seal predator. We examined gastrointestinal tracts (GITs) from 45 Greenland sharks in this study. These sharks ranged from 229 to 381?cm in fork length and 136–700?kg in body mass; all were sexually immature. Seal and whale tissues were found in 36.4 and 18.2%, respectively, of the GITs that had contents (n?=?33). Based on genetic analyses, the dominant seal prey species was the ringed seal (Pusa hispida); bearded seal (Erignathus barbatus) and hooded seal (Cystophora cristata) tissues were each found in a single shark. The sharks had eaten ringed seal pups and adults based on the presence of lanugo-covered prey (pups) and age determinations based on growth rings on claws (≤1?year and adults). All of the whale tissue was from minke whale (Balenoptera acutorostrata) offal, from animals that had been harvested in the whale fishery near Svalbard. Fish dominated the sharks’ diet, with Atlantic cod (Gadus morhua), Atlantic wolffish (Anarhichas lupus) and haddock (Melanogrammus aeglefinus) being the most important fish species. Circumstantial evidence suggests that these sharks actively prey on seals and fishes, in addition to eating carrion such as the whale tissue. Our study suggests that Greenland sharks may play a significant predatory role in Arctic food webs.     

Harbor seal pup dispersal and individual morphology,hematology, and contaminant factors affecting survival

Understanding the factors affecting individual harbor seal (Phoca vitulina) survival is essential for determining population level health risks. We estimated postweaning dispersal, and modeled the effects of morphology, hematology, and blubber contaminants on the survival of recently weaned harbor seal pups using a mark recapture framework. We deployed satellite transmitters on apparently healthy pups captured in San Francisco Bay (SFB, n = 19) and Tomales Bay (TB, n = 7), and pups released after rehabilitation that stranded along the central California coast preweaning (n = 21). Dispersal distances were further than previously reported for harbor seal pups (maximum = 802 km) which has implications for understanding risks to this vulnerable age class. We found differences in body condition, serum immunoglobulin and thyroxine (T4) concentrations, white blood cell count, and blubber organohalogen contamination (OH) among the three groups. Overall, increased T4, decreased OH, and increased mass were associated with greater survival probabilities; whereas, among stranded seals, greater mass gain, shorter time in rehabilitation, and admission to rehabilitation earlier in the season were associated with greater survival probabilities. Attention to these latter factors may improve the success of rehabilitation efforts. For wild pups, reduction of legacy contaminants and direct causes of mortality, such as ship strike, may enhance pup survival.     

BODY TEMPERATURE IN THE NEWBORN SOUTHERN ELEPHANT SEAL, MIROUNGA LEONINA, AT MACQUARIE ISLAND

Newborn southern elephant seal pups were reported by Laws (1953) to be "to some extent poikilothermic at birth." Rectal temperatures of known age southern elephant seal pups were recorded during the 1985 pupping season at Macquarie Island. The mean pup rectal temperature was found to be 381°C ± 0.1°C SEM ( n = 131, range = 36.5°-39.1°C). Pups at two hours, six hours, and one day after birth had significantly higher rectal temperatures than pups two, three, or four days of age. Rectal temperatures of neonatal southern elephant seals were within the range observed for other pinnipeds, (but never as low as the 31°C previously observed for southern elephant seals at Signy Island in 1953). A significant though weak positive correlation was found between pup temperature and body weight. However, no correlation between pup temperature and age or any environmental factor was found. These observations demonstrated that southern elephant seal pups at Macquarie Island are homeothermic, rather than heterothermic from birth.     

Dive types and circadian behaviour patterns of Saimaa ringed seals<Emphasis Type="Italic">Phoca hispida saimensis</Emphasis> during the open-water season

Diving and circadian behaviour patterns of 7 free-ranging Saimaa ringed sealsPhoca hispida saimensis Nordquist, 1899 were examined by VHF-radiotelemetry during open-water seasons between May and November in Lake Saimaa, eastern Finland. The mean recorded dive duration ranged from 2.8 to 6.5 min, with a maximum of 21 min. The mean dive depth ranged from 9.8 to 15.7 m, with maximum of 39.6 m. The maximum dive depth of each seal was limited by water depth in the study area. The dive depths were positively correlated with dive duration and body mass of the seal. Five different dive types were defined, as based on their depth-time characteristics, each falling into one of the three functional categories: travelling, feeding, and resting. Long duration diving bouts occurred mostly at night and were presumed to be resting dives. Saimaa ringed seals exhibited a circadian pattern of haul-out behaviour that shifted seasonally. During molting (May–June) the seals hauled-out both day and night, but later in summer haul-out was more frequent at night.     

Early-life density-dependence effects on growth and survival in subantarctic fur seals

Understanding the regulation of natural populations has been a long-standing research program in ecology. Current knowledge on marine mammals and seabirds is biased toward the adult component of populations and lacking are studies investigating the juvenile component. Our goal was to estimate demographic parameters on the pre-weaning stage of a subantarctic fur seal (Arctocephalus tropicalis) population on Amsterdam Island, suspected to be regulated by density-dependence. The influence of abundance on growth parameters (length and weight) and survival was assessed over a study period spanning 16 years. We evidenced a negative trend in population growth rate when density increased. Density-dependence models were favored for pup body size and mass growth. Abundance had a clear influence on body length at high population-density, pups grew slower and were smaller at weaning than pups born in years with low population density. Abundance partly explained pup body mass variation and a weak effect was detected on pre-weaning survival. The causal mechanisms may be increased competition for food resources between breeding females, leading to a reduction of maternal input to their pups. Our results suggested that pup favored survival over growth and the development of their diving abilities in order to withstand the extreme fasting periods that are characteristic of this fur seal population. This analysis provides significant insight of density-dependent processes on early-life demographic parameters of a long lived and top-predator species, and more specifically on the pre-weaning stage with important consequences for our understanding of individual long-term fitness and population dynamics.     

CLIMATE CHANGE AND RINGED SEAL (PHOCA HISPIDA) RECRUITMENT IN WESTERN HUDSON BAY

Climate warming is predicted to reduce the extent of ice cover in the Arctic and, within the Hudson Bay region, the annual ice may be significantly decreased or entirely lost in the foreseeable future. The ringed seal ( Phoca hispida ), a key species that depends on sea ice, will likely be among the first marine mammals to show the negative effects of climatic warming. We used 639 ringed seals killed by Inuit hunters from western Hudson Bay (1991–1992, 1999–2001) to assess trends in recruitment relative to snow depth, snowfall, rainfall, temperature in April and May, North Atlantic Oscillation (NAO) from the previous winter, and timing of spring break-up. Snowfall and ringed seal recruitment varied from lower than average in the 1970s, to higher in 1980s and lower in 1990s. Prior to 1990, seal recruitment appeared to be related to timing of spring ice break-up which was correlated with the NAO. However, recent 1990–2001 environmental data indicate less snowfall, lower snow depth, and warmer temperatures in April and May when pups are born and nursed. Decreased snow depth, particularly below 32 cm, corresponded with a significant decrease in ringed seal recruitment as indicated by pups born and surviving to adults that were later harvested. Earlier spring break-up of sea ice together with snow trends suggest continued low pup survival in western Hudson Bay.     

Brain size in neonatal and adult Weddell seals: Costs and consequences of having a large brain

Little is known about the ontogeny of brain size in pinnipeds despite potential functional implications of brain substrate (glucose, oxygen) requirements for diving, fasting, growth, and lactation strategies. We measured brain mass (brM) and cranial capacity (CC) in newborn and adult Weddell seals. Neonatal Weddell seals had brM that represented ~70% of adult brM. Weddell seals have the largest neonatal brain, proportional to adult brain, reported for any mammal to date, which is remarkable considering the relatively small size of Weddell seal pups at birth (6%–7% of maternal body mass) compared to neonates of other highly precocial mammals. Provision of sufficient glucose to maintain the large, well‐developed brain of the neonatal Weddell seal has a nontrivial metabolic cost to both pup and mother. We therefore hypothesize that this phenomenon must have functional significance, such as allowing pups to acquire complex under‐ice navigation skills during the period of maternal attendance.     

Diet composition and seasonal feeding patterns of a freshwater ringed seal (Pusa hispida saimensis)

The Saimaa ringed seal (Pusa hispida saimensis) is one of the few freshwater seal populations worldwide. The major conservation issue of this critically endangered population is bycatch mortality. We used digestive tract content and stable isotopes (δ¹³C and δ¹⁵N) to estimate the diet and seasonal feeding patterns for gaining better understanding of the seals feeding habits and potential conservation implications. The diet was similar across age groups. Altogether 15 fish species were identified and the most important were smelt (Osmerus eperlanus), ruff (Gymnocephalus cernuus), perch (Perca fluviatilis), vendace (Coregonus albula) and cyprinids. The high δ¹⁵N values suggested that the seals lose weight during winter and spring. Additionally the drop in δ¹⁵N values indicated that pups start to recover from postweaning stress and gain weight around the age of 6 mo. The isotope values differed regionally, which emphasizes that samples from consumers and prey should be collected from the same regions to improve interpretation of the stable isotopic results. Overall, diet composition suggests minimal to nonexistent competition with commercial or recreational fishing. However, observed weight loss of pups during summer may be related to higher risk of bycatch and this should be taken into account when planning temporal fishing closures.     

Rapid recovery of Dutch gray seal colonies fueled by immigration

Gray seals were first observed breeding in the Dutch Wadden Sea in 1985, after centuries of absence. The breeding colony there is now the largest on the European continent. We describe the changes in gray seal numbers and their geographical expansion, and estimate how these processes were influenced by immigration from other colonies. Counts of hauled out animals were carried out between 1985 and 2013, monitoring three different periods of the seals' annual cycle. Using priors determined for the UK population, a Bayesian demographic model was fitted to pup numbers to estimate the population parameters driving the growth. This included immigration of subadults into the breeding population, which contributed to an average growth rate in the pup counts of 19%/yr, much higher than expected in a closed population. This immigration may account for approximately 35% of the total annual growth. In addition, at least 200 gray seals from the UK visit the area temporarily. Recovery of the population in the Netherlands occurred more than 50 yr after gray seals were protected in the UK. These time scales should be taken into account when studying long living marine mammals, e.g., in impact and conservation studies.     

THE ROLE OF PREDATION IN THE ECOLOGY OF THE RINGED SEAL IN BARROW STRAIT, NORTHWEST TERRITORIES, CANADA

Predation on ringed seals ( Phoca hispida ) was examined in Barrow Strait between March and May 1984 to 1986. Polar bears were the most important predator. Evidence of bear predation was observed at 18–30% of the ringed seal subnivean structures we located. Ten to 24% of predation attempts were successful, with pups making up 75% to 100% of the seals killed. Bears killed an average of 0.08 to 0.51 seals/km², which comprised 8 to 44% of the estimated annual pup production. Bears were successful on average in 11.3% of their attempts to kill pups hidden inside birth lairs. On southeast Baffin Island where snow was soft and pups were exposed, bears were successful in 33.5% of their attempts to kill a seal. Negative correlations were found between mean snow depth and predation by polar bears ( r = -0.896, P = 0.04, n = 5) in 1985, and between snow depth and the number of predation attempts ( r = -0.613, P = 0.02, n = 14) in 1986.     

Lifetime survival rates and senescence in northern elephant seals

The aim of this study was to extend 40 yr of prior demographic work on northern elephant seals (Mirounga angustirostris) at Año Nuevo, California, by including the oldest animals. We used a Bayesian mark‐recapture analysis to estimate lifelong survival and lifespan of a cohort of 372 weaned pups branded in 1985–1987 and resighted until 2008. Annual survival probability of females averaged 86.3%/yr at ages 5–16, then declined until age 21, the age of the oldest female. Male survival was lower, averaging 67.7%/yr from age 1 to age 15, the age of the oldest male. Northern elephant seal females in the expanding population at Año Nuevo live longer than southern elephant seal females (M. leonina) at colonies whose populations are declining. This comparison suggests that high survival of females is a key factor in population growth.     

Spatio-temporal variability of snow over sea ice in western Hudson Bay,with reference to ringed seal pup survival

Snow-covered sea ice plays a significant role in the ecology of the Arctic marine system and is a critical habitat for ice-adapted ringed seals; however, limited research has focused on the role of snow. The first two objectives of this study characterize the spatial and temporal variability in snow over the sea ice of western Hudson Bay measured from satellite (2002–2010) and how this variability relates to ringed seal pup demographic parameters. The final objective uses a regional circulation model (RCM) to estimate the future snow cover within the study area. Results indicated that the snow cover experienced interannual and interseasonal variability, however, typically increased in late spring. In addition, the Moran’s I statistics indicated clustering at small spatial lags for both seasons, suggesting similar snow depths (i.e., large-scale drifting) occurring at distances of 125 km. There was greater interannual variability in the clustering of snow during spring, compared to the winter season. These trends in snow depth were related to variability in seal pup survival; however, seal pup growth and body condition were not related to winter/spring snow conditions. The results from the RCM member runs suggest that snow will decrease by the end of this century, with a larger decrease occurring in the spring period. In addition, there will also be an increase in interannual and spatial variability during both seasons, which may have significant consequences to ringed seal population abundance through reduced pup survival within the study area.     

BACULAR AND TESTICULAR GROWTH AND ALLOMETRY IN THE CAPE FUR SEAL ARCTOCEPHALUS P. PUSILLUS (OTARIIDAE)

The baculum in Arctocephalus p. pusillus reaches up to 14.1 cm in length, 13.5 g in mass, and 1.3 g/cm in density (= mass/length). A pubertal growth spurt occurs between 2 and 3 yr of age, when bacular length increases by 28%, mass by 124%, and density by 77%; concurrently, body length increases by 14%. A second, weaker spurt occurs at social maturity (9-10 yr of age). Testes grow most rapidly between 1 and 2 yr of age, when testicular length increases by 29%. After 3 yr of age, growth in bacular and testicular length slows, and bacular mass continues to increase approximately linearly. Bacular and testicular lengths average 6.8% and 3.4% (respectively) of body length in adults, compared with 9.9% and 5.7% in the promiscuous harp seal ( Pagophilus groenlandicus ). Bacular length, mass, and density, and testicular length, are positively allometric to body length over growth; bacular length is isometric to testicular length. Among animals of the same age, bacular length and mass are positively allometric to body length in young animals, with negative allometry or isometry thereafter; testicular length is isometric to body length in young animals and negatively allometric thereafter. Patterns of early growth and allometry of the baculum and testes are interpreted as adaptations for mating opportunities, years before territoriality is possible. The baculum and testes of adult Cape fur seals and other otariids are small compared with those of most phocids, because sperm competition among male otariids is weak.     

DIGESTIBILITY OF CRUSTACEANS and CAPELIN IN HARP SEALS (PHOCA GROENLANDICA)

Gross energy intake (GEI), apparent digestible efficiency (%DE), and body-mass change were studied both in recently weaned and in subadult harp seals fed capelin ( Mallotus villosus ) and crustaceans ( Parathemisto libellula and Thysanoessa sp.) ad lib. The median %DE of Parathemisto libellula (with a wet-weight energy density (ED) of 3.9 kJ/g) and Thysanoessa sp. (ED: 2.3 kJ/g) was 81% and 83%, respectively, while the median %DE of capelin (ED: 8.6 kJ/g) was 94% and 93% for subadult harp seals and one harp seal pup, respectively. No correlation between age and %DE was obtained (P > 0.05). Despite ad lib. access to the food, the harp seal pups were unable to maintain body mass while on a crustacean diet, and it is therefore suggested that harp seal pups most likely must supplement their crustacean diets with fish to maintain growth.     

Pup mortality in southern elephant seals at Marion Island

Pre- and early post-weaning pup mortality of southern elephant seals (Mirounga leonina) at Marion Island from 1990 through 1999 ranged from 1.6% to 7.3% and averaged 3.8%. Mortality of pups after weaning before their first trip to sea accounted for only 12% of the total mortality. We found no relationship between population size and percentage pup mortality, indicating that pup survival is independent of seal density, at least at the densities of breeding seals that prevailed. Indeed, pup mortality was greatest in the smallest harems, apparently owing to a greater number of younger, less experienced mothers. Small harems were generally also found on less suitable beaches than larger harems and this could have contributed to pup injury as a cause of pup mortality on these beaches. Mother-pup separation and injury caused by beachmasters is likely to be responsible for pup mortality in the larger harems. The low rates of pup mortality observed in this study obviate it being a major population regulating agent at Marion Island.     

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.