Seal Prey Research Articles

Absence of predator control increases cod extirpation risk in a Northwest Atlantic ecosystem: inference from multispecies modelling

Atlantic cod Gadus morhua in the southern Gulf of St. Lawrence (sGSL) declined to low abundance in the early 1990s and have since failed to recover due to high natural mortality, which has been linked to predation by grey seals Halichoerus grypus. Increased grey seal harvests have been suggested to improve cod survival; however, predicting the response of cod to changes in seal abundance in the sGSL is complicated by a hypothesized triangular food web involving seals, cod, and small pelagic fishes, wherein the pelagic fishes are prey for cod and grey seals, but may also prey on young cod. Grey seals may therefore have an indirect positive effect on pre-recruit cod survival via predation on pelagic fish. Using a multispecies model of intermediate complexity fitted to various scientific and fisheries data, we found that seal predation accounted for the majority of recent cod mortality and that cod will likely be extirpated without a strong and rapid reduction in grey seal abundance. We did not find evidence that reducing grey seal abundance will impair cod recovery by causing large increases in pelagic biomass so long as pelagic fishing mortality continues at historical levels.

Estimating the risks of exposure to harmful algal toxins among Scottish harbour seals

Harmful algal bloom (HAB) toxins consumed by marine predators through fish prey can be lethal but studies on the resulting population consequences are lacking. Over the past approximately 20 years there have been large regional declines in some harbour seal populations around Scotland. Analyses of excreta (faeces and urine from live and dead seals and faecal samples from seal haulout sites) suggest widespread exposure to toxins through the ingestion of contaminated prey. A risk assessment model, incorporating concentrations of the two major HAB toxins found in seal prey around Scotland (domoic acid (DA), and saxitoxins (STX)), the seasonal persistence of the toxins in the fish and the foraging patterns of harbour seals were used to estimate the proportion of adults and juveniles likely to have ingested doses above various estimated toxicity thresholds. The results were highly dependent on toxin type, persistence, and foraging regime as well as age class, all of which affected the proportion of exposed animals exceeding toxicity thresholds. In this preliminary model STX exposure was unlikely to result in mortalities. Modelled DA exposure resulted in doses above an estimated lethal threshold of 1900 µg/kg body mass affecting up to 3.8 % of exposed juveniles and 5.3 % of exposed adults. Given the uncertainty in the model parameters and the limitations of the data these conclusions should be treated with caution, but they indicate that DA remains a potential factor involved in the regional declines of harbour seals. Similar risks may be experienced by other top predators, including small cetaceans and seabirds that feed on similar prey in Scottish waters.

First observations of Weddell seals foraging in sponges in Erebus Bay, Antarctica

Attaching cameras to marine mammals allows for first-hand observation of underwater behaviours that may otherwise go unseen. While studying the foraging behaviour of 26 lactating Weddell seals (Leptonychotes weddellii) in Erebus Bay during the austral spring of 2018 and 2019, we witnessed three adults and one pup investigating the cavities of Rossellidae glass sponges, with one seal visibly chewing when she removed her head from the sponge. To our knowledge, this is the first report of such behaviour. While the prey item was not identifiable, some Trematomus fish (a known Weddell seal prey) use glass sponges for shelter and in which to lay their eggs. Three of the four sponge foraging observations occurred around 13:00 (NZDT). Two of the three sponge foraging adults had higher-than-average reproductive rates, and the greatest number of previous pups of any seal in our study population, each having ten pups in 12 years. This is far higher than the study population average of three previous pups (± 2.6 SD). This novel foraging strategy may have evolved in response to changes in prey availability, and could offer an evolutionary advantage to some individuals that exploit prey resources that others may not. Our observations offer new insight into the foraging behaviours of one of the world’s most studied marine mammals. Further research on the social aspects of Weddell seal behaviour may increase our understanding of the extent and mechanisms of behavioural transfer between conspecifics. Research into the specific foraging behaviour of especially successful or experienced breeders is also warranted.

The influence of prey availability on behavioral decisions and reproductive success of a central-place forager during lactation

Marine central-place foragers are increasingly faced with altered prey landscapes, necessitating predictions of the impact of such changes on behavior, reproductive success, and population dynamics. We used state-dependent behavioral life history theory implemented via Stochastic Dynamic Programming (SDP) to explore the influence of changes in prey distribution and energy gain from foraging on the behavior and reproductive success of a central place forager during lactation. Our work is motivated by northern fur seals (Callorhinus ursinus) because of the ongoing population decline of the Eastern Pacific stock and projected declines in biomass of walleye pollock (Gadus chalcogrammus), a key fur seal prey species in the eastern Bering Sea. We also explored how changes in female and pup metabolic rates, body size, and lactation duration affected model output to provide insight into traits that might experience selective pressure in response to reductions in prey availability. Simulated females adopted a central-place foraging strategy after an initial extended period spent on land (4.7–8.3 days). Trip durations increased as the high energy prey patch moved farther from land or when the energy gain from foraging decreased. Increases in trip duration adversely affected pup growth rates and wean mass despite attempts to compensate by increasing land durations. Metabolic rate changes had the largest impacts on pup wean mass, with reductions in a pup’s metabolic rate allowing females to successfully forage at distances of 600+ km from land for up to 15+ days. Our results indicate that without physiological adaptations, a rookery is unlikely to be viable if the primary foraging grounds are 400 km or farther from the rookery. To achieve pup growth rates characteristic of a population experiencing rapid growth, model results indicate the primary foraging grounds need to be <150 km from the rookery.

Animal-borne video cameras reveal differences in northern fur seal foraging behavior related to prey size selection

A key aspect of foraging ecology research is understanding how predator foraging behavior and success are influenced by variation in prey resources. For northern fur seals (Callorhinus ursinus), an understanding of predator-prey relationships is critical to help identify potential causes for the unexplained population decline in Alaska. To examine how foraging behavior differs based on prey size selection, we equipped northern fur seals on St. Paul and St. George islands (Alaska, USA) in September (2017, n=6) and August (2018, n=4, and 2019, n=3) with satellite-linked dive recorders and animal-borne video cameras. We categorized prey capture attempts based on relative prey size (small vs. large) and examined differences in capture depth, time of day, water temperature, and depth relative to the mixed-layer. Successful prey captures (n= 2224) primarily occurred at night (89.7 ± 3.1%) and small prey accounted for the majority of captures (70.5 ± 13.2%), but there was significant variation among individuals. Large prey were captured at nearly twice the depth of small prey (42.9 ± 3.7 m and 23.1 ± 1.8 m, respectively) and the proportion of large prey caught during the day was 3 times higher than at night (0.77 ± 0.1 vs. 0.25 ± 0.1). There was no relationship between prey size and water temperature after we accounted for temperature changes with depth. The highest proportion of prey captures occurred below the mixed-layer depth regardless of prey size, but the proportion of small prey captures above mixed-layer depth was double that of large prey. This enhanced understanding of northern fur seal prey capture behavior will be pivotal for better interpretation of decades of historical dive and diet data and can provide insight into how northern fur seals may respond to future variation in prey resources, which is essential to develop ecosystem-based approaches for northern fur seal conservation.

Significance of autumn and winter food consumption for reproduction by Southern Beaufort Sea polar bears, Ursus maritimus

Polar bears (Ursus maritimus) in the southern Beaufort Sea experience long annual periods when preferred seal prey are scarce or are unavailable. Consumption of bowhead whale (Balaena mysticetus) carcasses from native Alaskan subsistence hunting is increasingly common for onshore polar bears, yet the energetic consequences of this consumption remain unclear. We use data on bears captured repeatedly over periods that encompassed autumn and winter, combined with calculations, to show that adult female bears likely consume an average of at least 4 seal equivalents during both autumn and winter periods and that considerable variation in energy intake exists across individual bears. We further show that subsistence-caught whale carcasses provide an upper threshold of > 4000 seal equivalents, which could potentially meet mean consumption needs of ~ 80% of the southern Beaufort Sea bear subpopulation during autumn and winter periods. Finally, we modify an existing model to show that observed mass changes over autumn and winter could substantially alter spring foraging habitat choice by females with cubs and the chance that a female with reduced energy reserves would abort a pregnancy or abandon cubs in favor of increasing her own survival; these behaviors could potentially influence population vital rates. Our study highlights the importance of mass dynamics over the autumn and winter months, points to the need for additional data on foraging and energetics over this period, and indicates that the recent declines in polar bear body condition in some subpopulations could have complex effects on reproduction.

Dietary ecology of Alaskan polar bears (Ursus maritimus) through time and in response to Arctic climate change.

Arctic climate change poses serious threats to polar bears (Ursus maritimus) as reduced sea ice makes seal prey inaccessible and marine ecosystems undergo bottom-up reorganization. Polar bears' elongated skulls and reduced molar dentition, as compared to their sister species the grizzly bear (Ursus arctos), are adaptations associated with hunting seals on sea ice and a soft, lipid-rich diet of blubber and meat. With significant declines in sea ice, it is unclear if and how polar bears may be altering their diets. Clarifying polar bear dietary responses to changing climates, both today and in the past, is critical to proper conservation and management of this apex predator. This is particularly important when a dietary strategy may be maladaptive. Here, we test the hypothesis that hard-food consumption (i.e., less preferred foods including bone), inferred from dental microwear texture analysis, increased with Arctic warming. We find that polar bears demonstrate a conserved absence of hard-object feeding in Alaska through time (including approximately 1000years ago), until the 21st century, consistent with a highly conserved and specialized diet of soft blubber and flesh. Notably, our results also suggest that some 21st-century polar bears may be consuming harder foods (e.g., increased carcass utilization, terrestrial foods including garbage), despite having skulls and metabolisms poorly suited for such a diet. Prior to the 21st century, only polar bears with larger mandibles demonstrated increased hard-object feeding, though to a much lower degree than closely related grizzly bears which regularly consume mechanically challenging foods. Polar bears, being morphologically specialized, have biomechanical constraints which may limit their ability to consume mechanically challenging diets, with dietary shifts occurring only under the most extreme scenarios. Collectively, the highly specialized diets and cranial morphology of polar bears may severely limit their ability to adapt to a warming Arctic.

Monitoring of the leopard seal population (Hydrurga leptonyx) in waters of the Argentine Islands (Ant-arctica)

The state of the leopard seal population (Hydrurga leptonyx Blainville, 1828) in waters of the Argentine Islands was studied during the periods April 2015 — March 2016 and April 2018 — March 2019 according to the objectives of the State Target Scientific and Technical Research Programme of Ukraine in Antarctica for the period 2011–2020. During the study period, 14 males and 16 females were recorded within the archipelago (1M : 1.1F ratio). About 7 % of the seals were young individuals and more than 90% were adults. Leopard seals were recorded during all periods of the year. In the summer-autumn period, within the archipelago, there were 2 to 4 individuals simultaneously. The maximum period of stay of the predators in waters of the archipelago was about two weeks. Two individuals for at least two weeks were recorded twice in waters of the archipelago. The maximum period of absence of the seals in waters of the archipelago was 118 days. It was found that the occurrence of leopard seals and hence the traces of their life activities in various years were of different nature. In the autumn (April–May) of 2015, they were seen less frequently, on average every 6.3 ± 2.5 days, and in the autumn of 2018, on the contrary, more frequently, on average every 2.5 ± 0.5 days. The activity of the leopard seal in the winter (June, August) of 2015 decreased by half. It was recorded that the animals appeared in waters of the archipelago on average every 12.7 ± 5.5 days, and in the winter of 2018 — 5.5 ± 1.9 days. In the autumn of 2018, the predators and traces of their vital activities were seen less often — every 6.6 ± 1.6 days. During the study period, out of 78 recorded cases of the leopard seal’s occurrence, about 56 % of cases were recorded when they were on ice floes, in other cases (44 %) — when they were in water. In addition, several crabeater seals were recorded three times on an ice floe at an insignificant distance from a leopard seal. One of the main prey items for leopard seals within the archipelago are birds, in particular the gentoo penguin (Pygoscelis papua), as well as crabeater seals (Lobodon carcinophagus). The presence of two penguin colonies on Galindez Island attracts leopard seals to the archipelago. During the study period, successful leopard seal predation on penguins was recorded more than 20 times. Penguins were the most frequent prey of leopard seals in spring and summer, while crabeater seals in winter.

Modelled mid‐trophic pelagic prey fields improve understanding of marine predator foraging behaviour

Biophysical interactions are influential in determining the scale of key ecological processes within marine ecosystems. For oceanic predators, this means foraging behaviour is influenced by processes shaping the distribution of prey. However, oceanic prey is difficult to observe and its abundance and distribution is regionally generalised. We use a spatiotemporally resolved simulation model to describe mid‐trophic prey distribution within the Southern Ocean and demonstrate insights that this modelled prey field provides into the foraging behaviour of a widely distributed marine predator, the southern elephant seal.From a five‐year simulation of prey biomass, we computed climatologies of mean prey biomass (average prey conditions) and prey biomass variability (meso‐scale variability). We also compiled spatially gridded metrics of seal density and diving behaviour from 13 yr of tracking data. We statistically modelled these metrics as non‐linear functions of prey biomass (both mean and variability) and used these to predict seal distribution and behaviour. Our predictions were consistent with observations (R2adj = 0.23), indicating that seals aggregate in regions of high mesoscale activity where eddies concentrate prey. Here, seals dived deeper (R2marg = 0.12, R2cond = 0.51) and spent less time hunting (R2marg = 0.05, R2cond = 0.56), likely targeting deep but profitable prey patches. Seals generally avoided areas of low eddy activity where prey was likely dispersed. Most seals foraged south of the Subantarctic Front, despite north of the front exhibiting consistently high simulated prey biomasses. This likely reflects seal prey or habitat preferences, but also emphasises the importance of mesoscale prey biomass variability relative to regionally high mean biomass. This work demonstrates the value of coupling mechanistic representations of prey biomass with predator observations to provide insight into how biophysical processes combine to shape species distributions. This will be increasingly important for the robust prediction of species’ responses to rapid system change.

Fatty acid-based diet estimates suggest ringed seal remain the main prey of southern Beaufort Sea polar bears despite recent use of onshore food resources.

Polar bears (Ursus maritimus) from the southern Beaufort Sea (SB) subpopulation have traditionally fed predominantly upon ice‐seals; however, as the proportion of the subpopulation using onshore habitat has recently increased, foraging on land‐based resources, including remains of subsistence‐harvested bowhead whales (Balaena mysticetus) and colonial nesting seabirds has been observed. Adipose tissue samples were collected from this subpopulation during the springs of 2013–2016 and analyzed for fatty acid signatures. Diet estimates were generated for the proportional consumption of ringed seal (Pusa hispida), bearded seal (Erignathus barbatus), and beluga whale (Delphinapterus leucas), relative to onshore foods, including bowhead whale remains and seabird, as represented by black guillemot (Cepphus grylle mandtii) nestlings and eggs. Quantitative fatty acid signature analysis (QFASA) estimated that the ice‐obligate prey, ringed seal, remained the predominant prey species of SB polar bears (46.4 ± 1.8%), with much lower consumption of bearded seal (19.6 ± 2.0%), seabird (17.0 ± 1.2%), bowhead whale (15.0 ± 1.4%), and hardly any beluga whale (2.0 ± 0.5%). Adult and subadult females appeared to depend more on the traditional ringed seal prey than adult and subadult males. Diet estimates of SB polar bears showed significant interannual variability for all prey (F 12, 456 = 3.17, p < .001). Longer‐term estimates suggested that both types of onshore prey, bowhead whale remains and seabird, have represented a moderate proportion of the food resources used by SB polar bears since at least the start of the 21st Century.

Environment-sensitive mass changes influence breeding frequency in a capital breeding marine top predator.

The trade-off between survival and reproduction in resource-limited iteroparous animals can result in some individuals missing some breeding opportunities. In practice, even with the best observation regimes, deciding whether 'missed' years represent real pauses in breeding or failures to detect breeding can be difficult, posing problems for the estimation of individual reproductive output and overall population fecundity. We corrected fecundity estimates by determining whether breeding had occurred in skipped years, using long-term capture-recapture observation datasets with parallel longitudinal mass measurements, based on informative underlying relationships between individuals' mass, breeding status and environmental drivers in a capital breeding phocid, the grey seal. Bayesian modelling considered interacting processes jointly: temporal changes in a phenotypic covariate (mass); relationship of mass to breeding probability; effects of maternal breeding state and mark type on resighting. Full reproductive histories were imputed, with the status of unobserved animals estimated as breeding or non-breeding, accounting for local environmental variation. Overall fecundity was then derived for Scottish breeding colonies with contrasting pup production trends. Maternal mass affected breeding likelihood. Mothers with low body mass at the end of breeding were less likely to bear a pup the following year. Successive breeding episodes incurred a cost in reduced body mass which was more pronounced for North Rona, Outer Hebrides (NR) mothers. Skipping breeding increased subsequent pupping probability substantially for low mass females. Poor environmental conditions were associated with declines in breeding probability at both colonies. Seal mass gain between breeding seasons was (a) negatively associated with lagged North Atlantic Oscillation for seals at NR and (b) positively associated with an index of seal prey (Ammodytes spp) abundance at Isle of May, Firth of Forth (IM). Overall fecundity was marginally greater at IM (increasing/stable pup production) than at NR (decreasing). No effects of mass were detected on maternal survival. Skipping breeding in female grey seals appears to be an individual mass-dependent constraint moderated by previous reproductive output and local environmental conditions. Different demographic trends at breeding colonies were consistent with the fecundities estimated using this method, which is general and adaptable to other situations.

Do marine reserves increase prey for California sea lions and Pacific harbor seals?

Community marine reserves are geographical areas closed to fishing activities, implemented and enforced by the same fishermen that fish around them. Their main objective is to recover commercial stocks of fish and invertebrates. While marine reserves have proven successful in many parts of the world, their success near important marine predator colonies, such as the California sea lion (Zalophus californianus) and the Pacific harbor seal (Phoca vitulina richardii), is yet to be analyzed. In response to the concerns expressed by local fishermen about the impact of the presence of pinnipeds on their communities’ marine reserves, we conducted underwater surveys around four islands in the Pacific west of the Baja California Peninsula: two without reserves (Todos Santos and San Roque); one with a recently established reserve (San Jeronimo); and, a fourth with reserves established eight years ago (Natividad). All these islands are subject to similar rates of exploitation by fishing cooperatives with exclusive rights. We estimated fish biomass and biodiversity in the seas around the islands, applying filters for potential California sea lion and harbor seal prey using known species from the literature. Generalized linear mixed models revealed that the age of the reserve has a significant positive effect on fish biomass, while the site (inside or outside of the reserve) did not, with a similar result found for the biomass of the prey of the California sea lion. Fish biodiversity was also higher around Natividad Island, while invertebrate biodiversity was higher around San Roque. These findings indicate that marine reserves increase overall fish diversity and biomass, despite the presence of top predators, even increasing the numbers of their potential prey. Community marine reserves may help to improve the resilience of marine mammals to climate-driven phenomena and maintain a healthy marine ecosystem for the benefit of both pinnipeds and fishermen.

Bioaccumulation and biomagnification of perfluoroalkyl acids and precursors in East Greenland polar bears and their ringed seal prey

The bioaccumulation and biomagnification of 22 major perfluoroalkyl substances (PFAS) were investigated in tissues of polar bears (Ursus maritimus) and their major prey species, the ringed seal (Pusa hispida), from the Scoresby Sound region of East Greenland. In polar bear liver the mean Σ4PFSA (perfluoroalkyl sulfonic acid) concentration (C4, C6, C8 and C10) was 2611 ± 202 ng/g wet weight (ww; 99% perfluorooctane sulfonate (PFOS)) and two orders of magnitude higher than the 20 ± 3 ng/g ww (89% PFOS) concentration in fat. The mean Σ4PFSAs in seal liver was 111 ± 5 ng/g ww (98% PFOS) and three orders of magnitude higher relative to the 0.05 ± 0.01 ng/g ww concentration in blubber (100% perfluorohexane sulfonate). Perfluoro-1-octane sulfonamide (FOSA) was quantifiable in bear (mean 10 ± 1.4 ng/g ww) and seal (mean 0.6 ± 0.1 ng/g ww) liver but not in fat or blubber. The mean Σ13PFCAs (C4–C18; perfluoroalkyl carboxylic acids) in bear liver (924 ± 71 ng/g ww) was much greater than in seal liver (74 ± 6 ng/g ww). In bear fat and seal blubber, the mean Σ13PFCAs were 15 ± 1.9 and 0.9 ± 0.1 ng/g ww, respectively. Longer chain C11 to C14 PFCAs dominated in bear fat and seal blubber (60–80% of Σ13PFCA), whereas shorter-chain C9 to C11 PFCAs dominated in the liver (85–90% of Σ13PFCA). Biomagnification factors (BMFs) were orders of magnitude greater for PFHxS and C9 to C13 PFCAs when based on bear liver to seal blubber rather than bear liver to seal liver, and PFCA (C9 to C13) BMFs decreased with increasing chain length. Seal blubber to bear liver BMFs better reflects the dietary exposure relationship of PFAS between bears and seals.

Structure-Dependent in Vitro Metabolism of Alkyl-Substituted Analogues of Triphenyl Phosphate in East Greenland Polar Bears and Ringed Seals

Organophosphate esters (OPEs), used as plasticizers and flame retardants, are major emerging environmental contaminants in the Arctic. OPEs of environmental interest include triphenyl phosphate (TPHP) and a growing array of alkyl-substituted TPHP analogues. Using a microsomal assay of the liver tissue of polar bears and their ringed seal prey, the comparative in vitro metabolism of TPHP was investigated relative to the analogues of isodecyl diphenyl phosphate (IDDPP), (p-tert-butylphenyl) diphenyl phosphate (TBPDPP), tris(p-tert-butylphenyl) phosphate (TTBPP), and two tris(isopropylphenyl) phosphate isomers (T2IPPP and T4IPPP). Polar bear metabolism of the p-tert-butylphenyl-substituted OPEs, TBPDPP and TTBPP, had a substantially slower rate and percent metabolic depletion compared to those with TPHP. Isodecyl- and isopropyl-substituted OPEs, IDDPP, T2IPPP, and T4IPPP, were also more slowly depleted by polar bears than TPHP was. TPHP, IDDPP, T2IPPP, TBPDPP, TTBPP, and T4IPPP were all slowly metabolized by...

Fish prey of Weddell seals, Leptonychotes weddellii, at Hope Bay, Antarctic Peninsula, during the late summer

The study of the feeding habits of Weddell seals, Leptonychotes weddellii, in the area of west Antarctic Peninsula is essential to understand the role they play in the marine food webs, especially considering that this is one of the regions most affected by climate change. With the aim of detecting temporal changes in the fish predation pattern of seals, a total of 217 scats were collected at Hope Bay, during three consecutive summers (2003, 2004 and 2005). The family Nototheniidae comprised over 80% in numbers of fish preyed by seals. The Antarctic silverfish, Pleuragramma antarctica, was, by far, the most frequent and abundant prey species with a mean percentage frequency of occurrence of 48.7% and representing in average 52.1% in numbers of the fish consumed by seals. Other fish species of lesser importance were the nototheniids Trematomus newnesi, Lepidonotothen larseni, Gobionotothen gibberifrons and the channichthyid Chionodraco rastrospinosus. Temporal variation was observed not only in the relative proportions of the different fish prey taxa but also in the sizes of the dominant prey, P. antarctica. Given the high trophic vulnerability of this species to changes in abiotic factors and food web structure and dynamics, a possible influence of El Nino Southern Oscillation events of 2002–2003 and 2004–2005 should not be discarded. Moreover, special attention should be addressed to its population status, distribution and spatial/temporal availability as prey resource of upper trophic level consumers such as L. weddellii which largely depend on P. antarctica.

Polar bears experience skeletal muscle atrophy in response to food deprivation and reduced activity in winter and summer.

When reducing activity and using stored energy during seasonal food shortages, animals risk degradation of skeletal muscles, although some species avoid or minimize the resulting atrophy while experiencing these conditions during hibernation. Polar bears may be food deprived and relatively inactive during winter (when pregnant females hibernate and hunting success declines for other demographic groups) as well as summer (when sea ice retreats from key foraging habitats). We investigated muscle atrophy in samples of biceps femoris collected from free-ranging polar bears in the Southern Beaufort Sea (SBS) throughout their annual cycle. Atrophy was most pronounced in April-May as a result of food deprivation during the previous winter, with muscles exhibiting reduced protein concentration, increased water content, and lower creatine kinase mRNA. These animals increased feeding and activity in spring (when seal prey becomes more available), initiating a period of muscle recovery. During the following ice melt of late summer, ~30% of SBS bears abandon retreating sea ice for land; in August, these 'shore' bears exhibited no muscle atrophy, indicating that they had fully recovered from winter food deprivation. These individuals subsequently scavenged whale carcasses deposited by humans and by October, had retained good muscle condition. In contrast, ~70% of SBS bears follow the ice north in late summer, into deep water with less prey. These 'ice' bears fast; by October, they exhibited muscle protein loss and rapid changes in myosin heavy-chain isoforms in response to reduced activity. These findings indicate that, unlike other bears during winter hibernation, polar bears without food in summer cannot mitigate atrophy. Consequently, prolonged summer fasting resulting from climate change-induced ice loss creates a risk of greater muscle atrophy and reduced abilities to travel and hunt.

Dietary analysis of harbour seals (Phoca vitulina) from faecal samples and overlap with fisheries in Erimo, Japan

AbstractThe number of harbour seals in Japan has been rebounding since protection began in the mid‐1980s. With the increase in seal numbers, increased conflict with fisheries has occurred through depredation and the belief that seals compete with fisheries for prey. However, competition can only be determined if the prey species and quantities seals consume over time are known. We studied the diet of harbour seals in Erimo, site of the largest population of harbour seals in Japan, from 2011 to 2012 and assessed the degree of prey overlap with local fisheries. We used both hard parts and DNA techniques to identify prey items in seal scats, and compared these results to local fisheries data. A total of 46 prey occurrences was detected by both methods, of which 17 matched between techniques at least to the family level. Hard parts methods identified five incidences of prey undetected by DNA methods in five scats (one incidence per scat). DNA methods identified 24 additional prey occurrences in 13 scats, for which no hard part evidence for that prey had been found. This more than doubled the total number of prey occurrences across the 15 scats compared. Overall, the most frequently occurring harbour seal prey were walleye pollock (Theragra chalcogramma), sculpins and snailfishes. In contrast, the top three groups targeted by fisheries were codfishes, salmon and invertebrates. Many species common in the harbour seal's diet such as snailfishes and blennies were not targeted by fisheries. Fishes such as greenlings, sculpins, rockfishes and Japanese anchovy (Engraulis japonicus) were common in the diet of harbour seals, but made up a very small proportion of fisheries catches in Erimo. The importance of other prey species varied between seasons. Sculpins, greenlings and forage fishes were the top three prey groups for harbour seals in spring by percent modified frequency of occurrence, whereas the most important target groups by percentage mass caught by fisheries were codfishes, cephalopods and other invertebrates. Sculpins and rockfishes remained as important prey items for harbour seals in summer and autumn, in addition to codfishes, snailfishes and blennies. In contrast, the main groups caught by fisheries in summer were other fishes, particularly Japanese amberjack (Seriola quinqueradiata) and various species of sharks and eels, and invertebrates. By autumn, Erimo fisheries had focussed on catching salmon. Salmon were taken by harbour seals as well during this period, but at a relatively lower frequency compared to other prey groups. The results of our study show that although harbour seals consumed several of the prey species targeted by fisheries, the relative importance of these species to seals and fisheries and the seasons in which they were targeted were different.

Dietary Composition of Four Stocks of Pacific Harbor Seal (Phoca vitulina richardii) In the Northern California Current Large Marine Ecosystem As Synthesized From Historical Data, 1931–2013

I conducted a literature review of Harbor Seal dietary composition within the northern California Current Large Marine Ecosystem (CCLME). Papers examining quantitative dietary information from stomach contents and fecal hard-part analyses were used to create a comprehensive list of Harbor Seal prey in the northern California Current System. The study regions included Washington, Oregon, and the Columbia River, and were divided by Harbor Seal stock. Fourteen papers from the years 1931 to 2013 were compiled to obtain a comprehensive and quantitative evaluation of Harbor Seal dietary composition. Harbor Seals consumed a seasonally and spatially-varied diet, including fish, invertebrates, mammals, and birds of 120 species or genera from 37 taxonomic orders and 62 families. The Hood Canal, Oregon-Washington Coastal, and Southern Puget Sound Stocks of Harbor Seals were well-represented. Salmonids were detected in 13.3% of samples collected in Oregon, 27.8% in Washington, and 23.74% of samples overall. The large variety of prey species and regional differences are reflective of opportunistic foraging behavior in Harbor Seals. This paper summarizes findings for this comprehensive assessment of Harbor Seal dietary composition in the northern CCLME.

Reconstruction of historical changes in northern fur seal prey availability and diversity in the western North Pacific through individual-based analysis of dietary records

We analyzed long-term dietary records of northern fur seals (Callorhinus ursinus) to reconstruct historical changes in prey availability and diversity in the western North Pacific off northeastern Japan. The nominal relationships between the occurrence frequencies of fishes or squids in fur seal stomachs and the sampling locations reflected the spatial heterogeneity of fish and squid distributions along the shelf–slope–offshore continuum off northeastern Japan, whereas changes in the temporal occurrence frequencies reflected mainly the migration and foraging patterns of the fur seals. The occurrence probabilities of fishes and squids in fur seal stomachs were standardized by using generalized linear models to compensate for sampling biases in space and time. The reconstructed historical trends revealed decadal shifts in relatively high prey abundance—from mackerels in the 1970s to Japanese sardine in the 1980s and myctophids/sparkling enope squids in the 1990s—that were related to decadal shifts in the oceanographic regime. The sequential increase in mackerel and Japanese sardine abundances coincided with the annual catch trends of commercial fisheries. The index of overall prey availability calculated from the standardized occurrence probabilities of fishes and squids in fur seal stomachs was fairly stable over the decades.

Individual-based energetic model suggests bottom up mechanisms for the impact of coastal hypoxia on Pacific harbor seal (Phoca vitulina richardii) foraging behavior

Wind-driven coastal hypoxia represents an environmental stressor that has the potential to drive redistribution of gilled marine organisms, and thereby indirectly affect the foraging characteristics of air-breathing upper trophic-level predators. We used a conceptual individual-based model to simulate effects of coastal hypoxia on the spatial foraging behavior and efficiency of a marine mammal, the Pacific harbor seal (Phoca vitulina richardii) on the Oregon coast. Habitat compression of fish was simulated at varying intensities of hypoxia. Modeled hypoxia affected up to 80% of the water column and half of prey species’ horizontal habitat. Pacific sand lance (Ammodytes hexapterus), Pacific herring (Clupea pallasii), and English sole (Parophrys vetulus) were selected as representative harbor seal prey species. Model outputs most affected by coastal hypoxia were seal travel distance to foraging sites, time spent at depth during foraging dives, and daily energy balance.For larger seals, English sole was the most optimal prey during normoxia, however during moderate to severe hypoxia Pacific sand lance was the most beneficial prey. For smaller seals, Pacific herring was the most efficient prey species during normoxia, but sand lance became more efficient as hypoxia increased. Sand lance represented the highest increase in foraging efficiency during severe hypoxic events for all seals. Results suggest that during increasing hypoxia, smaller adult harbor seals could benefit by shifting from foraging on larger neritic schooling fishes to foraging closer inshore on less energetically-dense forage fish. Larger adult seals may benefit by shifting from foraging on groundfish to smaller, schooling neritic fishes as hypoxia increases. The model suggests a mechanism by which hypoxia may result in increased foraging efficiency of Pacific harbor seals, and therefore increased rates of predation on coastal fishes on the continental shelf during hypoxic events.