St Paul Island Research Articles

Should I stay or should I go? Behavioral adjustments of fur seals related to foraging success

Abstract Understanding foraging strategies and decision-making processes of predators provide crucial insights into how they might respond to changes in prey availability and in their environment to maximize their net energy input. In this work, foraging strategies of Antarctic fur seals (Arctocephalus gazella, AFS) and Northern fur seals (Callorhinus ursinus, NFS) were studied to determine how they adjust their foraging behavior according to their past prey capture experiences. AFS on Kerguelen Islands are exclusively oceanic divers, while NFS population of St Paul Island shows both oceanic and neritic divers. We thus hypothesized that the two species would respond differently to a change in prey capture success depending on their foraging strategy. To test this, 40 females were equipped with tags that measured tri-axial acceleration, dive depth, and GPS coordinates, from which we derived prey capture attempts and behavioral metrics. Influence of prey capture success on horizontal and vertical movements of seals was investigated at different time scales: multi-dive, night, and trip. Both AFS and NFS traveled further during the day if they encountered low prey capture periods during the previous night. However, at the multi-dive scale, neritic NFS differed from oceanic NFS and AFS in terms of decision-making processes, e.g., both AFS and oceanic NFS dived deeper in response to low prey capture rate periods, while neritic NFS did not. Similarities in decision-making processes between NFS and AFS foraging on pelagic prey suggest that pelagic vs. neritic prey type is a key factor in defining foraging decisions of diving marine predators.

Discard mortality rates in the Bering Sea snow crab, Chionoecetes opilio, fishery

Abstract Fish and invertebrates that are unintentionally captured during commercial fishing operations and then released back into the ocean suffer mortality at unknown rates, introducing uncertainty into the fishery management process. Attempts have been made to quantify discard mortality rates using reflex action mortality predictors or RAMP which use the presence or absence of a suite of reflexes to predict discard mortality. This method was applied to snow crab, Chionoecetes opilio, during the 2010–2012 fisheries in the Bering Sea. Discard mortality in the fishery is currently assumed to be 50% in stock assessment models, but that rate is not based on empirical data and is widely recognized to be in need of refinement. Over 19 000 crab were evaluated using the RAMP method. The estimated discard mortality rate was 4.5% (s.d. = 0.812), significantly below the rate used in stock assessment models. Predicted discard mortality rates from the 2010 to 2012 study were strongly correlated with the air temperature at the St Paul Island airport in the Pribilof Islands. Using this relationship, the discard mortality rate from 1991 to 2011 was estimated at 4.8% (s.d. = 1.08).

Update on the prevalence of the hookworm, Uncinaria lucasi, in northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska, 2011

Prevalence of hookworms (Uncinaria lucasi Stiles, 1901) was determined in the northern fur seal (Callorhinus ursinus Linnaeus, 1758) on St. Paul Island (SPI), Alaska in July and August, 2011. Three of 61 (4.9%) dead pups harbored 1 to 13 adult hookworms each in their intestines. Parasitic larvae (L(3)) of hookworms were recovered from the blubber of 4 of 133 (3%) of subadult males (SAMs) examined. One parasitic L(3) was detected from each infected SAM. Adult U. lucasi (n = 3) were found in the intestine of 1 of 105 SAMs examined (0.95%). This is the first documented finding of adult U. lucasi in SAMs of the northern fur seals. Continued low prevalence of hookworms the last several years parallels the tremendous decline in the number of fur seals on SPI over a similar time period.

Stable isotope and scat analyses indicate diet and habitat partitioning in northern fur seals Callorhinus ursinus across the eastern Pacific

We used stable isotope (SI) and scat analyses to describe and compare the foraging eco- logy of northern fur seals Callorhinus ursinus from different rookeries throughout their North Amer- ican range, including rookeries on the following islands: Bogoslof Island (BI), Alaska; Reef and Vos- tochni on St. Paul Island (SPI), Alaska; and San Miguel Island (SMI), California. SI samples were collected from 36 adult females and 37 juveniles in Alaska, and 9 adult females and 7 pups on SMI during fall 2006. Isotopic analyses of blood and fur indicated differences in stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values within an individual, between age classes, and among locations. At all sites, adult females generally had higher δ 13 C compared to their younger conspecifics for all tissues, suggesting that they forage in different locations. Mean δ 15 N values of adult females were lower com- pared to those of pups at SMI, higher than those of juveniles on SPI, and similar to those of juveniles on BI, suggesting differences in trophic level between age classes at all locations except on BI. We found differences in δ 13 C values at all islands, suggesting that animals at each location forage in dif- ferent oceanic domains. The δ 15 N values of all age classes indicated that animals at SMI and Vos- tochni feed at similar trophic levels within their respective communities, but feed at higher trophic levels than animals at Reef and BI. Scat analysis supported SI results in that animals from each loca- tion were found to feed on species associated with unique oceanic features. By using scat and SI analyses, we were able to acquire a better understanding of the foraging ecology of different-aged conspecifics from multiple locations.

Speciation chronology of rockhopper penguins inferred from molecular, geological and palaeoceanographic data

AbstractAim The Southern Ocean is split into several biogeographical provinces between convergence zones that separate watermasses of different temperatures. Recent molecular phylogenies have uncovered a strong phylogeographic structure among rockhopper penguin populations, Eudyptes chrysocome sensu lato, from different biogeographical provinces. These studies suggested a reclassification as three species in two major clades, corresponding, respectively, to warm, subtropical and cold sub‐Antarctic watermasses rather than to geographic proximity. Such a phylogeographic pattern, also observed in plants, invertebrates and fishes of the Southern Ocean, suggests that past changes in the positions of watermasses may have affected the evolutionary history of penguins. We calculated divergence times among various rockhopper penguin clades and calibrated these data with palaeomagmatic and palaeoceanographic events to generate a speciation chronology in rockhopper penguins.Location Southern Ocean.Methods Divergence times between populations were calculated using five distinct mitochondrial DNA loci, and assuming a molecular clock model as implemented in mdiv. The molecular evolution rate of rockhopper penguins was calibrated using the radiochronological age of St Paul Island and Amsterdam Island in the southern Indian Ocean. Separations within other clades were correlated with palaeoceanographic data using this calibrated rate.Results The split between the Atlantic and Indian populations of rockhopper penguins was dated as 0.25 Ma, using the date of emergence of St Paul and Amsterdam islands, and the divergence between sub‐Antarctic and subtropical rockhopper penguins was dated as c. 0.9 Ma (i.e. during the mid‐Pleistocene transition, a major change in the Earth’s climate cycles).Main conclusions The mid‐Pleistocene transition is known to have caused a major southward shift in watermasses in the Southern Ocean, thus changing the environment around the northernmost rockhopper penguin breeding sites. This ecological isolation of northernmost populations may have caused vicariant speciation, splitting the species into two major clades. After the emergence of St Paul and Amsterdam islands in the subtropical Indian Ocean 0.25 Ma, these islands were colonized by penguins from the subtropical Atlantic, 6000 km away, rather than by penguins from the sub‐Antarctic Indian Ocean, 5000 km closer.

Hookworms (Uncinaria lucasi) and acanthocephalans (Corynosoma spp. and Bolbosoma spp.) found in dead northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska in 2007

Intestines of dead northern fur seals (Callorhinus ursinus) on St. Paul Island (SPI), Alaska were inspected for specific internal parasites (hookworms and acanthocephalans) in July and August, 2007. Pups (n=64) were examined for adult hookworms (Uncinaria lucasi) and four (6.25%) were infected. The number of specimens per infected pup was 1, 2, 2, or 408. Low prevalence was similar to that determined in the last investigation (2001) in dead fur seal pups on SPI by two of the present authors (Lyons and Spraker). Subadult males (SAMS-3-4 years old, n=115) were examined for acanthocephalans and 25 (21.7.0%) were infected. Adult Corynosoma (C. obtuscens, C. strumosum, and C. validum) (n=56) and immature Bolbosoma spp. (n=4) were found. Apparently, this is a new host record for C. obtuscens and C. validum. Notes were made on finding tapeworms. in 114 of the 115 SAMs. Examination of some specimens revealed scolices characteristic of Diphyllobothrium spp.

Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska

AbstractScats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul (n=2968) and St George Islands (n=1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO>5%) included Pacific sand lance Ammodytes hexapteus, Pacific herring Clupea pallasi, northern smoothtongue Leuroglossus schmidti, Atka mackerel Pleurogrammus monopterygius, Pacific salmon (Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south‐west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.

Mammoth cave yields most recent animals

© Douglas Veltre of the University of Alaska, Anchorage. In 1999, hunters on St Paul Island literally stumbled across the cave: a 12metre-deep pit in the Arctic tundra. Seeing a wealth of bones, they alerted university archaeologists Douglas Veltre and David Yesner. The team launched an expedition in 2003 to gather as much as they could from the sticky mud in the cave, which they named Qagnax, the native Aleut word for 'bone'.

Radiocarbon evidence of mid-Holocene mammoths stranded on an Alaskan Bering Sea island.

Island colonization and subsequent dwarfing of Pleistocene proboscideans is one of the more dramatic evolutionary and ecological occurrences, especially in situations where island populations survived end-Pleistocene extinctions whereas those on the nearby mainland did not. For example, Holocene mammoths have been dated from Wrangel Island in northern Russia. In most of these cases, few details are available about the dynamics of how island colonization and extinction occurred. As part of a large radiocarbon dating project of Alaskan mammoth fossils, I addressed this question by including mammoth specimens from Bering Sea islands known to have formed during the end-Pleistocene sea transgression. One date of 7,908 +/- 100 yr bp (radiocarbon years before present) established the presence of Holocene mammoths on St Paul Island, a first Holocene island record for the Americas. Four lines of evidence--265 accelerator mass spectrometer (AMS) radiocarbon dates from Alaskan mainland mammoths, 13 new dates from Alaskan island mammoths, recent reconstructions of bathymetric plots and sea transgression rates from the Bering Sea--made it possible to reconstruct how mammoths became stranded in the Pribilofs and why this apparently did not happen on other Alaskan Bering Sea islands.

Observations in 2001 on hookworms ( Uncinaria spp.) in otariid pinnipeds.

Uncinaria spp. were recovered from the milk of California sea lions ( Zalophus californianus) collected from the: (1) teats of a cow just after parturition (one parasitic third-stage larva, L(3)), (2) stomach of her nursing pup (two L(3)), and (3) stomach of a dead pup about 2 days old (one L(3), one headless, probably L(3), and four L(4)) on San Miguel Island, California in May 2001. This, in addition to earlier research, indicates transmammary transmission of hookworms in this host. Uncinaria spp. were found in dead northern fur seals ( Callorhinus ursinus) in the: (1) intestines of 2 of 75 pups (either one or two adult specimens in each infected pup) and (2) ventral abdominal blubber of 3 of 78 subadult males (one to seven L(3) in each infected seal) on St. Paul Island (SPI), Alaska in July and August 2001. These findings verify the low current prevalence of Uncinariaspp. in fur seals on SPI. Rectal fecal samples taken from 50 live Steller sea lion ( Eumetopias jubatus) pups, about 1 month old, on Rogue Reef in Curry County, Oregon in July 2001, were all negative for the eggs of Uncinaria spp. The apparent zero infection rate in these pups is possibly because the rocky terrain of this rookery is not suitable for hookworm transmission.

Mass mortality of short‐tailed shearwaters in the south‐eastern Bering Sea during summer 1997

During summer 1997, hundreds of thousands of emaciated short‐tailed shearwaters (Puffinus tenuirostris) died in the south‐eastern Bering Sea. Using strip transect methodology, we documented the distribution and abundance of short‐tailed shearwaters during cruises conducted prior to, during, and after the die‐off, as well as the distributions and abundances of floating carcasses. The distributions and abundances of short‐tailed shearwaters in 1997 were similar to those found during the 1970s and early 1980s. In August–September 1997, we observed 163 floating shearwater carcasses, most of which were between St Paul Island and Nunivak Island. We estimated ≈ 190 000 carcasses were afloat in the study area, about 11% of the surveyed population. Between spring (June) and autumn (August/September), mean net body mass of shearwaters decreased by 19%, mean pectoral muscle mass decreased by 14%, and mean percentage body lipid content decreased by 46%, from 15.6% in spring to 8.4% in autumn. Compared with spring, short‐tailed shearwater diets broadened in autumn 1997, to include, in addition to adult euphausiids Thysanoessa raschii, juveniles of T. inermis, T. raschii and T. spinifera, crab megalops, fish and squid. We discuss how the ecosystem anomalies in the south‐eastern Bering Sea during spring and summer 1997 relate to the mortality event and suggest possible implications of long‐term climate change for populations of apex predators in the south‐eastern Bering Sea.

Variation in groundfish predation on juvenile walleye pollock relative to hydrographic structure near the Pribilof Islands, Alaska

Walleye pollock (Theragra chalcogramma) are an important forage fish in the eastern Bering Sea ecosystem. As part of an ongoing study of the processes affecting juvenile walleye pollock recruitment in the eastern Bering Sea, a concentrated effort has been focused on the hydrographic fronts near the Pribilof Islands, Alaska, as important nursery areas for these juveniles. Diel variation in the consumption of age-0 pollock by arrowtooth flounder (Atherethes stomias) was examined from a series of collections at a station at the tidal front located north of St Paul Island, Alaska. Age-0 pollock were the primary prey of arrowtooth flounder throughout the day, but they were least digested in the late day, indicating a diurnal feeding pattern. A similar diurnal pattern was not seen in the vertical distribution of age-0 pollock, suggesting that the feeding pattern exhibited by arrowtooth flounder was based on their diel migratory behavior. Lengths of age-0 pollock consumed by arrowtooth flounder were similar to those sampled with midwater trawls. Walleye pollock cannibalism was examined along a transect that included samples collected at the front and offshore of the front. Age-0 fish were the primary prey (by weight) at all locations. Adjacent cohort cannibalism was prevalent (age-0 pollock were 79% of the diet by weight) at the frontal region. Estimates of age-0 pollock cannibalism rates were highest at the front for age-1 pollock and offshore for the adults. Prey selectivity analysis indicated that age-0 pollock were more highly selected offshore than at the front.

A drift experiment to assess the influence of wind on recovery of oiled seabirds on St Paul Island, Alaska

We used wooden blocks to estimate the proportion of oiled seabird carcasses that were likely to be recovered on beaches of St Paul Island, Alaska following a near-shore oil spill. We released a total of 302 blocks 6 km north of the island in 1997 at the site of a 17 II 1996 oil spill. We used a paired design and released half the blocks when the winds were onshore and released the second half when the winds were offshore. We systematically searched beaches after the second release to recover blocks. We recovered 93 of 152 (61%) blocks released when winds were onshore but only 1 of 150 (0.7%) blocks released when winds were offshore. Given that winds following the 1996 spill were offshore, we conclude that most birds killed at sea following the 1996 spill were likely not recovered on beaches.

Persistence rates and detection probabilities of oiled king eider carcasses on St Paul Island, Alaska

Following an oil spill off St Paul Island, Alaska in February 1996, persistence rates and detection probabilities of oiled king eider ( Somateria spectabilis) carcasses were estimated using the Cormack-Jolly-Seber model. Carcass persistence rates varied by day, beach type and sex, while detection probabilities varied by day and beach type. Scavenging, wave action and weather influenced carcass persistence. The patterns of persistence differed on rock and sand beaches and female carcasses had a different persistence function than males. Weather, primarily snow storms, and degree of carcass scavenging, diminished carcass detectability. Detection probabilities on rock beaches were lower and more variable than on sand beaches. The combination of persistence rates and detection probabilities can be used to improve techniques of estimating total mortality.

Natal site fidelity in northern fur seals, Callorhinus ursinus

More than 37 000 records of northern fur seals tagged at their natal areas and resighted during a recent mark-recapture study and past commercial harvests, were analysed to study the age and sex variation, and temporal dynamics of natal site fidelity in this highly polygynous, long-lived, migratory species. Data were available on males (2-6 years old) and females (2-20 years old). All ages and sex classes with sufficient sample sizes to allow statistical tests showed a significant tendency to return to the same area of the island where they were born. The proportion of young male and female seals found at their natal area during the breeding season increased significantly with age. Young females showed significantly greater age-specific natal site fidelity than young males (ages 2-6 years) and apparently exhibited their maximum site fidelity at a younger age than males. The increasing expression of natal site fidelity with age appears to be related to sexual maturation and reproductive activity, the latter beginning later in males than in females. Within a season, natal site fidelity of juvenile males increased with time since arrival on St Paul Island. This change in site fidelity implies that they may be less particular in selecting a landing site when they first arrive, then begin to orient more specifically towards their natal area. This behaviour may indicate a transition from a general homing goal while migrating (the island as a whole) to a more specific goal (the natal area) upon arrival.

Mass Changes of Least Auklets Aethia pusilla During the Breeding Season: Evidence for Programmed Loss of Mass

Patterns of seasonal variation in body mass by adult and sub-adult least auklets (Aethia pusilla, Pallas) were investigated at St Paul Island, Alaska using electronic balances to evaluate whether mass changes during the breeding season resulted from reproductive stress, or from a programmed response to increased flight demands during chick-rearing. Male and female auklets did not differ significantly either in mass or in the pattern of mass change. Sub-adults (2-year olds) were significantly lighter in mass than adults. Among adults, breeders that reached the chick provisioning stage were significantly heavier than failed breeders and non-breeders

The intrinsic rate of increase of reindeer and caribou populations in arctic environments

The intrinsic rate of increase of an animal population, rm, is specific to the environment in which it is measured. Previous estimates of maximum growth rates for reindeer and caribou Rangifer tarandus populations were based on introductions to islands with cool oceanic climates. The mean intrinsic rate of increase of 6 populations was 0.26 ranging from 0.21 on St Paul Island in the Bering Sea to 0.29 in the Barff herd on South Georgia. I calculated rm for two Rangifer populations introduced to arctic environments to determine the effect of environmental severity on the intrinsic rate of increase. Reindeer on the Belcher islands increased at rm= 0.28 and caribou on Southampton Island increased at rm = 0.23 (mean = 0.26). The lower primary productivity and longer duration of snow cover in arctic environments did not affect the intrinsic rate of increase.

Bone mineral and vitamin D in Aleutian Islanders

Serum concentrations of vitamin D metabolites (chromatography) and bone mineral status (125I absorptiometry) were examined in a group of Aleutian Islanders age 40-75 from St Paul Island, Alaska. Based on 25-(OH)D (16.6 ng/ml) vitamin D status appeared adequate. However, high concentrations of 1,25-(OH)2D (44.3 pg/ml) and very low concentrations of 24,25-(OH)2D3 (0.6 ng/ml) were found. Among females, low bone mineral levels were associated with high concentrations of 1,25-(OH)2D. A low calcium intake in these Aleutians may be responsible for high concentrations of 1,25-(OH)2D and resorption of calcium from bone.

A redescription of Uncinaria lucasi stiles, a hookworm of seals

In an earlier paper (1933) the writer drew attention to the inadequacy of the only existing description of Uncinaria lucasi, given, under the name of Uncinaria sp., by Stiles & Hassall (1899). Through the kindness of Dr E. C. Dougherty, it has now been possible to examine specimens of an Uncinaria from the type-host of U. lucasi (the Alaskan fur-seal, Callorhinus alascanus). These were collected by Dr V. B. Scheffer, of the United States Fish and Wildlife Service, from the small intestine of a furseal pup at Polovina, St Paul Island (Pribylov group), in the Bering Sea in July 1945. There seems to be no reasonable doubt that they are of the same species as those originally described by Stiles & Hassall, the principal evidence being the identity of the host and locality, and the length of the spicules of the male worms. A new description is therefore presented, which it is hoped will place the species on a more satisfactory footing.