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Anthony S. Fischbach

Publications and source records attributed to Anthony S. Fischbach.

33 records · Page 2Linked to original sources
USGS2015

Rapid maturation of the muscle biochemistry that supports diving in Pacific walruses ( Odobenus rosmarus divergens )

Physiological constraints dictate animals’ ability to exploit habitats. For marine mammals, it is important to quantify physiological limits that influence diving and their ability to alter foraging behaviors. We characterized age-specific dive limits of walruses by measuring anaerobic (acid-buffering capacity) and aerobic (myoglobin content) capacities of the muscles that power hind (longissimus dorsi) and fore (supraspinatus) flipper propulsion. Mean buffering capacities were similar across muscles and age classes (a fetus, five neonatal calves, a 3 month old and 20 adults), ranging from 41.31 to 54.14 slykes and 42.00 to 46.93 slykes in the longissimus and supraspinatus, respectively. Mean myoglobin in the fetus and neonatal calves fell within a narrow range (longissimus: 0.92–1.68 g 100 g −1 wet muscle mass; supraspinatus: 0.88–1.64 g 100 g −1 wet muscle mass). By 3 months post-partum, myoglobin in the longissimus increased by 79%, but levels in the supraspinatus remained unaltered. From 3 months post-partum to adulthood, myoglobin increased by an additional 26% in the longissimus and increased by 126% in the supraspinatus; myoglobin remained greater in the longissimus compared with the supraspinatus. Walruses are unique among marine mammals because they are born with a mature muscle acid-buffering capacity and attain mature myoglobin content early in life. Despite rapid physiological development, small body size limits the diving capacity of immature walruses and extreme sexual dimorphism reduces the diving capacity of adult females compared with adult males. Thus, free-ranging immature walruses likely exhibit the shortest foraging dives while adult males are capable of the longest foraging dives.

Journal of Experimental Biology↗
USGS2014

Pacific walrus ( Odobenus rosmarus divergens ) resource selection in the northern Bering Sea

The Pacific walrus is a large benthivore with an annual range extending across the continental shelves of the Bering and Chukchi Seas. We used a discrete choice model to estimate site selection by adult radio-tagged walruses relative to the availability of the caloric biomass of benthic infauna and sea ice concentration in a prominent walrus wintering area in the northern Bering Sea (St. Lawrence Island polynya) in 2006, 2008, and 2009. At least 60% of the total caloric biomass of dominant macroinfauna in the study area was composed of members of the bivalve families Nuculidae, Tellinidae, and Nuculanidae. Model estimates indicated walrus site selection was related most strongly to tellinid bivalve caloric biomass distribution and that walruses selected lower ice concentrations from the mostly high ice concentrations that were available to them (quartiles: 76%, 93%, and 99%). Areas with high average predicted walrus site selection generally coincided with areas of high organic carbon input identified in other studies. Projected decreases in sea ice in the St. Lawrence Island polynya and the potential for a concomitant decline of bivalves in the region could result in a northward shift in the wintering grounds of walruses in the northern Bering Sea.

PLoS ONE↗
USGS2012

Spatial genetic structure and asymmetrical gene flow within the Pacific walrus

Pacific walruses ( Odobenus rosmarus divergens ) occupying shelf waters of Pacific Arctic seas migrate during spring and summer from 3 breeding areas in the Bering Sea to form sexually segregated nonbreeding aggregations. We assessed genetic relationships among 2 putative breeding populations and 6 nonbreeding aggregations. Analyses of mitochondrial DNA (mtDNA) control region sequence data suggest that males are distinct among breeding populations (Φ ST =0.051), and between the eastern Chukchi and other nonbreeding aggregations (Φ ST =0.336–0.449). Nonbreeding female aggregations were genetically distinct across marker types (microsatellite F ST =0.019; mtDNA Φ ST =0.313), as was eastern Chukchi and all other nonbreeding aggregations (microsatellite F ST =0.019–0.035; mtDNA Φ ST =0.386–0.389). Gene flow estimates are asymmetrical from St. Lawrence Island into the southeastern Bering breeding population for both sexes. Partitioning of haplotype frequencies among breeding populations suggests that individuals exhibit some degree of philopatry, although weak. High levels of genetic differentiation among eastern Chukchi and all other nonbreeding aggregations, but considerably lower genetic differentiation between breeding populations, suggest that at least 1 genetically distinct breeding population remained unsampled. Limited genetic structure at microsatellite loci between assayed breeding areas can emerge from several processes, including male-mediated gene flow, or population admixture following a decrease in census size (i.e., due to commercial harvest during 1880–1950s) and subsequent recovery. Nevertheless, high levels of genetic diversity in the Pacific walrus, which withstood prolonged decreases in census numbers with little impact on neutral genetic diversity, may reflect resiliency in the face of past environmental challenges.

Journal of Mammalogy↗
USGS2012

Walrus areas of use in the Chukchi Sea during sparse sea ice cover

The Pacific walrus Odobenus rosmarus divergens feeds on benthic invertebrates on the continental shelf of the Chukchi and Bering Seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase further in frequency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea from June to November of 2008 to 2011, years when sea ice was sparse over the continental shelf in comparison to historical records. The earlier and more extensive sea ice retreat in June to September, and delayed freeze-up of sea ice in October to November, created conditions for walruses to arrive earlier and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf from September to October caused walruses to forage in nearshore areas instead of offshore areas as in the past. Walruses did not frequent the deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occupied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and southwestern Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently depauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.

Alaska;Chukotka↗
USGS2012

Walrus distributional and foraging response to changing ice and benthic conditions in the Chukchi Sea

Arctic species such as the Pacific walrus ( Odobenus rosmarus divergens ) are facing a rapidly changing environment. Walruses are benthic foragers and may shift their spatial patterns of foraging in response to changes in prey distribution. We used data from satellite radio-tags attached to walruses in 2009-2010 to map walrus foraging locations with concurrent sampling of benthic infauna to examine relationships between distributions of dominant walrus prey and spatial patterns of walrus foraging. Walrus foraging was concentrated offshore in the NE Chukchi Sea, and coastal areas of northwestern Alaska when sea ice was sparse. Walrus foraging areas in August-September were coincident with the biomass of two dominant bivalve taxa (Tellinidae and Nuculidae) and sipunculid worms. Walrusforaging costs associated with increased travel time to higher biomass food patches from land may be significantly higher than the costs from sea ice haul-outs and result in reduced energy storesin walruses. Identifying what resources are selected by walruses and how those resources are distributed in space and time will improve our ability to forecast how walruses might respond to a changing climate.

Chukchi Sea↗
USGS2010

Molecular method for determining sex of walruses

We evaluated the ability of a set of published trans-species molecular sexing primers and a set of walrus-specific primers, which we developed, to accurately identify sex of 235 Pacific walruses (Odobenus rosmarus divergens). The trans-species primers were developed for mammals and targeted the X- and Y-gametologs of the zinc finger protein genes (ZFX, ZFY). We extended this method by using these primers to obtain sequence from Pacific and Atlantic walrus (0. r. rosmarus) ZFX and ZFY genes to develop new walrus-specific primers, which yield polymerase chain reaction products of distinct lengths (327 and 288 base pairs from the X- and Y-chromosome, respectively), allowing them to be used for sex determination. Both methods yielded a determination of sex in all but 1-2% of samples with an accuracy of 99.6-100%. Our walrus-specific primers offer the advantage of small fragment size and facile application to automated electrophoresis and visualization.

Journal of Wildlife Management↗
USGS2010

Results and evaluation of a survey to estimate Pacific walrus population size, 2006

In spring 2006, we conducted a collaborative U.S.-Russia survey to estimate abundance of the Pacific walrus ( Odobenus rosmarus divergens ). The Bering Sea was partitioned into survey blocks, and a systematic random sample of transects within a subset of the blocks was surveyed with airborne thermal scanners using standard strip-transect methodology. Counts of walruses in photographed groups were used to model the relation between thermal signatures and the number of walruses in groups, which was used to estimate the number of walruses in groups that were detected by the scanner but not photographed. We also modeled the probability of thermally detecting various-sized walrus groups to estimate the number of walruses in groups undetected by the scanner. We used data from radio-tagged walruses to adjust on-ice estimates to account for walruses in the water during the survey. The estimated area of available habitat averaged 668,000 km 2 and the area of surveyed blocks was 318,204 km 2 . The number of Pacific walruses within the surveyed area was estimated at 129,000 with 95% confidence limits of 55,000 to 507,000 individuals. This value can be used by managers as a minimum estimate of the total population size.

Bering Sea↗
USGS2010

Catalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort Sea and neighboring regions, Alaska, 1910–2010

This report presents data on the approximate locations and methods of discovery of 392 polar bear ( Ursus maritimus ) maternal dens found in the Beaufort Sea and neighboring regions between 1910 and 2010 that are archived by the U.S. Geological Survey, Alaska Science Center, Anchorage, Alaska. A description of data collection methods, biases associated with collection method, primary time periods, and spatial resolution are provided. Polar bears in the Beaufort Sea and nearby regions den on both the sea ice and on land. Standardized VHF surveys and satellite radio telemetry data provide a general understanding of where polar bears have denned in this region over the past 3 decades. Den observations made during other research activities and anecdotal reports from other government agencies, coastal residents, and industry personnel also are reported. Data on past polar bear maternal den locations are provided to inform the public and to provide information for natural resource agencies in planning activities to avoid or minimize interference with polar bear maternity dens.

Alaska↗
USGS2010

Divergent movements of walrus and sea ice in the northern Bering Sea

The Pacific walrus Odobenus rosmarus divergens is a large Arctic pinniped of the Chukchi and Bering Seas. Reductions of sea ice projected to occur in the Arctic by mid-century raise concerns for conservation of the Pacific walrus. To understand the significance of sea ice loss to the viability of walruses, it would be useful to better understand the spatial associations between the movements of sea ice and walruses. We investigated whether local-scale (~1 to 100 km) walrus movements correspond to movements of sea ice in the Bering Sea in early spring, using locations from radio-tracked walruses and measures of ice floe movements from processed synthetic aperture radar satellite imagery. We used generalized linear mixed-effects models to analyze the angle between walrus and ice floe movement vectors and the distance between the final geographic position of walruses and their associated ice floes (displacement), as functions of observation duration, proportion of time the walrus was in water, and geographic region. Analyses were based on 121 walrus-ice vector pairs and observations lasting 12 to 36 h. Angles and displacements increased with observation duration, proportion of time the walrus spent in the water, and varied among regions (regional mean angles ranged from 40° to 81° and mean displacements ranged from 15 to 35 km). Our results indicated a lack of correspondence between walruses and their initially associated ice floes, suggesting that local areas of walrus activities were independent of the movement of ice floes.

Marine Ecology Progress Series↗
USGS2009

Enumeration of Pacific walrus carcasses on beaches of the Chukchi Sea in Alaska following a mortality event, September 2009

On September 14, 2009, we encountered substantial numbers of fresh walrus carcasses on the Alaskan shores of the Chukchi Sea near Icy Cape. We enumerated 131 carcasses using geo-referenced strip transect photography and visual counts of solitary carcasses. All appeared to be young animals based on review of aerial photographs and reference to 12 carcasses that we examined on the ground. The events that led to the death of these animals are unknown, but appear to be related to the loss of sea ice over the Chukchi Sea continental shelf. In years prior to this event, other investigators have linked walrus deaths at other Chukchi Sea coastal haulouts to trampling, exhaustion from prolonged exposure to open sea conditions, and separation of calves from their mothers.

Open-File Report↗
USGS2008

Pacific Walrus Response to Arctic Sea Ice Losses

Sea ice plays an important role in the life of the Pacific walrus (Odobenus rosmarus divergens). U.S. Geological Survey (USGS) scientists are seeking to understand how losses of sea ice during summer over important foraging grounds in the Chukchi Sea will affect walruses. USGS scientists recently modified a remotely deployed satellite radio-tag that will aid in studying walrus foraging habitats and behaviors. Information from the tags will help USGS understand how walruses are responding to their changing environment.

Fact Sheet↗
USGS2006

Genetic characterization of brown bears of the Kodiak Archipelago

Here we examine genetic characteristics of brown bears of Kodiak and Afognak islands, using 14 variable nuclear microsatellite loci and nucleotide sequence information including the hypervariable domain I of the mtDNA control region (Wakely 1993). Because these markers, or a subset of them, have been used to characterize brown bears of the Kenai Peninsula (Jackson et al. 2005), Katmai National Park, Seward Peninsula, and nine other populations in Alaska (Talbot, unpublished data), we compared levels of genetic diversity and relationships among populations when possible. In addition, we obtained preliminary comparative information from class II DQA and DQB genes of the brown bear MHC, to examine levels of variation at this important immunology-mediating supergene. These data were used to answer the following questions: 1) are earlier findings of extremely low levels of variability at nuclear (biparentallyinherited) microsatellite loci from a small geographic area (Paetkau et al. 1998b) representative of Kodiak Archipelago populations as a whole? 2) Is the level and type of variation at the maternally-inherited mtDNA lower, or similar to, levels found in other populations in Alaska? 3) Is there concordance between low levels of genetic variation observed at neutral markers with levels of variation observed at functional genes? 4) Is there population substructuring within Kodiak and Afognak islands? 5) What is the connectivity between populations on Afognak Island and Kodiak Island? 6) What are the phylogeographic relationships between bears of the Kodiak Archipelago with brown bears on mainland Alaskan and other western Beringian populations? We also test whether these markers will provide an appropriate baseline for designing genetic tagging studies for use in future research and management activities, such as mark-recapture efforts, on the Refuge.

Alaska↗
USGS2002

The polar bear management agreement for the southern Beaufort Sea: An evaluation of the first ten years of a unique conservation agreement

Polar bears ( Ursus maritimus ) of the southern Beaufort Sea population, distributed from approximately Icy Cape, west of Point Barrow, to Pearce Point, east of Paulatuk in Canada, are harvested by hunters from both countries. In Canada, quotas to control polar bear hunting have been in place, with periodic modifications, since 1968. In Alaska, passage of the United State Marine Mammal Protection Act (MMPA) of 1972 banned polar bear hunting unless done by Alaska Natives for subsistence. However, the MMPA placed no restrictions on numbers or composition of the subsistence hunt, leaving open the potential for an overharvest with no possible legal management response until the population was declared depleted. Recognizing that as a threat to the conservation of the shared polar bear population, the Inuvialuit Game Council from Canada and the North Slop Borough from Alaska negotiated and signed a user-to-user agreement, the Polar Bear Management Agreement for the Southern Beaufort Sea, in 1988. We reviewed the functioning of the agreement through its first 10 years and concluded that, overall, it has been successful because both the total harvest and the proportion of females in the harvest have been contained within sustainable limits. However, harvest monitoring needs to be improved in Alaska, and awareness of the need to prevent overharvest of females needs to be increased in both countries. This agreement is a useful model for other user-to-user conservation agreements.

Beaufort Sea↗
USGS2002

Polar bear management in Alaska 1997-2000

Since the Twelfth Working Meeting of the IUCN/SSC Polar Bear Specialist Group in 1997, a number of changes in the management of polar bears have occurred in Alaska. On October 16, 2000, the governments of the United States and the Russian Federation signed the “Agreement on the Conservation and Management of the Alaska-Chukotka Polar Bear Population.” This agreement provides substantial benefits for the effective conservation of polar bears shared between the U.S. and Russia. It will require enactment of enabling legislation by the U.S. Congress and other steps by Russia before the agreement has the force of law. A copy of the agreement is included as Appendix 1 to this report. Also, during this period, regulations were developed to implement 1994 amendments to the Marine Mammal Protection Act (MMPA), which allow polar bear trophies taken in approved Canadian populations by U.S. citizens to be imported into the U.S. A summary of the regulatory actions and a table listing populations approved for importation and the number of polar bears imported into the U.S. since 1997 is included in this report. Regarding oil and gas activities in polar bear habitat, three sets of regulations were published authorizing the incidental, non-intentional, taking of small numbers of polar bears concurrent to oil and gas activities. Cooperation continued with the Alaska Nanuuq Commission, representing the polar bear hunting communities in Alaska, as well as with the North Slope Borough and the Inuvialuit Game Council in their agreement for the management of the Southern Beaufort Sea polar bear population. Harvest summaries and technical assistance in designing and assistance in conducting a National Park Service/Alaska Nanuuq Commission study to collect traditional ecological knowledge of polar bear habitat use in Chukotka were provided. In addition, a long-range plan was developed to address and minimize polar bear-human conflicts in North Slope communities. We continued to monitor the harvest of polar bears in Alaska and collect and analyze specimens for presence and level of organochlorine compounds and trace elements. A paper on genetic assessment of hunter reported sex of harvested bears was recently published (Schliebe et al. 1999). Population status and trend assessment efforts continued. An aerial survey of polar bears in the Eastern Chukchi Sea and western portions of the Southern Beaufort Sea was conducted from the U.S. Coast Guard icebreaker “Polar Star” in August 2000. The first year of a multi-year survey of barrier islands and coastlines during the open water and freeze-up phase was conducted in the central Southern Beaufort Sea during fall 2000.

Alaska↗