53 research outputs found
Monitoring the behavior and multi-dimensional movements of Weddell seals using an animal-borne video and data recorder
We have developed an animal-borne video and data recorder to observe Weddell seals foraging and to reconstruct their three-dimensional movements. The video and data recorder consists of a low-light-sensitive video camera with near-infrared light-emitting diodes that is mounted on top of the seal\u27s head to obtain close-up images of the seal\u27s muzzle and the area in front of the animal. The main housing, which is mounted on the animal\u27s back, contains an 8-mm video tape recorder that can record for 6 h, batteries, a microcomputer and transducers for pressure, water speed, compass bearing, and flipper stroke frequency. Sound is recorded on one audio channel of the tape recorder with a hydrophone. Using these instruments, we have recorded over 500 h of underwater video and over 1000 three-dimensional dive paths with corresponding swimming performance data from 31 adult Weddell seals. We have documented seals foraging in the water column, on the sea floor, and at the under-ice surface. Mid-water foraging included encounters with large Antarctic toothfish and smaller Antarctic silverfish. Multivariate statistical analysis of variables derived from the temporal and spatial characteristics of three-dimensional dive paths have enabled us to classify dive types and, in some cases, assign a function such as foraging
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Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework
The endangered western stock of the Steller sea lion (Eumetopias jubatus) - the largest of the eared seals - has declined by 80% from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980's, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in the eastern Gulf of Alaska region. The framework also highlights the necessity for demographic models based on age-structured census data to incorporate the differential impact of predation on multiple vital rates
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In cold blood: evidence of Pacific sleeper shark (Somniosus pacificus) predation on Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska
Temperature data received post mortem in 2008–13 from 15 of 36 juvenile Steller sea lions (Eumetopias jubatus) that had been surgically implanted in 2005–11 with dual life history transmitters (LHX tags) indicated that all 15 animals died by predation. In 3 of those 15 cases, at least 1 of the 2 LHX tags was ingested by a cold-blooded predator, and those tags recorded, immediately after the sea lion’s death, temperatures that corresponded to deepwater values. These tags were regurgitated or passed 5–11 days later by predators. Once they sensed light and air, the tags commenced transmissions as they floated at the ocean surface, reporting temperatures that corresponded to regional sea-surface estimates. The circumstances related to the tag in a fourth case were ambiguous. In the remaining 11 cases, tags sensed light and air immediately after the sea lion’s death and reported temperatures that corresponded to estimates of regional sea-surface temperatures. In these 11 cases, circumstances did not allow for inferences on the species of predator. Among reported poikilotherm predators of Steller sea lions, only the Pacific sleeper shark (Somniosus pacificus) is known to have body core temperatures that are near ambient. The data from this study indicate that Pacific sleeper sharks need to be considered as a possible source of mortality of juvenile Steller sea lions in the region of the Gulf of Alaska
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Physiological and behavioral response to intra-abdominal transmitter implantation in Steller sea lions
The absence of a direct, long-term measure of individual Steller sea lion survival led to the development of implanted, delayed transmission satellite tags specifically for this species (Life History Transmitter, LHX). To assess possible effects of implant procedures and LHX tags, we undertook a two-stage approach to monitor: 1) immediate physiological response under controlled conditions in temporary captivity, and 2) post-release movement and dive behavior via externally mounted satellite data recorders (SDR). Six juvenile sea lions were monitored up to 8 weeks post-implant for physiological indications of post-surgical effects. Overall, mass, body condition and blood parameters did not change during the study period. There was limited white blood cell elevation and acute-phase reaction in the first 2 weeks post-implant. During the 3 months of post-release tracking, all sea lions returned to their respective capture haul-outs. Shorter and shallower dives during the first week post-release suggested a possible recovery period similar to other non-LHX individuals released from temporary captivity. For all subsequent weeks, dive depth, duration, frequency and dispersal distances of LHX animals were comparable to free-ranging individuals. All physiological and behavioral responses noted were temporary in nature, supporting LHX implantation as a viable alternative for long-term survival monitoring of free-ranging sea lions.Keywords: Dive behavior, Steller sea lion, Acute-phase reaction, Satellite telemetry, Eumetopias jubatus, Intra-abdominal implan
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The Effect of Novel Research Activities on Long-term Survival of Temporarily Captive Steller Sea Lions (Eumetopias jubatus)
Two novel research approaches were developed to facilitate controlled access to, and long-term monitoring of, juvenile Steller sea lions for periods longer than typically afforded by traditional fieldwork. The Transient Juvenile Steller sea lion Project at the Alaska SeaLife Center facilitated nutritional, physiological, and behavioral studies on the platform of temporary captivity. Temporarily captive sea lions (TJs, n = 35) were studied, and were intraperitoneally implanted with Life History Transmitters (LHX tags) to determine causes of mortality post-release. Our goal was to evaluate the potential for long-term impacts of temporary captivity and telemetry implants on the survival of study individuals. A simple open-population Cormack-Jolly-Seber mark-recapture model was built in program MARK, incorporating resightings of uniquely branded study individuals gathered by several contributing institutions. A priori models were developed to weigh the evidence of effects of experimental treatment on survival with covariates of sex, age, capture age, cohort, and age class. We compared survival of experimental treatment to a control group of n = 27 free-ranging animals (FRs) that were sampled during capture events and immediately released. Sex has previously been show to differentially affect juvenile survival in Steller sea lions. Therefore, sex was included in all models to account for unbalanced sex ratios within the experimental group. Considerable support was identified for the effects of sex, accounting for over 71% of total weight for all a priori models with delta AICc < 5, and over 91% of model weight after removal of pretending variables. Overall, most support was found for the most parsimonious model based on sex and excluding experimental treatment. Models including experimental treatment were not supported after post-hoc considerations of model selection criteria. However, given the limited sample size, alternate models including effects of experimental treatments remain possible and effects may yet become apparent in larger sample sizes
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Intraperitoneal implantation of life-long telemetry transmitters in otariids
Background: Pinnipeds, including many endangered and declining species, are inaccessible and
difficult to monitor for extended periods using externally attached telemetry devices that are shed
during the annual molt. Archival satellite transmitters were implanted intraperitoneally into four
rehabilitated California sea lions (Zalophus californianus) and 15 wild juvenile Steller sea lions
(Eumetopias jubatus) to determine the viability of this surgical technique for the deployment of long-term
telemetry devices in otariids. The life history transmitters record information throughout the
life of the host and transmit data to orbiting satellites after extrusion following death of the host.
Results: Surgeries were performed under isoflurane anesthesia and single (n = 4) or dual (n = 15)
transmitters were inserted into the ventrocaudal abdominal cavity via an 8.5 to 12 cm incision along
the ventral midline between the umbilicus and pubic symphysis or preputial opening. Surgeries
lasted 90 minutes (SD = 8) for the 19 sea lions. All animals recovered well and were released into
the wild after extended monitoring periods from 27 to 69 days at two captive animal facilities.
Minimum post-implant survival was determined via post-release tracking using externally attached
satellite transmitters or via opportunistic re-sighting for mean durations of 73.7 days (SE = 9.0, Z.
californianus) and 223.6 days (SE = 71.5, E. jubatus).
Conclusion: The low morbidity and zero mortality encountered during captive observation and
post-release tracking periods confirm the viability of this surgical technique for the implantation of
long-term telemetry devices in otariids
Muscular Apoptosis but Not Oxidative Stress Increases with Old Age in a Long-Lived Diver, the Weddell Seal
Seals experience repeated bouts of ischemia–reperfusion while diving, potentially exposing their tissues to increased oxidant generation and thus oxidative damage and accelerated aging. We contrasted markers of oxidative damage with antioxidant profiles across age and sex for propulsive (longissismus dorsi) and maneuvering (pectoralis) muscles of Weddell seals to determine whether previously observed morphological senescence is associated with oxidative stress. In longissismus dorsi, old (age 17–26 years) seals exhibited a nearly 2-fold increase in apoptosis over young (age 9–16 years) seals. There was no evidence of age-associated changes in lipid peroxidation or enzymatic antioxidant profiles. In pectoralis, 4-hydroxynonenal-Lys (4-HNE-Lys) levels increased 1.5-fold in old versus young seals, but lipid hydroperoxide levels and apoptotic index did not vary with age. Glutathione peroxidase activity was 1.5-fold higher in pectoralis of old versus young animals, but no other antioxidants changed with age in this muscle. With respect to sex, no differences in lipid hydroperoxides or apoptosis were observed in either muscle. Males had higher HSP70 expression (1.4-fold) and glutathione peroxidase activity (1.3-fold) than females in longissismus dorsi, although glutathione reductase activity was 1.4-fold higher in females. No antioxidants varied with sex in pectoralis. These results show that apoptosis is not associated with oxidative stress in aged Weddell seal muscles. Additionally, the data suggest that adult seals utilize sex-specific antioxidant strategies in longissismus dorsi but not pectoralis to protect skeletal muscles from oxidative damage
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Linking marine predator diving behavior to local prey fields in contrasting habitats in a subarctic glacial fjord
Foraging theory predicts that animals will
adjust their foraging behavior in order to maximize net
energy intake and that trade-offs may exist that can influence
their behavior. Although substantial advances have
been made with respect to the foraging ecology of large
marine predators, there is still a limited understanding of
how predators respond to temporal and spatial variability
in prey resources, primarily due to a lack of empirical
studies that quantify foraging and diving behavior concurrently
with characteristics of prey fields. Such information
is important because changes in prey availability can influence
the foraging success and ultimately fitness of marine
predators. We assessed the diving behavior of juvenile
female harbor seals (Phoca vitulina richardii) and prey
fields near glacial ice and terrestrial haulout sites in Glacier
Bay (58°40′N, −136°05′W), Alaska. Harbor seals captured
at glacial ice sites dived deeper, had longer dive durations, lower percent bottom time, and generally traveled further to
forage. The increased diving effort for seals from the glacial
ice site corresponded to lower prey densities and prey
at deeper depths at the glacial ice site. In contrast, seals
captured at terrestrial sites dived shallower, had shorter
dive durations, higher percent bottom time, and traveled
shorter distances to access foraging areas with much higher
prey densities at shallower depths. The increased diving
effort for seals from glacial ice sites suggests that the lower
relative availability of prey may be offset by other factors,
such as the stability of the glacial ice as a resting platform
and as a refuge from predation. We provide evidence of differences
in prey accessibility for seals associated with glacial
ice and terrestrial habitats and suggest that seals may
balance trade-offs between the costs and benefits of using
these habitats
Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework
The endangered western stock of the Steller sea lion (Eumetopias jubatus) – the largest of the eared seals – has declined by 80% from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980's, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in the eastern Gulf of Alaska region. The framework also highlights the necessity for demographic models based on age-structured census data to incorporate the differential impact of predation on multiple vital rates
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