Markus Horning | Oregon State University (original) (raw)

Papers by Markus Horning

Electronic telemetry devices have enabled many novel and important data collection and experiment... more Electronic telemetry devices have enabled many novel and important data collection and experimental opportunities for difficult to observe species. Externally attached devices have limited retention and may affect thermoregulation, energetics, social and reproductive behavior, visibility, predation risk and entanglement. Internally placed, surgically implanted devices can mitigate some of these effects and may open additional experimental opportunities. How‑ ever, improper implementation can significantly affect animals and data. From a review of recent studies using fully implanted tags and studying their effects, we present 15 specific best practice recommendations for the use of such tags in pinnipeds. Recommendations address issues including device size, coating and sterilization, implantation surgery and effect assessment, within the framework of the Three R's: Reduction, Refinement, Replacement. While devel‑ oped for pinnipeds, these recommendations could apply to other aquatic mammals and vertebrates and to partially implanted or even external tags.

It is a golden age for animal movement studies and so an opportune time... more It

golden

age

for

animal

movement

studies

and

opportune

time

to
assess

priorities

for

future

work.

assembled

experts

identify

key
questions

this

ﬁeld,

focussing

marine

megafauna,

which

include

broad
range

birds,

mammals,

reptiles,

and

ﬁsh.

Research

these

taxa

has

both
underpinned

many

the

recent

technical

developments

and

led

fundamental
discoveries

the

ﬁeld.

show

that

the

questions

have

broad

applicability

to
other

taxa,

including

terrestrial

animals,

ﬂying

insects,

and

swimming

inverte
brates,

and,

such,

this

exercise

provides

useful

roadmap

for

targeted
deployments

and

data

syntheses

that

should

advance

the

ﬁeld

movement
ecology

A B S T R A C T Wind-driven coastal hypoxia represents an environmental stressor that has the pot... more A B S T R A C T 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.

Background: Pinnipeds, including many phocid species of concern, are inaccessible and difficult t... more Background: Pinnipeds, including many phocid species of concern, are inaccessible and difficult to monitor for extended periods using conventional, externally attached telemetry devices that are shed during the annual molt. Archival satellite transmitters were implanted intraperitoneally into three stranded Pacific harbor seal pups (Phoca vitulina richardii) that completed rehabilitation, to evaluate the viability of this surgical technique for the deployment of life long telemetry devices in phocids. The life history transmitters record information throughout the life of the host and transmit data to orbiting satellites after extrusion following death. Results: Surgeries were performed under general anesthesia and a single transmitter was inserted into the ventrocaudal abdominal cavity via a 7–8 cm incision along the ventral midline between the umbilicus and pubic symphysis or preputial opening in each animal. Surgeries lasted from 45 to 51 min, and anesthesic times ranged from 55 to 79 min. All animals recovered well, were released into dry holding pens overnight, and were given access to water the following day. All three animals exhibited an expected inflammatory response, with acute phase responses lasting approximately three to four weeks. All three animals were tracked via externally attached satellite transmitters after release at 58 to 78 days following surgery, and minimum post-release survival was confirmed through continued movement data received over 278 to 289 days. Conclusion: The initial findings of low morbidity and zero mortality encountered during captive observation and post-release tracking periods support the viability of this surgical technique for the implantation of long-term telemetry devices in phocids.

Background: There is a variety of evidence that increased anthropogenic noise (e.g., shipping, ex... more Background: There is a variety of evidence that increased anthropogenic noise (e.g., shipping, explosions, sonar) has a measureable effect on marine mammal species. Observed impacts range in severity from brief interruptions of basic life functions to physiological changes, acute injury, and even death. New research tools are needed to better measure and understand the potential effects of anthropogenic noise on marine mammals. Current behavioral response studies typically utilize ship-based sound sources to study potential acute behavioral responses in tagged animals experimentally exposed to noise. Integrating the sound source within animal-mounted passive acoustic and motion-sensing tags provides a novel tool for conducting additional highly controlled response studies. Results: We developed and conducted pilot field trials of a prototype tag on five juvenile northern elephant seals, Mirounga angustirostris, using experimental exposures to both natural and anthropogenic noise stimuli. Results indicate behavioral responses were elicited in tagged individuals. However, no pattern was found in the occurrence and types of response compared to stimulus type. Responses during the ascending dive phase consisted of a dive inversion, or sustained reversal from ascending to descending (8 of 9 exposures). Dive inversions following exposure were 4–11 times larger than non-exposure inversions. Exposures received during the descending dive phase resulted in increased descent rates in 9 of 10 exposures. All 8 exposures during dives in which maximum dive depth was limited by bathymetry were characterized by increased flow noise in the audio recordings following exposure, indicating increased swim speed. Conclusions: Results of this study demonstrate the ability of an animal-mounted sound source to elicit behavioral responses in free-ranging individuals. Behavioral responses varied by seal, dive state at time of exposure, and bathym-etry, but followed an overall trend of diving deeper and steeper and swimming faster. Responses did not consistently differ based on stimulus type, which may be attributable to the unique exposure context of the very close proximity of the sound source. Further technological development and focused field efforts are needed to advance and apply these tools and methods in subsequent behavioral response studies to address specific questions.

Background: Accurate estimates of thermoregulatory costs in air and water are necessary to predic... more Background: Accurate estimates of thermoregulatory costs in air and water are necessary to predict the impacts of
changing habitats to individuals and populations of ice-obligate seals. Investigations that would provide such estimates
of thermoregulatory physiology over natural activities in free-ranging marine mammals have been limited. This
study describes a biotelemetry method for measuring skin surface heat flux in free-ranging Weddell seals. These data
are then applied to estimations of thermoregulatory heat dissipation from multiple point measurements.
Results: Data loggers collecting skin surface heat flux telemetry at four body locations (head, neck, axilla and flank)
from 40 free-ranging Weddell seals were deployed and recovered over periods of 1–13 days in Erebus Bay, Antarctica.
We derive equations for estimating total body heat dissipation from these point measurements and demonstrate
the subsequent calculation of heat dissipated from obligate thermoregulatory costs. Heat lost to air or water was
described by heat flux sensor data extrapolated across the whole-body surface, as informed by skin surface infrared
thermal patterns. Heat lost directly to the ice surface during haul-out was best described by physical features of the
seal, rather than environmental variables. Heat flux inputs from the four sensors could be reduced to two principal
components, and corresponding regressions indicated that the axilla and flank sensors were most correlated with
total body heat dissipation in air and water. Variability in head sensor heat flux was least described by the two principal
components.
Conclusions: This method can be used to estimate total body heat dissipation during daily activities in marine mammals,
and under steady-state conditions, it can be used to identify obligate thermoregulatory heat costs. Ultimately
this type of data will provide relevant empirical information for parameterizing models of thermoregulatory energetics
in ice-obligate seals, which may improve our ability to predict outcomes of altered ice conditions at high latitudes.

Two novel research approaches were developed to facilitate controlled access to, and longterm mon... more Two novel research approaches were developed to facilitate controlled access to, and longterm
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.

Directly observing the foraging behavior of animals in the marine environment can be extremely ch... more Directly observing the foraging behavior of animals in the marine environment can be extremely challenging, if not impossible, as such behavior often takes place beneath the surface of the ocean and in extremely remote areas. In lieu of directly observing foraging behavior, data from time-depth recorders and other types of behavioral data recording devices are commonly used to describe and quantify the behavior of fish, squid, seabirds, sea turtles, pinnipeds, and cetaceans. Often the definitions of actual behavioral units and analytical approaches may vary substantially which may influence results and limit our ability to compare behaviors of interest across taxonomic groups and geographic regions. A workshop was convened in association with the Fourth International Symposium on Bio-logging in Hobart, Tasmania on 8 March 2011, with the goal of providing a forum for the presentation, review, and discussion of various methods and approaches that are used to describe and analyze time-depth recorder and associated behavioral data records. The international meeting brought together 36 participants from 14 countries from a diversity of backgrounds including scientists from academia and government, graduate students, post-doctoral fellows, and developers of electronic tagging technology and analysis software. The specific objectives of the workshop were to host a series of invited presentations followed by discussion sessions focused on (1) identifying behavioral units and metrics that are suitable for empirical studies, (2) reviewing analytical approaches and techniques that can be used to objectively classify behavior, and (3) identifying cases when temporal autocorrelation structure is useful for identifying behaviors of interest. Outcomes of the workshop included highlighting the need to better define behavioral units and to devise more standardized processing and analytical techniques in order to ensure that results are comparable across studies and taxonomic groups.

lower percent bottom time, and generally traveled further to forage. The increased diving effort ... more 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. Communicated by J. D. r. Houghton.

temperature (T ice ), relative humidity and cloud cover did not improve the model. Heat transfer ... more temperature (T ice ), relative humidity and cloud cover did not improve the model. Heat transfer model estimates suggested that radiation contributed 56.6 ± 7.7 % of total heat loss. Convection and conduction accounted for the remaining 15.7 ± 12.3 and 27.7 ± 9.3 %, respectively. Heat loss by radiation was primarily influenced by body mass and wind speed, whereas convective heat loss was influenced primarily by blubber depth and wind speed. Conductive heat loss was modeled largely as a function of physical traits of mass and blubber depth rather than any environmental covariates, and therefore was substantially higher in animals in leaner condition.

Background: The energy requirements of free-ranging marine mammals are challenging to measure due... more Background: The energy requirements of free-ranging marine mammals are challenging to measure due to cryptic and far-ranging feeding habits, but are important to quantify given the potential impacts of high-level predators on ecosystems. Given their large body size and carnivorous lifestyle, we would predict that northern elephant seals (Mirounga angustirostris) have elevated field metabolic rates (FMRs) that require high prey intake rates, especially during pregnancy. Disturbance associated with climate change or human activity is predicted to further elevate energy requirements due to an increase in locomotor costs required to accommodate a reduction in prey or time available to forage. In this study, we determined the FMRs, total energy requirements, and energy budgets of adult, female northern elephant seals. We also examined the impact of increased locomotor costs on foraging success in this species. Results: Body size, time spent at sea and reproductive status strongly influenced FMR. During the short foraging migration, FMR averaged 90.1 (SE = 1.7) kJ kg −1 d −1only 36 % greater than predicted basal metabolic rate. During the long migration, when seals were pregnant, FMRs averaged 69.4 (±3.0) kJ kg −1 d −1values approaching those predicted to be necessary to support basal metabolism in mammals of this size. Low FMRs in pregnant seals were driven by hypometabolism coupled with a positive feedback loop between improving body condition and reduced flipper stroking frequency. In contrast, three additional seals carrying large, non-streamlined instrumentation saw a four-fold increase in energy partitioned toward locomotion, resulting in elevated FMRs and only half the mass gain of normally-swimming study animals. Conclusions: These results highlight the importance of keeping locomotion costs low for successful foraging in this species. In preparation for lactation and two fasting periods with high demands on energy reserves, migrating elephant seals utilize an economical foraging strategy whereby energy savings from reduced locomotion costs are shuttled towards somatic growth and fetal gestation. Remarkably, the energy requirements of this species, particularly during pregnancy, are 70-80 % lower than expected for mammalian carnivores, approaching or even falling below values predicted to be necessary to support basal metabolism in mammals of this size.

This study builds on a continued effort to document potential long-term research impacts on the i... more This study builds on a continued effort to document potential long-term research impacts on the individual, as well as to identify potential markers of survival for use in a field framework. The Transient Juvenile Steller sea lion (TJ) project was developed as a novel framework to gain access to wild individuals. We used three analyses to evaluate and predict long-term survival in temporarily captive sea lions (n = 45) through Cormack-Jolly-Seber open population modelling techniques. The first analysis investigated survival in relation to the observed responses to handling stress through changes in six principal blood parameters over the duration of captivity. The second analysis evaluated survival compared with body condition and mass at entry and exit from captivity. Finally, the third analysis sought to evaluate the efficacy of single-point sampling to project similar survival trends for use in field sampling operations. Results from a priori models ranked through Akaike information criterion model selection methods indicated that mass gains (4.2 ± 12%) over captivity and increases in leucocytes (WBC, 1.01 ± 3.54 × 10 3 /mm 3 ) resulted in a higher average survival rate (>3 years). Minor support was identified for the single-point measures of exit mass and entry WBC. A higher exit mass predicted a higher survival rate, whereas a higher WBC predicted a lower survival rate. While changes in mass and WBC appear to be the best predictors of survival when measured as a change over time, single-point sampling may still be an effective way to improve estimates of population health. : Predicted model-averaged survival rates based on continuous covariates. The change in mass (dMASS, in kilograms; A) and white blood cell counts (dWBC, ×10 3 per millimetre cubed; B) had the most support in the data on modelling the apparent survival rates in juvenile temporarily captive Steller sea lions (Eumetopias jubatus). Single-point measures yielded exit mass (xMASS, in kilograms; C) and entry white blood cell counts (eWBC, ×10 3 per millimetre cubed; D) to be slightly less supported, but important in predictive survival. Continuous lines represent the general trend through loess smoothing. Dashed lines indicate 95% confidence intervals in predicted averaged survival.

doi:10.7755/FB.112.4.6, Oct 1, 2014

Temperature data received postmortem in 2008–2013 from 15 of 36 juvenile Steller sea lions (Eumet... more Temperature data received postmortem in 2008–2013 from 15 of 36 juvenile Steller sea lions (Eumetopias jubatus) that had been surgically implanted in 2005–2011 with dual life history transmitters (LHX tags) indicate 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 are 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 nature of the 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.

Frontiers in Physiology, 2012

Constraint lines-the boundaries that delimit point clouds in bivariate scattergrams-have been app... more Constraint lines-the boundaries that delimit point clouds in bivariate scattergrams-have been applied in macro-ecology to quantify the effects of limiting factors on response variables, but have not been applied to the behavioral performance and physiological ecology of individual vertebrates. I propose that behavioral scattergrams of air-breathing, diving vertebrates contain informative edges that convey insights into physiological constraints that shape the performance envelopes of divers. In the classic example of repeated cycles of apnea and eupnea in diving, air-breathing vertebrates, the need to balance oxygen consumption, and intake should differentially constrain recovery for dives within or exceeding the aerobic dive limit (ADL). However, the bulk of variance observed in recovery versus dive duration scattergrams originates from undetermined behavioral variables, and deviations from overall stasis may become increasingly apparent at progressively smaller scales of observation. As shown on dive records from 79 Galápagos fur seals, the selection of appropriate time scales of integration yields two distinct recovery boundaries for dive series within and beyond the estimated ADL. An analysis of the corresponding constraint lines is independent of central tendencies in data and avoids violating parametric assumptions for large data sets where variables of interest account for only a small portion of observed variance. I hypothesize that the intercept between these constraint lines represents the effective ADL, and present physiological and ecological considerations to support this hypothesis.

PLoS ONE, 2012

The endangered western stock of the Steller sea lion (Eumetopias jubatus) -the largest of the ear... more 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.

Endangered Species Research, 2009

To directly determine mortality and predation in the endangered western Steller sea lion Eumetopi... more To directly determine mortality and predation in the endangered western Steller sea lion Eumetopias jubatus, we deployed implanted, satellite-linked post-mortem data transmitters in 21 juveniles. Data recovered from 4 of 5 detected mortalities exhibited precipitous drops in ambient temperatures followed by immediate onset of transmissions (N = 3), or gradual cooling and delayed transmissions (N = 1). Precipitous drop data sets were classified as acute death at sea by trauma. A model to estimate algor mortis (body cooling) as a function of mass and ambient conditions was validated through simulations on 4 carcasses. Model outputs suggest that cooling rate masses can be qualitatively distinguished if well outside the prediction uncertainties. The observed gradual cooling rate was best described by a modeled mass one-sixth the animal's mass at release, supporting the classification of the fourth event as acute death at sea by trauma. This suggests that at least 4 in 5 detected mortalities likely represent acute deaths at sea, probably due to predation. We conclude that precipitous drop events with immediate transmissions can be classified as acute death likely by predation, but gradual cooling events with delayed transmission should be reviewed on a case-by-case basis. In 3 cases that provided both ante-mortem and post-mortem locations from external and implanted transmitters, respectively, these differed by less than 17 km, illustrating that this technique provides spatially explicit data of predation on individual sea lions.

BMC Veterinary Research, 2008

Background: Pinnipeds, including many endangered and declining species, are inaccessible and diff... more 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 longterm 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.

IEEE Journal of Oceanic Engineering, 2005

Despite the widespread use of sophisticated telemetry transmitters in behavioral, physiological a... more Despite the widespread use of sophisticated telemetry transmitters in behavioral, physiological and ecological studies, few studies on population dynamics of oceanic vertebrates use such technology, primarily due to the difficulty of obtaining multi-year records from individual animals. We present the first telemetry transmitter specifically designed for collecting vital data from marine vertebrates over extended periods, up to a decade. The implantable Life History Transmitter records data throughout the life of a host animal. After the host animal dies, the tag is extruded, and, while floating on the ocean or lying on a beach, transmits previously stored data to orbiting satellites. For tags relying solely on end-of-deployment transmission, reliability and proper recognition of tag state is crucial. The Life History Transmitter uses heuristic tag state determination, in combination with simple error detection and fault tolerance measures, to increase tag reliability and likelihood of data recovery. We used a computer simulation of tag deployments and various sensor failures on a PC platform, in combination with time-accelerated simulations running on the actual deployment platform, to test the functionality of fault tolerance and error detection protocols. . As part of this work he developed the first computer-based data-logger for recording diving activity and body temperature, and the first blood sampler to operate on study animals at depths up to 1000 m. Both of these devices were successfully deployed on free-swimming Weddell seals in the Antarctic in 1982 and 1983. Over the next few years he developed and deployed the first satellite-linked data-loggers to be deployed on free-ranging seals. These devices telemetered both physiological and environmental data via the Argos system from Crabeater seals in the Antarctic. In 1987, he moved to Woodinville, WA, and started Wildlife Computers with his wife Sue. He became both President and Chief Engineer and is now primarily responsible for new product development at the Wildlife Computers, which has flourished over the intervening years and now has 25 employees and is situated in Redmond, WA.

Journal of Experimental Biology, 2009

Classic aging theory postulates the absence of pronounced organismal senescence in wild animals s... more Classic aging theory postulates the absence of pronounced organismal senescence in wild animals since mortality probably occurs first. Large-bodied, long-lived mammals are a recognized exception to this tenet, yet organismal senescence has not been investigated to date in such mammals in the wild. Furthermore, oxidative stress theory of aging supports the suggestion that exercise hypoxia, as regularly incurred during apneustic foraging in diving mammals might lead to cellular dysfunction and accelerated aging. To determine if an aspect of organismal senescence occurs in wild marine mammals, we examined the pattern of skeletal muscle aging (contractile and connective tissue components of longissimus dorsi and pectoralis muscles) in freeranging adult Weddell seals (9-26 years). The average myocyte cross-sectional area was 22% greater with age in the longissiums dorsi, but no significant increase occurred in the pectoralis. Cross-sectional area was not related to body mass. Changes in myocyte number per area were consistent with the 35-40% age-increase in extracellular space in both muscle groups. Also consistent with extracellular space remodeling, total and relative collagen contents were significantly elevated in older seals (115% in longissimus dorsi; 65% in pectoralis). The ratio of muscle myocyte to collagen declined with age (50-63%) at both sites. Additionally, a shift towards a higher ratio of type I to type III collagen occurred with advancing age in both muscle groups (79% increase in pectoralis; 49% in longissimus dorsi). We reject the classic tenet and null-hypothesis that Weddell seals do not survive to an age where muscular senescence becomes detectable.

Journal of Experimental Zoology, Part A: Ecological Genetics and Physiology, 2011

It is a golden age for animal movement studies and so an opportune time... more It

golden

age

for

animal

movement

studies

and

opportune

time

to
assess

priorities

for

future

work.

assembled

experts

identify

key
questions

this

ﬁeld,

focussing

marine

megafauna,

which

include

broad
range

birds,

mammals,

reptiles,

and

ﬁsh.

Research

these

taxa

has

both
underpinned

many

the

recent

technical

developments

and

led

fundamental
discoveries

the

ﬁeld.

show

that

the

questions

have

broad

applicability

to
other

taxa,

including

terrestrial

animals,

ﬂying

insects,

and

swimming

inverte
brates,

and,

such,

this

exercise

provides

useful

roadmap

for

targeted
deployments

and

data

syntheses

that

should

advance

the

ﬁeld

movement
ecology

doi:10.7755/FB.112.4.6, Oct 1, 2014

Frontiers in Physiology, 2012

PLoS ONE, 2012

Endangered Species Research, 2009

BMC Veterinary Research, 2008

IEEE Journal of Oceanic Engineering, 2005

Journal of Experimental Biology, 2009

Journal of Experimental Zoology, Part A: Ecological Genetics and Physiology, 2011