Clive R. McMahon

Measuring devices on wild animals: what constitutes acceptable practice?

In a world that is increasingly perturbed by humans, the need to understand ecosystems is urgent. Attaching measuring devices to wild animals is often the only way to acquire vital life-history information on larger, charismatic species, and on cryptic species that do not lend themselves to observation. However, the ethics of acceptable practice for attached devices are poorly defined. Here, we consider the need for further research and attempt to identify a system that allows animal restraint practices and device-induced effects to be quantified and monitored, so that ethics committees can have a defined scale on which to base decisions.

Weaning mass and the future survival of juvenile southern elephant seals, Mirounga leonina , at Macquarie Island

Seals that survived their first year were on average 2% and 4% heavier at birth and at weaning than the “non-survivors”. First year survival rates calculated for weaners over 135 kg weaning masses showed these weaners had higher survival rates than those less than 95 kg at weaning (71.55% and 54.15% respectively). Heavy weaners had greater fat reserves than light weaners and gained relatively more mass during lactation. Size, and therefore condition at weaning, influences first year survival.

Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals

Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60°S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April–May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean–sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a “blind spot” in our sampling coverage, enabling the establishment of a truly global ocean-observing system.

Climate change and seal survival: evidence for environmentally mediated changes in elephant seal, Mirounga leonina, pup survival

Maternal and physical factors play a significant role in animal life-history variability, which means that large scale climate change has the potential to affect the size and dynamics of animal populations indirectly through maternal investment and directly through conditions that animals are exposed to. However, little is known about the effects of large-scale oceanographic events such as the El-Niño southern oscillation (ENSO) that influence productivity in the Southern Ocean and the abundance, quality and distribution of prey. The possible mechanisms by which physical factors and primary productivity could influence life-history traits, such as survival of apex predators, includes direct influences such as food availability and foraging success and indirect influences such as stored maternal investment and resource transfer during lactation. Here, we quantify the relative contribution of maternal investment and climate conditions at remote foraging sites to survival in the first year of life for southern elephant seals. We present evidence linking climate (ENSO) and variations in a key demographic parameter—first-year survival—and demonstrate that survival was highest during ENSO events and that the ability of mothers to store and acquire resources, which is typically related to ocean productivity, is the most important determinant of survival in the first year. This functional link provides valuable insights that can be used to model the responses of the seal populations to climate change scenarios.

Field immobilisation of southern elephant seals with intravenous tiletamine and zolazepam.

Southern elephant seals (Miroungo leonina) were immobilised with a mixture of tiletamine and zolazepam administered intravenously at a mean (sd) dose rate of 0.46 (0.08) mg/kg. This dose provided a satisfactory degree of anaesthesia with no side effects, and the induction, duration and recovery times were short. The mean (sd) induction time was 26 (9) seconds and the mean level of anaesthesia was 4.4 units on an eight-point scale. Male seals were given less drug than female seals, remained immobilised for shorter periods and recovered sooner. The mean (sd) dose of drug administered to males was 0.44 (0.06) mg/kg and to females 0.48 (0.08) mg/kg, and the mean (sd) duration times were 14.9 (4.5) minutes and 16.1 (5.3) minutes. The mean (sd) time taken to recover from immobilisation was 14.5 (4.6) minutes for males and 15.7 (5.3) minutes for females. Physiological condition and size significantly affected the duration of anaesthesia. Thin seals remained immobilised for 18 (7) minutes whereas fatter seals remained immobilised for 15 (4) minutes (P<0.0001).

Effects of age, size and condition of elephant seals (Mirounga leonina) on their intravenous anaesthesia with tiletamine and zolazepam

Southern elephant seals (Mirounga leonina) were caught as part of a long-term demographic study on Macquarie Island. Over 18 months, 1033 seals were caught by hand and anaesthetised intravenously with a 1:1 mixture of tiletamine and zolazepam. Assessments were made of the effects of variations in the body condition and age at capture of the seals on the characteristics of their anaesthesia, including induction time and weighted recovery time. The size and condition of the seals were assessed by morphometric and ultrasound measurements. Weighted recovery times decreased as the body condition and age of the seals increased, but there were no residual effects of sex. There were no fatalities, and no periods of apnoea longer than five minutes were recorded. In individual seals there was a significant increase in weighted recovery time with successive captures.

Estimates of the Southern Ocean general circulation improved by animal‐borne instruments

Over the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase.

Enhancing the use of Argos satellite data for home range and long distance migration studies of marine animals.

Accurately quantifying animals’ spatial utilisation is critical for conservation, but has long remained an elusive goal due to technological impediments. The Argos telemetry system has been extensively used to remotely track marine animals, however location estimates are characterised by substantial spatial error. State-space models (SSM) constitute a robust statistical approach to refine Argos tracking data by accounting for observation errors and stochasticity in animal movement. Despite their wide use in ecology, few studies have thoroughly quantified the error associated with SSM predicted locations and no research has assessed their validity for describing animal movement behaviour. We compared home ranges and migratory pathways of seven hawksbill sea turtles (Eretmochelys imbricata) estimated from (a) highly accurate Fastloc GPS data and (b) locations computed using common Argos data analytical approaches. Argos 68th percentile error was <1 km for LC 1, 2, and 3 while markedly less accurate (>4 km) for LC ≤0. Argos error structure was highly longitudinally skewed and was, for all LC, adequately modelled by a Student’s t distribution. Both habitat use and migration routes were best recreated using SSM locations post-processed by re-adding good Argos positions (LC 1, 2 and 3) and filtering terrestrial points (mean distance to migratory tracks ± SD = 2.2±2.4 km; mean home range overlap and error ratio  = 92.2% and 285.6 respectively). This parsimonious and objective statistical procedure however still markedly overestimated true home range sizes, especially for animals exhibiting restricted movements. Post-processing SSM locations nonetheless constitutes the best analytical technique for remotely sensed Argos tracking data and we therefore recommend using this approach to rework historical Argos datasets for better estimation of animal spatial utilisation for research and evidence-based conservation purposes.

First-year survival of southern elephant seals, Mirounga leonina, at sub-Antarctic Macquarie Island

Abstract Juvenile seals branded on the isthmus of Macquarie Island as pups displayed a high degree of philopatry. They returned more often and in greater densities to the northern third of the island within 10 km of their birth sites. Juvenile seals were observed to haul out more frequently and in greater numbers on the east coast as opposed to the west. Juvenile seals typically hauled out on two occasions, once during the winter, and once to moult. The probability of recapturing (resighting) branded and tagged seals was greater during the mid-year haulout. First-year survival estimates were obtained from searches of all Macquarie Island beaches for marked (branded and tagged) seals. From a branded population of 2000 seals, 897 were known to be alive at age 1 year, and minimum first-year survival was calculated at 44.85%. To this minimum estimate was added the number of seals overlooked during systematic and standardised searches of the island, and a revised estimate of 65.60% was calculated. Survival rates calculated using a custom model and a conventional mark-recapture model (MARK) were compared and no differences detected. Actual survival data and probability of sighting estimates were included in the revised estimate of first-year survival of southern elephant seals at Macquarie Island. There were no differences in the number of surviving males and females.

Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals

BackgroundDetermining the relative contribution of intrinsic and extrinsic factors to fluctuations in population size, trends and demographic composition is analytically complex. It is often only possible to examine the combined effects of these factors through measurements made over long periods, spanning an array of population densities or levels of food availability. Using age-structured mark-recapture models and datasets spanning five decades (1950–1999), and two periods of differing relative population density, we estimated age-specific probabilities of survival and examined the combined effects of population density and environmental conditions on juvenile survival of southern elephant seals at Macquarie Island.ResultsFirst-year survival decreased with density during the period of highest population size, and survival increased during years when the Southern Oscillation Index (SOI) anomaly (deviation from a 50-year mean) during the mothers previous foraging trip to sea was positive (i.e., El Niño). However, when environmental stochasticity and density were considered together, the effect of density on first-year survival effectively disappeared. Ignoring density effects also leads to models placing too much emphasis on the environmental conditions prevailing during the naïve pups first year at sea.ConclusionOur analyses revealed that both the state of the environment and population density combine to modify juvenile survival, but that the degree to which these processes contributed to the variation observed was interactive and complex. This underlines the importance of evaluating the relative contribution of both the intrinsic and extrinsic factors that regulate animal populations because false conclusions regarding the importance of population regulation may be reached if they are examined in isolation.