The Commercial Biology of the Elephant Seal (Mirounga leonina linn) on Macquarie Island - 1948
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Taken from the report prepared by R Kenny: In this report our comparatively brief knowledge of the Elephant Seal at Macquarie Island (based only on one year's observations) have been augmented by abstracting notes from "The Natural History of the Elephant Seal" by L. Harrison Matthews Discovery Reports, vol. 1 p. 233. 1929., based on observations at South Georgia. The Elephant Seal herds at the two islands are comparable - at South Georgia the animals had been overfished almost to the point of extinction by 1885, but were then not hunted for many years, and by 1929 had "increased in numbers till at the present time they are probably as numerous as ever", and are now fished under Government regulation to prevent extermination; the Macquarie Island herd has a similar history.
Marine mammal interactions with trawl gear
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Underwater video technology was used to observe marine mammal interactions (seals, in particular Australian fur seals) within midwater trawl nets. A camera system was placed inside the trawl net in the vicinity of a Seal Excluder Device, designed to prevent megafauna from entering the codend of the net and provide an escape point. Digital video data was described according to a range of operational, catch and interaction fields, and made time-specific to each trawl shot. Data is linked to commercial catch and effort data providing operational, environmental and catch information.
Ecology of Southern Elephant Seals
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Metadata record for data from ASAC Project 257 See the link below for public details on this project. From the abstracts of some of the referenced papers: Anatomical and physiological studies of southern elephant seals (Mirounga leonina), particularly in the post-natal period, raise questions of relative musculature growth, control of metabolism, circulation and temperature regulation, which could be important in our understanding of these processes in mammals and of their contribution to adaptation to environmental extremes. The diving behaviour of 14 adult southern elephant seals was investigated using time depth recorders. Each of the seals performed some dives that were longer than its theoretical aerobic dive limit. Forty-four percent of all dives made by post-moult females exceeded the calculated limit compared with 7% of those made by postbreeding females and less than 1% of those made by adult males. The extended dives displayed characteristics that suggested they were predominantly foraging dives, although some were apparently rest dives. Dives longer than the calculated aerobic limits often occurred in bouts; the longest consisted of 63 consecutive dives and lasted 2 days. Postmoult females performed longer bouts of extended dives than postbreeding females. Extended surface periods (longer than 30 min) were not related to the occurrence of extended dives or bouts of extended dives. The possible physiological mechanisms that permit such prolonged continuous dives are discussed. Southern elephant seals may increase the aerobic capacity of dives by lowering their metabolism to approximately 40% of the resting metabolic rate on long dives. There is substantial interseal variability in the methods used to cope with long dives. Some animals appear to use phsyiological strategies that allow them to prolong the time available to them at the bottom of a dive, while others use alternative strategies that may limit the time available at the bottom of their dives. Fourteen time-depth-temperature recorders were recovered from adult southern elephant seals (Mirounga leonina) returning to Macqaurie Island to breed or moult. The resulting temperature/depth profiles indicated that all four males spent most of their time in waters lying over the Antarctic Continental Shelf, whereas only one of the ten females spent any time there. Five of the females foraged just off the Antarctic Continental Shelf, and the other five remained near the Antarctic Polar Front. 1) Mark-resight data were analysed for thirteen cohorts from a declining population of southern elephant seals branded at Macquarie Island between 1951 and 1965. 2) First year survival was essential stable during the 1950s at about 46% for females and 42% for males. There was a dramatic fall in first year survival during the 1960s, declinging to less than 2% for both sexes in 1965. Post-year-1 survival did not change between the 1950s and the 1960s. 3) Comparisons with a stable population of southern elephant seals at South Georgia indicated that both first year and adult survival were lower in the Macquarie Island population. There were no changes in the age at first breeding of the Macquarie Island seals during the study, but this was on average 1 year later than at South Georgia. 4) It is hypothesised that the current decline in elephant seal numbers at several of their major breeding islands is due to the populations returning to pre-sealing levels after they had risen to abnormally high levels with the end of commercial exploitation early this century. 5) Possible tests of the hypothesis include studying the diet and foraging behaviour of southern elephant seals to gain an understanding of the predator-prey relationships, continuing to census the Macquarie Island population to determine if the population levels out at around the estimated pre-sealing levels, and monitoring northern elephant seal populations which were also severely exploited but are currently increasing
Food Consumption and Foraging Success of Free-ranging Southern Elephant Seals
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Elephant seals use a suite of physiological and behavioural mechanisms to maximise the time they can be submerged. Of these hypo-metabolism is one of the most important, so this study quantified maximum O2 consumptions relative to dove depth and swim speed. From the abstract of the referenced paper: The ability of air-breathing marine predators to forage successfully depends on their ability to remain submerged. This is in turn related to their total O2 stores and the rate at which these stores are used up while submerged. Body size was positively related to dive duration in a sample of 34 adult female southern elephant seals from Macquarie Island. However, there was no relationship between body size and dive depth. This indicates that smaller seals, with smaller total O2 stores, make shorter dives than larger individuals but operate at similar depths, resulting in less time being spent at depth. Nine adult female elephant seals were also equipped with velocity time depth recorders. In eight of these seals, a plot of swimming speed against dive duration revealed a cloud of points with a clear upper boundary. This boundary could be described using regression analysis and gave a significant negative relationship in most cases. These results indicate that metabolic rate varies with activity levels, as indicated by swimming speed, and that there are quantifiable limits to the distance that a seal can travel on a dive of a given swimming speed. However, the seals rarely dive to these physiological limits, and the majority of their dives are well within their aerobic capacity. Elephant seals therefore appear to dive in a way that ensures that they have a reserve of O2 available. Data were collected on Time Depth Recorders (TDRs), and stored in hexadecimal format. Hexadecimal files can be read using 'Instrument Helper', a free download from Wildlife Computers (see the url given below). Data for this project is the same data that was collected for ASAC projects 857 and 589 (ASAC_857 and ASAC_589).
Measuring the effects of human activity on Weddell Seals (Leptonychotes weddellii)
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The number of people travelling to Antarctica is growing, with much of the recent increase in visitor numbers attributable to an expansion in commercial tourism (Enzenbacher 1992; 1994). Most visitors to the region seek direct interactions with the wildlife and so visit breeding groups of seals and seabirds (Stonehouse 1965; Muller-Schwarze 1984). Invariably, this involves travelling to breeding sites by helicopter, inflatable motorised boat (e.g. zodiac) or over-snow vehicle, then making relatively close approaches on foot to photograph and observe the animals. At present, there is information to suggest that visitation can have a negative effect on some Antarctic wildlife, causing changes to behaviour, physiology and breeding success (Culik et al. 1989; Woehler et al. 1994, Giese 1996; Giese 1998, Giese and Riddle 1999). However, the responses of Weddell seals (Leptonychotes weddellii) to human activity have never been systematically examined. As a result, any guidelines to control human activity around these animals are based either on opportunistic observations of seal response, and/or assumptions as to the level of disturbance seals are experiencing. Therefore, the primary objective of the research is to measure the responses of Weddell seals to various human disturbance stimuli. In so doing, the research aims to make quality information available for the development of a comprehensive and scientifically based set of guidelines for managing interactions between people and Antarctic seals. The research will adopt an experimental approach, whereby seals are experimentally exposed to particular types and intensities of human activity while their responses are objectively quantified. As far as possible, experiments are designed to replicate actual disturbances that Weddell seals are presently exposed to in Antarctica. As such, the responses of cow/pup pairs to approaches by pedestrians, over-snow vehicles and helicopters will be examined. In particular, experiments will investigate how approach distance (or altitude), approach speed, time of day, weather conditions and the time of the breeding season, influence the responses of Weddell Seals to these disturbance stimuli. Disturbance responses will be quantified by measuring the behaviour and heart rate of individual seals and the haul-out behaviour of entire groups of animals. Experiments will also be conducted to quantify the sound generated by vehicle operations in Antarctica to help determine whether anthropogenic noise effects vocal communication among Weddell seal, as indicated by changes in their calling rates. Also see the metadata record entitled: Behavioural responses of Weddell seals to human activity. At this stage most of the analysis is in progress and therefore it is not possible to provide complete data sets. These will be submitted upon the completion of the work. The attached word document summarises the experiments that have been completed during the three field seasons to date (up to the end of the 2002/2003 season), which included, the experiment type, location and sample size. The two excel data sheets 'Experimental recording details' provide information on the video recordings that were made during the 2001/2002 and the 2002/2003 summers. These details state the experimental procedure, the details of the experimental, the time, date etc. They include Hi8 video camera recordings of Weddell seal behaviour and DAT recordings of vocalisations. Biological data collected during the 2002/2003 summer include: Collected 10 sample of blood (up to 50 ml each) Collected 6 samples of urine Collected 11 samples of fur Collected 9 samples of blubber Collected 6 samples of faecal swabs (from the ice or thermometer) Conducted a post mortem on a recently deceased seal and collected organ and tissue samples. These samples are being analysed by investigators in ASAC 1144. When results are available they will documented in either ASAC 1148 or 1144. The fields in this dataset