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Modelling energetics of fur seals and sea lions
thesisposted on 2022-03-28, 16:06 authored by Monique Ladds
Energy is the source of life, and at the most basic level, survival of a species is dictated by how efficiently animals gain and use their accumulated energy. Energetics, the study of how animals organise their daily or seasonal activities, allows us to understand how animal energy budgets are used and affected by life history or environmental changes. However, to comprehend fully how animals may respond to changes in their environment it is necessary to measure accurately behaviour and physiology of wild animals. This can be achieved by estimating time-energy budgets from accelerometers. In this thesis, energetic models were developed through experiments with a diverse group of captive fur seals and sea lions (otariids) and subsequently applied to wild fur seals. Otariids are an excellent study species as they predictably haul out at the same colony after foraging at sea (for data recovery) and must return to the surface to breathe (for energetics studies). Captive surrogates were used to develop baseline energetic data for the species of interest: Australian fur seals, New Zealand fur seals and Australian sea lions. The standard metabolic rate of otariids was measured over a year. Females were found to have generally higher metabolic rates than males, and fur seals, but not sea lions, have predictable changes in metabolic rate related to time of year and moult. The metabolic rate of activity was investigated by training adult and subadult otariids to swim submerged for varying durations. Otariids exhibited a dive response, as their metabolic rate decreased with extended periods of swimming, and juveniles had an additional cost of movement. Swimming trials with otariids swimming or diving to feeding tubes were used to validate accelerometers for measuring energy expenditure. Dive duration, total stroke rate and dynamic body acceleration (DBA) was found to accurately predict total energy expenditure for a swim and DBA explained more variation in the model than stroke rate and dive duration. The use of accelerometers to distinguish among groups of four ecologically important behaviours (grooming, foraging, travelling and resting) was validated on captive surrogates and time-energy budgets were developed from this information. These time-energy budgets, when applied to wild fur seals, indicated juvenile fur seals change their behaviour to cope with different energetic pressures between seasons. Juvenile fur seals also have higher energetic costs than adults that may limit their scope for increasing foraging effort during times of resource limitation. These findings indicate that time-energy budgets measured with accelerometers are a useful method of monitoring populations of seals over time that may be subject to limited food availability.