Assessing the body condition and migration timing of humpback and pygmy blue whales in Australia
Creators: name: Russell, Grace
Publisher: name: Southern Cross University
Year: 2023
Subjects: Balaenoptera musculus brevicauda
Baleen whale
Bioenergetics
Megaptera novaeangliae
Photogrammetry

description: Many baleen whales undertake seasonal periods of feeding and fasting, with clear temporal changes in body condition. During periods of fasting, individuals perform vital life history stages where success can be influenced by the individual’s body condition. A whale’s body condition not only relates to forging success but may also be influenced by ecological and anthropogenic stressors in their environment; including climate change, shipping, oil and gas exploration and tourism. While the complexity and long-term consequences of these are not fully understood, studies have highlighted the short term and potential population-level impact these may have on marine mammals. Given the conservation concern around the impacts of these stressors, the importance of measuring and monitoring body condition is apparent.
description: Despite the importance of body condition for migrating baleen whales, few studies have explored the relationship between body condition and migration timing. Exploring the significance of this will provide valuable insight regarding the potential trade-off’s whales may make between energy acquisition and reproduction. I used RPAs to quantify the body condition of the two Australian breeding populations (east and west coast) of humpback whales (Megaptera novaeangliae) and the population of southeast Indian Ocean pygmy blue whales (Balaenoptera musculus brevicauda). For the humpback whales, I examined whether their body condition varied according to their migration timing, and further contrasted the two populations to discern population-level differences. For the pygmy blue whales, I quantified and compared the body condition of northern and southern migrating individuals. There was an overall lack of statistical evidence for both humpback whale populations to support migration timing being a major influencing factor dictating their body condition. In both populations, juveniles exhibited a relatively large loss in body condition when compared to adults. Notably, sexually mature reproductive classes (adults and lactating females) in the west coast population were in poorer body condition when compared to their east coast counterparts. Pygmy blue whales were found to lose significant body condition between their northern and southern migration. This departure from expected mean body condition highlights the need for further empirical investigation regarding potential environmental and anthropogenic stressors, which could be inhibiting population growth and recovery from exploitation. The highly migratory life history strategy employed by both humpback and pygmy blue whales, along with their slow reproductive strategy, long-lived nature and dependency on lower trophic prey, make them sensitive to significant climatic and anthropogenic threats. Therefore, this thesis provides an important baseline for future studies or monitoring to assess temporal trends in the nutritional health status of individuals and populations to ensure the continued success of humpback whales, and provide greater insight regarding pygmy blue whales.