Drivers in the Distribution of Marine Mammals

Drivers in the Distribution of Marine Mammals

Using geospatial mapping the we aim to assess broad scale and mesoscale environmental variables which effect the distribution of marine mammals.

Overview

Along with oceanographic and anthropogenic elements, environmental factors have been attributed to influencing marine mammal distributions throughout the world (MacLeod, 2009, Learmonth et al., 2006, Dolar and Sabater, 2011). Physical parameters such as sea surface temperature (SST), winds, currents, upwelling and salinity have both direct and interrelated indirect effects on marine mammals ecology and habitat preference (MacLeod, 2009, Pikesley et al., 2011). The relationship between marine mammals and their environment is two way, however under a changing climate the environmental variables which influence distribution are being altered, with some effects on marine mammals already being documented, and range shifts occurring. (Lambert et al., 2011, Schumann et al., 2013). These shifts in species range are likely to cause changes in community composition, which has further implications for interspecific interactions and can lead to additional ecosystem pressures through competition, exclusion, and predator-prey relationships (Schumann et al., 2013, Nicol et al., 2008). In fact, due to climate change induced species range shifts, it has been proposed that temperature increases may affect the range of 88% of the worlds cetacean species, for which 47% may have unfavourable implications, and 21% may risk extinction.

The south-east Australian marine region is known globally for its high levels of endemism, with 80% of all marine life in the region not found anywhere else in the world. Composition changes, therefore put this unique area at further risk. Additionally, the region has been identified as a global warming hotspot with a rapid rate of warming at almost four times that of the global average (Hobday et al., 2013). The East Australian Current (EAC), circulating warmer waters along the east coast of Australia, has shown an intensification and extension southward since 1944, equating to a more than 300km extension which is expected to strengthen (Cai et al., 2005). The evidence that climate change is occurring and already having impacts within the region, as well as the high levels of endemism and already endangered species, highlights the importance of understanding the marine mammal assemblage and composition within the area.

Whilst a concurrent study that MMF is undertaking to create a biodiversity assessment of marine mammals in Victoria, will tell us which species have been found in Victoria and the composition, we already know we have a number of resident populations within the region. There are documented distributions of common dolphins, common bottlenose dolphins, Burrunan dolphins, Australian and long-nosed fur seals, and Australian sea lions. There are also a number of migratory whales documented in the region, observed in their annual migrations, including humpback, southern right, blue, and sperm whales. However, preliminary results of the biodiversity study demonstrate records of strandings and sightings of typically unexpected marine mammal species in Victoria that there are frequent, occasional or rare, visitors to our states waters. For example, the leopard seal and subantarctic fur seal, typically subantarctic species, as well as typically assumed tropical and sub-tropical species such as striped dolphins and dwarf or pygmy sperm whales.

Given the crucial role of marine mammals in both ‘bottom-up’ and ‘top-down’ ecosystem function within the oceans, the impacts of a changing environment, and the vulnerability of the south east Australian region, it raises the questions; has the species composition changed within Victoria? And if so, how does that affect the biodiversity and ecosystem function of this unique region? The MMF are investigating the presence of species who are typically classified as tropical, Antarctic/subantarctic, or otherwise have unknown distributions, to investigate the potential drivers for distribution of these species. The spatial and temporal patterns of these species occurrences as investigated by in Victoria are being looked at for potential correlations with environmental factors such as sea surface temperature, chlorophyll-a, and surface currents. The project aims to find environmental drivers of distribution of marine mammal species in Victoria, focussing on the rare and data deficient species. This will act as a projection tool, for predicting when some of these species will be entering our waters and help authorities to manage both human and environmental resources to assist in the research and conservation of these valuable species.

Aims

  • To investigate the environmental drivers of distribution for marine mammals in Victoria.

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