Seal & Sea Lion

Project Title: Assessing male influence on population structure in the Australian sea lion

Researchers: Associate Professor Adam Stow and Dr Heidi Ahonen.
Photo Credit: Andrew Lowther

Recently Sea World Research & Rescue Foundation funded a research project focused on the breeding habits of the Australian sea lion (Neophoca cinerea), one of the rarest sea lions in the world.

The researchers examined male, female and offspring genotypes and found they have the highest level of site fidelity in marine mammals. Across their range there was little or no swapping of females among breeding colonies and only few instances of males’ siring (fathering) offspring in more than one colony. Most males proved loyal to their own breeding ground even when colonies were separated by as little as 20km.

Australian sea lion males also exhibited relatively low levels of variation in the number of females with which they breed, there were no obvious dominant or alpha males that bred more than others and there were no strong seasonal differences. This is good news for sea lions as the risk of inbreeding, which is caused by a limited gene pool, would be greater if only a small number of males dominated mating. Crucially for conservation however, the extreme site fidelity means that each colony represents an essentially closed population and highlights the importance of careful population management, especially with respect to impacts such as local fisheries bycatch.

On top of being the major contributor to the Sea World Research & Rescue Foundation, Sea World also cares for sick and injured Australian sea lions and New Zealand fur seals that have beached on the coast of Queensland and northern NSW.

Listed as Endangered in 2008 (IUCN Red List) the Australian sea lion population is described as small, isolated and decreasing. Funding from the Research & Rescue Foundation has made possible this investigation into the site fidelity of the Australian sea lion population and this quantifiable research.

PROJECT TITLE: An integrated ecosystem study of an Australian marine biodiversity hotspot

RESEARCHERS: Mary-Anne Lea, Kerrie Swadling, Vanessa Lucieer & Clive McMahon

LOCATION: Southern Bruny Island, Tasmania

Throughout the world there are key areas characterised by a high diversity of species, including some animals that may not be found anywhere else. These are referred to as biodiversity hotspots.

Understanding the variety and abundance of predator and prey species present in these hotspots enables us to indirectly track changes in local productivity across different seasons and between years. These changes may ultimately affect the reproductive success and survival of those important species feeding in the hotspots.

Recent surveys suggest a marine biodiversity hotspot exists off the coast of Southern Bruny Island, Tasmania. This region is situated in an area of mixing where low-nutrient, warm water from the East Australia Current interacts with cold, nutrient-rich waters from the sub-Antarctic, promoting seasonal productivity and high plankton biomass (Harris et al. 1987).

This project aims to:

• quantify seasonal changes in abundance of top predators over time (seals, seabirds, penguins and cetaceans)
• describe the biological drivers of changes in predator abundance, by quantifying the biomass and species composition of the zooplankton prey field, as well as phytoplankton production describe the main physical drivers of the biological response, which include seafloor habitat mapping and characterising the oceanic water masses; and
• integrate the above information within a local model to identify the key drivers of the predator abundance and their prey, and how this will vary over time. Such a model could then be used to predict the existence of other similar biodiversity hotspots within southeastern Australia.

The research team will survey Bruny Island monthly from September 2015 to May 2016. By targeting these months they will record the predator breeding season, a time when foraging intensity is greatest due to the requirement to feed their young.

REFERENCES

Harris, G., et al. (1987) The water masses of the east coast of Tasmania: seasonal and interannual variability and the influence on phytoplankton biomass and productivity. Australian Journal of Marine and Freshwater Research, 38, 569-590.

PROJECT: Changing climate and the winter foraging behaviour of Antarctic fur seal populations

RESEARCHER: LEA, Mary-Anne, Ben Arthur (PhD student)

LOCATION: Three circumpolar breeding sites

Until recently little was known about the habitat use and foraging (feeding) ecology of the female Antarctic fur seal (Arctocephalus gazella) during the extreme climate experienced in the Southern Ocean winter.

To fill these gaps researchers tracked the winter movements of 186 fur seals between 2008 and 2013, with a further 20 tracked in 2014 at sub-Antarctic Marion Island. Such a large coordinated study greatly increased their ability to tackle larger questions surrounding climatic change and associated influences on higher trophic levels in the Southern Ocean ecosystem.

RESULTS:

Site fidelity

The majority of Antarctic fur seal studied show strong loyalty to open-ocean feeding sites, consistently returning to certain parts of the Southern Ocean to search for food over multiple years. These areas of consistent use are characterized by high levels of variability in physical parameters such as ocean temperature.

Such high levels of site fidelity raise questions about the ability of long-lived individuals to respond to future environmental change.

Winter diving

Seals exhibited two main foraging strategies:

1. Local foraging and remaining North of the Polar Front typically with deeper and longer dives and an increased foraging effort.
2. Foraging further afield, South of the Polar Front, with short, shallow dives and a reduced foraging effort. This reduced foraging effort potentially offsets the energetic costs for those animals investing in a long-distance trip South.

This is the first investigation into the winter diving behavior of Antarctic fur seals. Further analysis of dive and track data will enable the development of a spatial foraging index for Antarctic fur seals in winter that will be used to model changes to foraging habitat under various climate scenarios.

DEFINITIONS

Forage: Search for food

Site fidelity: loyalty to a particular location

Trophic level: the position an animal holds in the food chain