A multidisciplinary approach to assess the impacts of anthropogenic noise Researching human impact on the Australian Fur Seal Support of PhD Candidate, Jessalyn Taylor
"Amidst ever-increasing exposure to human influence, the Australian fur seal is currently in decline, highlighting an urgent need to assess potential threats to the species and prevent further biodiversity loss."
Jessalyn Taylor, Sydney School of Veterinary Science, The University of Sydney
Graceful, powerful and a key predator - the Australian Fur Seal is a stunning marine acrobat that plays an important balancing role in its ecosystem. It is one of the rarest fur seals in the world, making its protection critical to ensuring a sustainable future.
With one of the primary breeding grounds for the species - Seal Rocks, Victoria - also being a popular tourist destination, there is concern that anthropogenic noise may be harming their ability to communicate, therefore affecting parent-offspring interactions, and territorial behaviour.
FAME is partnering with PhD Candidate Jessalyn Taylor and the University of Sydney to research the impact of human-generated noise on this species, and develop appropriate mechanisms for limiting any impact.
ABOUT AUSTRALIAN FUR SEALS
The Australian Fur Seal (Arctocephalus pusillus doriferus; AFS) is the largest fur seal found in Australian waters. It lives along the south-east coast of Australia, ranging from the northern NSW coast - where it is listed as Vulnerable, down to Tasmania and across to South Australia - where it is listed as Rare.
An AFS bull can grow to 2-3 metres in length and can weigh up to 360kg. A well-grown yearling steer would weigh about the same. Females are much smaller, normally 20-30 percent of the weight of the males. AFSs differ from other seals with small external ear flaps that can appear quite out of proportion to the rest of the animal.
AFSs are one of the rarest fur seals in the world. A current estimate of their national population is a mere 120,000 animals, but this is likely to be at the optimistic end of the range, given the population was previously depleted to just a few thousand animals.
As a high-level predator, this species plays a critical role in their marine ecosystem by helping to manage populations of those further down the trophic system, making their protection critical. They suffer from a number of human impacts, including noise pollution, rising water temperatures and marine debris.
One team of scientists analysed data collected between 1997 and 2012 and found that most entanglements of AFSs were due to plastic twine or rope, and primarily impacted younger seals (Lawson et al, 2015).
This sort of research enables more targetted conservation initiatives, as will the focus of Taylor’s PhD.
WHERE DOES THE FUR SEAL’S NAME COME FROM?
The species is part of the Otariidae family – which derives from the Greek word otarion, meaning ‘little ear’. Their genus, Arctocephalus, gives you another clue to their appearance: Arctos means ‘bear’ and cephalus means ‘head’, so the bear-headed seal.
They are well equipped for their deep-sea swimming with two layers of fur – outer, dark hair and an undercoat of light, thick hair - which protects the seals’ skin and, remarkably, keeps them dry when underwater. Whilst they can dive to 200m to find food, this is physically demanding and requires a lot of rest time on land.
FUR SEAL ADAPTATIONS
An AFS cow has the ability to ‘delay implantation’ after breeding, meaning that a fertilised egg can remain dormant inside her for some time before development. This adaptation ensures her pup will always be born during the summertime, giving the pup the highest chance of survival with the warmer weather and better food supply.
Great White Sharks are natural predators of AFSs, and the seals are also caught in fishing nets, resulting in injury or death. Sadly, human activity has contributed significantly to the decline of this beautiful species. After being hunted during the 1800s for their skins, blubber and oil, the species has never recovered.
When ashore, the seals congregate in large groups - making them popular targets of wildlife tourism, creating the need for this research in order to minimise human impact.
AUSTRALIAN FUR SEAL RESEARCH
The title of Taylor’s PhD is: ‘A multidisciplinary approach to assess the impacts of anthropogenic noise on Australian Fur Seals (Arctocephalus pusillus doriferus): soundscape, behaviour, and stress hormone concentrations as key factors.’
The effect of vessels and other noise-generating equipment on marine life has been of growing concern this century, with everything from rockfish and prawns through to whales the focus of interest.
A study in 2019 conducted in Port Phillip Bay - not far from Seal Rocks - showed all types of vessels elicited increased alertness amongst AFSs, and that those breaching approach regulations - coming within 5m of the animals - caused a 32% increase in alert behaviours (Speakman, Johnstone and Robb, 2019). This is a clear indication that vessels are having an impact on the species, and Taylor’s research will help to crystallise our understanding of what this means long-term, and how to improve the situation.
Whilst little is known of the holistic impact human-generated noise may have on A. p. doriferus, we do know that vessel noise can interfere with their vocal communication. This is both a key part of mother-pup reunion methods, as well as an energy-conserving method of maintaining territorial boundaries in breeding males.
As such, disruption to this communication potentially delays mother-pup reunions, and may lead to unnecessary aggressive interactions between males. This sort of behavioural change, as well as potential physiological stress of the noise, can have negative consequences for the health and survival of all individuals in a population.
It is critical for us to understand just how the seals respond to the noise, the immediate and long-term effects to the population, and the best ways to manage this risk.
The aim of this PhD project is therefore to determine the impact of vessel noise on the Seal Rocks colony and whether or not the current management strategy at Seal Rocks is adequate.
Running from February 2022 to July 2023, the primary objective of this project will be the development of a novel and robust ‘acoustic impact model’ of vessel visitation. In other words, Taylor will create a detailed ‘map’ of how different vessel types, and different uses and distances, affect the seals.
This will be done through the integration of four variables into the model:
1. Vessel noise around Seal Rocks will be recorded using underwater recording devices (hydrophones) to monitor vessel visitation and its effect on the natural background noise.
2. Direct observation of vessels approaching Seal Rocks will be used to visually catalogue vessel visitation, provide reference points for acoustic data, and with the aid of drone mosaic images, identify ‘hotspots’ of visitation
3. Behavioural responses of seals to vessel noise (in-air) will be assessed using playback of recorded motor vessel noise
4. Pup health status will be evaluated using blood parameters and body condition index. To enable comparisons between seasons and between year, each type of data will be collected in high- (summer, breeding) and low-visitation (winter, non-breeding) periods for two consecutive years.
HOW CAN YOU HELP?
Not only does this research address a key knowledge gap in the conservation management of Australian fur seals, the methodology employed is readily transferable to other sites, and other pinniped, marine mammal and potentially seabird species.
Importantly, the results of this project will be communicated to government and other key stakeholders to inform management regulations at Seal Rocks and other sensitive marine sites.
The outcomes will also be used to promote and enhance best-practice guidelines for ecotourism, both locally and internationally.
All FAME projects depend on the support of people like you! To support the work of Taylor and other PhD Candidates through FAME projects, consider a tax-deductible donation to the ‘Where the need is greatest’ Fund:
Lawson, TJ, Wilcox, C, Johns, K, Dann, P and Hardesty, BD 2015. ‘Characteristics of marine debris that entangle Australian fur seals (Arctocephalus pusillus doriferus) in southern Australia.’ Marine Pollution Bulletin 98(1-2): 354-357
Speakman, CN, Johnstone, CP and Robb, K 2019. ‘Increased alertness behaviour in Australian fur seals (Arctocephalus pusillus doriferus) at a high vessel traffic haul-out site.’ Marine Mammal Science 36(2): 486-499