Seal Rocks, located two kilometres off the coast of the Nobbies on Phillip Island, is home to 20,000 seals - one-quarter of the entire population of Australian fur seals.

Seal research conducted at Phillip Island Nature Parks investigates seal numbers, range, diet and management issues.

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Seal numbers

In collaboration with other researchers in Victoria and other states, we monitor Australian fur seal populations by recording the number of pups. 
Australian fur seals were over-harvested during the 1800s and have taken a long time to recover. During most of the 1900s, less than 10,000 pups were born annually. Numbers started to increase during the 1980s and 1990s. A species-wide estimate of live pups in 2002 recorded a near-doubling of annual pup production since the 1980s.
To determine if pup production increased after 2002, we estimated live pup numbers again in 2007. Pups were recorded at 20 locations: 10 previously known colonies, three newly recognised colonies and seven haul-out sites where pups are occasionally born. Two colonies adjacent to the Victorian coast accounted for 51% of the pups: Seal Rocks (5660 pups, 25.9%) and Lady Julia Percy Island (5574 pups, 25.5%). Although some colonies were up and some were down in pup numbers, the 2007 total of 21,882 ± 187 (s.e.) live pups did not differ significantly from 21,545 ± 184 estimated for 2002, suggesting there was little change to overall population size. However, the colonisation of three new sites between 2002 and 2007 indicated population recovery continued.

To estimate the total population, we need to take into account pups that were born but died before we got to the colonies to count them and then, based on demographic data (survival rates and pupping rates), use a multiplier of pups born to estimate total seals. An average of about 15% of pups that are born can die in the first two months of life and a species-specific multiplier of 4.5 times pup births has been derived to estimate a total population for Australian fur seals. Using these figures, we estimate that the total population of Australian fur seals was in the vicinity of 120,000 individuals in 2007.
For more information:

  • Kirkwood et al. (2010) Continued population recovery by Australian fur seals. Marine and Freshwater Research 61, 695-701.

Seal diet
At Seal Rocks we assess Australian fur seal diet by identifying the remains of prey in bi-monthly scat (poo) collections. So far we have identified prey from 42 fish taxa, seven cephalopod taxa, no crustacea and no birds.
Six fish species represent 80% of the fish prey, in terms of frequency of occurrence, and the arrow squid (Nototodarus gould)i represented 70% of the cephalopod prey. Significant annual variability in diet is due to the presence of redbait (Emmelichthyis nitidis) in some years and its near absence in other years, and the replacement of redbait by barracouta (Thyrsites atun), red cod (Pseudophycis bachus) and leatherjackets (Family Triglidae).
The variation is related to mean sea surface temperature changes in western Bass Strait where the seals forage. Redbait proliferate in cooler years and are less abundant in warmer years. The propensity for diet regimes to exist for several years then change suggests multi-year cyclic fluctuations in the prey and in Bass Strait ecosystems  -a cyclic variation previously not recognised.
For more information:

Seal entanglement
We monitor seal entanglement rates at Seal Rocks to find how many seals get entangled and what they get entangled in. When we see an entangled seal, we try to catch it and remove the debris.
In the past 10 years, we have seen over 300 entangled seals and removed debris from over 150 seals. Trawl net (usually green) has been the most common material on entangled seals, but its frequency has decreased in recent years. Monofilament (fishing) line is next and has been increasing.
For more information:

Further links:
Seal tracking - Methods [PDF]

Seal tracking - Juveniles 2009 [PDF]

Seal information - Brochure [PDF]