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Marine investigation:
Changes in the abundance of Fur Seals
on Big Seal and Little Seal Islands
Seal Rocks, NSW, Australia
Note that the abundance values are only adjusted for unavoidable differences in the length of the transect..
Big Seal Island
(2.7 km out)
|
Little Seal Island
(3.7 km out)
|
View south from below Sugarloaf Point Lighthouse
Sugarloaf Point Lighthouse keeper's family with pet seal (1884)
Photo courtesy of Mark Sheriff
Through time..........
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~1923: Ending of the harvesting of seals for the Australian fur and oil trade. After this many states allow the culling of seals as it is perceived that seals compete for fish with fishermen
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1925: Five hundred seals estimated to be on Big Seal Island (Le Souef 1925, cited in Warneke 1982).
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1960s-1970s: By the 1960s approximately twenty Australian Fur Seals inhabited Big Seal Island all year round, with numbers increasing in summer. Occasional breeding occurred. By the end of the 1970s their numbers crashed - cause not clear (NPWS 2012 - Seal Rocks Nature Reserve draft plan of management)
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Last decade: Only small numbers of seals recorded on Big Seal Island, although some isolated peaks occur (e.g. a count of approx. fifteen in the 2017 winter). Virtually all seals were recorded on the western side of the island. (Dr David Harasti 22/8/24; Principal Marine Scientist , NSW Dept. of Primary Industries)
Valerie Taylor's recollections of seals about Seal Rocks in 1960/70s
(conversation on 26th August 2024)
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Valerie was adamant that Sea Lions were present on both BigSeal and LittleSeal Islands (this was based on flipper characteristics; Sea lions have larger furless flippers with nails most easily seen on the rear flippers)
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A maximum of 60 were seen at one time and all were on the western sides (landward) of the islands, although sometimes they followed divers around to the eastern sides
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When approached they would playfully rush down from the island and surround Valerie and Ron's boat, and when SCUBA diving, they would endlessly come face to mask
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Much to Valerie and Ron's distress, the seals/Sea Lions were regularly culled (shot) on the islands up to the 1980s
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Distressing also was the observation that pups were regularly taken from the islands by an unscrupulous animal trafficker and sold to marine-entertainment sites in Queensland (Invariably the pups would die after two weeks as they were not given suitable milk)​
Expected seasonal pattern? (hypothesis)
Background understanding:
Most fur seals on Big Seal Island are likely to be males.
Males intending to breed will leave Big Seal Island in late-winter--early-spring for Montague Island (out from Narooma), the key breeding site in NSW some 470 km to the south. In early summer the males leave the breeding site to take pressure off the females feeding the resulting pups,
Expected seasonal pattern on Big Seal Island:
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Late-winter--early spring = numbers reduce
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Spring = lowest numbers
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Summer-autumn = numbers increase
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Winter = highest numbers
​
Two species of fur seal possible?
Within 50 km of Seal Rocks NSW
Australian Fur Seals have been recorded on 23 occasions
and New Zealand Fur Seals on 16 occasions
(Atlas of Living Australia)
Even close up it is difficult to separate
Australian Fur Seals from New Zealand Fur Seals.
So with long-distance photography used in this case,
it is near impossible to tell the difference.
Most reliable separation of species: behaviour
(follows Goldsworthy et al. 1997)
Less reliable separation of species: body features
Some of these can change with aging, sex and seasons
Other possible seal species that may occur
at times on the islands?
Within 50 km of Seal Rocks NSW
Leopard Seals have been recorded on 4 occasions
and Sea Lions on 1 occasion
(Atlas of Living Australia)
Note that the abundance values are only adjusted for unavoidable differences in the length of the transect..