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Corella, 2020, 44: 74-76
Location: 14°4'15"S, 125°46'17"E. Oyster Rock Passage
between Long Reef to the north and the Institut Islands/
Montesquieu Islands to the south (Figure 1), Kimberley region,
north-western Western Australia. 3.7 km NE of Sterna Island,
11 km W of Low Rocks Nature Reserve, 23 km from the nearest
point on the mainland.
Status: Unallocated Crown land. Uunguu Exclusive Possession
Native Title. Part of the Uunguu Indigenous Protected Area and
subject to the Wunambal Gaambera Healthy Country Plan1.
Surrounding waters are part of the General Use Area of the
North Kimberley Marine Park, but just north of the Institut
Islands Special Purpose Zone (conservation and recreation) and
just south of the Long Reef and East Holothuria Reef Sanctuary
Zone2. Close to the Low Rocks and Sterna Island (Kimberley)
Important Bird Area.
Description: Little information exists on Oyster Rock and
it appears on very few maps or satellite images, presumably
due to its small size and it being away from the coast. The US
Hydrographic Ofce3 suggests that it is “on the southern side
of the channel [Oyster Rock Passage], is a small rock 8 feet
high, its top whitened by birds. A coral reef, awash at low water,
extends 200 yards northward of Oyster Rock”. We calculate
(from GoogleEarth) the rock to be approximately 1 ha in area,
160 m long and 50 m at its widest point. An approximately 8-10
m high cliff in the south is covered in guano (Figure 2) and the
Rock gradually slopes into the ocean in the north (Figure 3).
Various satellite images suggest that much of the rock’s surface
area could be submerged during high tides (Figure 4). The
rock appears to be mostly basalt with no obvious vegetation,
but there are ne, green algae in the tidal zone on the northern
part of rock, and oysters and other bivalves on the shoreline
throughout.
Landing: Landing was not attempted, but the rock was
circumnavigated. Landing would be difcult due to the nature
of the site (Figures 2 and 3).
Ornithological History: Very limited, with no or little
information in major reviews of Kimberley islands4,5. The US
Hydrographic Ofce3 noted the top of Oyster Rock “whitened
by birds”. Coate et al. 6 suspected that Pied Cormorants
Phalacrocorax varius had relocated from Low Rocks Nature
Reserve to Oyster Rock based on guano present, but did not
visit the rocks. Kevin Coate visited Oyster Rock in May 2005
and found 4 Eastern Reef Egrets Egretta sacra on 8 May, and
8 Australian Pelicans Pelecanus conspicillatus and 3 Pied
74
SEABIRD ISLANDS No. 268
Oyster Rock, Kimberley Region, Western Australia
Figure 1. Location of Oyster Rock in relation to other islands in the Institut Islands/Montesquieu Islands groups.
2020
J. A. Fitzsimons, B. Stephenson and J. L. Thomas : Oyster Rock, Kimberley Region, Western Australia
75
Cormorants Phalacrocorax varius on 9 May5. It is likely that
other visits have been made as part of tour groups visiting nearby
Sterna Island, but no details are available. We circumnavigated
the rock over the course of ~20 mins on 23 April 2017. Video
and photos of species and behaviour were taken.
Breeding Seabirds and Status of Other Seabirds
Recorded
We observed the following species (and estimated numbers)
in our circumnavigation of Oyster Rock: Roseate Tern Sterna
dougallii (at least 300), Greater Crested Tern Thalasseus bergii
(100), Pied Cormorant (50), Ruddy Turnstone Arenaria interpres
(20), Red-necked Stint Calidris rucollis (30), Silver Gull
Larus novaehollandiae (10), Brown Booby Sula leucogaster
(2), and Eastern Osprey Pandion cristatus (1) (Figure 5).
Multiple instances of courtship behaviour (bills raised, wings
lowered) and copulation between Roseate Terns were observed,
and courtship between Greater Crested Terns (provisioning of
sh) was observed. Although April is the start of the breeding
season for Roseate Terns7, laying may not occur until slightly
later. For example, on nearby Sterna Island breeding was well
advanced in early June 2003 for Greater Crested Terns, Lesser
Crested Terns Thalasseus bengalensis and Roseate Terns, but
not fully commenced in early May 20046, although we observed
one Greater Crested Tern pair with an egg on Sterna Island on
the same day as this Oyster Rock inspection (see below). Whilst
there was no sand on Oyster Rock, there were enough at areas
to support egg laying (e.g. some Roseate Terns on Sterna Island
placed eggs on sandstone slabs or ledges, with no attempt at
making a nest6).
A circumnavigation of Sterna Island on the same day as the
Oyster Rock inspection and close observation of the tern colony
on Sterna Island revealed the following species (numbers
approximate): Greater Crested Tern (50-100, 1 pair with an egg),
Roseate Tern (50), Lesser Crested Tern (10-20), Red-capped
Plover Charadrius rucapillus (1), Eastern Reef Egret (1) and
Eastern Osprey (1). A circumnavigation of Gabriel Island (north
of Sterna Island: Figure 1) on the same day revealed the Eastern
Reef Egret (1) and the Red-capped Plover (1).
Further surveys are needed to determine the importance of
Oyster Rock as a breeding site.
Implications for conservation
Two of the closest islands to Oyster Rock form the Low
Rocks and Sterna Island (Kimberley) Important Bird Area
(IBA)8 because they support more than 1% of the world
population of Roseate Terns, with up to 4,000 breeding pairs
using the site9. Considering the results of our brief survey of
Oyster Rock, we recommend adding it and surrounding waters
to the Low Rocks and Sterna Island Important Bird Area. Coate
et al. 6 suggested “It is Iikely that part of the former seabird
breeding colony on Low Rocks Island Nature Reserve (12-
13 kms NE of Sterna Island), which disappeared about four
years ago, has relocated to Sterna Island,” suggesting that
there is movement between these two islands. As Oyster Rock
is close to both islands (especially Sterna), bird movement to
this rock from these islands is also highly likely. The Roseate
Tern was the most common species on Oyster Rock during our
inspection, and we observed far more of them on Oyster Rock
than on Sterna Island (inspected on the same day). Regardless
of whether Roseate Terns successfully raise young on Oyster
Rock in substantial numbers, the population is connected to
other known breeding sites (particularly Sterna Island) in the
IBA, and Oyster Rock is, at a minimum used for courtship and
copulation, roosting/resting and feeding in the surrounding
waters.
Additionally, formally protecting Oyster Rock as part
of the protected area system, such as in a Nature Reserve, is
recommended.
Coate et al. 6 noted potential pressure on Sterna Island from
visits by Cruise ships, and whilst visitation of Oyster Rock
is likely to be less than that to Sterna (as landing is difcult),
similar issues with disturbance may occur if visits from tourist
vessels increase. No landing should be permitted at these sites,
with only observation from small boats being allowed.
Other vertebrates recorded
None
Banding
No banding records
Figure 2. Oyster Rock view from the south. Note whitewash on top. Figure 3. Oyster Rock from the north.
76
J. A. Fitzsimons, B. Stephenson and J. L. Thomas : Oyster Rock, Kimberley Region, Western Australia
Corella, 44
Bibliography
1. Wunambal Gaambera Aboriginal Corporation (2010).
Wunambal Gaambera Healthy Country Plan – Looking after
Wunambal Gaambera Country 2010 – 2020. Wunambal
Gaambera Aboriginal Corporation, Kalumburu.
2. Department of Parks and Wildlife (2016). North Kimberley
Marine Park Joint Management Plan 2016 Uunguu,
Balanggarra, Miriuwung, Gajerrong, and Wilinggin
Management Areas. Department of Parks and Wildlife, Perth.
3. US Hydrographic Ofce (1920). Australia Pilot Volume
IV: North, Northwest and West Coasts Between the Western
Approach to Torres Strait and Cape Leeuwin. First edition.
Government Printing Ofce, Washington, D.C.
4. Pearson, D. J., Cowan M. A. and Caton, W. (2013). The
avifauna of larger islands along the Kimberley coast,
Western Australia. Records of the Western Australian
Museum Supplement 81: 125-144.
5. Conservation Commission of Western Australia (2010).
Status performance assessment: biodiversity conservation
on Western Australian Islands. Phase II - Kimberley islands.
Final Report. Conservation Commission of Western
Australia, Perth.
6. Coate, K. H., Done, C. and Willing, T. (2004). Seabird
Islands No. 249. Sterna Island, Kimberley Region, Western
Australia. Corella 28: 112-114.
7. Higgins, P. J. and Davies, S. J. J. F. (eds.) (1996). Handbook of
Australian, New Zealand and Antarctic Birds. Volume Three -
Snipe to Pigeons. Oxford University Press, Melbourne.
8. Dutson, G., Garnett, S. and Gole, C. (2009). Australia’s
Important Bird Areas: Key Sites for Bird Conservation.
Birds Australia (RAOU) Conservation Statement No. 15.
Birds Australia, Melbourne.
9. BirdLife International (2019). Important Bird Areas
factsheet: Low Rocks and Sterna Island (Kimberley).
Downloaded from http://www.birdlife.org on 08/11/2019.
Acknowledgements
We thank Zegrahm Expeditions for facilitating access to this site
and Allan Burbidge for helpful comments on a draft of this manuscript.
Date compiled: 15 November 2019
James A. Fitzsimons, The Nature Conservancy, Suite 2-01, 60
Leicester Street, Carlton, Victoria 3053, Australia, and School
of Life and Environmental Sciences, Deakin University, 221
Burwood Highway, Burwood Victoria 3125, Australia.
Brent Stephenson, Wrybill Birding Tours, NZ., PO Box 157, Bay
View, Napier 4149, New Zealand.
Janelle L. Thomas, BirdLife Australia, Suite 2-05, 60 Leicester
Street, Carlton, Victoria 3053, Australia.
Email: jtzsimons@tnc.org
Figure 4. Oyster Rock exposure at different tide heights. (Source: satellites.pro – Apple map [left], Esri map [right]).
Figure 5. Oyster Rock with Roseate and Greater Crested Terns.