Penguin Island is located about south of Beachport and about south-east of the headland known as Cape Martin. The island consists of two outcrops which are reported as being unofficially known as Outer Penguin Island and Inner Penguin Island. The latter outcrop came into existence in 1968 when a storm caused the collapse of a section of Cape Martin thereby creating a channel of about in width between the remains of the headland and an isolated stack of remnant cliff now known as Inner Penguin Island. Both outcrops are surrounded by vertical cliffs that rise to between to in height above sea level, with exception to the south-western end of the outer island where the ground falls steeply to a rocky spit. A wave cut platform surrounds most of the island. The major outcrop along with minor outcrops and submerged strata form an island which is about long and up to wide. The island is partially covered with sand which itself has partially developed in a soil. The inner island was reported in 1994 as being accessible by foot at low water while the outer island could only be accessed by boat or by swimming.
Formation, geology and oceanography
Penguin Island was formed about 6000 years ago when sea levels rose at the start of the Holocene. The island is composed of Bridgewater Formation calcareous sandstone which is a remnant of now partially submerged Robe Range which was formed during the Pleistocene. The island which is located in relatively shallow water rises from a depth of within to its west, to its south and to its east.
As of 1996, Penguin Island was reported as accommodating breeding populations of little penguins, crested terns, short-tailed shearwaters and silver gulls. In addition to being notable as being a breeding ground for seabirds, the island is also known as a site for the study of both the crested tern and the silver gull. The crested tern and silver gull population has been the subject of banding programs respectively since 1953 and 1968. Feral birds such as starlings and feral pigeons have also been recorded on Penguin Island. Mammal species observed on the island include Australian fur seals and rabbits which have been specifically observed on the inner island.
As Penguin Island has been historically accessible by foot at low water, it is possible that local Aboriginal people may have used the island as a source of food, particularly sea birds such as little penguins and silver gulls.
European discovery
Penguin Island was first described by Baudin in 1802 possibly in respect to its relevance as a source of danger to navigation:
It ends in a fitting cape , at the tip of which there lies a small island , reaching about half a league out to sea. Its southern section is low and narrow, but the northern part is and can be seen from a fair way off. The island is completely surrounded by rocks and so is hardly approachable. The same applies to the whole coast, which is shielded by a reef and a line of more or less large rocks that prevent any landing there.
While it appears that Baudin did not name the island, it is likely that its naming was made in acknowledgement of the presence of little penguins on the island.
Navigation aids
The island was the site of an operating lighthouse from 1878 to 1960 until its service was replaced by the Cape Martin Lighthouse. As of 1994, the lighthouse tower, a shed and a small jetty on the east side of the island were still present with the former two reported as being in ‘reasonable condition’, while the jetty was reported as having ‘fallen into disrepair’.
