Marine life of Rottnest Island
The Rottnest Island Marine Reserve has a far greater range of habitats, marine plants and animals than that of the adjacent mainland coastline. Extensive seagrass meadows occur around Rottnest Island, and with nine species, it is second only to Shark Bay in species diversity.
Approximately 400 species of fish and twenty species of coral occur within the Marine Reserve. Fish include the Western Australian dhufish, baldchin groper, harlequin fish, cobbler, flathead, leatherjacket, samson fish, tailor, butterfly fish, moon wrasse, blue devil and migratory fish such as marlin and tuna. The Island is also a popular area for migrating humpback whales, bottle-nose dolphins and Australian sea lions.
Rottnest Island has a tropical influence with records of 135 species of tropical fish as compared to eleven species recorded off the metropolitan coastline. A major factor influencing this diversity is the position of the Island in the path of the warm Leeuwin Current. This Current often brings tropical visitors to our waters such as the Green Turtle.
Spearguns, gidgies, spear fishing and net fishing are prohibited within the Rottnest Island Marine Reserve. All reef animals except abalone, squid, cuttlefish and octopus are protected in waters around the Island.
The crustaceans around Rottnest Island include several species of crab, such as the blue manna, a favourite summer food for Western Australians. However, the best know crustacean of Rottnest Island is the Western rock lobster which occurs only in continental shelf waters of the Australian west coast between the North West Cape and Cape Leeuwin. It forms the basis of a lucrative export industry particularly to the United States and Japan. A wide variety of shrimps, prawns, barnacles and hermit crabs also inhabit the waters around the Island.
There is an enormous variety of shells on and around Rottnest Island. They are protected and should not be collected. They vary from bivalve mussels to the large baler shell. Various species of cowry, cone shells, clams, abalone and turban shells abound.
Whale watching in winter is a fascinating experience on Rottnest Island. The humpback whale which passes through the Indian Ocean off Rottnest is a baleen whale, which sieves planktonic organisms from the water, as distinct from the toothed whales which feed on squid, fish and marine mammals. The scientific name for the humpback whale is Megaptera novaeangliae, which comes from the Greek meaning "great wing" because of its huge, wing-like flippers. Land based whale watching is possible from Cape Vlamingh (The West End) during the migratory season.
Mature humpback whales weigh roughly forty tonnes and grow to nineteen metres in length. They have been protected from whaling in the Southern Hemisphere since 1963.
The population of humpback whales in Western Australian waters is believed to be about 2,000 to 3,000 animals and in Eastern Australia about 1,200 animals. They spend summer in the Antarctic and migrate north each winter towards their tropical calving grounds.
Female humpbacks are pregnant for about eleven to twelve months and the calves at birth are more than four metres long, weighing more than one tonne. The mother's milk is the consistency of chewing gum and has a thrity-five percent fat content (as compared with a human milk content of about two per cent fat). A female humpback can produce up to 600 litres of milk per day and a suckling calf can gain over 45kg a day during the first few weeks of life. Nursing ends at eleven months when the calf is approximately eight metres long.
For more information, visit diving, snokelling, fishing and Leeuwin Current pages. Or for details regarding fishing bag limits and catch sizes visit the Department of Fisheries website.