History of Moreton Bay
A paradise on Brisbane’s doorstep, Moreton Bay is a huge sub-tropical lagoon sheltered by the massive sand islands of Moreton and North Stradbroke. Although Moreton Bay is over 3400 square kilometres in size, it has an average depth of only 6 to 7 metres. Due the relatively shallow depth, the waters of Moreton Bay are warm and filled with sunlight – providing an extremely productive habitat for marine plants and animals.
The many islands of the bay nest in crystal clear waters, extensive tidal sand flats, sea-grass meadows, coastal mangroves and fringing reefs. This accessible sub-tropical island eco-system is home to many species of birds, fish and other wildlife.
Moreton Bay wetlands
Moreton Bay is an internationally significant protected site under the Ramsar Convention (protection of migratory shore birds). The predominant drawcard for these birds is the bay’s extensive coastal wetlands.
Moreton Bay wetlands range from tidal flats, freshwater lakes and swamps on the offshore islands, to intertidal mudflats, marshes, sandflats and mangroves on the bay’s western shores. These varied habitats contribute to the bay’s biological diversity which is due to both the location and climate of the bay – supporting tropical, subtropical and temperate wildlife species.
Seagrasses and mangroves
The seagrass beds and mangroves of Moreton Bay provide food and habitat for a wide variety of marine life.
Seagrasses are flowering plants like lilies or orchids. They need sunlight, clear water and nutrients to flourish – all present in abundance in Moreton Bay. The seagrasses in southern Moreton Bay in particular provide food and habitat for dugong, turtles, fish and crustaceans. Seagrass beds are also present along the western coast of Moreton Island.
Mangroves are a natural nursery for fish, prawns and crabs. Mangrove forests also act as stabilisers, helping to reduce excessive sediment flow and decreasing the threat of erosion caused by currents and water runoff.
Dugong, also known as sea cows, can grow to over 3 metres long and weigh up to 400kg. Adult dugong feed on seagrass and can consume up to 30kg per day. The female dugong takes up to 17 years to mature and even then, only produces one young every five years, and only if the conditions are suitable. Dugong are listed as a vulnerable species under the Nature Conservation Act 1992.
Every June the Australian humpback whale population migrates from their Antarctic feeding grounds, north along the eastern coastline of Australia, up to lagoons of the Great Barrier Reef. From July onwards, after calving, the humpbacks start to migrate south—back to their Antarctic home waters. Many stopovers in Moreton Bay on the return journey. Most humpbacks have left Queensland waters by early November.
The humpback whale is one of the great whales. Adult females grow up to 15 metres in length, slightly longer than the males. A mature humpback can weigh up to 40 tonnes. Humpbacks are generally blackish with white underbellies and sides, often adorned with barnacles as testament to their long lives at spent in at sea. They are listed as a vulnerable species under the Nature Conservation Act 1992.
Other whales known to visit Moreton Bay Marine Park throughout the year include killer whales (Orca), southern right whales, sperm whales, and minke whales.
Moreton Bay Marine Park has two resident dolphin species, the bottlenose dolphin and the Indo-Pacific hump-backed dolphin.
Bottlenose dolphins are large dolphins that have a short, stout beak (shaped like a bottle) marked with a crease where it meets the forehead. Their average size is about 3m and they feed on invertebrates, fish and squid. In Moreton Bay they form groups of about 15 individuals, while offshore these family groups may number in the hundreds. A single calf is born after a gestation period of about a year. Bottlenose dolphins have a life span of up to 45 years.
Indo-Pacific hump-backed dolphins are lighter in colour and smaller than their bottlenose cousins. They are found in Moreton Bay and in the nearby Tin Can Bay, in the Great Sandy Strait. Body colour ranges from white to pinkish to grey, with some individuals being heavily spotted. They grow to a length of about 2.7m and the beak is longer than the bottlenose. Less common than the bottlenose dolphin, the Indo-Pacific hump-backed dolphin is listed as rare under the Nature Conservation Act 1992.
The seagrass meadows of Moreton Bay Marine Park provide a vital feeding area for marine turtles. Species commonly seen in Moreton Bay include green turtles, loggerhead turtles and hawksbill turtles. Leatherback turtles and flatback turtles are also less regular visitors to the bay.
Green turtles have an olive-green shell and a relatively small, round head compared with the size of its body. While they commence life as carnivorous, eating tiny marine animals, the adult green turtle is totally herbivorous, feeding on algae and seagrass. This herbal diet has given the internal organs and flesh of the species a green colour, from which it takes its name. Slow reproducers, they take 30 to 50 years to mature and only breed every two to eight years. Green turtles are listed as vulnerable under the Nature Conservation Act 1992.
Loggerhead turtles are slightly more rare and listed as endangered under the Nature Conservation Act 1992. The shell is a dark brown, sometimes irregularly speckled. They are found at coral reefs, bays and estuaries in tropical and warm temperate waters. Unlike their green cousins, Loggerhead turtles are carnivorous, feeding mostly on shellfish, crabs, sea urchins and jellyfish.
Hawksbill turtles are distinguished by their bird like beak and have a shell that is heart-shaped and olive-green to brown, richly variegated with reddish-brown, dark brown and black. Hawksbill turtles are not fussy eaters, feeding on sponges, seagrasses, algae, soft corals and shellfish. Hawksbill turtles are listed as vulnerable under the Nature Conservation Act 1992.
Many species of migratory shorebirds visit Moreton Bay each year, including eastern curlews, grey-tailed tattlers, red-necked stints, ruddy turnstones, bar-tailed godwits and sandpipers.
Most of them are important migratory species listed under the Japan Australia Migratory Bird Agreement (JAMBA) or the China Australia Migratory Bird Agreement (CAMBA).
The birds travel huge distances every year – migrating from Arctic regions at the end of the breeding season, moving to the southern hemisphere and stopping to rest before the next stage of their long journey. When feeding at Moreton Bay, the weary shorebirds are storing energy for their return trip north to breed again.
The migratory shorebirds prefer muddy intertidal flats, sandy flats and coral rubble on islands in the middle of the bay.
The open sandy beaches of Moreton and North Stradbroke Islands provide ideal roosting and feeding sites for shorebirds in addition to the saltpans scattered in and behind the mangrove fringe, freshwater marshes and mangroves.
Moreton Bay also has about 3500 resident shorebirds, representing 10 species. These birds are lifelong locals, living and breeding in Moreton Bay. They include the pied oystercatcher, the bush stone-curlew and the red-capped plover. Some, such as the beach stone-curlew and the sooty oystercatcher are quite uncommon and are of international and national significance because ongoing development has drastically affected their habitat.
To breed, they build their simple nests just above the high-tide line of beaches and rocky shorelines. For this reason, they are vulnerable to damage from vehicles driving above high tide lines and from people camping on foredunes. Unfortunately, many young shorebirds are killed each year by beach traffic.