Geography and natural history
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The bay extends some 125 kilometres (78 mi) from Caloundra in the north almost to Surfers Paradise in the south. The bay's southern navigation entrance is the Gold Coast Seaway. The bay is 35 kilometres (22 mi) across at its widest point.
It is separated from the Coral Sea by a chain of three sand islands: Moreton Island in the north, North Stradbroke Island, and South Stradbroke Island in the south. Tipplers Passage is the main channel on the western coast of South Stradbroke Island. The Gold Coast Seaway is at the southern extent of Moreton Bay, before the Gold Coast Broadwater.
The bay itself contains around 360 islands in total. This includes the populated Russell, Macleay, Lamb and Karragarra Islands collectively known as the Southern Moreton Bay Islands. Together with Coochiemudlo and Garden Island these are bedrock islands. Residential development has also occurred on Coochiemudlo Island and Bribie Island. In the past Peel Island has been used as a sisal plantation, quarantine station, asylum and a leper colony.
Moreton Bay is generally shallow and sandy, though a substantive channel is maintained to allow access to the Port of Brisbane at Fisherman Islands at the mouth of the Brisbane River, for international shipping. Channels in the south of the bay are only rarely deep. Waves penetrate a small way into the bay at its four southern passages. Most waves in the bay are generated by local winds. The tidal range is moderate at 1.5–2 metres (4 ft 11 in – 6 ft 7 in) in range. Moreton Bay has an average depth of 6.8 metres (22 ft), however parts of the bay are deeper than 30 metres (98 ft). This relatively shallow depth lets light filter through to the seafloor, allowing an array of marine plants to grow which support a diverse range of fauna. The bay itself covers 1,523 square kilometres (588 sq mi) and has a catchment area 14 times larger, covering 21,220 square kilometres (8,190 sq mi). The waters of the bay are mostly blue in colour. Western parts of the bay are sometimes tinted green from algae, brown from suspended sediments or yellow-brown from humic runoff. The average annual temperature of the sea ranges from 21.0 °C (69.8 °F) in July to 27.0 °C (80.6 °F) in February.
As well as the Brisbane River, the Pimpama River, Logan River, Albert River, Pine River, Tingalpa Creek and the Schulz Canal all empty into Moreton Bay. Within Moreton Bay are the smaller bays of Waterloo Bay, Redland Bay, Raby Bay, Deception Bay and Bramble Bay.
The bay contains a number of island villages such as the settlement on the bayside of Moreton Island, Tangalooma and on North Stradbroke, Dunwich and Amity Point. Prominent coastal communities and mainland suburbs situated on the bay include Deception Bay, Scarborough, Redcliffe, Margate, Woody Point, Brighton, Sandgate, Cleveland, Victoria Point and Redland Bay. Other attractions in the bay include Pumicestone Passage and numerous boat ramps, marinas and jetties, including the Shorncliffe pier.
Sandbanks[edit]
Moreton Bay is filled with sandbanks from sand supplied via littoral drift along the coast of Moreton Island. The field of sandbanks extends across the entrance to Moreton Bay and evolved after sea level reached its present position, about 6,500 years ago after the last ice age Between Tangalooma and Skirmish Point on Bribie Island are the Middle Banks, Central Banks and Western Banks. From north of Moreton Island towards Caloundra are the Yulle Road, Spitfire Bank, and the Salamander Bank, amongst others.
Amity Banks are found just west of Amity Point, while the Moreton Banks lie to the west of the southern tip of Moreton Island. These banks can be hazard for marine navigation because they are constantly changing due to tidal currents.
The Middle Banks area close to Moreton Island has been used in the past as a source of sand for large projects such as the nearby Brisbane Airport and port facilities. Past dredging has removed 18 million metres3 and the removal of another 40 million metres3 is planned. Future sand extraction is expected to aid a major shipping channel straightening project.
To ensure the shipping channel remains open, several areas of the bay have been allocated for dredged material dumping sites. These sites have been selected to provide beach nourishment, aiding the natural long shore transport of sand along ocean beaches.
Flora and fauna[edit]
The bay's heritage protected wetlands, mudflats, and waterways are some of the healthiest in the region, supporting seasonally up to 25% of Australia's bird species. The combination of muddy habitats on the western side of the bay and sandy habitats on the eastern side of the bay together with coral and seagrass beds support more than 43 species of shorebird. Seven species of seagrass live in Moreton Bay. Zostera capricorni is the most common species. Seagrass has been lost since colonization due to increased turbidity and sedimentation from erosion in the catchment.
Collectively, around 50,000 wading birds visit the Moreton Bay each year, and its wetlands are classified by BirdLife International as an Important Bird Area (IBA). In its Shorebird Management Strategy, the Queensland Government notes that: "Moreton Bay's extensive intertidal areas are essential for shorebirds as they provide roosting, feeding and, in some cases, breeding habitat."
The bay is also home to other abundant wildlife, including whales, dolphins, dugong, sharks and turtles. From 1824 to 1950 turtles were hunted for commercial purposes. The loggerhead turtle population in the bay is the most significant in the country.
The bay is ranked among the top ten dugong habitats in Australia and together with the Gulf of Carpentaria and Torres Strait is considered one of the most important areas for dugong in Queensland. Moreton Bay is the only place in Australia where dugongs gather in herds. In the past the dugongs in herds numbered in the thousands. Some herds 5 km long by 250 m wide were seen during the 1800s. In 2009, there were just between 600 and 800 remaining. The dugongs were traditional foods of indigenous Australians. They were hunted for their oil and to make other products by early Europeans up until the 1920s.
Many whale and dolphin species can be found in Moreton Bay including humpback whales, killer whales, southern right whales, sperm whales, melon-headed whales, blue whales, Bryde's whales, minke whales, common dolphins, spinner dolphins and Risso's dolphins. Under Australia's EPBC Act the southern right whale is listed as endangered and the humpback whale is listed as vulnerable. Commercial tour operators offer whale watching cruises between June and September each year. Most of larger cetaceans observed in the bay are humpbacks, and several smaller dolphins live or regularly visit the bay.
The Moreton Bay bug (Thenus orientalis) is a species of slipper lobster found throughout the waters of Australia's north coast. The bug is a relatively expensive delicacy served in many restaurants in Queensland.
The Moreton Bay fig (Ficus macrophylla) is a large tree endemic to the east coast of Australia within a range centred on the shores and surrounds of Moreton Bay.
The southern and western parts of the bay contain shallow mud-layered waters that are protected from strong wave action by the barrier islands. This has provided excellent habitat for mangroves of which seven different species thrive within the bay, particularly in the sheltered, southern sections of the bay. The species Avicennia marina predominates.
About 1% of the bay is coral reef. Land clearing and settlement in the catchment has led to unfavourable conditions for coral growth. Climate change is expected to raise sea levels and produce warmer waters that will aid coral growth in the bay.
The bay may experience widespread outbreaks of bacteria lyngbya which can cause skin lesions and asthma attacks upon contact.
The eastern shovelnose ray is found in high abundance in Moreton Bay and has an important role in the trophic structure of the area.
Ship strikes to marine megafauna[edit]
One of serious threats to marine animals in Moreton Bay is ship-strikes. Dugongs and turtles in Moreton Bay are often killed or injured when struck by speeding boats.
Southern right whales[edit]
Unlike the southern and south-western population of Australia, southern right whales off the east coast of Australia, along with the west coast, Tasmania, and eastern Victoria, are critically endangered, consisting of only 10 or more individuals. Whales have not been seen on the east coast for many years (unlike humpbacks) as the first whale came back to both Australia and New Zealand in the early 1960s, largely due to mass illegal hunts by the Soviet Union as well as Japan, although at first it was reported to take only four whales.
Recent increases in sightings along the east coast indicate very slow but certain recovery of the species in that area, and Moreton Bay was probably a prominent calving ground for these coast-loving whales. Very small but steady appearances of southern rights have been confirmed in Moreton Bay, Gold Coast, and Hervey Bay. Seasonal presences of right whales have been recorded in Moreton Bay at least in the late 1990s, and small family groups of whales have been observed visiting the southern bay each year since 2002, especially around Toondah Harbour.
However, there was an instance of a southern right whale being fatally struck by a ferry in August 2014. This whale was a calf, and her mother was also seriously injured by the accident and her fate is still unknown. Another southern right whale, possibly with a calf was also hit few days prior to the incident with a sighting of possibly the same whales near Victoria Point. These ship-strikes and entanglements in fishing gear may contribute severely to preventing the future re-establishment of the species in the former habitats.
