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Dolphins on the Swan River

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Did you know that there are roughly 30 Indo Pacific Bottlenose Dolphins living In the Swan River (Derbarl Yerrigan)




















The Name 

Tursiops aduncus or Indo-Pacific Bottlenose Dolphin














About


The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb).[3] It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa.[3] Its back is dark grey and its belly is lighter grey or nearly white with grey spots.

Until 1998, all bottlenose dolphins were considered members of the single species T. truncatus. In that year, the Indo-Pacific bottlenose dolphin was recognized as a separate species. The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin, has a proportionately longer rostrum, and has spots on its belly and lower sides.  It also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw compared to 21 to 24 for the common bottlenose dolphin.

 Some evidence shows the Indo-Pacific bottlenose dolphin may actually be more closely related to certain dolphin species in the genera Stenella and Delphinus, especially the Atlantic spotted dolphin (S. frontalis), than it is to the common bottlenose dolphin.

Much of the old scientific data in the field combine data about the Indo-Pacific bottlenose dolphin and the common bottlenose dolphin into a single group, making it effectively useless in determining the structural differences between the two species. The IUCN lists the Indo-Pacific bottlenose dolphin as "data deficient" in their Red List of endangered species because of this issue.








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Description

Indo-Pacific bottlenose dolphins are very similar to common bottlenose dolphins in appearance. Common bottlenose dolphins have a reasonably strong body, moderate-length beak, and tall, curved dorsal fins; whereas Indo-Pacific bottlenose dolphins have a more slender body build and their beak is longer and more slender.[9] The Indo-Pacific population also tends to have a somewhat lighter blue colour and the cape is generally more distinct, with a light spinal blaze extending to below the dorsal fin. However, although not always present, the most obvious distinction can be made with the presence of black spots or flecks on the bellies of adults of Indo-Pacific bottlenose dolphins, which are very rare in common bottlenose dolphins.

Their teeth can number between 23 and 29 in each upper and lower jaw, and are more slender than those of common bottlenose dolphins.
 Size of Indo-Pacific bottlenose dolphins can vary based on geographic location; however, its average length is 2.6 m (8.5 ft) long, and it weighs up to 230 kg (510 lb).
The length at birth is between 0.84 and 1.5 m (2.8 and 4.9 ft).

The local population centering Mikura-jima is claimed to be a distinct form or species.


Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods(particularly squid).

In one study, researchers looked at the feeding ecology of Indo-Pacific bottlenose dolphins by analyzing the stomach contents of ones that got caught in the gillnet fisheries off Zanzibar, Tanzania. The prey items found in the stomach contents included 50 species of bony fish and three species of squid. From their results, the researchers concluded the most important prey group was fish, which accounted for 87% of the total number of prey items consumed and occurred in 24 of 26 stomachs examined. Cephalopods comprised the other 13% of prey items and were found in 13 of the 26 stomachs.

 The remains of some crustaceans were also found; they hypothesize, however, they were consumed secondarily, since a number were found intact in the fish prey stomachs and therefore were not included in the diet analysis.












Behavior



Indo-Pacific bottlenose dolphins live in groups that can number in the hundreds, but groups of five to 15 dolphins are most common.
n some parts of their range, they associate with the common bottlenose dolphin and other dolphin species, such as the humpback dolphin.

The peak mating and calving seasons are in the spring and summer, although mating and calving occur throughout the year in some regions. Gestation period is about 12 months. Calves are between 0.84 and 1.5 m (2.8 and 4.9 ft) long, and weigh between 9 and 21 kg (20 and 46 lb). 
The calves are weaned between 1.5 and 2.0 years, but can remain with their mothers for up to 5 years. The interbirth interval for females is typically 4 to 6 years.

In some parts of its range, this dolphin is subject to predation by sharks;[6] its lifespan is more than 40 years.

Indo-Pacific bottlenose dolphins located in Shark Bay, Australia, are thought to have a symbiotic relationship with sponges by doing what is called "sponging". 
A dolphin breaks a marine sponge off the sea floor and wears it over its rostrum, apparently to probe substrates for fish, possibly as a tool, or simply for play.

The first report and footage of spontaneous ejaculation in an aquatic mammal was recorded in a wild Indo-Pacific bottlenose dolphin near Mikura Island, Japan, in 2012.

A tribe of Austral indigenous people on the Mornington Island have been communicating with wild dolphins for millennia. They are said to have "a medicine man who calls the dolphins and “speaks” to them telepathically. By these communications he assures that the tribes’ fortunes and happiness are maintained."
Status and threats

The species is not considered to be endangered; its near-shore distribution, though, makes it vulnerable to environmental degradation, direct exploitation, and problems associated with local fisheries.

The major predators of this species are typically sharks, and may include humans, killer whales (Orcinus orca), and sting rays. In the early 1980s, many were deliberately killed in a Taiwanese driftnet fishery in the Arafura Sea, off northwestern Australia. 

Large-mesh nets set to protect bathers from sharks in South Africa and Australia have also resulted in a substantial number of deaths. Gillnets are also having an impact, and are a problem throughout most of the species' range.
Captivity

These small cetaceans are commonly found in captivity, causing conservation concerns, including the effects of removing the animals from their wild populations, survival of cetaceans during capture and transport and while in captivity, and the risks to wild populations and ecosystems of accidentally introducing alien species and spreading epizootic diseases, especially when animals have been transported over long distances and are held in sea pens.

Bottlenose dolphins are the most common captive cetaceans on a global scale.

Prior to 1980, more than 1,500 bottlenose dolphins were collected from the United States, Mexico, and the Bahamas, and more than 550 common and 60 Indo-Pacific bottlenose dolphins were brought into captivity in Japan. By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquaria has increased from only 6% in 1976 to about 44% in 1996.







Video 







Life span
Females – 40 years
Males – 30 -35 years

Size
An average size adult is 2.4 m long and weighs 155 kg.

Status
Common in their range
Protected by the Wildlife Conservation Act 1950

Reproduction
12 months gestation
Females have one calf about once every 4 years
Females can have 8 calves in her lifetime
Calf stays with the mother for 3-5 years
Females may first calf at around age 10-12
Males may not mate successfully until much later because of intense competition for access to females

Social structure
Females have a network of female friends
Males usually bond closely to one other and form a long-term partnership known as an ‘alliance’
After weaning, juvenile dolphins spend several years learning about their environment and the dolphin society they inhabit. During these years, they learn important social and feeding skills that they will need to survive as adults.

Home range in the Swan Canning Riverpark
The ‘Swan’ dolphins split their time between the estuary and coastal areas such as Owen Anchorage.
They are often seen in the Canning River and some will occasionally travel into the upper reaches of the Swan River.
Dolphin Watch volunteers can help us determine how far they travel upstream.
The dolphins most commonly seen in the Riverpark use the year-round and are thought to be long-term residents. 
It is likely that their mothers were also ‘river’ dolphins.



Interesting facts
In Shark Bay bottlenose dolphins use a feeding technique called “sponging”. 
To “sponge’, dolphins take a marine sponges off the sea floor and wear it on their beak (rostrum). The sponge provides protection while they probe around on the bottom for fish hidden in sand or under rocks.

Until recently, all bottlenose dolphins were considered members of one species. 
Now, scientists recognize two species: the Common Bottlenose Dolphin (Tursiops truncatus) and the Indo-Pacific Bottlenose Dolphin (Tursiops aduncus). In southwestern WA, Common Bottlenose Dolphins are generally found well offshore, while Indo-Pacific Bottlenose Dolphin occur in coastal and estuarine areas.

In coastal and estuarine areas, bottlenose dolphins are generally observed in small groups of less than ten dolphins. In the open ocean, groups may number to the hundreds.
Scientists identify dolphins by permanent marks on their dorsal fins. These markings are scars and allow for dolphins to be monitored across their life-times.
River Guardians’ members can become Dolphin Watch volunteers learn how to monitor dolphins in the rivers.

Murdoch and Curtin universities work together with the Swan River Trust to monitor dolphins in the rivers.
River Guardians’ members can become Dolphin Watch volunteers and learn how to monitor dolphins in the rivers www.riverguardians.com

Threats to dolphins
Dolphins live stressful lives. And adult needs to find more than 12-15kg of a fish a day and they are on constant look-out for sharks. A female also has to look after a dependent calf for 3-5 years.
Human add to the stress that dolphins experience and so the best thing we can do is leave them alone and let them do what they need to do.


Threats to dolphins include:
entanglement in discarded fishing line
health effects from some contaminants
loss of habitat and declines in food species
poor water quality from nutrient contamination
toxic algal blooms
disturbance from boat traffic
excessive underwater noise
people illegally feeding dolphins which can lead to boat strike and entanglement





where to see them


Perth - Swan river
anywhere from the river in North Fremantle to Belmont

They will work the deep and shallow as they tour around 

Shallow zones
frequent sightings of dolphins along the riverside if Perth cbd and South Perth and even inside the Elizabeth Quay 

Most common 
the larger area West side of the Narrows Bridge down to Peppermint Grove 


Deep water zones 
Blackwall Reach, Deepwater Point or the stretch between Matilda Bay and the Narrows Bridge.

Blackwall Reach is close to Point Walter, a pretty stretch of foreshore with a sand spit, where you can also see waterbirds feeding and resting and relax in the café.

The Narrows Bridge has the benefit of creating a natural funnel, which gives dolphins an opportunity to find a lot of fish in a small area. 
Look for them between here and Matilda Bay, and in the wake of the ferries. 






Ocean 
Rockingham and Mandurah dolphin spotting tours 










Ask the Pro



1. Swan River
2. Ocean Perth (Rockinham tours)






1. Swan river
Local Swan river boat tours from Elizabeth Quay 

ask the local skippers as they are out on the tide every day 





Liz Quay boat charters 

15 min to 1 hour charter for single to 8 people 







fleet of 11 seater heritage boats on slow quite solar powered route from Liz Quay around to Claisebrook cove with stops along the way 











Jet Boat Eco tour and Dolphin spotting on the Swan river
















2. Ocean Perth 


Rockingham Wild Encounters

tours to Rockingham and swim with dolphins




tours to view &/or swim with wild dolphins





















eBook



An identification catalogue of Dolphins on the Swan river park








FAQ



How many dolphins are in the Swan River?

Report says 36 dolphins live in Swan River. A report on dolphins in Perth's Swan Canning Riverpark confirms at least 20 permanent residents and 16 visitors. Prepared by Murdoch University for the Swan River Trust, the report shows 36 dolphins used the river in 2011-12.





Best time to see them?

all times of the day 
mornings and sunset you can spot them working the edges of the wall boarding Perth and South Perth - perhaps depends on the tide or simple they are doing the rounds or a change from fish to crabs 
 
in the day they can be anywhere working the waters 
your get the best intel from the loca river skippers 








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