Mandurah's Dolphins
Mandurah has a population of over ~85 Indo-Pacific bottlenose dolphins that reside in the Peel-Harvey Estuary all year round. They choose to call it home due to the abundance of fish - which is their favourite food, the calm & warmer waters - ideal for raising their calves, and absence of predators. This population is unique in that dolphins are born into it, there is no immigration (coastal dolphins moving in). In the Dawesville Cut and adjoining coastal waters there is another population of ~40 dolphins. These dolphins occasionally venture into the estuary and interact with this population.
Mandurah's dolphins use the entirety of the Peel-Harvey Estuary including the Peel Inlet, Harvey Estuary, town waters, Murray River, Serpentine River and Harvey River. The majority however have their favourite frequented areas.
They can live to over 40 years of age, growing to 2.3 – 2.5m and weighing up to 220kg. Excellent swimmers, dolphins have the ability to reach speeds of up to 40km/h - compare this to the world record for humans which is 9.66 km/h!
Learn about Mandurah's dolphins below and the the threats they face living in the Peel-Harvey Estuary.
See our Projects page for what we have/are working on, to educate the community and encourage the protection of dolphins and other wildlife that call our waterways home,
There's no question dolphins are smarter than humans as they play more.
- Albert Einstein
Identifying Mandurah's Dolphins
All of Mandurah's dolphins have a name. They are identified by their dorsal fin - all of which have different marks, notches, scratches and shape. Some also have obvious markings on their body such as bold white colouration on their back, which is sunburn scarring from stranding.
The Fin Book was created to help the community identify Mandurah’s dolphins and understand their behaviours.
Five editions have been produced to date. The latest fin book is available for download HERE or hard copies can be found at Estuary Guardians Events and Mandurah Cruises Gift Shop.
We'll soon be adding identification of dolphins not featured in the Fin Book here on our website.
Diet
A dolphin’s diet consists predominantly of fish and the Peel-Harvey Estuary excels in providing this resource. They consume between 6-8kgs a day during the summer months and 10-14kg a day during the winter months, when they have to maintain a thick blubber layer for the cooler conditions.
Dolphins most commonly work together with their group to trap fish by rounding them up and then attacking from all sides to eat. They can use rock walls and sandbanks to assist. They are also opportunistic feeders who catch what they can, when they can and so, Mandurah’s dolphins have developed some complex techniques to find and catch food that is unique to their habitat - including the shallow water tail whack.
Octopus and cobbler are popular treats for our dolphins. However, they must go to a lot of effort, tossing them multiple times to dismember their tentacles and venomous spines, to be able to eat them.
Read more about feeding techniques in the Fin Book and on Mandurah Cruises Dolphin Blog.
Social
Dolphins live together in groups. Here in Mandurah we typically see group sizes of 2 to 15 and sometimes up to 30. Our dolphins live in a fission-fusion society, which means that individuals come and go, groups form and break apart on a daily basis, with no matriarch or ‘dominant female’ in the group. Females are usually seen together and have a network of female friends while males usually bond closely to one other male and form a long-term partnership known as an ‘alliance’, where they feed, pursue females and do everything together. Males may also venture alone for periods of time.
They are very social creatures which is demonstrated predominantly by body contact with other group members, stroking each other with their tail flukes or fins and nudging each other. Other physical socialising can include tail slapping, leaping into the air, chasing each other or throwing around objects such as seaweed and octopus in a playful manner.
December - May is when our dolphins are most social, as it is mating season and the waters are warmer, so they spend less time having to feed to thicken up their blubber layer.
Newborns
Female dolphins in Mandurah generally have a calf every 3 years. With a 12 month pregnancy term, most calves are born during the mating season - the warmer months December to May. The calf will stay by its mothers side for up to 3 years and suckle her rich, nutrient milk for the first 18 months, before learning to catch its own fish.
When a calf is first born they weigh approximately 20kg and are around 1m in length. They have several vertical, light-coloured folds on their sides which is a result of foetal folding – from being in their mother’s womb. These folds turn into lines and usually disappear within six months.
When a calf is first born it has whiskers on the upper jaw (rostrum) which fall out soon after birth. This enables them to better sense their environment in the first few days. Read more about a dolphin's whiskers on Mandurah Cruises Dolphin Blog.
Keep up to date with our newborns through the Mums and Calves Page and on Facebook!
Sleep
Dolphins are an air breathing mammal and so must come to the water’s surface to breathe through the blowhole on top of their head. They can stay underwater for 8-10 minutes, however the average time they can stay under is 2 or 3 minutes.
Humans are unconscious breathers, meaning we do not think about every breath we take. Whereas a dolphin must consciously choose to breathe. Because of this they can’t just fall asleep in the water, otherwise they risk drowning. So, they lay on top of the water with their blowhole exposed and rest one half of their brain whilst the other half stays alert and reminds them to keep breathing.
Dolphins usually take what are called ‘micro naps’ on the surface, that last for a few seconds to minutes at a time. When adding up all these micro naps, dolphins are known to sleep up to 8 hours per day!
Watch a video of Mandurah's dolphins sleeping on our YouTube Channel: Nap Time for Mandurah's Dolphins
Threats
Being a dolphin in the Peel-Harvey Estuary has it's challenges including stranding, fishing line entanglement and litter ingestion, shark attacks, Morbillivirus and boat strikes. Read about these threats to Mandurah's dolphins below and watch the Mandurah's Dolphins - How to Protect Them video on our YouTube channel.
What to Do
If you find a Stranded, Injured, Entangled or Deceased dolphin
Call DBCA Wildcare Helpline 9474 9055 and Mandurah Volunteer Dolphin Rescue Group 0407 090 284.
Your safety is most important!
• Don't attempt to move the dolphin - this can cause serious injury to them and you.
• Keep clear of the tail - this is the most powerful part of its body and can cause serious injury.
• Check the dolphin is breathing through its blowhole - you should see it opening and closing every so often. Ensure it is not covered or underwater - gently roll the dolphin on its belly if it is.
• Keep the dolphin's skin wet with water - avoiding the blowhole as it can drown if it gets water in there.
• Shade the dolphin using a towel or sheet to keep them out of the direct sun. Avoid placing anything on its dorsal fin, pectoral fins and tail, as this is how the dolphin can regulate body temperature.
• While waiting for help, try not to make too much noise or sudden movements as this can stress the dolphin.
• If the dolphin is sunburnt do NOT apply sunscreen.
Stranding
Mandurah has been identified as a dolphin stranding hotspot, with the average depth throughout the 134 square kilometre Peel-Harvey Estuary, only half a metre! The dolphins can get themselves caught out by shallow areas when hunting fish, particularly as tides change. A third of Mandurah’s resident dolphins have stranded, some several times! If not found in reasonable time they can die.
Large parts of the estuary and rivers are extremely remote and can be inaccessible at times, which makes it hard to spot dolphins in trouble. So, we ask the community to 'Adopt a Spot' to regularly check for dolphins. Stranding hotspots in the Peel-Harvey Estuary and rivers where we need more eyes include: Cox bay (Falcon estuary side), Nairns (Coodanup reserve), Roberts bay (East side of Peel Inlet – Point Grey), Harvey Estuary Shallows – Island Point, Herron Point & behind the island, Austin Bay, City wetlands - Samphire Cove & Creery Wetlands, Serpentine River - Goegrup Lake, Black Lake, Yalbanberup Pool.
When a dolphin strands it can receive severe sunburn - particularly on hot summer days. Their skin will blister and then expose raw pink blubber underneath - a bit like humans suffering severe burns. Dolphins have a remarkable healing ability and this sunburn will heal over time and on many occasions leave bold white sunburn scarring. These photos are of resident dolphin Hayley who stranded past Island Point in 2014 and demonstrate the blistering, recovery and scarring stages.
On some occasions, dolphins that strand manage to get themselves out when the tide rises but on many occasions they need assistance to get to deeper water. The Mandurah Volunteer Dolphin Rescue Group work with the Department of Biodiversity, Conservation & Attractions to carry out such rescues.
If you find a stranded dolphin please report it immediately, noting the dolphins condition, exact location, take photos/videos and follow the steps above.
See some of the projects we are/have worked on to increase the survival rate of stranded dolphins in Mandurah.
Entanglement
Mandurah is a fisherpersons paradise. While most people dispose of their fishing line and tackle responsibly, some don't and it ends up in our waterways, potentially causing entanglement of our wildlife.
If a dolphin is unable to free itself, fishing line and rope entanglement can result in drowning - due to inability to swim, slice through its skin - causing infections and amputation, starvation and eventually an agonizing death.
Luca's Story
In August 2019, a 15-month old Mandurah dolphin, Luca, died after becoming entangled in fishing line for the third time in six months!
Luca was observed with an entanglement in February 2019, that involved fishing line around his pectoral fin and his body. A rescue was carried out by Department Biodiversity, Conservation & Attractions (DBCA) and Mandurah Volunteer Dolphin Rescue Group (MVDRG), in a small canal off the Dawesville Cut, successfully removing the line from Luca.
When entangled, the fishing line had cut deep into his pectoral fin, making him more prone to entanglements in the future. In June, Luca was observed entangled again but this time it was also around his dorsal fin. He was rescued again by DBCA and MVDRG at the Mandurah Ocean Marina, the fishing line was removed, and an antibiotic injection was given to support his recovery.
Unfortunately, this time with a severely damaged dorsal fin, it took only three days for Luca to become entangled again. At this stage Luca’s health also started to deteriorate. The open wounds made him vulnerable to infection, the entanglement causing pain and stress while restricting his movement, and likely his ability to feed properly. So, a third rescue was planned with the approach to amputate Luca’s dorsal fin, to ensure the notches on it would not snag fishing line again. In late August a rescue attempt was made, but unfortunately he didn't survive, passing away during surgery.
The post-mortem examination revealed that the cut to his pectoral fin during the first entanglement had caused a joint infection that had spread to the bones - making him gravely ill.
Read the full story - 'Luca's Legacy' in the Fin Book.
See some of the projects we are/have worked on to reduce the occurrence of entanglement for dolphins in Mandurah.
Shark Attacks
While dolphins are top predators, they do have a lot to fear from sharks, which are well known to inhabit WA’s coastal waters. In fact, some of Mandurah's' dolphins have observable scars from shark attacks – particularly those in the Dawesville Cut and Coastal waters - not so much the Peel-Harvey Estuary population because of the shallow waters.
These scars are usually on their upper back, because dolphins spin around to avoid being bitten on their vulnerable underbelly, where their organs sit. Most of the time, these wounds heal quite fast as their skin contains incredible antibacterial properties. Very few adult dolphins will die from being attacked.
Morbillivirus
Cetacean morbillivirus is a naturally occurring virus, closely related to human measles virus.
Dolphins can contract the morbillivirus disease through the inhalation of infected particles from another cetacean – dolphins, porpoises or whales. Once transmitted the virus suppresses the animal’s immune system, damaging the major organs, causing debilitation, severe pneumonia, and encephalitis (inflammation of the brain).
Signs of morbillivirus in a dolphin include appearing thin, displaying skin and rostrum lesions, breathing difficulties and acting abnormally (eg. frantically swimming in circles).
Unfortunately, there is no vaccine or treatment for dolphins suffering from the virus. Outbreaks tend to occur every 10 years and scientists believe that dolphins who survive previous morbillivirus exposure develop natural immunity, while those dolphins born after the previous outbreak are at increased risk of infection.
Morbillivirus is not a threat to humans.
Boat Strikes
Recreational boating is is a big part of our lifestyle in Mandurah. It's important that people remember we are sharing the waterways with others - including, dolphins, birds and other wildlife whos home it is.
Propellers and the solid construct of boats can cause severe injury and even death to dolphins, if struck. While it isn't something we often see in the Peel-Harvey Estuary, it's important people boating take the following measures to prevent such incidents:
• Avoid driving over or through groups of dolphins.
• Go slow for those below - especially in shallow areas where it's harder for dolphins to maneuver out of the way.
• Give dolphins space and watch from a distance, especially if young calves are present.
• Don't chase or circle dolphins, trying to encourage them to wake surf.
