Indo - Pacific BOTTLENOSE DOLPHINS
THERE ARE 90 - 120 DOLPHINS IN THE MANDURAH WATERS!
The Peel-Harvey estuary has a population of approximately 90 resident dolphins and another 40 that visit occasionally from coastal waters. Mandurah waterways are ideal for dolphins due to the abundance of fish which is their choice of food and the shallow, warmer, calm, protected waters which is great for birthing. The large population of dolphins in the region is a great sign of how healthy our waterways are to be able to sustain them.
The dolphins that inhabit the Peel-Harvey and adjacent coastal waters are Indo-Pacific bottlenose dolphins. Their scientific name is Tursiops aduncus. The larger, offshore variety are common bottlenose dolphins whose scientific name is Tursiops truncatus. Bottlenose dolphins are small, toothed whales and belong to the oceanic dolphin family known as ‘Delphinidae’.
They get the name bottlenose because their beak is shaped like a bottle. They have a prominent dorsal fin and are grey in colour with a white belly. Their skin is smooth and feels rubbery. Their thick blubbery under layer is what keeps them warm.
2 Size and Weight: The size of an adult dolphin in Mandurah ranges from 2.3 – 2.6 metres long and they weigh up to 220kg. At birth they are approximately 1 metre in length, weighing up to 20kg. The dolphins in Mandurah and the South West are much larger in size than the dolphins in Monkey Mia, despite being the same species (as shown by the current laser research conducted by Martin Van Aswegen). This is because body mass decreases with increasing water temperature, as the dolphins in warm water do not need the extra mass/warmth.
Bottlenose dolphins can live to over 40 years of age. In fact, we have a number of dolphins in Mandurah older than 25 years that are happy and healthy including Nikki, Bendy Wendy Fourteen, Bitts, Blake, Jack Daniels, Frankenstein, Twenty Two and Zero One.
They are very powerful swimmers with the ability to reach up to 40km/hour. That’s pretty impressive when you consider the fastest ever human 100 freestyle swimmer, another West Australian, Eamon Sullivan, managed just under 8kph in his world record. They generate the power they need from their tail flukes which, unlike fish, moves up and down instead of side to side. With the powerful up and down strokes, this makes upward and downward thrust to lift the animals through the water, a bit like wings on a bird. They’re also built for great agility. The vertebrae in their spines are very loosely connected making it sinuous like a whip, enabling fast turns and movements.
Breathing and Sleeping:
They are an air breathing mammal and so must come to the water’s surface to breathe through the blowhole on top of their head. Bottlenose dolphins can stay underwater for 8-10 minutes, however the average time they can stay under is 2 or 3 minutes. When a dolphin dives the blowhole shuts completely, otherwise their lungs would fill with water and they would drown. 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 up to a minute. They can also sleep underwater near the bottom, slowly coming to the surface to take a breath before diving again. When adding up all these micro naps, dolphins are known to sleep up to 8 hours per day.
3 Group Structure, Birthing and Mating:
Dolphins live together in groups. They can have as little as 2 dolphins in their group to over a thousand. Here in Mandurah we typically see group sizes of 2 to 15 and sometimes up to 30. Swimming in numbers offers social benefits and protection from predators such as sharks.
Our dolphins live in a fission-fusion society, which basically means that individuals come and go, groups form and break apart on a daily basis, with no matriarch or ‘dominant female’ in the group.
Few dolphin species actually live in a matriarchal society (orca, pilot whales), where related individuals will stay together as family groups known as a ‘pod’. Whereas one or more dolphins in a fission-fusion society is/are defined as a ‘group’. So with the Mandurah dolphins, it is best to refer to a fission-fusion society. (fission pronounced fish-n)
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.
Females have a baby which is called a calf every 2 to 3 years. The calf will then stay by its mothers side for up to 3 years and suckle her milk for the first 18 months, just like human babies do. At about 6 years of age the males will venture off from their mother and form strong bonds with other males, where as the females will usually continue to associate with their mother and birth pod.
Bottlenose dolphins predominantly take part in mating when the water temperature is above 20/21 degrees and here in Mandurah that is the warmer months from November to June. Some mating activity does continue through the cooler months here in Mandurah which is a good sign of how healthy our waterways are. The food must be plentiful and few environmental stressors.
With a 12 month pregnancy term most calves are born during the mating season also. In 2017 we had 5 new calves in our inland waterways – Splash, Sea, Speckle, Nikaila and Andrew, on top of 10 new calves in 2016.
During the birthing season we often see large groups (sometimes consisting of more than 20 dolphins) form. These are nursery pods. Female dolphins who have bonded with each other swim together to help care for and protect their young and mothers with newborns are often seen with other mothers and their newborns.
Mothers are very protective of their newborns and so they stay close to their calf at all times, keeping them in the calf position Scar & Speckle (April 2017) 4 and attentively direct its movements. Immediately after birth the mother will commonly be seen pushing / guiding her newborn to the surface of the water to teach it to surface and breathe so that is doesn't drown. The calf swims close to its mother and is carried in the mother’s “slip stream,” the hydrodynamic wake that develops as the mother swims. This helps the baby to swim and enables the mother and calf to stay up with the pod. Newborn calves will often be seen to mimic their mother’s behaviour as she teaches them the dolphin ways of life.
If a mother has a calf, she will be giving it fat-rich milk several times a day, so she has to keep feeding in order to provide sustenance for herself and her calf. If the calf is in its first winter and cannot build and maintain a thick blubber layer, it may not survive its first year. This is why we see such massive growth during the first few months of life, as this is where the calf is building up blubber and body condition via the mum’s rich milk. After a year or so, this growth becomes slower but more steady once the calf reaches optimal body condition.
Newborn calves have several vertical, light-coloured lines on their sides which is a result of foetal folding from being in their mother’s womb. These lines usually disappear within six months. The first few days after birth, the calf’s dorsal fin and tail flukes are like a piece of jelly flopping around - they lack firmness, but gradually stiffen.
Dolphin Gender and Mating
Sighting of the genital slits on the under-belly near the tail flukes is required to confirm the sex of a dolphin. In this area, there will be two slits: the genitals and the anus. For the males, these slits will be visibly separate. For the females, these slits will be next to each other and will appear as one long slit. Also, females have smaller slits on either side of the genital slits that are called “Mammary Slits” and they house the mammary glands.
Socialising & Communication:
Dolphins are very social animals that have a very playful and cheeky manner about them. The most obvious sign of socialising between dolphins is body contact. Examples of body contact include rubbing their bodies against each other, stroking each other with their tail Splash -1 week old (March 2017) 5 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.
They’re also social with animals outside their species. Off Mandurah’s coast they have been observed playing with whales as the whales migrate down the west coast to the Southern Ocean.
They are very curious creatures and like to socialise with us humans too. Here in Mandurah they can often be seen surfing on the wake of boats, swimming around vessels and looking at people observing them.
Why do the dolphins really surf in vessels wake? Not only do they often do it for fun, they predominantly do so as a free ride to where they are heading. As the boat moves it pushes the water in front of it, creating like an underwater wave. By positioning themselves in front of this wave, the dolphins can save their energy by not having to swim and simply gliding along.
Communication and Hearing:
Dolphins communicate with each other through squeaks, whistles, squeals and body language. They don’t have voice boxes though. These sounds come from within their blowhole and are often too high pitched for us humans to hear. They have signature whistles for each other, like us humans have a name, this enables the dolphins to be able to locate each other, which is particularly important for mothers and calves. They can actually communicate over many kilometers, depending on the water depth and habitat.
They have great hearing. Their ear openings are tiny and barely visible. The sound actually travels through their jaw. They have 10 times better hearing than humans and a greater frequency than bats.
They also use their hearing to ‘see’. Dolphins produce high frequency clicks, which act as a sonar system called echolocation. They send out clicks from a cavity in their forehead, called a melon, and when the clicking sound hits an object in the water, like a fish or rock, they bounce off and come back to the dolphin as echoes. These echoes tell the dolphin the shape, size, speed, distance and location of the object. Although they have good eyesight, this echolocation allows them to ‘see’ far further than eyes could manage. It is believed that they can actually see an object over 80 metres away using their echolocation. It is highly effective in murky/low visibility water where visual sight doesn’t help a great deal.
Dolphins have 300 degree range of vision – forwards, backwards and to the side but they can’t see up. This is why often they chase fish belly side up (called ‘snacking’ and when you have multiple dolphins doing it is called a ‘snack party’) and when bow riding they turn on their back and sides to look at the humans watching them. Each eye can also move 6 independently which means they can look in 2 different directions at once.
They have lenses, which give them a ‘swimming goggle’ effect. Although they also use underwater echo location or sonar to ‘see’ far further than eyes could manage.
Dolphins predominantly eat fish. They most commonly work together with their pod to trap fish by rounding them up and then attacking from all side to eat. They also use rock walls and sandbanks to assist them with this herding technique. Dolphins feed on a large variety of fish and although they may specialize in and target certain species, they are also opportunistic feeders who catch what they can, when they can - other seafood delights on their menu includes octopus and crustaceans.
The amount of food they eat depends on the season – During summer water conditions, when they are warm, they do not need to maintain a thick blubber layer so they usually consume between 6-8kg per day. Whereas in winter they do a lot of feeding to maintain a thick blubber layer for the colder, winter conditions, consuming between 10-14kg a day!
Dolphins have teeth. But they don’t chew their food. They use their teeth to grab the fish and then swallow their food whole and head first.
Here in Mandurah we have observed some extraordinary feeding techniques. Small fish, like garfish, are caught with rapid chases, sometimes the dolphin swimming belly-up (snacking) while the fish tries to escape at the surface. Salmon is usually pursued against rock walls, mullet chased in the shallows and often stunned with an impressive tail whack, while an octopus gets tossed in the air.
The most common fish to be tossed up in the air is the estuary catfish, also known as cobbler. Cobblers are bottom dwelling, scaleless fish that have venomous spines on their dorsal and pectoral fins. It is thought that dolphins toss a cobbler to disable the use of these spines as defence, making it a safer and easier swallow for the dolphin. Usually cobblers get tossed anywhere between one and eight times before being consumed, or sometimes let go. However, on occasions some of our dolphins have been observed to toss them more than 20 times before consuming.
They eat cuttlefish by carefully removing the head and cuttlebone so that they are left with a nice piece of soft meat. So if you are ever walking on the beach and find cuttlebone, check the bone for puncture marks from the pointy dolphin teeth.
In April/May each year we experience the ‘salmon run’ along our coast. The salmon start spawning on the South coast and can be found in Esperance towards the end of summer. From there, they make Eating Cuttlefish 7 their way west along the coast and head north in massive schools usually as far as Rottnest Island by May. In May this year (2017) researchers saw 6 Mandurah dolphins coordinating in very skilled way to hunt salmon. They had synchronized to move the salmon into a very large, tight ball, with all dolphins side by side with their heads pointed towards the fish. Then they simultaneously charged the fish to capture them. As the salmon are too big for them to swallow whole and head first, they must break them up by throwing them on the waters surface or pushing them down in the water.
The octopus toss is by far one of the most spectacular feeding events we observe in Mandurah. Most often the octopus gets tossed multiple times, in Mandurah counted up to 15 by the Mandurah Dolphin Research Group – presumably to disable and dismember the tentacles to ensure a safe swallow for the dolphin.
Our population of dolphins have also adapted to environmental changes over the years, especially when it comes to foraging. For example, the manmade canals are perfect for herding fish against, which are then picked off by the dolphins.
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, the Mandurah dolphin population has a fair proportion of observable scars from shark attacks – Particularly those in the Dawesville Cut and Coastal waters. These are usually on the upper back, because dolphins spin around to avoid being bitten on their vulnerable underbelly where their organs sit. These wounds heal over time and very few adult dolphins will die from being attacked.
Humans pose one of the biggest threats to our dolphins by destruction and pollution to their marine environment and over fishing. Discarded fishing line and net, plastics and other Rob Eating Salmon Eating Octopus 8 rubbish that ends up in our waterways can see the dolphins become entangled or digest it. This can result in them suffering starvation, amputation and eventually an agonising death. It is not only dolphins, but also birds, whales, turtles, seals and sea lions that are impacted by marine debris.
In May 2016, 3 month old calf named Halo was spotted by our crew entangled in fishing line and rope. It wrapped around his fins and tail fluke. Luckily the youngster was still able to swim, but with difficulty. We immediately contacted the Mandurah Dolphin Rescue Group, and along with them observed Halo for a few days to get photos and videos so a successful rescue could be planned. The rescue was then carried out which involved 7 hours of following the pair around to be able to get in the right position to cut it free. Hatrick was very protective of her young calf which made it difficult to get close. They were eventually herded into a shallow area and the rope cut by an extendable hook. This was very stressful for Hatrick and Halo, when then swam off at great speeds into the Peel Inlet. All rope and line was removed from Halo and he was left with some scars where the rope wrapped around, which are still visible today. The mother and calf who spent most of their time in town avoided the area for a period and any boats. Today we see them most days on our cruises and they have regained the trust of vessels to surf with us.
Here in Mandurah we are lucky to have the Mandurah Dolphin Rescue Group who have been rescuing our dolphins for over 20 years. They are volunteers and with over 35 rescues involving approximately 60 dolphins, they have done an incredible job saving our dolphins from all kinds of situations including strandings and entanglement. Without this amazing group of people, many of our dolphins we see gracing our waterways every day wouldn’t be doing so. Mandurah Cruises are a proud supporter of the group, we regularly hold fundraising events to raise money for specialised rescue equipment.
You can also do your bit to help our dolphins by not getting too close to them, not feeding them and importantly making sure their home is kept free of litter. And if you don’t live locally, now you know a bit more about these wonderful creatures, spread the word and look for opportunities to help protect them and their environment if you have the chance.
Mandurah a Stranding Hotspot:
Mandurah is identified as a dolphin a stranding hotspot. The estuary is a very shallow system and the dolphins can get stuck in the shallows and end up stranded when they navigate into these shallow areas and get caught out by the tide. They don’t get stuck while catching fish but rather because of where they go to catch the fish. When a dolphin strands, if not attended to quickly, can be fatal. The animals which strand are often healthy, and sometimes repeat offenders. We can identify dolphins that have stranded in Mandurah in a few ways. In the 90’s a couple of mass strandings occurred and department of parks and Halo 9 wildlife would freezebrand the dolphin so it could be easily identified for monitoring. In total 23 dolphins were freezebranded in the 90’s number 01 up to 23. Toady we still see 01, 14, 21 and 22 still healthy and happy in our waterways. Another indication of dolphins that have stranded is distinct white scarring. They can get severe sunburn if stranded for a long time. It can be quite nasty and as long is it doesn’t get infected will usually heal to white scarring. Those who have stranded for a long time can commonly end up with a collapsed dorsal fin also eg. Crook, Hayley, Scar, Bendy Wendy.
Identification All of our dolphins have names, they are identified by their dorsal fin and unique marks and scars on their body. One of the easiest dolphins to identify is Nikki who has only half a dorsal fin. The top was chopped off many years ago from becoming tangled in fishing line which cut right through. No 2 dolphins are the same they all have the individual personalities and different behaviours like we do.
Estuary Guardians Mandurah have worked together with MDRG, MDRP and Mandurah Cruises to develop a fin guide to help people be able to identify the dolphins. It was designed similar to the River Guardians Perth Fin Book.
The aboriginal Noongar word for dolphin is Kwilena (pronounced kwool-oo-na). The aboriginal people always had a great relationship with the dolphins, viewing them as family and bringing joy and love. In the dreamtime they recognised them as people.
Dolphins would regularly assist the aboriginal fishers by herding fish towards them in the shallows. The aboriginal people say the dolphins were never selfish unlike cormorants. Mandurah Cruises