Everyone knows the face of one of the most iconic animals in the world, the bottlenose dolphin. They have the cute smile, the sleek grey body, great acrobatic capabilities, and are seen all around the world. Dolphins all around the world have different feeding behaviours the same way that people from different countries have different ways to eat and prepare food.
There is a surprising amount of variability in the feeding behaviour of dolphins in different areas of the world. I’m sure many people have seen in documentaries dolphin herding a bait ball of fish into a tight sphere and taking turns taking fish from it. This is a common feeding technique for many species of dolphins, not just the bottlenose. The dolphin population in Sarasota, Florida have been observed herding fish up against dock walls and catching them as they jump in a futile attempt to escape.
If you’ve spent time watching dolphins in the UK you have probably seen other behaviours as well such as tail slapping or kerplunking. Tail slapping is pretty self-explanatory, dolphins slap their tails against the surface of the water in order to stun fish with the resulting shockwave. Kerplunking is a cool behaviour that is named after what it sounds like. It’s basically a much stronger and more pronounced tail slap that hits a fish very hard in order to stun it. These behaviours are very common among dolphins all around the world. This might mean that this way of feeding is a very good one.
A behaviour you may not have been able to see is dolphins using their tails and noses to stir up mud and drive fish and other prey out. Dolphins will sift through the mud, much like a plough, and scare fish who were hiding in the mud. They can also use their tails to make a cyclone of mud to unveil hiding fish as well. They can also make many plumes of mud to make a “mud net” that traps fish within them. It’s similar to the “bubble nets” that humpback whales make.
Bottlenose dolphins are very famous for all the strange and amazing sounds they make. Many people know that dolphins use echolocation to find and hunt for prey. But did you know dolphins also hunt by “passive listening” where they stay quiet in order to hear their prey. In the North West Atlantic bottlenose dolphins hunt these little fish called “croakers”. They are called croakers because they make a croaking sound that even you can hear if you stick your head underwater. The bottlenose dolphins will remain quiet and try to find these fish as they croak as not to scare them away. When they get close to them they start using echolocation to get a better fix of where they are. The dolphins basically let the fish do all the work for them. It’s not just bottlenose dolphins that use passive listening either. Orca’s in the Strait of Gibraltar have also been seen listening for their prey to make sounds or swim but while remaining unnoticed.
Now that you know some of the conventional feeding habits of dolphins now we can get into some of the weird stuff. One of our interns wrote a blog about dolphin strand feeding earlier this summer. Check it out if you want to learn more in-depth stuff about it. Strand feeding is an interesting behaviour in which dolphins will swim up onto land just to chase and eat a single fish, now that’s dedication. What’s interesting is that dolphins always strand on their right side. This is thought to be because their oesophagus is on the left side of their body. So if they stranded on their left side they wouldn’t be able to swallow the very fish they were chasing.
Dolphins in Australia exhibit some weird behaviours such as wearing a sponge over then noses and hydroplaning to get food. Dolphins will take sponges and put them on their noses in order to protect their noses from spines or stinging animals while they hunt. It’s a very odd behaviour and is one of the few instances of “tool” use in marine animals. Hydroplaning is a really cool behaviour in which bottlenose dolphins will swim very close to the shore where they skim along the beach while chasing a fish. The behaviour is similar to strand feeding except that the dolphins do not strand themselves onto the beach but glide on it instead.
Dolphins are very smart and they are very aware of our use of the oceans. Dolphins understand that we also fish for food as well and use us to help them with their food. Dolphins have been known to follow fishing boats to catch any leftover fish that either escape the nets or are thrown overboard. Sometimes dolphins, and other toothed whales such as pilot whales and even sperm whales, interact much closer with fishing boats. They have been known to take fish off of fishing lines and hooks. This is called “depredating” and in certain areas of the world it is a major source of food for them. Another not so favourable interaction is begging. Much how pets beg at the dinner table dolphins will go up to boats and open their mouths begging for food. In the same way that it’s not ok for pets to beg at the table, it is not ok for dolphins to do so either. Actually feeding the dolphins is super not ok and can lead to problems. There was a case in Sarasota where a dolphin’s major food source was food it got from begging (Cunnigham et al., 2006). This is harmful to dolphins because it encourages them to not hunt. If they didn’t hunt I wouldn’t be able to write this blog about the many cool ways they do it. You should never approach and feed any marine mammal ever.
So we’ve talked in detail about all the cool and different way that dolphins eat all around the world. However, there is something about these feeding behaviours that is just as if not more interesting. It turns out that in many areas around the world some feeding habits are taught only to females by their mothers. For some reason females gain exclusive knowledge of these feeding habits from their mothers. It just adds to the long list of questions we have about dolphin communities and how individuals function within them.
Written by Valentin Neamtu, Sea Watch Research Intern 2015.
References:
Cunningham-Smith, Petra, et al. “Evaluation of human interactions with a provisioned wild bottlenose dolphin (Tursiops truncatus) near Sarasota Bay, Florida, and efforts to curtail the interactions.” Aquatic Mammals 32.3 (2006): 346-356.
