Dolphins Rub Shoulders With Fishermen!

In the coastal waters of Laguna, Brazil, a shoal of mullet is in serious trouble. Two of the most intelligent species on the planet – humans and bottlenose dolphins – are conspiring to kill them. The dolphins drive the mullet towards the fishermen, who stand waist-deep in water holding nets. The humans cannot see the fish through the turbid water. They must wait for their accomplices.

As the fish approach, the dolphins signal to the humans by rolling at the surface, or slapping the water with their heads or tails. The nets are cast, and the mullet are snared. Some manage to escape, but in breaking formation, they are easy prey for the dolphins.

In the coastal waters of Laguna, Brazil, a shoal of mullet is in serious trouble. Two of the most intelligent species on the planet – humans and bottlenose dolphins – are conspiring to kill them. The dolphins drive the mullet towards the fishermen, who stand waist-deep in water holding nets. The humans cannot see the fish through the turbid water. They must wait for their accomplices.

As the fish approach, the dolphins signal to the humans by rolling at the surface, or slapping the water with their heads or tails. The nets are cast, and the mullet are snared. Some manage to escape, but in breaking formation, they are easy prey for the dolphins.

According to town records, this alliance began in 1847, and involves at least three generations of both humans and dolphins. Today, there are around 55 dolphins in the neighbourhood, and around 45 per cent of them interact with the fishermen.

Now, Fabio Daura-Jorge from the Federal University of Santa Catarina, Brazil studied Laguna’s dolphins to learn how their unusual collaboration has shaped their social networks. He spent two years taking photographs of the local dolphins, and noting where they travelled and who they were associated with. As is typical for bottlenose dolphins, the Laguna individuals formed a ‘fission-fusion’ society – they all belonged to the same large group, but they had specific ‘friends’ whom they would spend more time with.

The dolphins roughly split into two separate groups, based on their tendency to hunt with humans. Those that co-operated with the fishermen were more likely to spend time with each other than the uncooperative individuals. Likewise, the uncooperative dolphins showed a tendency to stick to their own clique.

One individual even seemed to act as a “social broker”, and spent time with individuals from both groups.

Of the two groups, the human-helpers seemed to form stronger social ties. It is not clear if helping humans means they spend more time together, or vice versa. But certainly, their close associations increase the odds that one dolphin will learn the hunting technique from its peers.

This fits with what we know about bottlenose dolphins. They are extremely intelligent animals and different populations have developed their own quirky foraging traditions by learning from one another. Some use sponges to guard their snouts when they root about the ocean floor for food. Others can prepare a cuttlefish meal by sequentially killing and stripping them.

Daura-Jorge now wants to understand why only some of the dolphins help the fishermen, given that doing so clearly provides them with benefits, and all of them have the opportunity to help. By analysing the dolphins’ genes, he hopes to piece together their family trees, and work out if mothers pass on the behaviour to their calves.

There are several cases around the world where dolphins feed on the discarded remains of fish thrown away by humans. But the Laguna animals do far more than that – the fisherman wouldn’t catch any fish at all without their help. A similar alliance takes place half a world away in Burma, where Irrawaddy dolphins also fish cooperatively with humans.

 

Brain + Teamwork = Fishes Into The Mouth

Bottlenose dolphins are one of the fastest animals on Earth and the ones off the coast of Florida have invented a new way of hunting their elusive and fast swimming prey. Swimming in ever decreasing circles the dolphins stir up the mud from the sea floor with their tails, and trap schools of fish inside the resulting ring of mud. The panicked fish jump out of the water away from the ring and straight into the waiting mouths of the other dolphins. Developing this sort of advantage over other groups of bottlenose dolphins may give this population the edge in the battle for survival of the fittest.

The bottlenose dolphin has a grayish skin tone that varies from dark to light gray starting at the dorsal fin and ending near the lower body. The under-body is much lighter in color and is closer to white than gray. They have slim aero dynamic bodies and a short beak with conical-shaped teeth, which helps these dolphins find and capture various prey. As far as size goes these dolphins can reach lengths between 6.5 – 13.5 ft and weigh anywhere from 300 – 1,400 lbs. when fully matures. Unlike other species of dolphin the male is typically larger and heavier than its female counterpart.

HABITAT

These dolphins can often be found living in warm tropical/sub tropical environments in waters above 50° F.

They can be found both in coastal and offshore waters in areas such as South Africa, Australia, Cape Cod, Chile, Hawaii, the Gulf of Mexico, Japan, Nova Scotia, Norway and Southern California and Florida in the United States.

They are also found in various parts of the Atlantic and Pacific oceans, the Black Sea and the Mediterranean.

DIET

The diet for the bottlenose dolphin consists of a variety of fish, squid and crustaceans.

While these dolphins do possess teeth they only use their teeth to grab their prey and swallow their food whole.

During hunting periods several dolphins can often be found working in groups pushing the fish towards the shore and circling or entrapping them so that they can have the best opportunity of successfully capturing their prey.

A group of dolphins may work together to herd the fish into a small ball or corner then take turns darting in and eating their immobilized prey.

They may also use their tail or flukes to hit and stun the fish, so that they will be easier to capture.

While they sometimes hunt in groups these dolphins may also be found hunting alone and both the hunting methods and number of dolphins found hunting in a pod can vary depending on the dolphin’s habitat and environment.

In addition to using sophisticated hunting strategies these dolphins are also equipped with echolocation, which allows them to detect where their prey is, alerts them of threats and helps them avoid collision with nearby objects.

DOLPHINS AND HUMANS

Bottlenose dolphins are known to be boisterous and outgoing when in contact with humans and may display curiosity or excitement when communicating with people.

These marine mammals are highly intelligent and can learn complex tricks and behaviors that are taught to them by trainers.

They’ve even been featured as the primary attraction at marine shows and have played specialized roles in the military where they help soldiers locate mines and rescue people who have been lost at sea.

Their high level of intelligence has been so interesting to humans that scientists have been trying to devise a way to communicate with dolphins through technology and hope to one day be able to have a conversation with these amazing marine mammals.

From a cultural perspective dolphins have been popularized by movies and tourism, considered angelic beings by certain cultural societies and considered the reincarnation of family members through the beliefs of various groups.

Since their discovery humans have been attracted to the bottlenose dolphin as these dolphins have been attracted to us.

THREATS

These dolphins are known to face threats from poachers and dolphin hunters looking to sell their meat to stores and restaurants for consumption by humans, used for crab bait and killed in order to maintain fish supplies since dolphins may make it difficult for fisheries to work effectively at capturing fish due to large stocks of dolphins eating the fish and/or attacking fish in fishing nets.

Bottlenose dolphins also face threats from accidentally being captured in fish nets intended for fish.

In these instances a dolphin may mistake a balled group of fish for easy prey and run right into the fishing net.

Because dolphins are mammals they must come to the surface for air, so there is a good chance that they could drown when caught in a fishing net, which prevents them from getting adequate oxygen to the lungs.

Most species of dolphin can only hold their breath for a few minutes (5 – 15 minutes) before they need to come up for air.

Recently extreme tourism has also been noted as a threat due to large quantities of people and boats in the ocean, which could cause collisions with the dolphins or even contribute to water pollution.

In terms of natural threats these dolphins may face occasional threats from sharks or groups of hungry killer whales as well as getting sick from natural diseases and parasites.