Dolphins are highly sociable mammals that establish close links with other individuals of the same species and even with dolphins of other species sometimes. They seem to show empathic, cooperative, and altruistic behaviors.

Most species live in groups called pods composed of 2 to 30 dolphins as the number varies, but in some areas with abundant food, many pods can merge forming superpods with more than 1,000 members.

Dolphins depend on this interaction for hunting, mating and defending themselves. In some cases, these superpods include more than one species of cetaceans that seem to interact well together.

PODS, THE REASON

Why do dolphins group? They have several reasons to join, besides following a sample learned since they born. Small dolphin species gather into multi-member pods as a way to compensate for their size when facing predators.

In this sense, these groups provide protection to an animal that does not have large jaws or razor sharp teeth. When Dolphins are together, it is easier for them to survive if they cooperate with each other, either through communication or intimidating the predator if it is a large number of individuals.

DYNAMIC OF THEIR SOCIAL STRUCTURES

It seems that dolphins are free spirits. Studying the dynamic of the social composition of the pods, scientists discovered that when dolphins belong to a group, nothing binds them to it in a matter of space and time, this means that they can move freely to different pods that are in their vicinity, then the movement of members is continuous.

This type of social network is flat and open, and scientists found no evidence of a rigid, closed or semi-closed structure, so dolphins do not have permanent “membership” in any pod.

These open associations are another indication of their high intelligence since these actions require a lot of brain capacity. Likewise, the hydrodynamic shape of their body supports the need to move continuously between several groups of different environments.

Even though pods do not lack social hierarchy, this depends on the species. For example, bottlenose dolphins (Tursiops truncatus) establish dominance biting, chasing and striking their tails or fins against the surface of the water. The marks of teeth remain in the skin of the dolphins and are practically in all the species meaning that confrontations are also part of their life. That is why, when they want to demonstrate “who rules here,” they may not be so charming as usual but more aggressive than we think.

On the other hand, the composition and structure of the groups depend on certain circumstances: age, sex, family ties, reproductive condition and even the history of associations. Studies on the behavior of dolphins indicate that dolphins can have preferences for meeting with particular individuals and that they can be remembered and recognized after experiencing extended periods of separation. Amazing, right?

Dolphin social structure.

TYPES OF PODS

The characteristics of the groups differ according to the number of members and the circumstances mentioned above. Dolphins do not behave the same when they change from one pod to another.

There are three types of pods:

Nursery groups (mothers-offspring).
A calf stays with its mother from birth up to a few years after weaning. Usually, the mother’s bond with her son is very close and continues until the young dolphin is 6 or 8 years old. Since offspring are vulnerable, the females with calves join and form groups where they help each other to feed and protect their offspring. If a young female gets pregnant, she can return to her natal pod to give birth and care for her calf along with her female relatives, forming a multigenerational group.

The males usually do not get close to these groups.

Juvenile pods.
When reaching a certain age, both males and females leave their breeding group and join with other young dolphins, but curiously, they go to the group of their mothers occasionally for a while and then return to their youth group.

Two male dolphins can stay together for 10, 15 or 20 consecutive years.

The members of these groups are engaged in socializing with others and establishing a preamble to mating. Genres, however, are not intimately related for extended periods of time and once a female becomes pregnant, she joins the nursery group.

Adult males.
The structure of the male pods is very complex and similar to a human male group, you will see why.

Often males are related to 2 or 3 individuals of the same gender and create partnerships for cooperation purposes. Two male dolphins can stay together for 10, 15 or 20 consecutive years. The smaller groups have the objective of cooperating to ensure the mating of the others with a specific female. The larger groups make alliances with other herds of males to defend themselves but also to compete. They continue moving from pod to pod throughout their lives.

INTERNAL SOCIAL STRUCTURE

Males are dominant in all groups, but there is no evidence of strong social bonds between them and females. An example of social interaction and their high intelligence is the regular playing activities they perform. Juvenile and adult dolphins often chase each other and toss items such as seaweed back and forth.

Most experts believe that the social relationships formed by dolphins are long lasting.

Dolphins often have close body contact with other dolphins through rubbing, petting, and even hitting each other.

COMMUNICATION, THE GROUND FOR SOCIALIZATION.

Dolphins communicate with their pods usually through whistles. Each dolphin has a unique whistle that identifies it with other members of its group. If an individual is in distress, it uses a particular sound that indicates help is needed, so the pod responds quickly.

SOCIAL ACTIVITY BEYOND LIMITS.

Although it would be normal that dolphins socialize only with their kind, the interest of some species of dolphins to interact with humans is evident. In the wild, dolphins are extremely curious, and they will often engage in contact with people if a chance comes up. In captivity, dolphins are very attached to the people that usually interact with them, like trainers or researchers.

References

William F. Perrin, Bernd Würsig, J.G.M. ‘Hans’ Thewissen. Encyclopedia of Marine Mammals. Academic Press, 2009.

Karen Pryor, Kenneth S. Norris. Dolphin Societies: Discoveries and Puzzles. University of California Press, 1998.

https://link.springer.com/chapter/10.1007/978-1-4757-9909-5_7#page-1

http://www.cbmwc.org/wp-content/uploads/2012/01/Social-structure-of-bottlenose-dolphins-in-Cardigan-Bay-by-Cally-Barnes.pdf

]]> https://www.dolphins-world.com/endangered-dolphins/ Thu, 27 Apr 2017 05:31:03 +0000 http://www.dolphins-world.com/?p=121 Threats and Dangers to Dolphin Survival

Think for a moment: where is your garbage going? Where is your residual water going? What is your pollution footprint on the planet?

Do you know that some dolphin species are in danger of extinction? Although it seems obvious because there is a long list of animals which are in such condition, the truth is that many people ignore the critical preservation condition in which many dolphin species are.

Dolphins live in an environment in which threats from predators, although rare, are possible. Thanks to their complex social structure and their sense of echolocation, they can usually circumvent the risks that killer whales (even though these are dolphins) and sharks represent, however, the human activities have had a powerful impact on these animals.

Yes, some of the cute and friendly dolphins are in danger of extinction and others go the same way if we do not act now. And yes, it is humanity who must act because they have the greatest responsibility in the situation. Do you help protect dolphins?

About ten species of dolphins are in a severe danger of extinction.

STEPS TO THE END

According to the Red List of the International Union for Conservation of Nature (IUCN), all species have a level of danger or conservation. This organization makes this assessment classifying animals after a study that reveals their status on the planet and ranks them in one of the categories: Not Evaluated, Data deficient, Least Concern, Vulnerable, Near Threatened, Endangered, Critically Endangered, Extinct in Wild and Extinct.

An animal is in danger if it has a classification in the Red List starting from the Vulnerable category. However, the first two categories are also worrying, since ignorance implies the lack of actions, that is, if a species classification is Data Deficient, could be threatened, but we just do not know it, and there are not strategies to preserve it.

SOME DOLPHINS FALLING IN THIS STATUS ARE:

– Commerson’s Dolphin (Cephalorhynchus commersonii). Data Deficient.
– Heaviside’s (Cephalorhynchus heavisidii). Data Deficient.
– Long-beaked Common Dolphin (Delphinus capensis). Data Deficient.
– Clymene dolphin (Stenella clymene). Data Deficient.
– Guiana dolphin (Sotalia guianensis). Data Deficient.

For its part, the Burrunan dolphin (Tursiops australis) it is the only one that does not have any classification.

SEVERELY THREATENED DOLPHINS

About ten species of dolphins are at serious risk. The number seems small, but we must take into account that the number of species of dolphins is around 43, so we are close to 25%. One of every four species of dolphins is close to extinction.

A particular case is the Baiji or Chinese river dolphin (Lipotes vexillifer), a species that inhabited only the Yangtze River in China. For a long time, the population gradually reduced as result of pollution and bycatch, and nobody took action, and when a river inspection was carried out in 2006, the researchers did not find a single dolphin.

As result of this investigation the species Lipotes vexillifer was declared to be functionally extinct, and although probably there were only a few specimens not seen by scientists at that time, the species will not be able to recover. In 2007 there was a report of a sighting, but although there is no confirmation of this, it is possible that there are a few river dolphins alive yet.

According to the International Union for Conservation of Nature, the most threatened dolphins are:

– Baiji or Chinese river dolphin (Lipotes vexillifer). Critically Endangered.
– Hector’s Dolphin (Cephalorhynchus hectori). Endangered.
– Ganges River Dolphin (Platanista gangetica gangetica) and Indus River dolphin (Platanista gangetica minor). Both Endangered.
– Chilean dolphin (Cephalorhynchus eutropia). Near Threatened.
– Australian snubfin dolphin (Orcaella Heinsohni). Near Threatened.
– Chinese white dolphin (Sousa chinensis). Near Threatened.
Sousa chinensis includes the subspecies Sousa chinensis chinensis and Sousa chinensis plumbea.
– Atlantic Humpback Dolphin (Sousa teuszii). Vulnerable.
– La Plata dolphin (Pointporia blainvillei). Vulnerable.
– Irrawaddy dolphin (Orcaella brevirostris). Vulnerable.

As can be seen, there are several river dolphins in the list, which is a major problem for their recovery, as their distribution is very limited, the rivers are more polluted than the ocean, and river populations are usually smaller than the oceanic ones.

THE FUTURE OF THREATENED DOLPHINS

This scenario should not be underestimated. The rate of exploitation and reduction of the populations is no longer sustainable, and if some other dolphin species get extinct, this will create imbalances in the food chain, as these animals are at the top of the chain.

Some dolphins have an uncertain future, but the positive side of all this is that there are people concerned and not only that but also working actively to protect these animals. If you want to know the specific strategies implemented to attack the problem, visit the Dolphins conservation strategies article.

THREATS AND DANGERS TO DOLPHIN SURVIVAL.

Wild dolphins face some natural dangers in the ocean. However, the most overwhelming threats to their existence are the consequences of human activities.

Some dolphin species are in danger of becoming extinct, and alarming statistics suggest that illegal dynamite fishing, entanglement in fishing nets, collisions with boats and propellers, marine pollution, disease and beaching due to sonar interference, kill an increasing number of dolphins every year.

Research suggests that over 95% of dolphin deaths are directly attributable to anthropogenic causes.

SOME OF THE DOLPHIN THREATS RELATED TO MAN ARE:

INCREASING CAPTIVITY

The capture of dolphins for research and entertainment is contributing to their mortality at an alarming rate. Conservationists insist that the capture process itself is resulting in more deaths and the transportation, the exposure to diseases in captivity tanks, are added dangers that dolphins have to face when extracted from their natural environment.

The increased popularity of swimming with dolphins programs have brought more dolphins into captivity.

UNSTOPPABLE CHEMICAL POLLUTION

Another threat to dolphins in the wild is the contamination of their natural habitat from oil, chemical and heavy metal pollutants which cause them illness and higher infant mortality rates.

Since dolphins are at the top of the food chain, the impact of contamination on them is even higher as they eat fish and animals contaminated in different places.

NOISE POLLUTION.

Noise pollution is also a dangerous threat to dolphins in the wild.
Activities like oil drilling, navigational sonars, and even ship engines create continuous streams of underwater sounds that can disorient or even damage their hearing capabilities.

SEA TRAFFIC

Another cause of death are the injuries suffered by the entanglement in cages, shark safety nets and fishing nets as well as collisions with ships and propellers.

The increasing maritime traffic produces this kind of inconvenience for all the marine life.

NATURAL CAUSES.

In addition to anthropogenic threats, wild dolphins are also victims of predators. Regardless they are at the top of the food chain. Still, they have to compete with sharks and larger toothed whales for food.

The effect of Global Warming or seasonal weather changes has reduced their food sources, impacting the survival of dolphins in the wild.

References

Erich Hoyt. Marine Protected Areas for Whales, Dolphins and Porpoises: A World Handbook for Cetacean Habitat Conservation and Planning. Routledge, 2012.

seethewild.org/dolphin-threats/

https://www.theguardian.com/environment/2011/sep/28/hectors-dolphins-near-extinction

Judith S Weis. Physiological, Developmental and Behavioral Effects of Marine Pollution. Springer Science & Business Media, 2013.

Judith S. Weis. Marine Pollution: What Everyone Needs to Know. Oxford University Press, 2015.

]]> https://www.dolphins-world.com/what-type-of-herring-do-dolphins-prey-upon/ Wed, 02 Oct 2013 20:13:18 +0000 http://www.dolphins-world.com/?p=368 Answer:

There are several species of herring, being the most common the Atlantic Herring.

This species is registered as the most available fish in the ocean by the Guinness book of records, which makes them at the same time, the most hunted species by dolphins.

The Atlantic Herring dwells on both sides of the Atlantic.

The food that dolphins eat is different for each species.
While some dolphins eat fishes like herring, cod or mackerel, some others eat squids or other cephalopods.

Even more, large dolphins like killer whales, eat marine mammals like seals or sea lions and sometimes even turtles.

Usually, the amount of fish that they eat depends on the kind of fish that they hunt. While mackerels or herrings have a lot of fat, squids do not have much fat, therefore, to get the energy required for their activities, dolphins have to eat more of the latter.

On average, a dolphin with a weight of 200 – 250 Kg will eat between 10 Kg to 25 Kg of fish every day.

Usually, to hunt fish, some species of dolphins use a method called herding which is a cooperative hunting performed by a pod where some of them surround a school of fish to compress them as much as possible, while some others take turns to eat through the compacted school of fish.

Another method is corralling where dolphins take fish to shallow waters where they cannot escape.

Some species catch larger fish by hitting them with their tails to stun them and in the case of killer whales, they

Therefore the question about what do dolphins eat has to be answered for every species in particular.

In this video, you can watch a pod of dolphins working together to feed themselves and using the technique called herding to catch the fish as they surround the school of fish, and then some of them take turns to eat.

In the video, you can learn more about What do dolphins eat.