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Frequently Asked Questions

Bottlenose dolphins have white bellies and ventral areas but are uniform grey on their head, sides, tail and dorsal area. Indeed they can be distinguished from other species of dolphin that occur in Ireland by having no strong markings or colour patterns. Young animals are much lighter in colour and very young animals and can be identified by pale vertical lines on their body. These are the remnants of crease marks from when the foetus was curled up in the mothers womb and it may take up to two years for them to disappear completely. Bottlenose dolphins are one of the largest of the dolphin species, and adults can range in size from 1.9 to 3.9 metres and weigh from 150 to 650 kg. Dolphins found in temperate waters such as the Shannon estuary tend to be larger and more robust than those found in warmer tropical waters and have relatively shorter, more stubby, snouts or beaks. The bottlenose dolphin gets its name due its characteristic stubby bottle-shaped beak.

Where would you find bottlenose dolphins in Ireland?

Bottlenose dolphins have been observed around the whole coast of Ireland but more frequently off the south and west coasts. Indeed these coasts have some of the greatest concentrations of this species in Europe. There may be a strong seasonal variation in the abundance of bottlenose dolphins where they are more frequently seen in the summer. This may be due in some parts to the better weather experienced during the summer months and that more people are out visiting the coast but evidence from around the coast of Britain and Ireland do suggest that there is a seasonal component. So called solitary dolphins may occur (e.g. Fungi) and become tolerant, and sometimes very playful towards, people

How long do dolphins live for?

Dolphins can live an extremely long time and we are only just learning how long this can be. Dolphins, like other species of mammal, lay down growth rings in their teeth (like trees and like trees this represents different periods of growth with growth generally much slower during the winter when food is less available). By slicing a thin section of tooth in half and applying a dye or using light to create a shadow these growth lines can be counted and the animals age determined. It is thought that female bottlenose dolphins live into their forties and sometimes even into their fifties. Males have a slightly shorter lifespan, living between 30 and 40 years of age. There are always extreme cases and there is one female in the US that is over 50 and still producing healthy calves.

What do bottlenose dolphins eat?

The diet of bottlenose dolphins includes fish, squid and sometimes small crustaceans. They eat approximately 6% of their body weight per day, which for a species averaging around 300 kg is a lot of food! The diet can be reconstructed from prey remains recovered from the stomachs of dead individuals. We do not know what the dolphins in the Shannon actually eat but it is thought that the movement of salmon in the estuary during the summer greatly influences the movements of the dolphins which they are most likely preying upon. Bass, flatfish, and a huge variety of other fish can also be found in the Shannon estuary to satisfy the dolphins' large appetites. Dolphins in the Shannon estuary have been observed tossing salmon into the air, although this may be associated with playing, and groups of dolphins in the Shannon have also been observed circling salmon. This involves cooperative hunting, wherein several dolphins will surround a school of fish with individuals taking it in turns to dash through the fish and feed. The Shannon dolphins have also been observed chasing schools of pelagic fish such as sprat or young herring that have entered the estuary.

How do dolphins catch their prey and communicate?

Sound travels five times faster in water than it does in air, and thus is an important means of communication for dolphins, particularly when vision can often be hampered in the dark and murky depths of the underwater world. Echolocation allows the dolphins to perceive their underwater world with remarkable accuracy. In fact, dolphins in captivity have been known to navigate blindfolded, as well as catch fish using echolocation. A series of clicks and pulses are emitted into the water from an area near the blowhole called the melon. When this sound hits for example a fish, the echoes will bounce back and the dolphin will pick up these echoes through the lower jaw and transmit them to the inner ear. By continually monitoring these sounds, the dolphin can determine the size, shape, speed and direction of its prey, as well as mapping out the seabed and the surrounding environment.

How often do bottlenose dolphins have calves?

The Shannon estuary is a calving (and probably breeding) ground for bottlenose dolphins, with calves typically born from June to September. Calves are very distinctive, in that they are very small and pale in comparison to the larger darker adults. Calves also tend to have neonatal folds - white lines on their sides, thought to be as a result of the relatively large calf being slightly crumpled whilst in the womb. Female bottlenose dolphins reach sexual maturity at 5-12 years of age, and males at 10-12 years of age. The genitals of the bottlenose dolphins are contained within the body, behind slits on the ventral surface. The gestation period (time between conception and birth) is 11-12 months after which time a live calf is born. The calf is born tail first, otherwise if it was born head first, it would probably drown. Calves can be up to one metre in length at birth. The newborn dolphin will suckle from the mother at a rate of up to four times per hour in the first few weeks of life. Dolphin milk is four times richer than cows milk, providing the youngster with all the nutrition that it needs. The calf will suckle for at least 12 and up to 18 months, but even after it can fish for itself, it will retain a very close association with the mother for several years. This mother calf bond is probably the strongest of all dolphin alliances. The male dolphins play no part in rearing the young.

Do bottlenose dolphins live in families?

Bottlenose dolphin society appears to be quite complex and their social groups are very fluid - often called a fission-fusion system with groups coming together, separating, often with groups made up of different individuals. Generally individual dolphins tend to form groups with other animals of the same sex and sexual maturity thus groups of females, their calves, and juveniles of both sexes are often found together. Males tend to associate in bachelor groups or sometimes will pursue a solitary life. Other groups may be comprised of sexually immature but independent animals, however all these groups are very fluid and indeed what constitutes a "group" is subject to some considerable scientific debate. Group sizes obviously vary considerably with all this activity but generally groups are small, up to 6 individuals but up to 20 are frequently seen. Visitors to the Shannon will often witness this dynamic behaviour during dolphin trips and perhaps start to wonder what is going on. Trying to understand the behaviour and ecology of dolphins his is one of the fascinations of these highly evolved and socially developed animals. The same questions visitors are asking themselves are often the same ones the scientists are asking and the answers are still uncertain. Indeed casual observations are very valuable to the study of the dolphins in the Shannon and visitors are encouraged to participate in the Shannon Dolphin and Wildlife Foundation.

How can we study dolphins?

The study of dolphins and other species of marine mammal does pose some additional problems compared to the study of terrestrial mammals. Seals do come ashore for at least some part of the year to breed but dolphins are born, feed, mate and die entirely in water. Dolphins do occasionally strand on the shore, some may still be alive when this happens. Often people attempt to help the animal back into the water but this may not always be the best action as the animal may be sick and dying and unable to survive at sea. A dead animal can provide a lot of information about its life: remains of prey items may be found in the stomach and intestines, the sexual maturity can be assessed and, for females, the number of previous pregnancies determined, a tooth can be extracted to assess the animals age, tissue samples can be analysed for persistent pollutants such as pesticides and heavy metals and parasite loads and pathological lesions also described. Sightings of dolphins or whales can also be very useful even if you do not know the species. The ferry which crosses the Shannon between Killimer and Tarbert have been recording sightings since 1993 and this has built up a very good picture of when dolphins occur (May - August) and at what states of the tide (mid-ebb tide) are you most likely to see them from the ferry. Any sightings should be sent to the Shannon Dolphin and Wildlife Foundation or the Irish Whale and Dolphin Group (see Research)

How long have dolphins been in the Shannon estuary?

In the Shannon estuary, many local people recall seeing "porpoises" leaping out of the water when they were children. However, since the harbour porpoise has rarely been observed breaching and have not been seen in the estuary during hundreds of hours of shore watches and boat transects, it is believed that they were actually observing bottlenose dolphins. There are reliable records of bottlenose dolphins in the estuary since 1849 and they may have been there for considerably longer. Ancient legend tells of a sea-monster, the Caithaith, that lived on Scattery Island in the Shannon estuary. This monster would devour any person visiting the island and attack boats in the estuary. Legend tells of how St Senan cast out the monster from the island and established the first monastery in the 6th century. Early descriptions of the monster do at times sound remarkably like dolphins and it is possible that the monster was in fact bottlenose dolphins. If this was the case then dolphins have been living in the Shannon for over one thousand years and many dolphin generations.

How many bottlenose dolphins are there in the Shannon estuary?

Counting cetaceans at sea poses many problems and although it is important to know how many animals there are in a population it can be extremely difficult to determine. As visitors to the Shannon dolphins will appreciate it is difficult to count the number of individuals in a group once more than half a dozen dolphins occur. The daily and seasonal movements of dolphins are poorly understood as is the maximum range. However there are a number of techniques which can be used to provide best estimates. A minimum number estimate, which involves counting dolphins in the estuary simultaneously from a number of advantage points showed that at least 58-65 individuals occurred in the estuary in October 1993. Recent studies using photo-identification suggests that approximately 115 bottlenose dolphins may use the Shannon estuary, at least for some period of the year. Groups of dolphins are found throughout the estuary from Tarbert to Loop and Kerry Head but the average group size is only 5-6 animals. However groups of 30-40 are often observed as well as solitary individuals. The estuary is probably home to around 30-40 dolphins that are there for most, if not all the year, while other dolphins only use the estuary periodically during the summer.

Have dolphins occurred in the folklore of the Shannon estuary?

For years, stories have abounded of mermaids, sea serpents and seamonsters residing in the Shannon and sometimes even terrorising the local people. The origins of these stories are unclear. perhaps the head of a seal or dolphin poking out of the water into the air gave rise to the belief that there are half-human, half fish creatures living in the sea. Certainly, there are plenty of tales about mermaids in Irish waters and indeed in waters around the globe. One Kilrush man recalls being told stories of mermaids by his grandmother, whereby a mermaid married a human man and he hid her magic cap lest she get the urge to return to the sea. The couple had children and were happy for a while. However after some time the mermaid began to long for the sea and greatly desired to return to her aquatic origins. But since she did not have her cap, she could not do so. Then, many years later, while she was cleaning out the house, she found her magic cap in the attic, put it on and quickly returned to the sea. Before she left, she cursed her family so that if they went beyond a certain point on the shore that they would die . And not long after, her husband and children drowned.

Another story talks of Kilstiffen village being covered by a great big flood. Every 70 years the village reappears, and once a ship dropped anchor in the area and a head poked out of the water scolding the captain for having dropped the anchor down the chimney. A dolphin spy-hopping perhaps!! Stories abound of the legendary seamonster "An cathach" that lived at Scattery Island in the Shannon for a while. St. Sennan is reputed to have banished the cathach, thus saving the local people from terror. Although traditionally described as a sea-serpent, this monster of the sea has often been attributed dolphin characteristics.

Are their any threats to the Shannon dolphins?

The dolphins in the Shannon estuary are particularly susceptible to disturbance, since they live so close to human habitats. It is essential to identify potential threats to the dolphins and attempt to eliminate or at least minimise them, before they have a detrimental effect. Pollution can cause serious damage to dolphin populations, therefore it is vital that we attempt to control the input of pesticides, sewage and industrial wastes into the Shannon. Persistant chemicals such as organochlorines, that are used in industry and in pesticides. and are particularly destructive in that they can build up in the fatty tissues of dolphins, and other marine animals. Examples of these are the PCBs (polychlorinated biphenyls) and the insecticide DDT . It is thought that these chemicals may reduce fertility in both male and female dolphins as well as compromising their ability to fight diseases. Many industries are located on the river Shannon, therefore it is essential that the levels of persistent pollutants and other associated pollutants be monitored closely.

One less tangible, but no less serious threat to dolphins is that from increased boat traffic. The effects of the engine noise of boats and in particular small powerful crafts, including for example jetskis are of concern with regards the wellfare of the dolphins. It is thought that these noises can interfere with the echolocation of the dolpins particularly if they operate on a similar frequency to that of dolphins. Increased dive time and boat avoidance may be signs that a dolphin is unhappy with a boat's presence. This is a very real threat to the dolphins, particularly in summer time when there is increased boat traffic in the Shannon estuary.

How can I help and learn more about dolphins in Ireland?

There are many gaps in the knowledge of the behaviour of the Shannon dolphins, and other species of whale and dolphin in Ireland.

The Irish Whale and Dolphin Group is dedicated to the conservation of cetaceans (whales, dolphins and porpoise) in Irish waters through study, education and interpretation. They co-ordinate a sighting and stranding scheme and can be contacted at:
Secretary, Irish Whale and Dolphin Group, Gortnagrenane, Castlefreke, Clonakilty, Co Cork.
Tel: 023 31911
Email: info@iwdg.ieSend an e-mail to info@iwdg.ie
Website: www.iwdg.ieLink to external site: www.iwdg.ie

If you find a live stranded dolphin there are several basic rules to be followed. Firstly Don't Panic - although dolphins are liable to overheat whilst out of the water, they can survive for considerable periods of time. The IWDG should be contacted at 023 31911 or 086 8545450. If you find a dead stranded animal, it is important to report these to the IWDG. Valuable information can be determined from the body of a dead dolphin.

 


The Bottlenose Dolphin
Wild, Sociable Bottlenose Dolphins
Further Reading
Frequently Asked Questions
Whale & Dolphin Roadshow
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The SDWF is supported by the following agencies... Shannon Development Department of the Environment, Heritage and Local Government Marine Institute Clare County Council Kilrush Urban District Counil
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