Bottlenose dolphin and calf
Image: zassle | Creative Commons

Introduction

Find out about the bottlenose dolphins and the impact humans are having on this species.

In this section

Bottlenose dolphins (Tursiops truncatus) have a relatively short beak and a high, with a hooked and prominent dorsal fin. 

They are dark or light grey on the back grading to white on the undersides, although their colour and shape can be variable. The size of a newborn is around 85 cm - 1.3 m in length, and an adult 1.9 - 3.9 m.

Bottlenose dolphins are particularly susceptible to human impacts due to their coastal nature.

Bottlenose dolphins, Doubtful Sound. Photo: S.Hayes.
Bottlenose dolphins, Doubtful Sound. Photo: S.Hayes.

Where to find them

Bottlenose dolphins are widely distributed throughout the world in cold temperate and tropical seas and generally do not range poleward of 45° in either hemisphere.

New Zealand is therefore at the southern most point of their range. Limits to the range of this species appear to be temperature related.

They are found both offshore and in many enclosed areas such as the Mediterranean, Black and Red Seas. Population densities appear to be higher close to shore, where these dolphins tend to travel in groups of about 30 individuals.

Population

Two global ecotypes have been recognised: those living in pelagic or open ocean environments and those living in coastal areas. Population sizes are largely unknown but this species is relatively common worldwide.

In New Zealand three main coastal populations exist:

  • Around 450 individuals live in the Bay of Islands area, ranging from Doubtless Bay in Northland to Tauranga
  • Around 63 live in Doubtful Sound, Fiordland (as at 1998)
  • Another group range from the Marlborough Sounds to Westport. Bottlenose dolphins are commonly associated with other cetaceans including pilot whales, rough-toothed and Risso’s dolphins, and humpback whales. 

Diet and foraging

Individuals living close to the shore feed primarily on a variety of inshore bottom-dwelling fish and invertebrate species. Those offshore feed on mid-water fish species and oceanic squid.

Their dives rarely last longer than 3-4 minutes inshore, but may be longer offshore. Individual feeding appears to be the most prevalent foraging method but individuals are also known to work together to herd schools of fish.  

Breeding

Females tend to reach sexual and physical maturity before males, leading to sexual dimorphism in some regions. Females usually reach sexual maturity at 5-13 years with males not maturing until 9-14 years of age. Females breed every 3-5 years and calves suckle for around 2-3 years.

Calving peaks are known to occur for most populations between spring and summer/autumn. Female bottlenose dolphins can live up to more than 50 years of age, and males can reach as old as 40-45 years.

Pod of bottlenosed dolphins Fiordland Marine Area. Photo: Lou Hunt.
Pod of bottlenosed dolphins in Fiordland Marine Area

Threats

Predators

Sharks are probably the most important predators of bottlenose dolphins with the numerous shark-bite scars found on as many as half of all bottlenose dolphins providing evidence of such encounters. Killer whales are also likely to be one of the main predators.

Human impact

Bottlenose dolphins are particularly susceptible to human impacts due to their coastal nature. In New Zealand, the main threat to this species is likely to be the adverse effects of tourism. Bottlenose dolphins are the focus for dolphin watching in the Bay of Islands and Fiordland areas.

Studies have found the presence of boats to interfere with dolphins’ normal behaviour and boat strike in areas of high boating activity is always a threat. Common sense rules should therefore apply when boating around dolphins to reduce stress on the animals. Such rules are outlined in the Marine Mammal Protection Regulations (1992).

Adult and juvenile bottlenosed dolphin, entangled with polypropylene rope in the Bay of Islands. Photo © Ingrid Visser.
Adult with a juvenile bottlenosed dolphin, entangled with rope in the Bay of Islands

Our work

We use photo-identification to monitor the population ecology of this species in Fiordland and the Bay of Islands.

The impacts of tourism at these two sites is also currently being assessed, and in order to minimise disturbance to the animals this industry will need to be carefully managed.

We are also responsible for managing stranding events.

Report sightings

You can report sightings of dolphins to our conservation hotline 0800 DOCHOT (0800 362 468). You can also report a sighting online.

Reports of sightings are always valuable and help increase our knowledge of dolphin distribution and movements around New Zealand.

If you need help identifying species, download the marine mammal sighting form (PDF, 416K) (Word, 4,300K). You can use the images and descriptions to find out which species of dolphin you observed.

Record the details

Include as much information as possible with your sighting:

  • the date, time and location (GPS coordinates if possible)
  • the number of dolphins and estimated sizes
  • the direction they were travelling
  • take photographs or video if possible.

You can help

How to approach dolphins

From a boat:

  • carefully approach dolphins from their side and slightly to the rear.
  • operate your boat slowly and quietly at ‘no wake’ speed within 300 m.
  • don't approach a group of dolphins if three or more boats are already within 300 m of the group.
  • manoeuvre your boat carefully. Do not obstruct their path, cut through a group, or separate mothers from calves.

From a boat or swimming:

  • avoid loud or sudden noises that could startle dolphins.
  • don't swim with dolphins when calves are present.
  • don't try to touch the dolphins or feed them.
  • co-operate with others so all may see the dolphins without putting them at risk.

Stranded dolphins

How you can help in a stranding.

If you catch or harm a dolphin

If you accidentally catch, harm or kill a dolphin you must report it as soon as possible to our emergency hotline  0800 DOCHOT (0800 362 468) or the Ministry for Primary Industries (0800 008 333).

If a dolphin is alive you should release it back into the water as quickly and gently as possible, provided it is safe to do so. 

If the dolphin is dead, either release the carcass at sea or preferably bring it to shore for us to recover.

Find out more about sharing our coasts with marine mammals.

Set nets

If you are set netting always remain with your net. Remove your net from the water if dolphins are seen in the area. 

If you see set nets being used within areas closed for netting, contact the Ministry for Primary Industries on 0800 4 POACHER (0800 4 76224).

How you can help Doubtful Sound bottlenose dolphins

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