Bottlenose dolphins of Peru
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Tursiops truncatus (Montagu, 1821)
English = Bottlenose dolphin Spanish = Bufeo, Delfin nariz de botella
Conservation status of bottlenose dolphins:
- Bottlenose dolphins are listed in Annex 2 of the Convention on International Trade in Endangered Species;
- Bottlenose dolphins are listed in Annex C1 (strongest category of protection) of Regulation 3626/82 of the European Union;
- Bottlenose dolphins are protected by the Marine Mammal Protection Act of the United States of America and the mid-atlantic stock is declared to be “depleted”;
- Bottlenose dolphins are listed as “insufficiently known” by the International Union for Conservation of Nature and Natural Resources
- Bottlenose dolphins in Peru are protected since 1990 by Ministerial ordenance and by national law since 1996
Distribution of bottlenose dolphins in Peru:
There are two distinct populations – coastal bottlenose dolphins and off-shore bottlenose dolphins. Both are very common all along the Peruvian coast
Present threats for bottlenose dolphins:
- illegal killing of dolphins as shark bait in Peru
- continued illegal dolphin killing for human consumption in Peru
- live-catches for captivity all around the world;
- coastal whaling in Japan, Sri Lanka, West Africa, Venezuela, West Indies, Mexico, Guatemala, Costa Rica, St. Helena, St. Vincent and the Grenadines, St. Lucia, Indonesia;
- Negative environmental impacts from dolphin watching operations (for example in the bay of Paracas in Peru)
Taxonomy of the bottlenose dolphin
The taxonomy of the genus Tursiops has been somewhat confused. Only since the late 1990s there is consensus about the existence of two species: Tursiops truncatus and Tursiops adunctus.
Tursiops aduncus (Ehrenberg, 1833) – The Indo-Pacific bottlenose dolphin
The Indo-Pacific bottlenose dolphin was long seen as a subspecies of Tursiops truncatus. Recently however it is recognized as a separte species. The Indo-Pacific bottlenose dolphin is found in the Indo-Pacific: around South-China, India and northern Australia. This dolphin is somewhat smaller than the the bottlenose dolphin (male: 2.6 m and female: 2.5 m) and less robust, with a more slender and longer beak, a less convex melon and a proportionally larger dorsal fin and flippers. Indo-Pacific bottlenose dolphins tend to have more teeth (23-29 pairs) than bottlenose dolphins (21-24 pairs). They generally have a lighter coloration than bottlenose dolphins and while aproaching sexual maturity they develop a dark ventral spotting that spreads over belly, throat, flippers and half of the face.
Tursiops truncatus (Montagu, 1821)
The bottlenose dolphin (Tursiops truncatus) is probably the most familiar of the small cetaceans because of its coastal habits, prevalence in captivity worldwide, and frequent appearance on television and in advertising. The body of the bottlenose dolphin is long and somewhat stocky. The melon is well-defined. The lower jaw extends beyond the upper jaw, curving slightly upwards at the tip. This dolphin is usually dark grey dorsally and white or pinkish ventrally. The dorsal fin is large and falcate. The flippers are medium-sized and slightly rounded. The flukes are broad, thin and somewhat rounded at the tips and have a well-defined median notch.
The primary color of the bottlenose dolphin (Tursiops truncatus) varies from very dark to light gray. This color is darker on the top or dorsal surface of the dolphin. It gradually lightens as it moves down to the belly area. Bottlenose dolphins have a dark line that runs from its beak to the blowhole and two more lines from beak to the eyes as well as a faint line from eye to flipper. .
Often there is a light blaze intruding into the darke cape on the bottlenose dolphins back. This pattern of dark on top and light on the bottom is a classic example of “counter-shading”, which is common in many cetaceans. It is thought that this coloration pattern helps serve the bottlenose dolphins to avoid being seen by both predators and prey alike. When viewed from above the dark dorsal surface of the bottlenose dolphin blends in with the dark waters and sea floor below. When viewed from below the light underside blends in with the bright sky and shimmering surface of the water above.
Adult bottlenose dolphins (Tursiops truncatus) range from 1.9 to 3.8 m, with males somewhat larger than females. There is incredible variation between different populations. Maximum weight of bottlenose dolphins is at least 650 kg, although most animals are much smaller. In the Northwest Atlantic, bottlenose dolphins are on average 2.5-2.6 m, with a maximum of 3.09 m. In Peru bottlenose dolphins are much larger and 3.4 meters is reported as maximum length.
Because of the great regional variation in size, coloration, as well as other morphological and genetical differences a number of subspecies are in discussion:
Tursiops truncatus gilli:
A subspecies of the bottlenose dolphin, but by some authors even elevated into species status: Tursiops gilli. Its common name is Pacific Bottlenose dolphin and as the name suggests you will find this dolphin subspecies in the Pacific Ocean. The name is commonly applied for dolphins of the Californian and Mexican Pacific coast.
Tursiops truncatus ponticus
A subspecies of bottlenose dolphin living in the Black Sea. It is naturally referred to as the Black Sea bottlenose dolphin.
Inshore and coastal bottlenose dolphins versus offshore forms:
In order to complicate matters even more there are also distinct bottlenose dolphin populations one inhabiting inshore and coastal habitats (inshore/coastal form), the other inhabiting neritic and pelagic habitats (offshore form). Both differ in morphology (skull and body measurements), physiology (characteristics of their blood), genetics, parasites, prey and behavior. This difference of the two ecotypes (forms) of the bottlenose dolphin was first described for the northwest Atlantic:
In general, the inshore/coastal ecotype seems to be adapted for warm, shallow waters. Its smaller body and larger flippers suggest increased maneuverability and heat dissipation. These bottlenose dolphins frequent harbors, bays, lagoons, and estuaries.
The offshore ecotype of the bottlenose dolphin is darker than its inshore counterpart and it seems to be adapted for cooler, deeper waters. The offshore form, which needs to dive deeper, has higher levels of hemoglobin and more red blood cells and can therefore store more oxygen. Its larger body helps to conserve heat and defend itself against predators. There are considerations to assign both forms to different species.
Relatively little is known about the distribution of the offshore ecotype except that it is typically concentrated along the continental shelf break in deeper waters and can, in lower concentrations, extend beyond the continental shelf into continental slope water. Although the ranges of the coastal and offshore ecotypes overlap to some degree, a statistically significant break in the distribution of the two ecotypes was found at 34 km (18 nautical miles) from shore. The offshore ecotype is reported seaward of 34 km and in waters deeper than 34 m and the coastal ecotype is found within 7.5 km offshore.
Similar differences between offshore and inshore/coastal bottlenose dolphins have been described for Australia, South Africa, and the eastern North Pacific. In Peru van Waerebeek et.al. noted that there were sufficient indications for the fact that at least in the central Peruvian coast there is a inshore and a separate offshore bottlenose dolphin population .
Indeed offshore bottlenose dolphins in Peru are darker and show a very long and slender extreemly backwards curved dorsal fin in comparrison to the shorter and sometimes near triangular dorsal fins of the Peruvian inshore/coastal dolphins.
Inshore/coastal bottlenose dolphins usually stay in very shallow areas: Near Aberdeen Harbour in Scotland dolphins were encountered in 65% of the samples within the navigation channel of the port at ‹10.3 m of depth. In the Lower Barataria and Caminada Bay, Louisiana inshore dolphins can be observed all year around at distances of 3-800 m from shore, and water depths of 0.4 – 12.5 m. In the Drowned Cayes region, near Belize City the water depth measured during 216 sightings, ranged from 0.9 m to 11.8 m (average = 4.3 m).
In Peru coastal bottlenose dolphins were observed by Mundo Azul in depths of 1 to 20 meters and always close to the shoreline.
Distribution of bottlenose dolphins
The bottlenose dolphin lives in most of the world’s oceans in temperate and tropical waters, both offshore and coastal. It does not occur in polar waters. In non-tropical waters, bottlenose dolphins are found mostly in the coastal zone, sometimes to the edge of the continental shelf and beyond. Bottlenose dolphins can also be found in river estuaries.
In the Pacific Ocean, bottlenose dolphins are found from northern Japan and California to Australia and Chile. They are also found offshore in the eastern tropical Pacific as far west as the Hawaiian islands. Off the California coast bottlenose dolphins have been observed as far north as Monterey, particularly during years of unusual warmth.
In the Atlantic Ocean, bottlenose dolphins are found from Nova Scotia and Norway to Patagonia and the tip of South Africa. They are the most abundant dolphin species along the United States from Cape Cod through the Gulf of Mexico.
Bottlenose dolphins are also found in the Mediterranean Sea, and in the Indian Ocean from Australia to South Africa.
Population size of the bottlenose dolphin
There are no Population estimates for the global population of bottlenose dolphins available. Some local and regional estimates are already very old and the survey methods are very different from case to case. The separation of Tursiops into two different species additionally complicates population estimates. For example the assessment conducted for the 1996 Red List of the International Union for the Conservation of Nature (IUCN) incorporated Tursiops aduncus. Due to the muddled taxonomy, the widespread distribution ranges and considerable overlap in occurrence, both species are currently listed as Data Deficient in the IUCN Red List .
There are no population estimates for bottlenose dolphins in Peru. Only in recent years some work is developing to research inshore populations along the central Peruvian coast. All results of this work must be seen so far as preliminary as the research effort is low due to restrictions in finance and infrastructure, and the research time is short (a few years).
The Peruvian NGO Acorema conducted field surveys on two dolphin populations. Group A was defined as the dolphins present in the area from the Bay of Paracas to the Mouth of the river Pisco. Group B was defined as the specimen present in the area between Lagunillas and Supay beach. In 1999 35 specimens were photo-identified and that catalogue increased in the next survey to 45 specimen. Residence was confirmed for at least one specimen of group A that was first seen in 1991 and could be observed till the year 2000. Travel ranges were confirmed for one specimen that was sighted within the Bay of Paracas and in front of Tambo de Mora, suggesting a posible range on individual level of aproximately 50 kilometers.
The group observed between the Bay of Paracas and the River Pisco was estimated to consist of a minimum of 70 specimens and the group south of the Paracas Peninsula by maximum 15 specimens. The range estimated for specimen of the second group is 11 kilometers. The Peninsula of Paracas can not be seen as a geographoical barrier as Acorema was able to confirm the presence of at least one specimen observed in the Bay of Paracas within group B.
Research of Mundo Azul however, showed that the information given by Acorema needs correction:
The home range for group B is too small to be correct. A survey in the south of the Peninsula of Paracas showed that the density of bottlenose dolphins within the protected area is by far smaller than the density of dolphins north of the Peninsula. We are contributing this fact to the lack of adequate feeding habitat within the reserve. Members of group B could not be located in this survey indicating that either the home range of this dolphins is much larger or that they are not a resident group but have been there for a while and later disappeared.
The number of dolphins registered by Mundo Azul in the area between Paracas and Pisco is much higher, with more than 140 specimens.
In our dolphin research we did so far (Jan 2010) identify 1512 dolphins between Lima and the Bay of Paracas (180 km of coastline), with more than 600 of them supposed to be resident dolphins. This indicates one of the highest coastal bottlenose dolphins world wide.
Population estimates for other areas:
There is a population estimate for the Eastern Tropical Pacific in 588.000 bottlenose dolphins in this area. However this 30 year old estimate is unlikely to be correct at present, especially not after the loss of millions of specimens from different dolphin species due to the Tuna fisheries in this area .
For the North East Coast of the United States 400 to 700 inshore/coastal dolphins and 9.300 – 12.100 offshore dolphins have been estimated.
For the western Gulf of Mexico coastal bottlenose dolphin stock (= the bottlenose dolphins inhabiting the nearshore coastal waters in the U.S. Gulf of Mexico from the Texas border to the Mississippi River mouth, from shore or presumed bay boundaries to 9.3 km seaward of the 18.3 m isobath) and based on a 5% visual coverage of the survey area, bottlenose dolphin abundance was estimated to be 3,499 dolphins. The data are not sufficient to conduct a statistical trend analysis, but the 1994 population size estimate is significantly lower than the 1983 estimate and suggests a decline in stock abundance. This stock was subject to higher than usual mortality levels in 1990, 1992, and 1993-94, and the incidente of bottlenose dolphin strandings along the Texas coast in those years was significantly higher than the 1984-94 mean stranding rate. Some of these mortalities may have been related to accumulation of anthropogenic hydrocarbon contaminants.
The area of the eastern Gulf of Mexico coastal bottlenose dolphin stock extends from approximately 84o W Longitude to Key West, Florida, from shore, barrier islands, or presumed bay boundaries to 9.3 km seaward of the 18.3 m isobath. Approximately 5% of the total survey area was visually searched. Bottlenose dolphin abundance was estimated to be 9,912 dolphins.
The bottlenose dolphin population for the Barataria Basin in the Gulf of Mexico (a roughly 110 km long and 50 km wide basin containing approximately 145,000 ha of salt marsh) was estimated in 138 and 238 specimen using a closed-population model.
Population estimates for two of the five remaining inshore estuarine bottlenose dolphin populations in Louisiana waters are: Bay Boudreau/Mississippi Sound region: 1401 and Terrebonne/Timbalier Bay complex: 100.
Baird et.al. (2001) reported the results of a Mark-recapture Photo-ID field survey for the waters around the Hawaiian Islands Maui, Lana´i and Hawai´i. During 328 hours in 49 field days they covered 1300 km2 of ocean surface and took 1250 pictures. They identified 72 animals. Together with the animals identified in the same are in previous years they identified a total of 88 Bottlenose dolphins.
The 2002 NOAA Stock Assessment estimates abundance of bottlenose dolphins in Hawaiian waters at 743.
Barlow (2006) estimated a dolphin abundance (taking into account several species together) of 26 specimen per 1,000 km2. He noted that this “is much lower than the total delphinid density estimated for most warm–temperate and tropical locations worldwide and is even lower than all but one stratum in oligotrophic Mediterranean waters. The total delphinid density for Hawai‘i is also far lower than the range of estimates (112–2,342 per 1,000 km2) for 5◦ latitude × 5◦ longitude strata in the eastern tropical Pacific.” He concludes that the low density is related to “the low productivity of the subtropical gyre water that bathes most of the Hawaiian Islands.”
A photo-ID study in the years between 1997-2001 in Santa Monica Bay, California (approximately 460km2) identified a total of 290 specimens.
The resident Bottlenose dolphin population in the Moray Firth in Schotland is considered to be of national and international significance, as it is one of just two known populations of bottlenoses in British waters (the other being in Cardigan Bay, Wales), and the only population in the North Sea. Therefore an area of the inner Moray Firth has been designated as a candidate marine Special Area of Conservation (SAC) for the species under the European Community’s “Habitats Directive”. The size of this population (129 animals) is well below the limit of 250 individuals used by the IUCN to identify isolated populations as ‘critically endangered’. Given current estimates of survival and reproductive rates for bottlenose dolphins in the Moray Firth, an annual decline of almost 6% per annum for this population has been predicted.
The Mediterranean population is estimated at less than 10,000 .
In the Adriatic sea the only well-known resident Bottlenose dolphin population inhabits the waters around the islands of Cres and Lošinj (Kvarneriæ, Croatia) and has been studied by the Adriatic Dolphin Project since 1987. Two photo-ID estimates of this population size showed a number of about 130 individuals. In addition, 53 dolphins have been photo-identified in the waters off Venice, by the Tethys Research Institute.
In a Photo-ID Survey in Venezuela the study area was comprised of two surveyed zones. The northeast coast, which is the coastline of the east region of Margarita Island from Punta Ballenas to El Tirano, including Los Frailes Archipelago, is strongly influenced by coastal upwelling from the mainland. The second sampled portion was the southeast coast, from Punta Ballenas to Punta de Mangle toward the west, within a submarine depression called Las Marites. A relative abundace of 35 Bottlenose dolphins per 4.27 daily hours of observation suggests a dolphin population of less than 60 individuals in the study area.
The population estimate for the area within Turneffe Atoll (17º 20’N; 87º 50’W), 56 km off the mainland coast of Belize, Central America is 82-86 Bottlenose dolphins. The total area of the atoll is 531.4 km². The study area included all areas within the atoll except for the shallow and inaccessible waters of the Northern Lagoon and north of Rendezvous Point.
In the Drowned Cayes region, near Belize City, Belize, Central America 115 dolphins were identified in 392 photo-identification surveys conducted during 1997-1999 in an area of aproximately 150 km2, resulting in a closed population estimate of 122 animals for the area.
Social system of bottlenose dolphin communities
Bottlenose dolphins live in a predominantly three-dimensional world where many species realize daily patterns of vertical movements. It is unlikely for bottlenose dolphins living in a strongly threedimensional environment to be able to defend a territory, or even defend a large resource. In fact resource defending behaviour (and be it even a relative small resource like for example a receptive female like it occurs in sea lions on the breeding beaches or for coastal dolphins to defend a territory) has not been reported for dolphins so far. Additionally, the marine environment is typically characterized by highly clumped and mobile prey. Thus, contest-type competition where animals defend their access to food resources is unlikely in the ocean. Bottlenose dolphin communities therefore do not constitute closed demographic populations. Bottlenose dolphins live in a “fusion-fission” society, with animals not remaining with one particular group for long periods of time, although long-term bonds do seem to exist for some individuals.
Bottlenose dolphin groups can vary significantly in size depending on environmental factors and group composition. Groups are composed of different social units:
Mother-calf pairs and pods of mature females with their most recent offspring
Subadults in mixed-sex and single-sex groups.
Adult males are often observed alone, or in pairs or occasional trios. Adult males commonly move between female groups in their range, and may pair up with females for brief periods. Adult males rarely associate with subadult males.
In general, size of bottlenose dolphin groups tend to increase with water depth and openness of habitat. Group size of offshore bottlenose dolphins for Peru was reported in up to 1000 specimens per group.
According to our research the group size of coastal bottlenose dolphins varies between 1 and 107 animals.
Reproduction of bottlenose dolphins:
Male bottlenose dolphins reach sexual maturity at 10-12 years of age, females at 5-12 years. The average lifespan is estimated to be about 25 years, although some live to their late 40’s. Females bear a single calf every two or three years and gestation is about 12 months. At birth, calves are usually 90 – 130 cm in length and may weigh from 13.5 – 41 kg.
The gestation period is approximately 12 months. A female bottlenose dolphin therefore can potentially bear a calf every two years, but calving intervals generally average three years. Calves are nursed for a year or more, yet stay with their mothers for up to five years. During this extended period of dependence, calves spend their time learning practical skills such as how to find and capture food, how to recognize other dolphins, and who fits where in the dolphin social hierarchy.
The approximate average calf survival rate in bottlenose dolphins is 50%. Maternal bond and experience are extremely important to calf survival and all three increase with the mother’s age and with each successive pregnancy. Infant survival is much lower with very young and/or inexperience mothers.
Feeding behavior of bottlenose dolphins
Almost without exception, bottlenose dolphins appear opportunistic in their feeding habits, taking a wide variety of fish and invertebrates. Feeding behavior is flexible and adapted to a dolphin’s particular habitat and available food resources. They can be seen feeding alone and cooperatively with one another, herding fish onto mud banks and, in some parts of the world, working with humans to catch fish.
Bottlenose dolphins are quite adaptable and have learned to capitalize on human disturbance of the environment for new food sources such as feeding behind shrimp boats or expanding their natural range to feed in newly created ship channels.
Bottlenose dolphins often cooperate when hunting and catching fish. In open waters, a dolphin pod sometimes encircles a large school of fish and herds them into a small, dense mass, sometimes using their tail flukes to stun the fish. The dolphins take turns charging through the school to feed. Occasionally dolphins herd schools of fish against a sand bar or shoreline to trap them in shallow water where they are easy prey. Bottlenose dolphins also feed on individual, nonschooling fishes. To hunt larger fishes, a bottlenose dolphin may use its tail flukes to kick a fish out of the water, then retrieve the stunned prey.
Adult bottlenose dolphins eat approximately 4% to 5% of their body weight in food per day. A nursing mother’s daily intake is considerably higher: about 8%. Larger subspecies, such as the Pacific bottlenose dolphin, may eat up to 16 kg per day.
In Peru the inshore/coastal population feeds on anchovies (Engraulis ringens) and sardines (Sardinops sagax) as well as a variety of demersal fish species. The offshore form feeds on mesopelagic fish and oceanic cefalopods.
Whale watching and conservation initiatives:
Whale and dolphin watching offers an economic alternative to whaling and support species conservation. Whale watching tours are also offering research opportunities. Support species conservation and research, while enjoying whales and dolphins in Peru with Nature Expeditions.
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What we do to stop the dolphin slaughter in Peru:
According to our estimate between 5000 and 15000 dolphins are killed illegally in Peru each year to be used as shark bait by Peruvian fishermen. Additionally up to 3000 dolphins are killed each year illegally in Peru for human consumption. In 2002 Mundo Azul started investigating the Peruvian black market on illegally caught dolphin meat. The dolphin meat is regularly landed at night on beaches near the ports in order to avoid the controls of harbor officials. At this point, the meat is already cut into small pieces and hidden in boxes, while heads, flukes, bones and intestines have been thrown over board before or while entering the harbor. The meat is then openly sold on local markets. In 2013 Mundo Azul uncovered the massive dolphin kill for shark bait. Stefan Austermühle, Executive Director of Mundo Azul, managed to travel in a full month fishing trip and filmed the brutal killing of dolphins – pictures that sent a shock wave around the world. Please support our campaign to pressure the Peruvian government to act decisively in order to end the dolphin killing in Peru.;
Mundo Azuls volunteers are engaged in undercover investigation of illegal sales of dolphin meat. We are then providing the collected intelligence to the Peruvian police and are actively supporting the implementation of police raids. We are also supporting the Peruvian police thru capacity building. Raising public awareness and environmental education are further activities of our dolphin conservation campaign. We are engaged in dolphin research providing us with important baseline information for conservation planning. Finally we are promoting whale and dolphin watching as a sustainable economic alternative to illegal dolphin killing.
We are also active on an international level against dolphin captivity and whaling.
What you can do to stop the dolphin slaughter in Peru
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