Sotalia guianensis
INFORMATION AND CHARACTERISTICS.
The Guiana dolphin (Sotalia Guianensis) is a small South American dolphin which is often confused with the Tucuxi (Sotalia fluviatilis). In fact, these two species were recently taxonomically separated because they are two genetically different species. The data collected on this species is still quite limited given the recent change of its taxonomy, so the information is not comprehensive. It is also known as the estuarine dolphin.
Order: Cetacea
Family: Delphinidae
Genus: Sotalia
HOW DO THEY LOOK? PHYSICAL DESCRIPTION.
Morphology.
It is a species with an appearance similar to the familiar bottlenose dolphin (Tursiops truncatus) but smaller. Also, it is almost identical to the Tucuxi (Sotalia fluviatilis), and they are easily confused where their distribution range overlaps. However, the Guiana dolphin is approximately 30% larger than the Tucuxi.
It has a narrow and pronounced “snout,” very defined and with a medium size. Its curved dorsal fin is small and has a triangular shape and a rounded tip.
Weight and size.
Despite the similarities, its size is smaller than that of the bottlenose dolphin mentioned above but is larger than its closest relative, the tucuxi (Sotalia fluviatilis). It reaches 2.1-2.2 meters in length and an average weight of 60 kilograms.
Coloring.
It has a countershading with blue or gray on the dorsal area and white, light gray or even pink in the ventral region. The dorsal fin has the same dark color of such part, but the flippers are darker than the vicinity with a darker color similar to that of the dorsal part.
Distinctive marks.
Between the flippers and the dorsal fin, this dolphin has an area of light skin. Besides this and the size differences, it is somewhat difficult to distinguish it from the two species mentioned above.
WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.
The Guiana dolphin inhabits the waters of eastern South America and Central America, from northern Nicaragua to the state of Santa Catarina in southern Brazil. It is, therefore, present in the western Atlantic Ocean including some regions of the Caribbean Sea, the Amazon River, and its tributaries. In this regard, there are two ecotypes: one in the Amazon basin and another exclusively marine.
It inhabits coastal waters, bays, estuaries and shallow areas of the river and its tributaries as well as its delta, as long as the water is shallow.
WHAT DO THEY EAT? FEEDING.
The carnivorous diet of this dolphin includes a vast diversity of fish species, but it also consumes squids and crabs. Part of its diet incorporates fish of the family Sciaenidae and the species Largehead hairtail (Trichurus Lepturus), Sardinella brasiliensis, Pellona barroweri, Harengula clupeola; Shrimp Penaeus schmitii and cephalopods of the species Lolliguncula brevis.
The Guiana dolphin is intelligent. It observes the habits and social structure of the fish (mainly of those that form schools) and uses its behavior to capture them and feed on them. Their method of hunting is creating a cooperative group, which once they detect a school of fish, they follow it, surround it and then take turns to feed while others keep the school compact and controlled.
HOW DO THEY BEHAVE? BEHAVIOR.
It is a highly sociable species but creates small pods. The number of individuals in a pod usually ranges from 10 to 15, but occasionally there are groups up to 20 or 30 members. In some areas of Brazil, they swim in groups of 2 to 10 individuals. In fact, the size of the pods varies depending on the area where they live in, the activity they perform and even the time of the day.
The Guiana dolphins do not usually approach the boats because they are a bit shy. What they usually do is perform stunning acrobatics, ride the bow waves of boats, jump out of the water and hit the water with its tail and flippers. Therefore, most observations are made from far which makes research difficult as well as knowing more about their behavior.
HOW DO THEY REPRODUCE? REPRODUCTION.
Observations indicate that this dolphin reproduces every two years using a polygamous system. Sotalia guianensis reach sexual maturity between five and eight years of age, but females mature before males.
The gestation period lasts about 12 months, after which the female gives birth to 1 offspring with a length of 0.7-0.9 meters.
As all dolphin species, the mothers take care of their calves for a long time until they reach a size and age to defend themselves from predators.
THREATS AND CONSERVATION.
WHAT IS THEIR CONSERVATION STATUS?
The Guiana dolphin faces the constant threat of purse seiners and fishing gillnets where they get trapped or entangled and die. In several regions of South America, hundreds of these dolphins die every year due to bycatch. To give an example, just in the Amazon delta, about 2,000 Guiana dolphins die each year, and in other areas, people directly hunt they for human consumption.
About 2,000 Guiana dolphins die annually just in the Amazonas River delta.
Additionally, collisions with ships and vessels due to the high traffic in some areas of its distribution range, the degradation of their habitat because of pollution or coastal development and the disturbance as a result of human activities as industry and tourism complete the list of anthropogenic threats.
In the wild, it is predated by killer whales and sharks.
Conservation Status: “Data Deficient.”
The Red List of the International Union for Conservation of Nature (IUCN) does not have enough data to evaluate its conservation status, so it has a classification as “Data Deficient.” However, the CMS (Convention on the Conservation of Migratory Species of Wild Animals) has included the Guiana dolphin in Appendix II of species with an unfavorable conservation status.
References
http://www.iucnredlist.org/details/181359/0
http://rspb.royalsocietypublishing.org/content/early/2011/07/21/rspb.2011.1127?sid_=35f01848-638a-4256-bab8-b75325534842
http://onlinelibrary.wiley.com/doi/10.1111/j.1748-7692.2007.00110.x/full
https://en.wikipedia.org/wiki/Guiana_dolphin