Monday, December 12, 2016

Resident dolphins today

Today we saw Risso's, common and bottlenose dolphins. We are always happy to find all kind of species but seeing Rissos is always cause of joy as we don't see them that often, even thought it is considered as a resident specie of the Açores.

Here some detailed information about our beautiful Risso's:

The Risso’s dolphins (in Portuguese known as Grampo) is the fifth largest of the delphinids and one of the 3 resident species in Azores. Its anterior body is extremely robust, tapering to a relatively narrow tail stock and its dorsal fin is one of the tallest in proportion to body length of any cetacean, exceeded only by that of the adult male killer whale (Orcinus orca). A cetacean that can reach 4 meters long and weight as much as 500kg. They have a morphological characteristic that results in an adaptation to the feed, which consists in a square design of the head that facilitates the catching of squids. They can be found in a wide range of colors, because they are born with a dark color and as they grow older, they gain a whiter color and the body full of scars (Colour patterns change dramatically with age). Older animals can appear completely white on the dorsal surface. This is a widely distributed species, inhabiting deep oceanic and continental slope waters 400- 1,000 m deep from the tropics through the temperate regions in both hemispheres. Sighting records indicate this species occurs roughly between 60°N and 60°S latitudes, where surface water temperature are above 10 °C. Risso's dolphins are pelagic, mostly occurring seaward of the continental slope. They frequent subsurface sea-mounts and escarpments where they are thought to feed on vertically migrant and mesopelagic cephalopods. In the North Atlantic and western Pacific, there appears to be a summer calving peak and a winter calving peak in the eastern Pacific. They are are often seen surfacing slowly, although they can be energetic, sometimes breaching or porpoising, and occasionally bowriding. Normally Risso’s associate in groups tend to be small to moderate in size, from 2-100 individuals, averaging 30 animals, but groups of up to 4,000 have been reported, presumably in response to abundant food resources. Risso's dolphins prey on a mix of neritic, oceanic, and occasionally bottom dwelling cephalopods and they normally feed at day. Risso’s are often seen surfacing slowly, although they can be energetic, sometimes breaching or porpoising, and occasionally bowriding
The most threats of Risso’s are:
·      Direct catch (in Sry Lanka); Incidental catch (southern Caribbean, the Azores, Peru);
·      Culling (Off Japan, Risso's dolphins were killed in the drive fishery (oikomi) in response to competition with commercial fisheries);
·      Pollution (Increasing levels of plastics and other refuse at sea may pose a threat to wild populations: Necropsies of specimens from Japan revealed that they had eaten foreign materials such as plastic bags, soda cans, and pieces of rope, which may have been fatal);
·      Noise pollution (In early 2004 and in 2005, several unusual stranding events including Risso’s dolphins occurred in Taiwan during a period when large-scale naval exercises were conducted in and on nearby waters)

The IUCN lists G. griseus as "Least Concern"
(Text by Rafael Martins)
 Some photos of today's encounter with the Risso's dolphins

Here we can appretiate the round head they have


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