'True' dolphins

Atlantic spotted dolphins (Stenella frontalis) are the most frequently identified dolphin species during offshore survey work off Angola (with sightings also recorded during limited surveys off Gabon).  Most sightings of this species have involved animals that approached the vessel to bow-ride, enabling a higher number of positive identifications than for other dolphin species.  Group size of Atlantic spotted dolphins off Angola and Gabon appears higher than in the western Atlantic Ocean, with schools frequently consisting of several hundred animals.  Sightings have been recorded over a wide range of water depths from 200 m to over 2,200 m, and this species therefore seems to primarily inhabit shelf edge and oceanic habitat off Angola.  Atlantic spotted dolphin sightings have occurred throughout the year, and this species is probably a common 'resident' in Angolan waters.

Pantropical spotted dolphins (Stenella attenuata), have been positively identified off both Angola and Gabon, but are probably relatively more numerous off Gabon.  Positive sightings have consisted of between 3 and 70 animals, and occurred over a water depth range of 328-894 m, suggesting that this species may favour upper shelf edge habitat off West Africa.  It is likely that identification problems have resulted in under-recording of this species off Angola, and its exact status in the region remains unclear.  

The Clymene dolphin (Stenella clymene) has been positively identified twice during our survey work off West Africa.  A pod of 12 dolphins were observed off Angola during March 2004 (amongst a large group of unidentified dolphins), and a sighting of 250 dolphins was recorded off Congo during September 2005.  These sightings have been incorporated into a scientific paper on this poorly known species, which has been published in African Zoology (Download).

There has been only one positive sighting of the long-snouted spinner dolphin (Stenella longirostris) off Angola.  However, there have been at least six further sightings that were identified as either spinner or Clymene dolphins, and many of the unidentified Stenella dolphins seen 'spinning' during aerial behaviour are also likely to have comprised one of these two species.  Unfortunately the great distance of many of the sightings from the survey vessel usually prevents conclusive identification of, and separation between, these two very similar species.

Striped dolphins (Stenella coeruleoalba) have been recorded on at least seven occasions off Angola, and apparently inhabit the region throughout the year.  They have been sighted only in deep water of between 1,600 and 2,400 m seaward of the shelf edge.  Group size of striped dolphins off Angola is usually between 8 and 50 animals, with one record of a larger group of 125 animals.  We suspect that striped dolphins have been under-recorded during the surveys, with many further dolphin groups showing some characteristics of this species but remaining too distant from the vessel for positive identification.  On one occasion, striped dolphins were observed in a mixed-species association with common dolphins.

Both species of common dolphin (short-beaked (D. delphis) and long-beaked (D. capensis)) occur off Angola, with most sightings occurring too far from the ship to accurately distinguish between them and therefore being simply recorded as 'common dolphin sp.'.  Common dolphin sightings involved groups of between 1 and 400 dolphins (mean = 56).  Sightings have been recorded over water depths ranging from 75 m to 2,300 m, and this is therefore one of the few cetacean species that inhabits the entire depth range off Angola. Common dolphins appear to be one of the most abundant cetacean species off Angola, but the relative status of the two species within the area remains unclear.  Further information on the taxonomic status of Delphinus off Angola is available here.

Rough-toothed dolphins (Steno bredanensis) have been recorded on four occasions off Angola and once off Gabon.  On three of these occasions the dolphins were observed in mixed species assemblages, once with an unidentified small 'blackfish' species (possibly melon-headed whales) and twice with short-finned pilot whales (one sighting also including bottlenose dolphins).  Rough-toothed dolphins are probably a regular component of the Angolan cetacean fauna but are certainly not numerous.  The sightings to date have comprised small groups of 11 to 20 animals, and have occurred over deep-water shelf edge habitat of between 400 and 2,100 m water depth.

Bottlenose dolphins (Tursiops truncatus) have been recorded reasonably regularly off Angola, Congo and Gabon, occurring over shallow continental shelf waters (<200 m), over the shelf edge and also out in very deep water of over 3,000 m.  This species has been recorded in the immediate vicinity of the coast in Luanda Harbour and at Soyo in Angola, and off Port Gentil in Gabon.  Bottlenose dolphin groups comprised between 1 and 50 animals, but with most groups consisting of 15 or fewer animals.  Many of the bottlenose dolphin sightings in deeper water involve mixed-species schools in association with short-finned pilot whales.  

Fraser's dolphins (Lagenodelphis hosei) has been positively identified only once to date off Angola, when a group of 120 animals was recorded in 1,900 m water depth.  Based on it's geographic distribution elsewhere, this species is expected to occur throughout tropical deep waters off West Africa.

Risso's dolphins (Grampus griseus) have been sighted irregularly off Angola, although the sightings tend to occur in clusters.  Records involve relatively small group sizes of between 4 and 25 animals, and this species appears to be less abundant than many other dolphin species in the region.  The distribution data suggest that Risso's dolphins may be relatively more numerous in 'blue water' areas off Angola rather than in waters influenced by the freshwater Congo outflow.  Risso's dolphins are usually recorded over deep water exceeding 1,000 m water depth.  However, a large group of dolphins containing at least 10 Risso’s dolphins was observed over shelf waters (>200 m) off Gabon during April 2004.  Records of this species occur throughout the year, suggesting that Risso's dolphins are a regular, though not numerous, component of the Angolan cetacean fauna.  

'Blackfish'

The term 'blackfish' is applied to six species of large dolphin, which due to their size and appearance are commonly referred to as whales.  All six of these species potentially occur off Angola, and five have been confirmed in the region to date.  

The survey work has revealed that killer whales (Orcinus orca) occur fairly regularly off Angola, with eight sightings between September 2004 and December 2006.  Killer whale pods have comprised between 4 and 10 animals, and several of the sightings have included young calves.  All of the survey records were located over deep water of 969 to 2,600 m water depth.  Some opportunistic records provided by observers along the Angolan coast also indicate that this species occurs in shallow waters.  During January 2005, killer whales were observed in an apparent attempted predatory attack on a group of sperm whales, images of which can be viewed here. 

Short-finned pilot whales (Globicephela macrorhynchus) are the most frequently recorded 'blackfish' species off Angola and inhaibt the region year-round.  Although unconfirmed, it is likely that the long-finned pilot whale (G. melas) also occurs in southern Angola where the sea temperature is influenced by the cold-water Benguela Current.  The relative distributions of these two species off Angola remains uncertain, but most records in tropical northern Angola are presumed to be short-finned pilot whales.  In December 2006 we were able to get some close-range images of short-finned pilot whales which confirmed they show a uniform dark pigmentation off Angola and lack the pale cape and eye stripe seen in some populations.  As in most other parts of their range, pilot whales appear to inhabit exclusively shelf edge and deep waters off West Africa, with recorded depths ranging from 402 to over 4,100 m, and this is the most common cetacean species recorded in very deep water (>3,000 m).  The data indicate that pilot whales are probably most numerous in 'blue' water areas off Angola, and are less common in the turbid water influenced by the Congo River outflow.  Recorded group size ranges from 3 to over 200 animals, but most groups comprise between 8 and 40 animals.  Pilot whales are gregarious animals and are often observed off Angola in mixed-species schools with dolphins, most frequently the bottlenose dolphin.  

False killer whales (Pseudorca crassidens) are a relatively uncommon inhabitant of Angolan waters.  Sightings to date have peaked during the austral spring months, although the data are currently too few to determine whether this is a genuine seasonal trend.  School size of most false killer whale sightings was relatively small at between 2 and 20 animals, but an aggregation possibly containing as many as 100 animals was recorded in October 2004.  False killer whales are a shelf-edge and deep-water species, with all sightings occurring at 1,500 to 2,600 m depth.  

There have been three confirmed sightings of melon-headed whales (Peponocephala electra), all involving large active schools of between 100 and 300 animals.  The sightings all occurred during the austral spring and summer, and over deep waters of between 1,300 and 2,300 m.  Several further sightings have involved animals identified as either melon-headed whales or pygmy killer whales (Feresa attenuata), such as a group of 15 small blackfish recorded in in November 2006 (photo).