Atlantic Humpback Dolphins occur exclusively in shallow (<30 m) waters that are frequently (but not exclusively) nearshore (Weir and Collins 2015). Recorded sightings are typically coastal, but the species may also occur some distance from mainland shores where suitable habitats are present (Van Waerebeek et al. 2004, Weir and Collins 2015). Preferred habitats appear to be strongly influenced by tides and include areas of sandbanks, deltas, estuaries and mangrove systems (Maigret 1980, Ross et al. 1994, Van Waerebeek et al. 2004, Weir et al. 2011, Weir and Collins 2015). They also occur on some exposed coastlines, although the available evidence suggests that densities in these areas are lower (Collins et al. 2010, Weir et al. 2011). Work completed by Weir (2015) suggests that in the area of the Rio Nuñez Estuary (Guinea) different S. teuszii groups “may vary in their site fidelity, habitat use and movements, and consequently in their home ranges.”

They have been recorded some distance up rivers but there is no evidence that they ascend beyond the limit of marine intrusion (Maigret 1980, Van Bree and Duguy 1965, Van Waerebeek et al. 2004, Weir and Collins 2015). Maigret (1980) described a sighting at Foundiougne, in the main channel of the Saloum River, some 33 miles (53 km) from the estuary mouth, an area within the influence of tides (Van Waerebeek et al. 2004). In Guinea Bissau, they have been recorded 30 km upstream from the mouth of the Rio Grande de Buba and 20 km upstream from the mouth of the Rio Cacine (Leeney et al. 2015b, Van Waerebeek et al. 2000). A skull was collected in Gabon ca. 1949 at Kango, a village 95 km from the Gabon Estuary mouth and at the limit of saline intrusion; collection details are scant and the skull’s true origin is unconfirmed (Van Waerebeek et al. 2004, Vande weghe 2005). More recent surveys in the Gabon Estuary, including as far upstream as Kango, yielded no sightings of S. teuszii (Collins et al. 2004). They are not known to enter the coastal lagoons that are a prevalent feature of equatorial West African coasts. For more detailed discussion of habitat preferences, see Weir and Collins (2015).

Knowledge of the feeding ecology of S. teuszii is incomplete, as few stomach samples have been examined and direct observations of feeding are rare (Van Waerebeek et al. 2004). It is however clear that S. teuszii diets consist largely of coastal, estuarine and reef-associated fishes, many of which are characteristically vocal (Cadenat and Paraiso 1957, Cadenat 1959, Ladich 2000, Van Waerebeek et al. 2004, Weir 2009). Examination of the gut contents of net-entangled animals has provided direct evidence of S. teuszii diets and thus overlap with important fisheries. In Senegal the stomachs of net-entangled animals contained Sompat grunt (Pomadasys jubelini), bongo shad (Ethmalosa fimbriata) and mullet (Mugil spp.) (Cadenat 1956, Cadenat and Paraiso 1957, Maigret 1980). The stomach of a humpback dolphin entangled in the line of a fishing trap in Guinea Bissau contained snapper (Lutjanus goreensis), Atlantic emperor (Lethrinus atlanticus) and West African spadefish (Chaetodipterus lippei), (Sequeira and Reiner 1992). Initial analysis of otoliths and other remains recovered from the stomachs of humpback dolphins killed in coastal gillnets in the Republic of Congo indicates a diet of predominantly Longneck and Cassava croakers (Pseudotolithus typus, Pseudotholithus senegalensis), as well as unidentified flounders (Paralichthodes spp., Pseudorhombius spp.) and grunts (Pomadasys spp.). The full stomach of one of these animals, an adult, contained 29 royal threadfin (Pentanemus quinquarius) and a mantis shrimp (Squilla mantis; Collins 2015).

Accounts of observed predation are few. In Mauritania single humpback dolphins were twice observed among pods of common bottlenose dolphins (Tursiops truncatus) fishing cooperatively with Imraguen fishermen for mullet (Mugil cephalus, Liza aurata) (Busnel 1973). Duguy (1976) reported S. teuszii at the Banc d’Arguin chasing mullet in the channels between the Tidra and Nair islets. In Angola, S. teuszii were seen to feed primarily on South African mullet (Liza richardsonii). Also observed were the capture of an Atlantic bonito (Sarda sarda) and herding of sardines (Sardinella spp.) although it was unclear if they were prey (Weir 2009).

Foraging has been linked to rising (flood) tides (Van Waerebeek et al. 2003, 2004; Weir 2009 and references therein). In the Saloum Delta tides were thought to provide access to inner reaches of mangrove channels (referred to locally as ‘bolons’) and mangrove edges (Maigret, 1980). In the Banc d’Arguin the link between tides and foraging was less evident, although daily movements into channels inshore were coupled with flood tides (Maigret 1980), and Duguy (1976) reported S. teuszii chasing fish in tidal channels between the Tidra and Nair islets. In the Bijagós Archipelago (Guinea Bissau), S. teuszii were most frequently observed during low tide, suggesting that they fed when fish were concentrated in “gullies and creeks” (Spaans 1990, Weir 2009).). In Angola animals performing longer dives (>1 min) were presumed to be in pursuit of demersal fishes and benthic prey (Weir 2009); tail-up behaviours consistent with dives on demersal prey were also observed in deeper waters of the Rio Nuñez estuary (Weir 2015). Foraging has been observed at river confluences within the Rio Grande de Buba (Van Waerebeek et al. 2000). In the Saloum Delta preferential feeding areas include Djinack Creek, Bandiala, and Sangomar Point (Van Waerebeek et al. 2004).

Observations in Guinea, although limited, suggest that S. teuszii observed in the shallow waters west of the Île de Taïdi spent relatively more time foraging than those in the deeper waters of the outer Río Nuñez estuary (Weir 2015). S. teuszii observed off Flamingos, Angola, spent approximately half of their daylight time engaged in travel and foraging. Dolphins foraged preferentially around rocks and reefs, as well as at the mouths of rivers, including the typically dry Flamingo River (Weir, 2009). These tendencies may be shared in Gabon (Collins et al. 2004). Feeding activity in some areas is coincident with observations of larger aggregations, including the largest group sizes (20-40) recorded (Collins et al. 2004, Maigret 1980, Van Waerebeek et al. 2004 and references therein; Van Waerebeek et al. 2015).

Information on reproduction is extremely scant. In the Saloum Delta, births were thought to occur in March and April, based upon observations of juveniles (Maigret 1980). This pattern was also suggested for Guinea Bissau (Krömer et al. 1994, as cited in Van Waerebeek et al. 2004). No neonates have been examined, but lengths at birth may be similar to those in S. plumbea (Van Waerebeek et al. 2004). In Congo, a lactating female caught in a net during May (2013) measured 2.50 m (T. Collins unpub. data). The species is suspected to be sexually dimorphic (males larger at maturity and with a more prominent dorsal hump), but the current sample size (~20 animals) is too small to assess statistically (Jefferson and Rosenbaum 2014). Taylor et al. (2007) estimated a generation length of 18.4 years for S. teuszii, although Moore (2015) provided a figure closer to 25 years for S. chinensis and S. plumbea. The data required to estimate generation length and other S. teuszii vital rates remain unavailable.

Migrations and movements are poorly understood. Localized movements have been linked to feeding opportunities facilitated by tides (e.g., Dupuy 1983, Maigret 1980, Van Waerebeek et al. 2003, Weir 2009). Cadenat (1949) stated that in the Saloum Delta they are “observed daily on the dropping tide between Pointe Jackonsa and the mouth of the Djiombos” (Maigret, 1980; Dupuy, 1983), a tendency that helped to optimize encounters in later surveys (Van Waerebeek et al. 2003).

Movements on larger scales are rarely documented, but have been inferred. Fishermen’s accounts from the Baie du Lévrier and sightings at the Banc de Corbine suggested movement north of the Banc d’Arguin (Maigret 1980); sightings between Nouamghar and Nouakchott may indicate occasional movements south (Robineau and Vely, 1998). Maigret (1980) mused that animals from the Saloum Delta moved as far north as “Yenne” (Yene Kao, ~100 km north of Saloum), and as far south as the Gambia River Estuary (~15 to 25 km). Landings of S. teuszii on the Petit Côte of Senegal provided some support for this idea (Cadenat 1956, Cadenat and Paraiso 1957), although capture locations were unknown (Van Waerebeek et al., 2004). More recent observations of S. teuszii groups passing between Barra and Buniada Points indicate routine movement between Senegal and The Gambia (Murphy et al. 1997), and a dolphin photographed crossing this border at Djinack (October 2000) provided the rationale for the species’ Convention on Migratory Species (CMS) listing (Van Waerebeek et al. 2003; 2004).

Larger migrations between the populations at Dakhla Bay and the Banc d’Arguin (ca 450 km), and the Banc d’Arguin and Saloum-Niumi (ca 750 km) regions are likely to be atypical, if they occur at all, given the distances involved (Maigret 1980, Van Waerebeek et al. 2003), although Robineau and Vely (1998) believed it “inconceivable” that the Dakhla animals were isolated. Contemporary records led Maigret (1980) to hypothesise that Saloum Delta animals swam north to Mauritania during the May-December period; a stranding ‘midway’ between Saloum Delta and the Banc d’Arguin provided minor support (Robineau and Vely 1998), but Van Waerebeek et al. (2003) rejected the idea given the availability of a larger dataset. These include bycatch and interview data, indicating year round occurrence in the Saloum Delta. There are no records between Dakar and St Louis, and very few from south of Nouakchott (Maigret 1980, Van Waerebeek et al. 2004). Van Waerebeek et al. (2004) suggested that movements between Saloum-Niumi and the Bijagós Archipelago are probable, “considering the relatively limited distance (ca. 280 km)”. Recent sightings near the Tristão Islands (Van Waerebeek et al. 2015) and in the Rio Nuñez suggest this connectivity extends into Guinea (Weir and Collins 2015) and Van Waerebeek et al. (2015) have since proposed a single 'Guineas stock', which combines the former 'Rio do Jêba-Bijagos' (Guinea-Bissau) and 'South Guinea' stocks (sensu Van Waerebeek et al. 2004) into one.

Beach-based observations by dedicated observers indicate routine movements of S. teuszii across the Gabon/Congo border within the Mayumba-Conkouati transboundary protected area (each containing 60 km of protected beach); it remains unclear if these animals range further afield (Collins et al. 2010). The very small population at Flamingos (Angola) appears to be both resident and highly localized in its occurrence (Weir et al. 2011). Records elsewhere suggest opportunities for transboundary movements (e.g., Ayissi et al. 2014, Bamy et al. 2010, Zwart and Weir 2014). Inferring demographic exchange (or the lack of such exchanges) between populations through analyses of genetics and/or photographs is not possible at this point, given a lack of samples or photo-identified individuals from almost all areas. If their distribution was once continuous (or less fragmented than it now appears to be), localized movements of the kind observed at Saloum-Niumi and between Congo and Gabon may have been sufficient for ensuring step-wise exchanges (and thus gene flow) between adjacent sub-groups (sensu Mendez et al. 2011).

Atlantic Humpback Dolphins are endemic to the tropical and subtropical nearshore waters of western Africa (Jefferson et al. 1997, Van Waerebeek et al. 2004, Weir and Collins 2015), ranging from Dahkla Bay (Rio de Oro) in Western Sahara (23°52'N, 15°47'W) to Tombua (Namibe Province) in Angola (15°46’S, 11°46’E). Each of the 19 states between (and including) Western Sahara and Angola are presumed to be part of the species' natural range. The current distribution is uncertain given incomplete research coverage, including an absence of survey effort in many areas. However the species has been recorded in 13 of these countries to date, including Western Sahara, Mauritania, Senegal, The Gambia, Guinea, Guinea Bissau, Togo, Benin, Nigeria, Cameroon, Gabon, Republic of Congo and Angola (Bamy et al. 2010, Collins et al. 2010, Van Waerebeek et al. 2004, Van Waerebeek et al. 2015, Weir et al. 2011, Weir and Collins 2015, Zwart and Weir 2014). There are no confirmed records for Sierra Leone. Liberia, Côte d'Ivoire, Ghana, mainland Equatorial Guinea or the Democratic Republic of Congo. The species is not known to occur around any of the larger offshore islands of the Gulf of Guinea, including Sao Tome and Principe or Bioko (Fernando Póo) and Annabon (Pagalu) (Van Waerebeek et al. 2004).

Areas of known occurrence
Research in a few relatively well studied areas suggest that the species is patchily distributed and generally uncommon. Areas of regular occurrence in West Africa include the Banc d’Arguin (Mauritania), the river deltas of the Saloum-Niumi region (Senegal and The Gambia), the estuaries and islands of Guinea Bissau and the estuaries of northern Guinea. In Central Africa areas of localised density appear to be limited to Gabon (particularly the coasts of Wonga wongue, Ozuri-Loango and Mayumba) and the northernmost half of the Republic of Congo. Recent work suggests that densities are very low in the Gulf of Guinea states north of Gabon (e.g., Segniagbeto et al. 2014, Van Waerebeek et al. 2015). There have been recent sightings and/or records in Guinea, Benin, Togo, Nigeria, Cameroon, Gabon and the Republic of Congo (Collins 2010, Minton 2015, Van Waerebeek et al. 2015, Zwart and Weir 2014).

Areas of known absence/gap areas
Research indicates that the species does not routinely occur between Dakhla Bay (Western Sahara) and the Banc d’Arguin (separated by over 400 km) and the Banc d’Arguin and Saloum-Niumi regions (separated by over 700 km). This suggests that the distribution of S. teuszii may be discontinuous across this wider region, with highest densities in optimal habitats and occurrences on intervening coasts rare (e.g., Maigret 1980, Ross et al. 1994, Jefferson et al. 1997, Van Waerebeek et al. 2004, Zwart and Weir 2014, Van Waerebeek et al. 2015).

Areas of unknown occurrence
Many areas, including within countries with confirmed records of the species, have received little or no systematic cetacean or coastal research. The presence of humpback dolphins in these areas is thus unknown and uncertain. This includes the coasts of Liberia and Sierra Leone, Equatorial Guinea, The Democratic Republic of Congo and much of the coastline of Angola (including Cabinda).

Distribution gaps in some areas are likely to be the result of increasing anthropogenic pressure in once pristine regions (Van Waerebeek and Perrin 2007, Weir et al. 2011). For instance several sightings and bycatches were reported from the ‘Petite Côte’ region in Senegal (between Dakar and the Saloum Delta) during the 1950s (e.g., Cadenat and Paraiso 1957), but neither areas were reported to yield sightings between 1975 and 1980 (Maigret 1980) and only one catch (in Fadiouth/Joal 1997) was later identified by Van Waerebeek et al. (2004) despite extensive survey effort.  No records of S. teuszii have been reported in Ghana where there is an active dolphin fishery and extensive monitoring over many years at several fisheries landing sites; this suggests that the species has either been extirpated or is extremely rare (Van Waerebeek et al. 1999, Van Waerebeek et al. 2009, Debrah et al. 2010).

Future work in poorly surveyed or unknown areas may well lead to new records. However they are unlikely to be frequent and the evidence from other parts of the range suggests that if humpback dolphins occur they will not be abundant (Van Waerebeek et al. 2015, Collins 2015).

Accurately mapping the current distribution of this species is very difficult task given uneven and inconsistent effort across most of the range. The map provided with this account uses the 30 m depth contour as a limiting bound, and provides a very broad approximation of suitable habitats and (perhaps) an original range. The text provided in this account provides a more accurate description of current distribution, and should be used as the primary reference.

Conserving the Atlantic Humpback Dolphin requires the proactive and urgent implementation of practical conservation measures (Ayissi et al. 2014, IWC 2011, Maigret 1994). Of utmost concern will be confronting the causes of localised declines, particularly fisheries bycatch, directed hunts and habitat loss (Perrin and Van Waerebeek 2007, Weir et al. 2011). Inshore gillnet fisheries are considered the most significant threat, and explicit fisheries management measures to reduce bycatch need to be identified and implemented. Addressing fundamental ecological and biological data gaps is also vital, particularly for improving conservation and management decisions, especially in areas of development. This should include efforts to generate robust and comparable abundance estimates for areas of described occurrence and areas that are under sampled. Surveys for this species can be challenging, but the biggest limitations to date have been an absence of sufficient resources and local capacity to conduct needed work (Ayissi et al. 2014, Collins et al. 2010, Maigret 1980, Reeves et al. 2003, Van Waerebeek et al. 2004, Weir et al. 2011).

The scale of coastal development and associated anthropogenic pressures suggests that identifying and protecting critical habitats (hotspots and foraging sites and areas between) will be pivotal for the conservation of this species. Nine range states (Western Sahara, Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, Cameroon, Gabon and Republic of Congo) and two states within the wider range (Equatorial Guinea and Democratic Republic of Congo), have Marine Protected Areas (MPAs) that incorporate proven or potential S. teuszii habitats (Hoyt, 2012; Weir et al., 2011). Their effectiveness varies; artisanal fishing and associated bycatches within these MPAs are known issues (Collins et al. 2013, Hoyt 2012, Van Waerebeek et al. 2003, Weir and Pierce 2013), and financing and lack of management capacity are common problems (e.g., Gallegos et al. 2005, Bennett and Dearden 2014). Explicit consideration of S. teuszii (and other threatened taxa) should be included in threat assessments (such as impact assessments) associated with coastal and estuarine industries (e.g., DEFRA 2011, BBOP 2012, IFC 2012) and where necessary additional and appropriate research undertaken to improve information gaps. If appropriately directed, mitigation actions associated with these projects could improve management of MPAs and/or other critical habitats (e.g., Bull et al. 2013, Pilgrim and Bennun 2014).

Significant conservation concerns for S. teuszii have been raised for decades (e.g., Cadenat and Paraiso 1957, Maigret 1980, Van Waerebeek 2003, Van Waerebeek et al. 2004, Weir et al. 2011). In 2003, the IUCN Species Survival Commission’s Cetacean Specialist Group identified S. teuszii as a high priority for research and conservation (Reeves et al. 2003). In 2010 a range of specific research and conservation objectives for Atlantic humpback dolphins were also identified by the Small Cetacean Sub- Committee of the International Whaling Commission (IWC) Scientific Committee (IWC 2011). They represented a balanced consensus of scientific opinion and included deliberate consideration of earlier strategies, including the CMS Action Plan for the Conservation of Small Cetaceans of Western Africa and Macaronesia (CMS 2008, Perrin and Van Waerebeek 2007). Immediate action is clearly required if additional losses, local extirpations, and potentially even the extinction of the species, are to be avoided in the next few decades.