|Scientific Name:||Sousa teuszii (Kükenthal, 1892)|
Sotalia teuszii Kükenthal, 1892
|Taxonomic Notes:||The Sousa teuszii holotype (a skull) was recovered in the “Bucht des Kameruner Kriegsshiffhafens,” (“Bay of Warships” or ‘Man O’War Bay’), in Cameroon by the German agronomist Eduard Tëusz. The German zoologist Willy Kükenthal examined it at Jena and described it as the new species Sotalia teuszii in honour of its discoverer (Kükenthal 1891, Kükenthal 1892, Van Beneden 1892, Ayissi et al. 2014). The species was originally placed in the genus Sotalia; the genus name Sousa came into general use only in the 1960s (Fraser and Purves 1960, Fraser 1966). Thorough reviews of the species taxonomy are provided by Van Waerebeek et al. (2004) and Jefferson and Rosenbaum (2014). Photographs of the holotype are provided by Kükenthal (Table 21, Kükenthal 1892), Pilleri and Gihr (1972) and Jefferson and Van Waerebeek (2004). Illustrations of the holotype were provided by Van Beneden (1892). The holotype is now held by the British Museum (catalogue number 1822.214.171.124).
The collection details for the holotype are unclear but were of consequence. The dolphin skull and a shark-mauled carcass of a West African manatee were apparently recovered by Tëusz following a heavy rain storm and were subsequently confused (Van Waerebeek et al. 2004). The stomach of the manatee contained vegetable matter, leading Kükenthal to hypothesize that the species was perhaps riparian and vegetarian, an impression reinforced by the dolphin’s rounded (worn) teeth. The Belgian zoologist Pierre Joseph Van Beneden (with whom Kükenthal corresponded) compounded the misunderstanding in a separate publication (Kükenthal 1891, Kükenthal 1892, Van Beneden 1892, Van Waerebeek et al. 2004). Necropsies of fresh animals in the 1950s confirmed that they were piscivorous and marine (Cadenat 1956, Cadenat and Paraiso 1957).
Recent genetic and morphometric work has served to clarify the taxonomy of the genus Sousa (Jefferson and Rosenbaum 2014, Jefferson and Van Waerebeek 2004, Mendez et al. 2013). The available data indicate that there is “strong and significant genetic and morphologic differentiation between S. teuszii and all other sampling units…with no evidence of exchange or contact” (Mendez et al. 2013). Principal components analysis demonstrated that S. teuszii have significantly shorter rostra, wider skulls and lower tooth counts (an average of about 30 teeth per row vs. about 33-37 for other species) when compared with Southeast African, Arabian/Persian Gulf and Indian Sousa specimens (Jefferson and Rosenbaum 2014, Jefferson and Van Waerebeek 2004). There are no shared mtDNA haplotypes with other species in the genus, but a phylogenetic assessment of combined nuclear and mtDNA datasets indicates that S. teuszii is most closely related to Indian Ocean Humpback Dolphins (Sousa plumbea) from South East Africa (Mendez et al. 2013). The most plausible mechanism for their isolation is the Benguela upwelling system, an area dominated by cold upwelling that is located within the ~2,000 km distribution gap between S. teuszii and S. plumbea (Jefferson and Van Waerebeek 2004, Mendez et al. 2013).
|Red List Category & Criteria:||Critically Endangered A3cd+4cd; C2a(i) ver 3.1|
|Assessor(s):||Collins, T., Braulik, G.T. & Perrin, W.|
|Reviewer(s):||Taylor, B.L. & Reeves, R.|
As with other species in the genus, Sousa teuszii has very precise habitat requirements, limiting its resilience and ability to escape environmental and anthropogenic stressors (Davidson et al. 2011). Remnant populations are faced with a suite of “largely intractable threats” (Ayissi et al. 2014) that either affect them directly, or contribute to the rapid and widening deterioration of their inshore habitats (Perrin and Van Waerebeek 2007, Van Waerebeek et al. 2004, Weir et al. 2011). Although there are no empirically derived abundance estimates for either the species as a whole or any of the putative populations, the available information indicate that these dolphins occur in very low and declining numbers throughout most or all of their range. Most populations for which any data are available are extremely small and several appear to be isolated. Available published estimates indicate that the total species’ population size plausibly falls well below 3,000 individuals, suggesting that the number of mature individuals is less than 1,500 (following Taylor et al. 2007).
Declines have been observed or are suspected for every known population, and continued declines are considered inevitable given the ongoing expansion of all identified threats throughout the species’ known range. Bycatch in fisheries, the principal cause of the declines, has been identified or suspected everywhere the species has been studied. Directed killing has also been identified or suspected in several areas, and major threats to habitats (including ports) are increasingly prevalent (Perrin and Van Waerebeek 2007; Van Waerebeek et al. 2004, 2015; Collins 2015). Ecosystem impacts that compromise vital rates may also have deleterious effects, including increasing the susceptibility of populations’ to environmental stochasticity (Moore 2015, Weir et al. 2011). Appropriate management interventions that limit habitat loss and mortality from bycatch and hunting are limited or entirely lacking across the range, and in the absence of targeted and sustained conservation management efforts, long-term prospects appear grim.
The available data for other species in the genus can be used to infer that S. teuszii has a low reproductive rate and thus a low intrinsic potential for population increase (Jefferson and Rosenbaum 2014, Moore 2015, Taylor et al. 2007). Given the small apparent population sizes, any mortality over and above natural rates is likely to lead to appreciable declines in abundance. Moore (2015) estimated that given an inferred generation time of 25 years (as estimated for S. plumbea and S. chinensis), an average annual adult mortality rate of 5.3% would lead to an 80% decline over 75 years (three generations). Limited data for some areas (e.g., Congo) clearly demonstrates that non-natural mortality (particularly captures) is high and when considered alongside the scale of anthropogenic pressures, a population reduction of more than 80% over three generations is highly likely.
The available information, much of it characterized by high levels of uncertainty, suggests that the Atlantic Humpback Dolphin merits classification as Critically Endangered (CR) under criteria A3cd+4cd. For the A criterion, a reduction of more than 80% in the total population over three S. teuszii generations (~75 years) is suspected, with declines likely to have begun with the rapid expansion of West African coastal fisheries during the 1980s, and bycatch likely to increase as new areas are targeted and fishery pressures increase. The reduction has not ceased, nor have its causes – nor is there any reason to think they will in the foreseeable future. The inference and suspicion of the large decline in population size are based on the declining quality of the species’ habitat (subcriterion c) and its vulnerability to mortality in artisanal fisheries (subcriterion d).
|Previously published Red List assessments:|
|Range Description:||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.
Native:Angola (Angola); Benin; Cameroon; Congo; Gabon; Gambia; Guinea; Guinea-Bissau; Mauritania; Senegal; Togo; Western Sahara
Present - origin uncertain:Nigeria
|FAO Marine Fishing Areas:|
Atlantic – eastern central; Atlantic – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There are no global abundance estimates for S. teuszii. Assessments for the stocks described by Van Waerebeek et al. (2004) were derived from survey work that was typically localized, sporadic and of limited duration. Varied survey methods were used that do not allow rigorous abundance estimation or comparison. The few associated “guesstimates” are subjective and based on the experience of a limited number of researchers; these provide a crude index of abundance at best.|
Populations at the northern (Dakhla Bay, Western Sahara) and southern (Namibe, Angola) extremities of the range appear to be very small, which may indicate the limits of habitat suitability (Weir 2009). Beaubrun (1990) described the Dakhla Bay population as “miniscule”, and sightings in the same area by Notarbartolo di Sciara et al. (1998) reinforce this impression. This population is likely limited to “a few tens of individuals” (Van Waerebeek et al. 2004). Recent sightings verified with photographs suggest that the subpopulation is still extant (Weir and Collins 2015). The Banc d’Arguin (Mauritania) and Saloum-Niumi (Senegal/The Gambia) populations have been estimated repeatedly at ~100 animals since the mid-1970s (Maigret 1980; Van Waerebeek et al. 2003, 2004). Incidental sightings from the southern Banc d’Arguin suggest that the species is sighted relatively frequently (Antonio Araujo, Fondation Internationale du Banc d’Arguin, pers. comm. January 2014). However, the stock has never been considered large by those who have completed assessments (Maigret 1980, Robineau and Vely 1998). In the Saloum-Niumi region, encounter rates and group sizes recorded during more recent surveys indicate a small population “unlikely [to] exceed low hundreds, maybe less” (Van Waerebeek et al. 2000, 2004).
Data and sighting records for Guinea Bissau suggest the continued occurrence of a significant population of S. teuszii into at least the late 1990s (Powell et al. 1996; Spaans 1990; Van Waerebeek et al. 2000, 2004). Van Waerebeek et al. (2004) ventured a guess of “at least several hundred, if not more”. A more recent review of sightings records indicates that S. teuszii is still widely distributed in Guinea Bissau (Leeney et al. 2015b), but sightings appear to be declining in regularity (P. Campredon, IUCN country program for Guinea Bissau, pers. comm. 11 May 2015). Recent sightings in the Rio Nuñez (northern Guinea) suggest that distribution across the Guinea Bissau/Guinea border may be continuous (Weir 2015, Van Waerebeek et al. 2015).
Recent surveys in Cameroon yielded a single humpback dolphin sighting, despite extensive beach- and boat-based survey effort. A recorded encounter rate of 0.39 sightings per 100 km suggests that abundance there is very low (Ayissi et al. 2014). Boat surveys in Gabon have also yielded low sightings rates. Sporadic surveys between 2003 and 2006 yielded five sightings at an average rate of 0.15 sightings per 100 km. Recent surveys in the Gamba/Sette Cama region of Gabon yielded three sightings of S. teuszii with an encounter rate of 0.13 sightings per 100 km (Collins et al. 2010, Minton 2015). However, sightings rates during shore-based work in Congo are much higher (though are not comparable), and suggest that the coasts of southern Gabon and a limited area in the adjacent Republic of Congo harbour a total population in the high tens or low hundreds (Collins et al. 2013). Most of the Angolan coast is unsurveyed, but localised survey effort demonstrated that a small group of 10 individuals was resident in the Flamingos area (Weir 2009). A limited number of surveys on the Angolan side of the Congo River mouth between 2007 and 2009 failed to yield any sightings (WCS 2011).
The absence of robust estimates precludes any quantitative assessments of trend. However, the evidence of recent work in some areas and a consensus of expert opinions indicates that most populations of S. teuszii are small and that all have experienced significant declines in recent decades (IWC 2011, Collins 2015). The principal cause of these declines are bycatches and directed takes although habitat loss is also likely a contributing factor (Ayissi et al. 2014; IWC 2011; Perrin and Van Waerebeek 2007; Van Waerebeek et al. 2004, 2015; Weir et al. 2011). Limited research effort for each putative S. teuszii population has either identified significant mortality or yielded strong evidence to infer it. Of particular concern are recently reported dolphin bycatches and suspected declines in Guinea Bissau, which together with neighbouring Guinea, is believed to harbour the largest extant population (Leeney et al. 2015b).
The prior IUCN Red List status assessment concluded that “considering the relatively small numbers observed, and even taking account of the many areas of the species’ range where there has been little or no assessment, the total population probably numbers only a few thousand” (Reeves et al. 2008). A review by Collins (2015) reinforces general inferences of small total population size. Considering the relatively small numbers observed, and even taking account of the many areas of the species’ range where there has been little or no assessment, the available information suggests that the species’ total abundance is below 3,000 individuals (Collins 2015). If it is assumed that 50% of these are mature (following Taylor et al. 2007), the likely number of mature animals in the total population is likely less than 1,500.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||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).
|Generation Length (years):||25|
|Use and Trade:||The sale of dolphin meat (of a variety of species) for either human consumption or bait has been documented or suspected from almost every S. teuszii range state. Evidence for the consumption and sale of S. teuszii specifically has been reported from Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, Sierra Leone (unverified interview data), Togo (suspected), Nigeria, Cameroon and the Republic of the Congo. Many instances involve the secondary (i.e. non-targeted) use of dolphin bycatch, but it is clear that the species has been, and is currently, directly and increasingly, targeted for food in many areas (Ayissi et al. 2014, Bamy et al. 2010, Cadenat 1956, Clapham and Van Waerebeek 2007, Collins et al. 2013, Lewison and Moore 2012, Moore et al. 2010, Van Waerebeek et al. 2004, Van Waerebeek et al. 2015, Weir and Pierce 2013). Leeney et al. (2015a) report that “42% of fishermen interviewed in Guinea-Bissau stated that they had accidentally caught a dolphin at least once and 37% of interviewees had eaten dolphin meat.”|
The nearshore habitats of S. teuszii greatly increase its susceptibility to many anthropogenic threats. High human population densities, widespread poverty and habitat degradation (and destruction) associated with development are considered important determinants of the species’ distribution and status (Perrin and Van Waerebeek 2007, Weir et al. 2011). Fisheries within the range of S. teuszii are extensive and are a major source of income and protein (Belhabib et al. 2015, Brashares et al. 2004, Kaczynski and Fluharty 2002, Weir et al. 2011). Bycatches of S. teuszii in artisanal gillnets have been reported from most areas and for as long as the species has been studied, including the first records for some areas (e.g., Busnel 1973; Cadenat 1949; Campredon and Cuq 2001; Collins et al. 2010; Murphy et al. 1997; Robineau and Vely 1998; Van Waerebeek et al. 2000, 2004). This includes unverified fishermen's accounts of S. teuszii bycatches in Sierra Leone (Moore et al. 2010).
Recent work in Conkouati Douli National Park (Republic of Congo) provides some indication of the substantial bycatch risk. A programme of intensive monitoring, enforcement, and cooperative (incentivized) reporting, identified 19 dolphin bycatches across all artisanal landing sites (n=14) on a 60-km stretch of protected beach over five years of work. Of these, 10 were S. teuszii, and the testimony of fishermen showed that all were caught in gillnets less than 1 km from shore (Collins et al. 2013). Although alarming mortality figures have been reported for other areas, including the Banc d’Arguin (Campredon and Cuq 2001, Robineau and Vely 1998) and the Saloum Delta (Van Waerebeek et al. 2004), the monitoring of bycatches is generally non-existent or limited to very few landing sites (e.g., Debrah et al. 2010, Moore et al. 2010). These figures are considered unrepresentative of the true toll, but bycatches are considered the principal cause for their range-wide decline and the greatest immediate threat for most populations (Ayissi et al. 2014; Clapham and Van Waerebeek 2007; Collins et al. 2010, 2013; Debrah et al. 2010; Jefferson et al. 1997; Northridge 1984; Perrin and Van Waerebeek 2007; Van Waerebeek et al. 2004; Weir et al. 2011).
Accounts of the deliberate capture of S. teuszii are rare (e.g., Cadenat 1949, 1956, 1957; Duguy 1976; Maigret 1980; Van Waerebeek et al. 2004), but directed captures likely occur in some areas (Perrin and Van Waerebeek 2007; Van Waerebeek et al. 2000, 2015). Maigret (1994) believed that there were no traditional marine mammal fisheries in West Africa, but there is evidence that the opportunistic use of bycatches may develop into “directed entanglement” or “non-target-deliberate acquisition” (respectively, Clapham and Van Waerebeek 2007, Robards and Reeves 2011). The scale of this practice is unknown, but appears to be part of a developing global trend in the utilization of “marine bushmeat” and reflective of general fisheries declines (Alfaro-Shigueto and Van Waerebeek 2001, Brashares et al. 2004, Clapham and Van Waerebeek 2007, Leeney et al. 2015a, Robards and Reeves 2011, Uwagbae and Van Waerebeek 2010, Van Waerebeek et al. 2004). Debrah et al. (2010) noted that the sale of cetaceans and sea turtles contributes to the economic viability of gillnet fisheries in Ghana. This included the killing of live entangled animals, and the supply of dolphin meat to markets for shark bait (Van Waerebeek et al. 2004, Weir and Pierce 2013). Captures may be concealed, given legal prohibitions (Reeves et al. 2003), hindering the acquisition of reliable data from surveys in some areas (Moore et al. 2010, Van Waerebeek et al. 2004).
A related concern is the pervasive spread of migrant fishermen across western Africa over the past few decades (e.g., Bakhayokho and Ke´be´ 1991, Binet et al. 2012, Campredon and Cuq 2001, Cormier-Salem 2000, Duffy-Tumasz 2012, Leeney et al. 2015b). Migrant fishermen (including those who move within states) may not abide by local injunctions, taboos or laws, and are often better resourced and more aggressive in their exploitation of local resources (Campredon and Cuq 2001, Binet et al. 2012, Leeney et al. 2015b). They have been implicated in the captures of S. teuszii in areas adjacent to the Banc d’Arguin (Campredon and Cuq 2001). Fishermen from Senegal, Guinea (Conakry), and Sierra Leone exploit the waters of Guinea Bissau, which has a limited artisanal fishing tradition; captures of dolphins and manatees, and declines of nesting sea turtles have been reported, raising concern for S. teuszii (Almeida e Silva et al. 1999, Campredon and Cuq 2001, Leeney et al. 2015b, Maigret 1994, Powell 1990).
Fisheries declines in general may affect populations of S. teuszii in a variety of ways, including reductions in the prey base and increased artisanal fishing effort, leading to greater risk of capture (Weir and Pierce 2013). Industrial fisheries compound this problem by competing for increasingly scarce resources, as well as fishing in zones set aside for artisanal fishermen and dolphins. For instance, trawlers fishing illegally within Conkouati Douli National Park (Republic of Congo) force artisanal fishermen to set their nets closer to shore (for fear of losing their nets in trawls), raising bycatch risks for coastal species (Collins et al. 2013).
Coastal developments and their varied cumulative effects represent largely understated, unquantified and poorly recognized threats for S. teuszii (Van Waerebeek et al. 2004, Weir et al. 2011). The species appears to be timid, and avoidance by dolphins of research boats making close approaches is seemingly prognostic of their susceptibility to disturbance (Van Waerebeek et al. 2004, Weir 2015). Anthropogenic noise is an identified threat for cetaceans in general (e.g., Weilgart 2007), and for humpback dolphins specifically; noise from shipping and other industrial activities are considered threats to S. chinensis in Taiwan (Wang et al. 2007) and Hong Kong (Jefferson et al. 2009). Port developments are particularly prevalent, and preferred sites frequently overlap with the habitats of coastal dolphins; the scale of some ports suggests that they present effective physical barriers, and thus have potential for disrupting longshore movements throughout their operation. Indirect or “non-lethal” disturbances are likely during construction, and may become more permanent if maintenance (e.g., dredging) and urban development occurs at port sites (Jefferson et al. 2006, 2009). Animals seeking to avoid disturbance might be forced into less optimal areas, with unknown but presumably negative consequences for population health and fecundity, problems that can be exacerbated by coincident ecological constraints (e.g., Pirotta et al. 2013, Ayissi et al. 2014).
Environmental contamination is a potential threat in some areas and may increase as development accelerates. The habitat preferences of S. teuszii increase the potential for exposure to terrestrial sources of pathogens and pollution (Weir et al. 2011). Phosphorite mining in coastal Togo contaminates inshore sediments with trace elements, including cadmium (Segniagbeto and Van Waerebeek 2010, Segniagbeto et al. 2014). Oil exploration and development are underway in many marine areas within the species’ range. Spills and chronic pollution associated with some of these facilities may be detrimental to dolphin health but remain completely uninvestigated in S. teuszii.
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.
|Citation:||Collins, T., Braulik, G.T. & Perrin, W. 2017. Sousa teuszii. The IUCN Red List of Threatened Species 2017: e.T20425A50372734.Downloaded on 23 June 2018.|
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