Document presented to the Scientific Council of the Convention on Migratory Species
Sousa teuszii, Conservation status, CMS, Atlantic humpback dolphin, threats, Bycatch
Background 1. Of all cetaceans occurring in tropical and subtropical waters of West African, the Atlantic humpback dolphin is the only endemic species. It is also the cetacean that lives nearest to shore year-round, often just beyond the surf, and thus comes in closest contact with humans and their activities. It is also one of the species that displays the greatest wariness towards humans. If approached, it will flee even small boats, evidencing its great sensitivity to the lightest of disturbances. Recognizing this especially vulnerable situation, the species has since 1991 been assigned to CMS Appendix II. Since then coastal development and degradation has continued to increase region-wide (e.g. Khan and Mikkola, 2002) and pressure on the dolphin’s habitat can only have risen. Moreover, despite improved search effort, sightings remain scarce. One of the aims of the CMS/UNEP-sponsored WAFCET-2 project, implemented in Senegal and The Gambia (and to a lesser degree in Guinea-Bissau), consisted of comprehensively evaluating the current status of the Atlantic humpback dolphin (Van Waerebeek et al., 2003, 2004). Distribution and populations 2. Intraspecific geographic variation in morphology and molecular genetics of S. teuszii has not been studied. However, for practical and conservation purposes Van Waerebeek et al. (2004) provisionally designated eight biogeographically defined management stocks, seven of which are known to be extant, comparable to the IWC management units for large whales where biological stock data are absent or deficient (Donovan, 1991). Documented habitats include: Dahkla Bay (Rio de Oro-Western Sahara), Banc d’Arguin (Mauritania), Saloum-Niumi (Senegal-The Gambia), Canal do Gêba-Bijagos Archipelago (Guinea-Bissau), southern Guinea, Gabon and Angola. An 8th, historical stock, the Cameroon Estuary (where the holotype was collected in 1892), remains hypothetical. Potential existence of a 9th management stock of the western Togo/Volta delta requires investigation. At least some of these are expected to have biological population status; notably, the three northernmost stocks seem relatively isolated, possibly a recent phenomenon following local extirpation of communities in between as the result of mounting human pressure. Some other stocks may coalesce into single biological populations with further knowledge. While a quasi-continuous distribution from Rio de Oro south to Angola 2 may have existed historically, indications of contemporary distribution gaps are emerging, presumably the result of sustained bycatches and creeping human encroachment on once desolated coasts. It has never been considered a common species. Abundance 3. No abundance estimates for S. teuszii are available from any area, but density is certainly low compared with that of widely distributed, oceanic delphinids. The above-mentioned stocks are thought to amount to at most hundreds, not thousands, of animals. For example, the Banc d’Arguin stock, which arguably enjoys the best protection due to the size of the PNBA Marine Reserve, its remoteness and the fact that no engine-powered craft are allowed, was suggested not to exceed more than 100 individuals (Maigret, 1980). A more recent guess had put it ‘at least at high hundreds’. However a recent 3-day survey covering 226 nmiles on effort in excellent conditions made 11 sightings of common bottlenose dolphins but did not encounter Atlantic humpback dolphin (Van Waerebeek and Jiddou, 2006). This suggests that the species may have become, or has remained (Maigret, 1980) quite rare, even under optimal circumstances. A guesstimate of “not more than 100 animals” was also cited for the Saloum Delta population (Maigret, 1980) and based on own observations of the Saloum-Niumi stock since 1997, it appears highly unlikely that abundance could exceed the low hundreds. The Canal do Gêba and Bijagos Archipelago in Guinea-Bissau may host one of the healthiest extant stocks, perhaps several hundreds. Nothing can be said about the Guinea-Conakry and Angola stocks, except that they are extant. Groups seen off southern Angola were small, less than ten individuals, off Gabon three groups ranged from 6-35 individuals (Collins et al., 2004). No meaningful guesses can be made for Cameroon, Togo, and intermediate areas, nor for any other West African country (Van Waerebeek et al., 2004). Captures 4. The majority of specimens archived in collections are derived from dolphins taken either incidentally or directly in small-scale coastal fisheries. However, the true extent of fisheriesrelated mortality in range states is thought to be considerably higher than these few opportunistic findings suggest, considering that capture reporting is next to nonexistent. Based on specimens recovered and well-documented steep increases in artisanal fishing effort (e.g., Khan and Nikkola, 2002), incidental mortality from net entanglements may be one of the most important threats to the species’ survival and one of the hardest to address. The species lives in an area of high human population growth and protein food deficit, so there is potential for fisheries for human consumption (Klinowska, 1991). Their nearshore habits make them readily accessible targets. Habitat deterioration 5. The Atlantic humpback dolphin is a very shy species. All possible forms of coastal development with accompanying disturbance and degradation known to occur in West Africa (see Khan and Mikkola, 2002) will directly or indirectly affect the species. These include, but are not limited to, over-exploitation of mangroves, coastal construction (harbours, residences, refineries, shipyards), aquaculture, oil and gas exploration and extraction (drilling), accidental spills, increased shipping, tourism, and effluents (domestic, agricultural, chemical). Vast fisheries effort, 3 both artisanal and industrial, exploiting neritic fish stocks (e.g. Deme, 1996) is thought to cause a significant impact. Reduced foraging success may hamper recovery from high bycatch mortality. Conclusion 6. IUCN’s Cetacean Specialist Group appropriately tagged S. teuszii as a high priority for research and conservation because of its restricted range, narrow ecological niche, generally low abundance, and continuing threats (Reeves et al., 2003). Most of what we know about the Atlantic humpback dolphin is sketchy, uncertain or unconfirmed except regarding the trend of the status of its habitat. For the foreseeable future, accelerated development of West Africa’s coastal areas and concomitant progressive deterioration as a viable biotope for a human-averse cetacean is not only certain, it is also tragically inevitable in a region with strong human demographic growth. Ecologically challenged by its high evolutionary adaptation to a very narrow niche of warm, shallow inshore waters, this dolphin species will have nowhere to turn. For the Atlantic humpback dolphin to have a genuine chance to survive the 21th century it will need all possible protective measures including, to start with, the maximum achievable legal protection.