Conservation of cetaceans in The Gambia and Senegal, 1999-2001, and status of the Atlantic Humpback Dolphin. WAFCET- 2 Report
Van Waerebeek, K.; Barnett, L.; Camara, A.; Cham, A.; Diallo, M.; Djiba, A.; Jallow, A.O.; Ndiaye, E.; Samba Ould-Bilal, A.O.; Bamy, I.L. (2003). Conservation of cetaceans in The Gambia and Senegal, 1999-2001, and status of the Atlantic Humpback Dolphin. WAFCET- 2 Report. CMS Convention on Migratory Species of Wild Animals/UNEP: Bonn. 47 pp.
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Document type: Project report
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| Authors | | Top |
- Van Waerebeek, K., more
- Barnett, L.
- Camara, A.
- Cham, A.
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- Diallo, M.
- Djiba, A.
- Jallow, A.O.
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- Ndiaye, E.
- Samba Ould-Bilal, A.O.
- Bamy, I.L.
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| Abstract |
A second project of the West African Cetacean Research and Conservation Programme (WAFCET-2) was implemented in Senegal and The Gambia, from December 1999 till December 2001. It generally aimed at collecting information on the conservation status of coastal cetaceans, with emphasis on the Atlantic humpback dolphin, and support activities to improve it. A base for the recently formed ngo COREWAM (Conservation and Research of West African Aquatic Mammals) was made operative near Dakar. Nineteen new cranial specimens, representing six cetacean species, were added to the COREWAM reference collection: short-snouted and long-snouted common dolphins (n= 9), bottlenose dolphins (n= 3), Atlantic humpback dolphin (n= 1), harbour porpoise (n= 3), ordinary Bryde’s whale (n= 1) and incomplete bony remains of unidentified delphinids (n= 2). Presently, 34 skeletal voucher specimens are curated. The Gambian cetacean reference collection was enriched with at least a dozen skulls, mostly bottlenose dolphins, conserved at Kiang West National Park. With support from this project, the Gambian Department of Parks and Wildlife Management implemented an aquatic mammal sightings and by-catch monitoring programme jointly with the Department of Fisheries. Eighteen data collection points were set up on the Atlantic coast and Gambian River shores. No specific cases of by-catch (2001) but more than 200 sighting records were reported. Few of these were sufficiently documented as to allow positive species identification. The majority seem to refer to bottlenose dolphins in the Gambia River. An intensive, one-day training workshop was organized, aimed at instructing fisheries officers who themselves train field observers. Also, a Gambian Aquatic Mammal Working Group was established. Unquantifiable, but presumed low to moderate, levels of cetacean by-catch, affecting several species (bottlenose dolphin, Atlantic humpback dolphin, common dolphins, harbour porpoise) continue to occur in both The Gambia and Senegal. In addition, unknown numbers are illegally netted or otherwise killed directly for their meat in both countries. Small cetacean meat is consumed locally and likely used also as shark bait. These insights confirm results from earlier surveys (WAFCET-1). Atlantic humpback dolphin was found to be taken, at least occasionally, in Guinea-Conakry and Mauritania. There are no clear indications of a ‘marine bushmeat’ black market spreading beyond the coastal region, but monitoring should be continued. As before, the illegality of cetacean catches caused the unwanted sideeffect that any evidence of catches is concealed or destroyed, which seriously hampers the collection of information and specimens. An unprecedented case of unauthorized livecapture of bottlenose dolphin was documented in Saloum National Park, Senegal. This episode (4 of 5 died) serves as a warning that the captive display industry may form a formerly unrecognized threat to some aquatic mammal populations in the subregion. The surreptitious nature of the exploitation of small cetaceans is highly obstructive to any attempts at monitoring. Nine countries, three newly recognized (N), are confirmed range states for Sousa teuszii: Morocco (Western Sahara), Mauritania, Senegal, The Gambia, Guinea-Bissau, Guinea- Conakry (N), Cameroon, Gabon (N) and Angola (N). There is some anecdotal indication for Togo and, based on purely geographic considerations, the Democratic Republic of Congo, People’s Republic of Congo, Equatorial Guinea and Nigeria are likely range states. Sousa teuszii is documented to regularly cross international borders between Senegal and The Gambia and thus technically qualifies as a ‘migratory species’ under the CMS Convention. The distribution of Sousa teuszii from Dahkla Bay (23º54’N), Morocco, southeast to Tombua (ca.16°S), southern Angola, appears to be ‘discontinuous’ i.e. with gaps of low to very low density in several areas. Humpback dolphins for instance have not been found in Ghana, possibly the result from the important dolphin fishery there. We propose the preliminary recognition of eight management stocks of Sousa teuszii, each stock named for a known core distribution locality in Atlantic Africa. Six stocks are of the ‘confirmed-contemporary’ type, supported by recent sightings or specimen records: (i) Dahkla Bay, (ii) Banc d’Arguin, (iii) Saloum-Niumi, (iv) Gêba-Bijagos, (v) southern Guinea and (vi) Angola. The Cameroon and Gabon stocks are known from historical records. Additional, unnamed, stocks most probably exist in the equatorial eastern Atlantic. The degree of polymorphism and genetic isolation between stocks need to be established. Several management stocks may actually form a single population. No biological population status is claimed for the proposed management stocks. The principal habitat of Atlantic humpback dolphins includes shallow, nearshore waters, outer estuaries of large rivers, sea-arms and wide, outer channels of river deltas, where seawater or brackish water predominate. There is no evidence for occurrence in freshwater (upriver) environments. Bottlenose dolphins, which we know to enter the Casamance and Gambia Rivers, may have been mistaken for humpback dolphins by some observers. We document the first sightings of Atlantic humpback dolphin in the Senegal’s Siné- Saloum delta since 1979. An apparently semiresident community of some 40 specimens was discovered at the entrance of Djinack Creek, a foraging site. In Guinea-Bissau, based on raw data by Wolff (1998), group size ranged from 1- 20 individuals with a mean of 6.50 (SD=6.09; n= 15). A re-interpretation from data by Spaans (1990) from the same area shows a comparable mean of 4.39 individuals SD= 4.19, n= 54, range 1-15, mode 2, median 2.5. These are significantly smaller (p< 0.001) than the group size observed in the Saloum delta (mean 22.9; SD= 9.33; n= 8; range 10-37). However, interpretation of what precisely constitutes a group may differ between observers. Further field work, including region-wide surveys of abundanve, are necessary to establish whether certain stocks of S. teuszii should be assigned ‘endangered’ status. Habitat encroachment, frequent by-catches and some directed take, as well as massive coastal overfishing, are thought to be the main causes for the low population levels in S. teuszii. With scientific stock size estimates lacking, the aggregated body of circumstantial evidence suggests that each of the named stocks may consist of hundreds of individuals rather than thousands. The long-beaked common dolphin Delphinus capensis, a skull of which appropriately picked up during a demonstration beach-combing activity, is a newly reported mammal for The Gambia. A Bryde’s whale calf stranded in Senegal was genetically determined as ‘ordinary’ form Balaenoptera brydei Olsen. Reports of mid-sized whales seen in nearshore waters of The Gambia remain unidentified. Although a novel awareness about aquatic mammal conservation is slowly taking hold in Senegal and The Gambia, this has not yet acquired a mainstream character. Biology students do not consider marine mammal science a feasible career. The Gambia’s Department of Parks and Wildlife Management and the Department of Fisheries have an important role to play in order to change attitudes. Principal challenges for COREWAM include maintaining generated momentum, attract follow-up projects, increase sources of documented information, broaden bases of public interest and stimulate region-wide cooperation. |
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