SOME ASPECTS OF THE ECOLOGY OF WEST AFRICAN MANATEE (Trichechus senegalensis LINNK, 1795) IN PANDAM WILDLIFE PARK, PLATEAU STATE, NIGERIA

Abstract

The study on the distribution, abundance and habitat condition of the West African manatee in Pandam Lake was conducted between 2010 and 2012 to enhance greater understanding of its ecology and conservation status. Rapid Rural Appraisal (RRA) approach (questionnaire and focus group discussion) was used to collect Traditional Ecological Knowledge (TEK) data on manatee. One hundred and twenty (120) questionnaires were distributed to all the fishermen in Pandam (35), Aningo (20) and Sabongida (65) villages in the study area. Also eight groups were created from the fishermen in the three villages. The visual non-motorized boat point scan was used for manatee survey. Six permanent transect lines were established in the three arms (GU, ZU, MS) and the ML. The survey covered both wet and dry seasons and lasted for 2 years (2011 to 2012). A line intercept sampling method was used to explore the vegetation found on the shoreline and flood plain areas. The species utilized as food and the parts utilized were identified. The species diversity index was calculated using Shannon-Wiener diversity index. The water parameters investigated include; depth, surface area, transparency, temperature, salinity, DO2 and pH. Data on fishing pressure were collected by counting the number of boats and the number of set nets. Data on years of fishing experience were correlated with data on abundance. Graphs, bar and pie charts, tables, percentages and frequencies were used to describe data both from field survey and questionnaire. Data obtained on the water depth at manatee feeding sites and physico-chemical parameters were analysed using ANOVA. The data on fishing effort expressed as the number of fishing nets sets in the dry and wet seasons were pulled together and analysed using t-test. The age of the respondents ranged from 21 to 80years. The age class 31-40years had the highest number 31 (25.83%) while age class 71-80years has the lowest number of 5 (4.17%). The years of fishing experience ranged from 10-60years. All the respondents in the three villages have sighted manatee in MS, GU & ZU but 54.17% did not sight manatee in the ML. Also 63.33% (n=76) usually sight manatee >4 times/month in the dry season while 0.83% (n=1) usually sight manatee >4 times/month in the wet season. 63% (n=75) of the respondents sight manatee mostly in the evening (18-21hr), 27% (n=33) sight manatee mostly in the early hours (5-11hr). Sighting of 2-3 manatees together is more common 56.67% (n=68) of the respondents, 33.33% (n=40) mostly sight 1 manatee while 10% (n=12) mostly sight 4-6 manatees together but none of them sighted >6 manatees together. Manatee presence indicators/indices include: Grazed bank vegetation, Torn net, Trails or cloud of mud, Dung, oil extract and bone. The field survey result showed that the mean seasonal water surface area increase was highest in the ML (72.78m±7.48) and lowest in GU (61.79m± 13.34). The mean water depth in the dry season ranges from 1.94m±0.4 to 2.87m±0.34 (MS/ML) while the wet season values range from 3.54m±0.12 to 6.01m±0.01. Water transparency was highest in ML (70.29cm±2.14, 117.41cm±5.04 for wet and dry seasons), while MS recorded the lowest (60.14cm±0.02, 107.94cm±8.52). The highest pH value of 6.74 was recorded in GU while MS has the least value of 6.42. Water salinity ranges from 0.00mg/l (MS&ML) to 0.01mg/l (ZU & GU). Mean annual temperature was 27.42±1.380C in 2011 and 27.34±1.46 in 2012.The plant species identified to be fed upon by manatee include; Nymphea lotus, Echinocloa stagnina, Echinocloa pyramidalis, and Polygonum lanigerium. The mean water depth at the feeding sites ranges from 1.05m±0.04 (ZU) to 1.75m ± 0.14 (MS). Test of homogeneity showed a significant difference (p<0.05) in the mean water depth at the feeding sites. A total of 69 plant species from 31 families were recorded in the LS and FP areas of Pandam Lake. The LS recorded 38 species belonging to 23 families while 34 species belonging to 11 families were recorded in the FP. The family Poaceae has the highest number of species (22) (30.56%), followed by the families Mimosaceae and Rubiaceae with 5 (6.94%) species each. The family and species diversity indices are higher in the LS (2.937, 3.72) than the FP (1.893, 2.706) for family and species respectively. Manatees were sighted 21 times through both direct (5 times) (23.81%) and indirect (16 times) (76.19%) means. Eighteen (18) (85.71%) of the sightings were recorded in the dry season with 3 (14.29%) sightings recorded in the wet season. Manatees were mostly sighted in a group of 2-4 individuals (4 times) with one sighting of one manatee. The estimated number of manatee is put at five (5). On the average 58 fishing nets were set/day in the wet season while 120 fishing nets/day were set in the dry season in Pandam Lake. There was a significant difference in the number of nets set in the two seasons (t=3.18, p=0.09). A total of 24 fish species belonging to 17 families were identified from the fish species caught by the fishermen and park staff. The family Cichlidae has the highest number of species (4), the families Bagridae, Claridae, Citharinidae, and Characidae have two species each while others have one species each. Also a total of 21 bird species belonging to12 families were identified in Pandam Lake some of which include; Ardea goliath, Ardea cinerea, Ceryle maxima, Alcedo cristata and Haliaeetus vocifer. Other aquatic fauna species in Pandam Lake include; Common hippo, Red river hog and Royal python. This study has clearly shown that manatee is still present in Pandam Lake, but the actual population has not been ascertained. However, one can still say that the population is not encouraging but the habitat is conduceive for manatee. Therefore, better knowledge of the manatee population with modern equipments will help future conservation of the species in Pandam Lake. The present estimate of manatee population size in Pandam Lake cannot be interpreted against any previous estimate because no study has ever been conducted on that. It is therefore suggested that the park should be taken over by the Federal government for effective protection of the resources most especially manatee.