Habitat Selection Of Chinese White Dolphin (Sousa Chinensis)

Preventing species from extinction is one of the major tasks in Animal Ecology andConservation Biology research. The population distribution, abundance and habitatselection of the rare and endangered species are the most important issues.The Chinese white dolphin (Sousa chinensis) is one of the most endangered marinemammals in the world. The geographic distribution ranges from the tropical tosub-tropical, extending widely in coastal and inshore waters of the Indian and westernPacific oceans from more than 40 countries. As the only marine cetacean species listed inthe Categoryâ… of Key Protected Wildlife List, the Chinese white dolphin is also placed inaddendumâ… of Convention on International Trade in Endangered Species of Wild Faunaand Flora (CITES). Moreover, the World Conservation Union (IUCN) considered it asone data deficient species.No comparative studies have been involved on both physical distribution and thestudy sample scales. Furthermore, few field studies have been conducted on integrating allhabitat factors, especially on biotic factors before.In this paper, sea-and land-based field surveys with reference searching were madeboth in the Dajin waters and the whole distribution area. The habitat information of thedolphin distribution area in the world was obtained by the reference and Google Earthsatellite photograph. The major habitat pattern was classified by cluster analysis and theprimary factor referring to the result was analyzed with stepwise regression method. Therelation between the dolphin abundance and the river mean annual runoff was confirmedthrough correlation analysis. The field survey was carried on from May, 2005 toSeptember, 2006. The dolphin abundance was assessed by shipboard sighting survey, byusing line-transect method. The spatial distribution pattern was studied by GeographicInformation System (GIS) tools. The fish resources were investigated based on the gillnetstation and bottom trawl surveys and the fish community was studied by usinghierarchical cluster analysis. The whole year was divided into the dry season (winter andspring) and wet season (summer and autumn) The seasonal changes in dolphindistribution were analyzed by using Mann-Whitney U test. Both the biotic and abioticfactors involving thirteen ecological varibles were selected to analyze habitat selection ofthe dolphin. Chi-square test, correlate analysis and factor analysis were used to examinethe relationship between the dolphin distribution with the habitat variables by using GIS tools. The main factors affecting the dolphin distribution were studied through thePrincipal Component Analysis (PCA). Based on the field data and GIS, the dolphinhabitat suitability was evaluated. The population health status of the dolphin major preyspecies was primarily analyzed by morphology method. In the meanwhile, the idea forprotecting the species and suggestion for future management were discussed in the paper.1. Forty-one habitat samples from the published information all over the world werecollected. It can be classified into 7 major habitat patterns involving Estuary and Reefpattern 41.4%, Bell-mouthed 31.7%, Reef but no Estuary12.2%; Estuary and Gulf andStraight Coast4.9%, Gulf and Reef and Gulf but no Reef 2.4%. Stepwise regressionshowed that the estuary (t=2.95, p＜0.05) and reef distribution (t=2.38, P＜0.05) werethe two habitat domination characters. Besides, the dolphin population size was correlatedpositively with the river average runoff (Spearman, r=0.857, P＜0.05).2. The result showed that the population density was 0.2231±0.1704 (inds·km^-2) and thetotal size were 200-270 individuals in Chuanshan archipelago including Dajin waters. Thespecies distributed continuously, however, it also has two relatively clumped regions,which were at Dajin and Shang-Xiachuan. But the distribution was more concentrated atDajin than the other.3. There was no significant difference between the dry and wet season for the dolphindistribution (Mann-Whitney, U=729.00, n=56, P＞0.05) in Dajin waters. Among thephysical factors, the dolphin occurrence per survey effort varied significantly in differentwater depth (x²=73.8, df=3, P＜0.01), bottom salinity (x²=10.4, df=4, P＜0.05),the distance to the river mouth (x²=72.9, df=4, P＜0.01) and the bank (x²=133.1,df=10, P＜0.01), but not significantly for the surface water temperature (x²=0.93, df=2, P＞0.05), bottom water temperature (x²=4.57, df=2, P＞0.05) or surface salinity (x²=0.7, df=4, P＞0.05). The dolphin preferred to the small aggregated estuary andinshore prey species and appeared significantly different in the four fish communities (x²=73.2, df=4, P＜0.01). The dolphin occurrence was positively correlated with the fishbiomass per survey effort (Spearman, r=0.68, p＜0.05) and the fish species quantities(Spearman, r=0.75, p＜0.05). For the human activity factors, it was negatively correlatedwith the fishing line density ( Spearman, r=-0.94, p＜0.01 ). But it showed no significantcorrelation between the dolphin occurrence with the gillnet density (Spearman, r=0.02, p＞0.05)and the trawl net density(Spearman, r=0.26, p＞0.05). The distance to the estuary,fish community patterns and the water depth were probably the main factors limiting thedolphin distribution by the Principal Component Analysis (PCA). While the distance tothe shore, the density of the sea lines and the fish biomass may also influence the dolphinhabitat selection.4. With GIS analysis, and based on the physical environmental and biotic factors, theresult showed that the most suitable habitat area for the dolphin accounted for 27.5%, thesuitable, marginally-suitable and unsuitable were 20.5%, 35.7% and 16.3%, respctively.The most suitable and suitable habitat declined by 7.5% and 1.3% under the humaninfluence, respectively. The major prey species of the dolphin inclined to miniaturization(Pearson, r=0.96, n=9, p＜0.0001), the fish population structure was not reasonableas it presented a normal distribution: there were less adult or calve individuals (1-SampleKolmogorov-Smirnov test, P＞0.05). All these made it clear that it was urged for thehabitat conservation in order to protect the dolphin.