A Study On The Population Biology And Conservation Of The Chinese White Dolphin In Xiamen, China

This study provides a systematic survey on the population biology and conservation of the Chinese white dolphin (Sousa chinensis) in Xiamen, China. Main conclusions include:1. Photo-Identification and social organizationFrom February, 2004 to April, 2007, 40 individuals was identified based on pigmentation and speckle patterns, wound marks and various scars occurring on the upper body. The cumulative number of identified animals increased throughout the study period, the increases in the discovery rate could not reach the plateau. Calculation of association indices between pairs of dolphins showed that most pairs of dolphins never or only rarely occurred in the same group. The average association index (AI) for these pairs ranged from 0 to 1, with an average of 0.1235±0.1792. Although the social system of Chinese white dolphins appears to be fluid, some individuals often occur as members of sub-group within short time. Group size of Chinese white dolphins ranged from one to 20, the overall mean group size is 5.24±4.49. Group size was not affected by month.2. Distribution of dolphins in Xiamen watersOverall, Xigang (West Harbour) and Jiyu represented the major area of distribution in Xiamen, and no significant variance on the distribution pattern of dolphins in these waters from 2004 to 2007. Significant seasonal changes in distribution in all the Xiamen waters were found. In spring, significant numbers of dolphins occurred in Xigang and few in other areas, while in other seasons, the sighting rate in Xigang decreased relatively with sighting rate in Jiyu, Dapan, and Dadeng increasing obviously, suggesting an outward movement pattern of Chinese white dolphins from the inside harbour to outside waters after spring. Furthermore, Xiamen west harbour and waters from Jiyu to Wuyu were identified as the 'key habitats' and Dadeng waters may serve as the 'sanctuary' for Xiamen population. 3. Habitat selectionThe selections of habitat factors, i.e., distance offshore, water deep, ebb and flow, tide direction and salt degree, were analyzed by using finding frequency and x~2-test. The results showed high level of selections of distance offshore within 500 meters, water depth between 10-20 meters and salt degree about 30.4. Home rangeFew studies have examined the home range characteristics of Chinese white dolphins, up to now, only was carried out in Hong Kong/Pearl River Estuary. In this study, the location data of 20 dolphins from Xiamen waters, with a range of 4-27 sightings each, were analyzed. The estimated mean range size of individuals was 52.88±46.85 km~2, varying greatly from 16.6 km~2 to 152.23 km~2, with the largest linear range of 36.65 km. Age class, uneven survey effort and seasonal immigration, all influenced home range size. Chinese white dolphins in the Xiamen waters had small overlapping ranges, the overlap ratio varied from 1%-77.5%, with an average of 9.78%.The mean overlapping ratio among the individuals with smaller home range was significantly larger than that larger home range. Calves have significant overlapping ratio than juveniles, sub-adults and adults.5. Abundance estimates based on 3 methodsIn this study, the abundance of Chinese white dolphin (Sousa chinensis) in Xiamen waters was estimated by three methods. Line-transect method (LTM) only was used to estimate the population size in all the Xiamen waters. Based on photo-identification data, capture-recapture method (CRM) was used to estimate the abundance of Chinese white dolphins in Xiamen waters and western waters respectively. Additionally, regression method (RM) was tried to be used in this study. As a result, the LTM generated the seasonal abundance estimates ranged from 67 (CV = 41.6%) (Summer) to 93 (CV = 26.34%) (Spring), with an average of 86 (CV = 20.16%, 95%CI=58-128) in Xiamen waters. CRM (75-107) and RM (92-146) methods generated the similar abundance estimates to LTM. As a result, it was regarded reasonable and reliable that the abundance estimate ranged from 70 to 100 in all the Xiamen waters, and only 40-50 dolphins in the Xiamen western waters.6. The population dynamics of Chinese white dolphin in XiamenProgram VORTEX 9.61 was used to model the population dynamics of Chinese white dolphins (Sousa chinensis) in Xiamen within 100 years, test the sensitivity of parameters, and estimate the population finite rate of increase (λ). It was found that under the ideal condition (no stochastic fluctuations, no inbreeding depression, no limitation of mates, etc), the deterministic population finite rate of increaseλ=0.919, intrinsic rate of increase r = -0.084, and net reproduction rate Ro=0.278. After 100 years, the mean growth rate(r) will be -0.0601 (SD=0.1449), abundance will decline to six individuals, survival rate will decrease to 0.7%, and the median time to first extinction will be 52 years. The population was especially sensitive to mortality, female breeding proportion P (0), and catastrophes. We simulated population dynamics under 64 scenarios with different parameter combination. Of these, population modelling under 63 scenarios generatedλ<1, while only one modelling generateλ=1. These results suggested a gloomy future for Chinese white dolphins in Xiamen. Human activities, especially underwater blasting, yachts, and fishing nets, should be strictly managed and controlled to avoid or reduce the direct kill of or indirect impact on dolphins. In addition, it was found that enhancement of gene flow with adjacent populations, or supplement of individuals to Xiamen population from adjacent waters, will effectively delay the median time to first extinction for the Xiamen population.7. A preliminary Analysis on Trace elements Concentrations in the Chinese White Dolphins (Sousa chinensis) in XiamenThe concentrations of some trace elements, such as Cu, Zn, Cd, Pb, Hg, Ni, Se, As, Mg, Mn and Al, in nine tissues from five Chinese white dolphins (Sousa chinensis) collected from Xiamen waters, were measured. The results showed the concentrations of Cu (p<0.05) and Mn (p<0.01) in liver, and Zn in live (p<0.01), intestine (p<0.05), stomach (p<0.05) and heart (p<0.05) in juvenile individuals were significantly higher than those in muscle, with no significant variation of other trace element concentrations in different tissues. In adult individuals, concentration of Pb in lung was significantly higher than that in liver (p<0.001), muscle (p<0.01), stomach (p<0.01) and heart (p<0.05), and concentration of Hg in liver was higher than that in pancreas (p<0.05), however, no significant variation of other trace element concentrations were found. Overall, concentrations of most trace elements in adults were higher than those in juvenile, showing the trace elements were accumulated with age. The concentrations of some toxic heavy metals such as Hg, Pb and Cd, were mainly accumulated in liver, kidney and ovary, suggesting a high toxicity-pressure on these tissues.8. Genetic diversity of Chinese White Dolphins in Xiamen 610 bp of 13 new mitochondrial control region sequences of Sousa chinensis were sequenced. Homologous sequences for 5 Sousa available in GenBank were combined. 7 haplotypes were defined. Lipotes vexillifer and Neophocaena phocaenoides were used as outgroup taxa, and the MP, ML, BI, and NJ tree shared similar topology, in which the samples of different waters were not grouped in an absolute clade, indicating that differentiation for the different populations were not significant. Nucleotide and haplotype diversities were 0.0049 and 0.536±0.123 for Xiamen population which were lower than other dolphins. Xiamen samples were not group in a single clade. Considering there was common haplotype between Xiamen population and Jiangsu Rugao, Guangdong and Guangxi Beihai, protection of genetic diversity of Xiamen population is very important.9,Threat factors were analyzed, and some suggestions were put forward.