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Abundance, distribution and conservation of Chinese White Dolphins (Sousa chinensis) in Xiamen, China
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ORIGINAL INVESTIGATION
Abundance, distribution and conservation of Chinese White Dolphins (Sousa chinensis) in Xiamen, China Bingyao Chena, Dongmei Zhengb, Feifei Zhaia, X. Xua, P. Suna, Q. Wanga, G. Yanga, a
Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210046 China b College of Oceanography and Environmental Science, Xiamen University, Xiamen 361005, China Received 29 August 2006; accepted 14 December 2006
Abstract In recent years, human activities appear to present the greatest threat to the Chinese white dolphin (Sousa chinensis). Increasing death records of this species in Xiamen have already become a focus of attention among the local government, the public, and the media. A comprehensive understanding about the status of Xiamen population is important not only to evaluate the conservation measures taken previously, but to design adaptive measures appropriate to this population. In this study, a survey using line-transect methodology was carried out to cover an area of about 700 km2 in Xiamen waters. A total of 102 separate sightings were made on 6157 km of transect line. The abundance estimate ranged from 67 (CV ¼ 41.6%) to 93 (CV ¼ 26.34%), with an average of 86 (CV ¼ 20.16%). Overall, Xigang (West harbor) and Jiyu represented the major area of distribution in Xiamen. Significant seasonal changes in distribution 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 sightings in Jiyu, Dapan, and Dadeng increasing obviously, suggesting an outward movement pattern of Chinese white dolphins from the inside harbor to outside waters after spring. Some suggestions for redesigning the Xiamen Nature Reserve and other management measures are put forward. r 2007 Published by Elsevier GmbH on behalf of Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Keywords: Sousa chinensis; Abundance; Distribution; Conservation
Introduction The Chinese white dolphin, Sousa chinensis, is distributed throughout shallow, coastal waters of the Indian and western Pacific oceans, from South Africa in the west to northern Australia and southern China in the east (Ross et al. 1994). The Chinese white dolphin is a species protected under the Convention on International Trade in Endangered Species of Wild Fauna and Corresponding author.
E-mail address: [email protected] (G. Yang).
Flora (CITES) (Klinowska 1991, and is classified as an ‘insufficiently known’ species by The World Conservation Union (IUCN) (Klinowska 1991; Reeves and Leatherwood 1994). In China, this species was listed as a Grade 1 National Key Protected Animal under the Wild Animal Protection Law issued in 1988. Within China, five resident populations of Chinese white dolphin were, respectively, found in Pearl River Delta (including Hong Kong) (Jefferson 2000; Parsons 1998; Parsons and Chan 1998; Parsons et al. 1995; Ng and Leung 2003; Jefferson and Hung 2004), Xiamen (Wang 1965; Huang and Liu 2000; Liu and Huang
1616-5047/$ - see front matter r 2007 Published by Elsevier GmbH on behalf of Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. doi:10.1016/j.mambio.2006.12.002 Mamm. biol. 73 (2008) 156–164
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2000), Beibuwan Gulf (Wang and Sun 1982), the west coast of Taiwan (Wang et al. 2004), and Leizhou, Guangdong Province (Unpublished data). However, up to now, abundance information is only available for Hong Kong, the Pearl River Estuary, and Xiamen waters (Liu and Huang 2000; Jefferson 2000; Jefferson and Hung 2004). Based upon surveys conducted in mid1990s, the population abundance of Chinese white dolphins in Xiamen was estimated about 60 individuals (Liu and Huang 2000). Most occurrences were found in Xigang (West harbor) in the west and Tongan Bay in the east of Xiamen (Liu and Huang 2000), but analyses of potential seasonal distribution patterns were not available (Jefferson and Hung 2004), which is not advantageous for designing and taking some adaptive conservation measures appropriate to this population. The Xiamen population was thought to be decreasing (Liu and Huang 2000), although not supported by solid statistics data (Jefferson and Hung 2004). As well known (Karczmarski 2000), the coastal distribution characteristic of Chinese white dolphins renders them particularly susceptible to various extreme anthropogenic pressures. These pressures have posed some serious impacts on Chinese white dolphins especially in Xiamen. For example, at least 11 dead dolphins were recorded from 1994 to 1999 (Huang and Liu 2000). The number of death has been increasing to six in 2002 and 10 in 2004. Some of these dead individuals were identified to die from underwater blasting in coastal construction projects (Wang et al. 2003). Other human activities, such as agricultural and industrial pollution, vessel traffic, and fishing, etc., also have some potential adverse impacts on Chinese white dolphins. For example, extensive mariculture in the nearshore waters might result in habitat loss for local dolphins (Jefferson and Hung 2004). Destructive fishing, especially trawl netting, is likely to result in habitat degradation and resource depletion of dolphins (Jefferson and Hung 2004). The present survey followed systematic line-transect sampling method widely used in cetacean populations (Buckland et al. 1993, 2001; Jefferson 2000; Calambokidis and Barlow 2004) to provide some updated data on the abundance and distribution of Chinese white dolphins in Xiamen waters. These data will help us to design some new and adaptive conservation and management measures that are important for the longterm survival of this population.
Material and methods Study area Xiamen is located in southeast China between latitudes 241120 N and 241400 N and longitudes 1171500 E and 1181300 E.
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Jiulong River is the most important freshwater resource with a mean annual flux of 8.2 billion m3 (Liu and Huang 2000). Besides, there are many other small rivers in the north and northwest of Xiamen, which mainly affect the marine environment off the western coast of Xiamen by influencing the salinity. Daily tide changes are normal semi-diurnal, and the mean tidal height at spring tide is about 5.68 m (Liu and Huang 2000). Between 1995 and 2000, the total 89.2 km2 tideland was reclaimed (Liu and Huang 2000). Extensive mariculture, and oyster or laver farms still exist in Tongan Bay, Dadeng, and Jiyu in Xiamen.
Line-transect sampling The field survey was conducted from February to December, 2004 and covered all the Xiamen waters and partial Chinmen waters, Taiwan Province, and some neighboring waters belonging to Zhangzhou, an administrative district adjacent to Xiamen, which is about 700 km2 in total, following line-transect methods (Buckland et al. 1993, 2001; Jefferson 2000). The dolphins were mainly found in inshore waters of approximately o1.5 km (Ross et al. 1994; Jefferson 2000; Karczmarski et al. 2000a), with most sightings (over 80%) recorded within 400 m of shore (Karczmarski et al. 2000a). This shows that the density gradient is most probably perpendicular to the shoreline, and we placed the transect lines accordingly. We used a zigzag pattern in designing transect lines (Dahlheim et al. 2000; Buckland et al. 2001; Hines et al. 2005) to equalize the effort on all parts of the Xiamen waters. Field survey was mainly conducted by a single boat using a 12 m flat boat powered by a 36 HP engine. The boat had open upper deck allowing for observer eye heights of about 4–5 m above water level. When on effort, the boat traveled along determined lines at a speed of approximately 8 km/h. Because of the large survey area, it is difficult for a single boat to cover all the Xiamen waters in 1 day. Therefore, the boat was directed toward the place where the effort was terminated in the previous day for the purpose of equalizing survey effort in each part of Xiamen waters. In addition to the single-boat surveys, multiple-boat surveys were carried out on 11 days, i.e., 15–16 March, 21–24 May, and 3–7 November to cover all the Xiamen waters simultaneously. In the multiple-boat surveys, four boats were used to cover respective parts of Xiamen waters at the same time. When dolphins were sighted in the wild, searching effort was typically terminated, and the boat was directed toward the sighted individual or group. The maximum possible time was dedicated to following dolphin groups. Sighting time, radial distance, sighting angle, group size, group membership, various behaviors of dolphins, human activities around dolphins, e.g., fishing, were recorded. Age structure of each group was determined according to the description by Jefferson (2000) that unspotted dark gray or gray individuals represented calves and juveniles, mottled and speckled individuals were considered as sub-adults, and less spotted or unspotted pink or white individuals were adults. Latitude and longitude of all sightings, boat speed and routes were recorded using a global positioning system (GPS). Some environmental conditions, such as visibility, wind power
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and direction, ebb and flow, water temperature, and Beaufort sea state were also recorded.
Table 1. Summary data for boat surveys carried out in Xiamen waters in 2004
Line-transect estimates
Time
Population abundance estimate was carried out using the program DISTANCE 5.0. Density (D) and abundance (N), and their associated coefficient of variation (CV), were, respectively, estimated with the following formulae: D¼
nf ð0ÞS , 2L
nf ð0ÞSA , 2L qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi CV ¼ fCV2 ðn=LÞ þ CV2 ½f ð0Þ þ CV2 ðSÞg,
N¼
where n is the number of on-effort sightings, f(0) the probability density function at zero perpendicular distance, S the unbiased mean group size, A the size of the study area, and L the length of transect-line surveyed. Most parameters of these equations, e.g., function f(0), group size (S), encounter rate (n/L), were calculated via DISTANCE. Twelve detection models were compared in the analysis of f(0), i.e., uniform/hermite polynomials, uniform/ cosine, uniform/simple polynomial, half normal/hermite polynomials, half normal/cosine, half normal/simple polynomial, hazard rate/hermite polynomials, hazard rate/cosine, hazard rate/simple polynomial, negative exponential/hermite polynomials, negative exponential/cosine, negative exponential/simple polynomial. Based on Akaike’s information criterion (AIC), the best model was determined and chosen for the subsequent abundance analysis. The CVs of f(0), S and n/L we presented also corresponded to the output of DISTANCE (default). The coefficient of variation for abundance was calculated as the square root of the sum of the squared CVs of f(0), group size (S) and encounter rate (n/L). Environmental conditions, observers’ capability of sighting, survey protocol, and the boats used all might influence sighting rate of dolphins. When the abundance is calculated, these factors are usually combined in the parameter of g(0), the probability of recording a sighting on the transect line (Slooten et al. 2004). Due to unavailability of data to quantify the proportion of missed sightings, the g(0) was unable to be calculated exactly at present. This might lead to underestimations of real density and abundance, so we interpret the value of N obtained in the present study as a minimum or conservative estimate for population abundance of Chinese white dolphins in Xiamen.
Results About 181 boat surveys were conducted in Xiamen, which covered approximately 6157 km of transect line in total (Table 1). Chinese white dolphins were sighted for 102 times with a total of 473 individuals recorded and directly observed for over 100 h. Most dolphins were sighted in waters less than 20 m in depth (94% sightings)
No. survey days
Sighting nos.
Individual Length of nos. transect lines (km)
Single-boat survey February 10 March 19 April 23 May 15 July 16 August 14 October 20 November 17 December 5
15 10 10 4 5 4 11 6 4
64 33 59 30 24 22 68 33 29
405.77 578.01 876.36 554.30 426.14 370.22 627.28 442.44 112.79
Subtotal
139
69
362
4393.31
Four-boat survey March 8 May 14 November 20
7 11 15
25 43 43
405.04 547.08 901.56
Subtotal
42
33
111
1853.68
181
102
473
6156.74
Total
and within 500 m of the shore (62.2% sightings). Of the 102 sightings, 27.45% were of single animals, whereas groups of p3 individuals constituted 52% and 12.75% were of groups of ten animals or more. The group size ranged from minimum 1 to maximum 18 individuals with an average of 4.6473.85. Of the 473 individuals recorded, the calves and juveniles comprised 18.18% of the counts, whereas sub-adult and adults accounted for 45.24% and 36.58%, respectively.
Distribution Chinese white dolphins occurred year-round throughout Xiamen waters, but with most sightings recorded in Xigang and the waters around Jiyu Island (Fig. 1). However, the distribution of sighting records changed at different seasons or months. From February to May, 2004, the dolphins occurred predominantly in Xigang (59.65%), Jiyu (15.79%), and around the mouth of Tongan Bay (12.28%), whereas from July to August, 2004, the sightings mainly located in Dapan waters (55.56%), and from October to December sightings located in Jiyu waters (41.67%), Xigang (30.56%), and Dadeng waters (19.44%).
Abundance Base on AIC values, the best model was chosen for each season (Table 2). In most cases, the Uniform model
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Fig. 1. Locations of Chinese white dolphin sighted in Xiamen waters in 2004.
Table 2.
Density, abundance and other associated parameters for different months in Xiamen
Time
Selected model
ESW (m)
ER (km1)
D (km2)
N
CV (%)
Single-boat survey February March April May July August October November–Decembera
Uniform/polynomial Neg Exp/cosine Uniform/polynomial Uniform/polynomial Uniform/hermite Uniform/polynomial Uniform/hermite Uniform/cosine
210 433 259 175 303 308 433 314
0.0123 0.0156 0.0114 0.0074 0.0117 0.0108 0.0132 0.0180
0.1408 0.1040 0.1296 0.1546 0.0929 0.0965 0.1019 0.1826
99 72 89 108 65 67 71 127
46.31 59.96 32.41 58.09 61.25 60.18 54.10 61.96
Average
Uniform/cosine
275
0.0135
0.1232
86
20.16
Four-boat survey March May November
Uniform/polynomial Uniform/polynomial Uniform/hermite
200 190 200
0.0148 0.0091 0.0122
0.1358 0.1587 0.0971
95 111 68
37.21 52.55 47.95
Average
Uniform/cosine
213
0.0146
0.1417
99
31.99
Combined data February–May July–August October–December
Uniform/cosine Uniform/polynomial Uniform/cosine
164 300 245
0.0110 0.0113 0.0122
0.1350 0.0963 0.1249
93 67 87
26.34 41.60 38.78
Average
Uniform/hermit
255
0.0135
0.1240
87
21.83
ESW, effective strip width, n, number of on-effort sightings, L, total length of transect surveyed, ER, encounter rate (n/L), D, estimated density, N, abundance, CV, coefficient of variation. a The December data were pooled with November data due to that only five single-boat surveys were conducted in this month.
was identified as the best one. The estimated effective strip width (ESW) ranged from 164 to 433 m. The highest value (0.018 sightings/km) of encounter rate
(n/L) was found in the single-boat surveys of November– December 2004, whereas the lowest one (0.0074 sightings/km) was in single-boat surveys of May.
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Estimates of abundance from single-boat survey data varied in months (Table 2), from 65 in July to 127 in November–December, with an average of 86. The multiple-boat survey generated abundance estimates of 95, 111 and 68, respectively, for March, May and November data, with an average of 99. In order to explore the seasonal change of abundance, the data of February–May, July–August, and October–November from single- and multipleboat surveys were pooled, respectively. The February– May data generated an estimate of 93 dolphins, whereas the July–August data resulted in a slightly less estimate of 67 dolphins and the estimate increased to 87 for October–December data. The average abundance estimate of 87 dolphins was obtained based on the combined data of single- and multiple-boat surveys.
The coefficients of variation of the estimates should be taken into account when evaluating abundance estimates (Jefferson 2000). An estimate with CVso20% represented relatively high levels of statistical precision, whereas the estimates with CVs ranged from 21% to 42% represented moderate levels of statistical precision (Jefferson 2000). In addition, the fit of detection function to the distance data should be also considered (Calambokidis and Barlow 2004; Slooten et al. 2004) (Fig. 2). According to these criterion, the averaged estimate of 86 dolphins for single-boat survey (CV ¼ 20.16%) (Fig. 2A) is regarded reliable and could serve as appropriate bases for the conservation and management of this population. Further, the seasonal abundance estimates ranged from 67 (July–August, CV ¼ 41.6%) to 93 (February–May, CV ¼ 26.34%, Fig. 2C) were considered moderately reliable.
Fig. 2. Best line-transect models (smoothed curves) fit to distributions of Chinese white dolphin perpendicular distances (histograms).
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Discussion Abundance estimate precision The variances in f(0), n/L and S unevenly contributed to the total variance of abundance estimates from singleboat survey (Table 3). Relative to variance of f(0), variances in n/L and S made more important contribution. For this reason, some more efforts should be made in the future to reduce the variances of n/L and S. Accuracy and precision of the estimates would be improved by more precise matching of survey effort to the dolphins’ distribution and counting for group size.
Distribution Sightings of Chinese white dolphin were recorded in all the Xiamen waters during our field surveys, Xigang and Jiyu, however, represented the major distribution areas (Fig. 1) considering 69.61% sightings were found in these areas. This may be resulted from freshwater input from the Jiulong River, which could lead to an increase in the level of biodiversity and especially the biomass of fishes in this area. In addition, dolphins’ prey species, e.g., reef-associated Nibea albiflora (Wang et al. 2003), mainly concentrate in the inshore and shallow rocky reefs in this area, which may increase the feeding opportunities for dolphins (Karczmarski et al. 2000b). Seasonal change in distribution was found significant. In spring, most dolphins (59.65%) occurred in Xigang whereas very few individuals were found in other waters. From summer to winter, the sightings in Xigang decreased to some degree, but still account for 31.11% of the total sightings. In contrast, the sightings in Jiyu, Dapan and Dadeng waters increased significantly in Table 3. Percentage contributions of parameters to estimate of variance in density Time Single-boat survey February March April May July August October November Multiple-boat survey March May November
f(0)
27.1
21.4
66.5 43.3 31.4
ER
S
73.1 47.2 87.6 66.2 55.6 59.7 34.6 63.8
26.9 25.7 12.4 33.8 44.4 40.3 44 36.2
5.5 22.9 40
28 33.8 28.6
f(0), probability density function at zero perpendicular distance, ER, encounter rate (n/L), S, unbiased mean group size.
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these seasons. The seasonal changes of distribution pattern suggested an outward movement from inside harbor to outside waters after spring. However, further surveys should be conducted to confirm this behavior and reveal its significance. Although the Baozhuyu Island presented a previous important distribution area of Chinese white dolphins (Wang 1965), very few dolphins were found in this area in the present study (Fig. 1). The decrease in sighting rate in this area might result from the more and more constructions of sea wall in the past decades and the presence of extensive shallow waters of less than two meters and oyster farms, etc. Based on Liu and Huang’s (2000) surveys, Tongan Bay was one of the two ‘major distribution areas’ of Chinese white dolphins in Xiamen, where dolphins occurred yearround at high density. However, in the present study, the sightings in Tongan Bay are much less than in other waters especially Xigang and Jiyu. Besides, most dolphins sighted in Tongan occurred in spring, whereas few in other seasons (Fig. 1). The extensive mariculture and pollutant release in this area might be the reason that caused habitat loss and water deterioration and then made this water unsuitable for the survival of dolphins. Although we conducted relatively fewer surveys in Dadeng waters due to special political reason, the encounter rate was relative high especially in autumn and winter. For example, the encounter rate in November, 2004 increased to 2 sightings per survey over the average value of 0.564. Fishermen interviewed in the questionnaire surveys also told of more sightings of dolphins in autumn and winter than in other seasons. This distribution pattern might relate with the better water quality and less disturbances in Dadeng. According to the report on marine environment quality of Xiamen by the Oceans and Fisheries Bureau of Xiamen, 2005, although most waters in Xiamen were classified as ‘contaminated area’ or even worse, water quality in Dadeng is relatively better than other waters in Xiamen. Although mariculture still existed in Dadeng, other human disturbances, which commonly happened in other waters, such as vessel traffic, coastal construction projects, etc., are very scarce in this area. For this reason, the Dadeng waters might be the better habitat for Chinese white dolphins and should be preserved as a ‘sanctuary’ for Xiamen population in the future. It is still unclear whether the Xiamen population is an ‘open’ or an ‘isolated’ population, or whether there is an exchange between dolphins in Xiamen and in other waters adjacent to Xiamen. Liu and Huang (2000) suggested that dolphins never move to outside Wuyu Island and Chinmen Island. However, this is not well supported by the present study. Some individuals, e.g., an identified individual of JY040222, was observed swimming out of Xiaodeng Island in November. Actually, some individuals were found to inhabit Shishi,
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Quanzhou where is about tens kilometers away from Xiamen. Considering the Chinese white dolphins might have a linear range of a few hundred kilometers as reported by Karczmarski (2000), dolphins in the above areas are obviously within the linear range of this species. Thus, dolphins distributed in Shishi, Quanzhou, and Xiamen might constitute a single population. Some further surveys should be conducted in the future to confirm this, in collaboration with local governments of above areas.
Population tendency of Chinese white dolphins in Xiamen The present abundance estimate of 86 dolphins is greater than previous estimate of 60 individuals by Liu and Huang (2000). However, this can not be explained with population increasing. The increase in abundance estimate relative to Liu and Huang (2000) was largely due to the difference in survey method, sighting effort, and analysis method. Liu and Huang (2000) made the estimate mainly based on the data collected from landbased observations. Only 84 boat surveys covering transect line of 2836 km were conducted. For this reason, it is not appropriate to make a direct comparison for both results. In addition, under the high death pressure as mentioned above, it is unlikely for the small population estimated by Liu and Huang (2000) to remain as current population size level. Further, it is worthy of noting that Jefferson and Hung (2004) mentioned a preliminary abundance estimate for Xiamen population by using line-transect sampling technique. They used the data collected in 1997–1998 with transect line of 1208 km and 28 groups of dolphins sighted to generate an abundance estimate of 80 dolphins in Xiamen. Although the information in Jefferson and Hung’s (2004) survey is relatively inadequate and not comparable to the present study, their result give some support for the present study. Of course, some more surveys should be conducted to monitor this population and accumulate data to get a more accurate estimate in the future. Further, some evidences in the decrease in encounter rate were found to support the population decline in this population. According to the field data provided by Liu and Huang (2000), it was easy to calculate that the encounter rates were 2.7 sightings/100 km and 16.4 individuals/100 km in 1994–1999, whereas both rates significantly decreased to 1.7 and 7.7, respectively, in the present surveys. Actually, many kinds of human activities were found in Xiamen, which imposed great impacts on the Chinese white dolphins distributed there. For example, the area of Xigang to Jiyu is the busiest area in the Xiamen harbor with a great deal of vessel traffics and other associated
human activities. Due to coastal harbor constructions, underwater blasting or dredging are very common in Xiamen waters especially in Xigang, Haicang, etc. Extensive mariculture was found in Tongan Bay and Dadeng, and oyster or laver farms were commonly found in Tongan Bay and Jiyu, respectively. Fishing activities were found in all the Xiamen waters. Besides, water contamination is another serious problem in Xiamen. Most waters in Xiamen were classified as ‘contaminated area’ or even worse. It is well known that the above mentioned human activities have led to habitat degradation, and the pressure on resident dolphins will be inevitable. These human activities, therefore, must be effectively reduced or managed in the near future if we want to prevent the Chinese white dolphin population from declining further.
Conservation considerations The Xigang and Tongan Bay were defined as respective west and east core areas when the Xiamen Nature Reserve for Chinese White Dolphin was established in 1997 (Fig. 3). The present study showed Xigang and Jiyu waters the major area of distribution, whereas Tongan Bay was mainly utilized in spring. In contrast to the few sightings and low encounter rate in Tongan Bay, the encounter rate in Dadeng which is adjacent to Tongan Bay was relatively high as revealed above. For this reason, we recommend to extend the previous east core area of Xiamen Nature Reserve to cover the Dadeng area in order to provide more and better habitat for Chinese white dolphins (Fig. 3). Although the status of the Xigang area except for the area from Xiamen Bridge to Haicang Bridge as the major habitat of Chinese white dolphins was further clarified in this study due to high sighting rate in various seasons, area of Jiyu to Wuyu was proved the major habitat for Chinese white dolphins especially in autumn and winter. Thus, the north borderline should be shifted from Xiamen Bridge southward to Haicang Bridge, and the west core area should be expanded to cover the Jiyu to Wuyu area. The redesigned core areas of Xiamen Nature Reserve were shown in Fig. 3. As discussed above, the Xiamen population of Chinese white dolphin is small in size and may be declining. To conserve this population, we recommend: (1) Underwater blasting operations in the Xiamen Harbor should be strictly managed and effectively controlled. The blasting power and its impact on the Chinese white dolphin should be monitored and evaluated. Some strategies should be taken to drive the dolphins from the blasting sites to the safe area. (2) In order to effectively reduce the impacts of vessel traffics on the Chinese white dolphins, some ‘go slow’ zones should be established especially in
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Fig. 3. The previous and redesigned core areas of Xiamen Nature Reserve for the Chinese White Dolphin.
the Xigang and Jiyu, where the maximum velocity of all kinds of vessels especially yachts should be set to 8–10 km/h. (3) Fishing activities, especially gillnetting and trawling, should be managed and controlled to recover the local fishery resources and improve the food supply for the Chinese white dolphins. The mariculture in Tongan Bay and laver farms around Jiyu should be reduced or banned to improve the habitat quality for dolphins. (4) Some more researches should be conducted on the population abundance, distribution, habitat selection, human impacts, social structure, genetic diversity, etc. The information will be valuable for the conservation of this population. (5) Stranding and incidental catch network should be established to monitor the human impacts on the Chinese white dolphins in Xiamen, to cure and release injured dolphins, and to collect samples from the individuals for the purpose of conservation and scientific researches. For doing so, it is urgent to train local fishermen and fishery related persons to improve their knowledge and techniques to deal with incidentally captured or killed, and stranded dolphins.
Acknowledgments This research was financially supported by the Oceans and Fisheries Bureau of Xiamen (OFBX), China. Xirong Zhang, Rongbiao Hong, Lifeng Zhang, and Bingyu Chen are greatly appreciated for providing
useful data and for their invaluable support throughout the study. We thank Yazhong Zhou, Shiqiang Zhou, Anda Chen, Huirong Wang, Jinlong Wu, Zhi Yang, Min Zhang, Sandong Hong and Huqiu Hong for their kind assistance in the field surveys.
Zusammenfassung Anzahl, Verbreitung und Schutz von chinesischen Su¨ßwasserdelphinen Seit Jahren ist das Verhalten der Menschen die gro¨ßte Bedrohung fu¨r die chinesischen Su¨ßwasserdelphine. Die immer steigende Sterbequote der Su¨ßwasserdelphine ist bereits im Fokus der regionalen Regierung, der Bevo¨lkerung sowie der Medien in Xiamen gewesen. Es ist von großer Bedeutung die derzeitige Situation der Su¨ßwasserdelphine in Xiamen zu erfassen, damit man sowohl die fru¨her ergriffenen Schutzmaßnahmen bewerten, als auch die fu¨r diese Art geeigneten Schutzmaßnahmen ergreifen kann. Diese Studie mit ‘‘Line-Transect’’Methodologie’’ ist eine fachliche Untersuchung fu¨r das Gewa¨sser von 700 Quadratkilometern in der Na¨he von Xiamen. Auf der 6157 km langen Linie wurden die chinesischen Su¨ßwasserdelphine 102 mal entdeckt. Die Menge betra¨gt 67 Tiere (CV ¼ 41.6%) bis 93 Tiere (CV ¼ 26.34%), im Durchschnitt 86 Tiere (CV ¼ 20.16%). Im Großen und Ganzen sind Xigang und Jiyu die Hauptverbreitungszonen der chinesischen Su¨ßwasserdelphine. Die Verbreitung a¨ndert sich mit der Jahreszeit. Im Fru¨hling konzentrieren sich die
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meisten Su¨ßwasserdelphine in Xigang, sehr wenige in anderen Gebieten. Wa¨hrend der anderen Jahreszeiten sind die Su¨ßwasserdelphine in Xigang nur wenig zu finden. Dafu¨r sind in Jiyu, Dapan und Dadeng entsprechend sehr viele anzutreffen. Das bedeutet, die chinesischen Su¨ßwasserdelphine verlagern sich nach dem Fru¨hling vom Hafen nach draußen.
References Buckland, S.T., Anderson, D.R., Burnham, K.P., Laake, J.L., 1993. Distance Sampling: Estimating Abundance of Biological Populations. Chapman & Hall, London. Buckland, S.T., Anderson, D.R., Burnham, K.P., Laake, J.L., Thomas, L., Borcher, D.L., 2001. Introduction to Distance Sampling: Estimating Abundance of Biological Populations. Oxford University Press, Oxford, UK. Calambokidis, J., Barlow, J., 2004. Abundance of blue and humpback whales in the eastern North Pacific estimated by capture–recapture and line-transect methods. Mar. Mammal Sci. 20, 63–85. Dahlheim, M., York, A., Twell, R., Waite, J., Breiwick, J., 2000. Harbor propoise (Phocoena phocoena) abundance I Alaska: Bristol Bay to Southeast Alaska, 1991–1993. Mar. Mammal Sci. 16, 28–45. Hines, E.M., Adulyanuiosol, K., Duffus, D.A., 2005. Dugong (Dugong dugon) abundance along the Andaman coast of Thailand. Mar. Mammal Sci. 21, 536–549. Huang, Z., Liu, W., 2000. Dead and freed dolphins in Xiamen waters in 6 years (1994–1999). J. Oceanogr. Taiwan Strait 19, 42–47 (in Chinese). Jefferson, T.A., 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters. Wildl. Monogr. 144, 1–65. Jefferson, T.A., Hung, S.K., 2004. A review of the status of the Indo-Pacific humpback dolphin (Sousa chinensis) in Chinese waters. Aquat. Mammals 30, 149–158. Karczmarski, L., 2000. Conservation and management of humpback dolphins: the South African perspective. Oryx 34, 207–216. Karczmarski, L., Cockcroft, V.G., Mclachlan, A., 2000a. Habitat use and preferences of Indo-Pacific humpback dolphins Sousa chinensis in Algoa Bay, South Africa. Mar. Mammal Sci. 16, 65–79. Karczmarski, L., Cockcroft, V.G., Mclachlan, A., 2000b. Daylight occurrence of humphack dolphins Sousa chinensis in Algoa Bay, South Africa. Afr. J. Ecol. 38, 86–90.
Klinowska, M., 1991. Dolphins, Porpoises, and Whales of the World: The IUCN Red Data Book. IUCN, Gland, Switzerland. Liu, W.H., Huang, Z.G., 2000. Distribution and abundance of Chinese white dolphins (Sousa chinensis) in Xiamen. Acta Oceanol. Sinica 22, 95–101 (in Chinese). Ng, S.L., Leung, S., 2003. Behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Mar. Environ. Res. 56, 555–567. Parsons, E.C.M., 1998. Strandings of small cetaceans in Hong Kong territorial waters. J. Mar. Biol. Assoc. UK 78, 1039–1042. Parsons, E.C.M., Chan, H.M., 1998. Organochlorines in IndoPacific hump-backed dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) from Hong Kong. In: Morton, B. (Ed.), The Marine Biology of the South China Sea. Hong Kong University Press, Hong Kong, pp. 423–437. Parsons, E.C.M., Felley, M.L., Porter, L.J., 1995. An annotated checklist of cetaceans recorded from Hong Kong’s territorial waters. Asian Mar. Biol. 12, 79–100. Reeves, R.R., Leatherwood, S., 1994. Dolphins, Porpoises and Whales: 1994–1998 Action Plan for the Conservation of Cetaceans. IUCN, Gland, Switzerland. Ross, G.J.B., Heinsohn, G.E., Cockcroft, V.G., 1994. Humpback dolphins Sousa chinensis (Osbeck, 1765), Sousa plumbea (G. Cuvier, 1829) and Sousa teuszii (Kukenthal, 1892). In: Ridgway, S.H., Harrison, R. (Eds.), Handbook of Marine Mammals, vol. 5. San Diego Academic Press, San Diego, pp. 23–42. Slooten, E.S., Dawson, M., Rayment, W.J., 2004. Aerial surveys for coastal dolphins: abundance of Hector’s Dolphins off the south island west coast, New Zealand. Mar. Mammal Sci. 20, 477–490. Wang, W.Y., 1965. Preliminary observations on Sotalia sinensis off the coast of Xiamen. Newslett. Fujian Fish. Soc. 3–4, 16–21 (in Chinese). Wang, P., Sun, J., 1982. Studies on the Zhonghua white dolphin, Sousa chinensis from the South China Sea. Trans. Liaoning Zool. Soc. 3, 67–74 (in Chinese). Wang, D., Liu, R.J., Zhao, Q.Z., Yang, G., Xu, X.R., Huang, Z.G., Xin, J.J., Chen, B.Y., 2003. Pathological anatomy and analysis of death causes for a Chinese white dolphin. Acta Theriol. Sinica 23, 183–184 (in Chinese). Wang, J.Y., Hung, S.K., Yang, S.C., 2004. Records of IndoPacific humpback dolphins, Sousa chinensis (Osbeck, 1765), from the waters of western Taiwan. Aquat. Mammals 30, 189–196.
www.elsevier.de/mambio
ORIGINAL INVESTIGATION
Abundance, distribution and conservation of Chinese White Dolphins (Sousa chinensis) in Xiamen, China Bingyao Chena, Dongmei Zhengb, Feifei Zhaia, X. Xua, P. Suna, Q. Wanga, G. Yanga, a
Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210046 China b College of Oceanography and Environmental Science, Xiamen University, Xiamen 361005, China Received 29 August 2006; accepted 14 December 2006
Abstract In recent years, human activities appear to present the greatest threat to the Chinese white dolphin (Sousa chinensis). Increasing death records of this species in Xiamen have already become a focus of attention among the local government, the public, and the media. A comprehensive understanding about the status of Xiamen population is important not only to evaluate the conservation measures taken previously, but to design adaptive measures appropriate to this population. In this study, a survey using line-transect methodology was carried out to cover an area of about 700 km2 in Xiamen waters. A total of 102 separate sightings were made on 6157 km of transect line. The abundance estimate ranged from 67 (CV ¼ 41.6%) to 93 (CV ¼ 26.34%), with an average of 86 (CV ¼ 20.16%). Overall, Xigang (West harbor) and Jiyu represented the major area of distribution in Xiamen. Significant seasonal changes in distribution 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 sightings in Jiyu, Dapan, and Dadeng increasing obviously, suggesting an outward movement pattern of Chinese white dolphins from the inside harbor to outside waters after spring. Some suggestions for redesigning the Xiamen Nature Reserve and other management measures are put forward. r 2007 Published by Elsevier GmbH on behalf of Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Keywords: Sousa chinensis; Abundance; Distribution; Conservation
Introduction The Chinese white dolphin, Sousa chinensis, is distributed throughout shallow, coastal waters of the Indian and western Pacific oceans, from South Africa in the west to northern Australia and southern China in the east (Ross et al. 1994). The Chinese white dolphin is a species protected under the Convention on International Trade in Endangered Species of Wild Fauna and Corresponding author.
E-mail address: [email protected] (G. Yang).
Flora (CITES) (Klinowska 1991, and is classified as an ‘insufficiently known’ species by The World Conservation Union (IUCN) (Klinowska 1991; Reeves and Leatherwood 1994). In China, this species was listed as a Grade 1 National Key Protected Animal under the Wild Animal Protection Law issued in 1988. Within China, five resident populations of Chinese white dolphin were, respectively, found in Pearl River Delta (including Hong Kong) (Jefferson 2000; Parsons 1998; Parsons and Chan 1998; Parsons et al. 1995; Ng and Leung 2003; Jefferson and Hung 2004), Xiamen (Wang 1965; Huang and Liu 2000; Liu and Huang
1616-5047/$ - see front matter r 2007 Published by Elsevier GmbH on behalf of Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. doi:10.1016/j.mambio.2006.12.002 Mamm. biol. 73 (2008) 156–164
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2000), Beibuwan Gulf (Wang and Sun 1982), the west coast of Taiwan (Wang et al. 2004), and Leizhou, Guangdong Province (Unpublished data). However, up to now, abundance information is only available for Hong Kong, the Pearl River Estuary, and Xiamen waters (Liu and Huang 2000; Jefferson 2000; Jefferson and Hung 2004). Based upon surveys conducted in mid1990s, the population abundance of Chinese white dolphins in Xiamen was estimated about 60 individuals (Liu and Huang 2000). Most occurrences were found in Xigang (West harbor) in the west and Tongan Bay in the east of Xiamen (Liu and Huang 2000), but analyses of potential seasonal distribution patterns were not available (Jefferson and Hung 2004), which is not advantageous for designing and taking some adaptive conservation measures appropriate to this population. The Xiamen population was thought to be decreasing (Liu and Huang 2000), although not supported by solid statistics data (Jefferson and Hung 2004). As well known (Karczmarski 2000), the coastal distribution characteristic of Chinese white dolphins renders them particularly susceptible to various extreme anthropogenic pressures. These pressures have posed some serious impacts on Chinese white dolphins especially in Xiamen. For example, at least 11 dead dolphins were recorded from 1994 to 1999 (Huang and Liu 2000). The number of death has been increasing to six in 2002 and 10 in 2004. Some of these dead individuals were identified to die from underwater blasting in coastal construction projects (Wang et al. 2003). Other human activities, such as agricultural and industrial pollution, vessel traffic, and fishing, etc., also have some potential adverse impacts on Chinese white dolphins. For example, extensive mariculture in the nearshore waters might result in habitat loss for local dolphins (Jefferson and Hung 2004). Destructive fishing, especially trawl netting, is likely to result in habitat degradation and resource depletion of dolphins (Jefferson and Hung 2004). The present survey followed systematic line-transect sampling method widely used in cetacean populations (Buckland et al. 1993, 2001; Jefferson 2000; Calambokidis and Barlow 2004) to provide some updated data on the abundance and distribution of Chinese white dolphins in Xiamen waters. These data will help us to design some new and adaptive conservation and management measures that are important for the longterm survival of this population.
Material and methods Study area Xiamen is located in southeast China between latitudes 241120 N and 241400 N and longitudes 1171500 E and 1181300 E.
157
Jiulong River is the most important freshwater resource with a mean annual flux of 8.2 billion m3 (Liu and Huang 2000). Besides, there are many other small rivers in the north and northwest of Xiamen, which mainly affect the marine environment off the western coast of Xiamen by influencing the salinity. Daily tide changes are normal semi-diurnal, and the mean tidal height at spring tide is about 5.68 m (Liu and Huang 2000). Between 1995 and 2000, the total 89.2 km2 tideland was reclaimed (Liu and Huang 2000). Extensive mariculture, and oyster or laver farms still exist in Tongan Bay, Dadeng, and Jiyu in Xiamen.
Line-transect sampling The field survey was conducted from February to December, 2004 and covered all the Xiamen waters and partial Chinmen waters, Taiwan Province, and some neighboring waters belonging to Zhangzhou, an administrative district adjacent to Xiamen, which is about 700 km2 in total, following line-transect methods (Buckland et al. 1993, 2001; Jefferson 2000). The dolphins were mainly found in inshore waters of approximately o1.5 km (Ross et al. 1994; Jefferson 2000; Karczmarski et al. 2000a), with most sightings (over 80%) recorded within 400 m of shore (Karczmarski et al. 2000a). This shows that the density gradient is most probably perpendicular to the shoreline, and we placed the transect lines accordingly. We used a zigzag pattern in designing transect lines (Dahlheim et al. 2000; Buckland et al. 2001; Hines et al. 2005) to equalize the effort on all parts of the Xiamen waters. Field survey was mainly conducted by a single boat using a 12 m flat boat powered by a 36 HP engine. The boat had open upper deck allowing for observer eye heights of about 4–5 m above water level. When on effort, the boat traveled along determined lines at a speed of approximately 8 km/h. Because of the large survey area, it is difficult for a single boat to cover all the Xiamen waters in 1 day. Therefore, the boat was directed toward the place where the effort was terminated in the previous day for the purpose of equalizing survey effort in each part of Xiamen waters. In addition to the single-boat surveys, multiple-boat surveys were carried out on 11 days, i.e., 15–16 March, 21–24 May, and 3–7 November to cover all the Xiamen waters simultaneously. In the multiple-boat surveys, four boats were used to cover respective parts of Xiamen waters at the same time. When dolphins were sighted in the wild, searching effort was typically terminated, and the boat was directed toward the sighted individual or group. The maximum possible time was dedicated to following dolphin groups. Sighting time, radial distance, sighting angle, group size, group membership, various behaviors of dolphins, human activities around dolphins, e.g., fishing, were recorded. Age structure of each group was determined according to the description by Jefferson (2000) that unspotted dark gray or gray individuals represented calves and juveniles, mottled and speckled individuals were considered as sub-adults, and less spotted or unspotted pink or white individuals were adults. Latitude and longitude of all sightings, boat speed and routes were recorded using a global positioning system (GPS). Some environmental conditions, such as visibility, wind power
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and direction, ebb and flow, water temperature, and Beaufort sea state were also recorded.
Table 1. Summary data for boat surveys carried out in Xiamen waters in 2004
Line-transect estimates
Time
Population abundance estimate was carried out using the program DISTANCE 5.0. Density (D) and abundance (N), and their associated coefficient of variation (CV), were, respectively, estimated with the following formulae: D¼
nf ð0ÞS , 2L
nf ð0ÞSA , 2L qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi CV ¼ fCV2 ðn=LÞ þ CV2 ½f ð0Þ þ CV2 ðSÞg,
N¼
where n is the number of on-effort sightings, f(0) the probability density function at zero perpendicular distance, S the unbiased mean group size, A the size of the study area, and L the length of transect-line surveyed. Most parameters of these equations, e.g., function f(0), group size (S), encounter rate (n/L), were calculated via DISTANCE. Twelve detection models were compared in the analysis of f(0), i.e., uniform/hermite polynomials, uniform/ cosine, uniform/simple polynomial, half normal/hermite polynomials, half normal/cosine, half normal/simple polynomial, hazard rate/hermite polynomials, hazard rate/cosine, hazard rate/simple polynomial, negative exponential/hermite polynomials, negative exponential/cosine, negative exponential/simple polynomial. Based on Akaike’s information criterion (AIC), the best model was determined and chosen for the subsequent abundance analysis. The CVs of f(0), S and n/L we presented also corresponded to the output of DISTANCE (default). The coefficient of variation for abundance was calculated as the square root of the sum of the squared CVs of f(0), group size (S) and encounter rate (n/L). Environmental conditions, observers’ capability of sighting, survey protocol, and the boats used all might influence sighting rate of dolphins. When the abundance is calculated, these factors are usually combined in the parameter of g(0), the probability of recording a sighting on the transect line (Slooten et al. 2004). Due to unavailability of data to quantify the proportion of missed sightings, the g(0) was unable to be calculated exactly at present. This might lead to underestimations of real density and abundance, so we interpret the value of N obtained in the present study as a minimum or conservative estimate for population abundance of Chinese white dolphins in Xiamen.
Results About 181 boat surveys were conducted in Xiamen, which covered approximately 6157 km of transect line in total (Table 1). Chinese white dolphins were sighted for 102 times with a total of 473 individuals recorded and directly observed for over 100 h. Most dolphins were sighted in waters less than 20 m in depth (94% sightings)
No. survey days
Sighting nos.
Individual Length of nos. transect lines (km)
Single-boat survey February 10 March 19 April 23 May 15 July 16 August 14 October 20 November 17 December 5
15 10 10 4 5 4 11 6 4
64 33 59 30 24 22 68 33 29
405.77 578.01 876.36 554.30 426.14 370.22 627.28 442.44 112.79
Subtotal
139
69
362
4393.31
Four-boat survey March 8 May 14 November 20
7 11 15
25 43 43
405.04 547.08 901.56
Subtotal
42
33
111
1853.68
181
102
473
6156.74
Total
and within 500 m of the shore (62.2% sightings). Of the 102 sightings, 27.45% were of single animals, whereas groups of p3 individuals constituted 52% and 12.75% were of groups of ten animals or more. The group size ranged from minimum 1 to maximum 18 individuals with an average of 4.6473.85. Of the 473 individuals recorded, the calves and juveniles comprised 18.18% of the counts, whereas sub-adult and adults accounted for 45.24% and 36.58%, respectively.
Distribution Chinese white dolphins occurred year-round throughout Xiamen waters, but with most sightings recorded in Xigang and the waters around Jiyu Island (Fig. 1). However, the distribution of sighting records changed at different seasons or months. From February to May, 2004, the dolphins occurred predominantly in Xigang (59.65%), Jiyu (15.79%), and around the mouth of Tongan Bay (12.28%), whereas from July to August, 2004, the sightings mainly located in Dapan waters (55.56%), and from October to December sightings located in Jiyu waters (41.67%), Xigang (30.56%), and Dadeng waters (19.44%).
Abundance Base on AIC values, the best model was chosen for each season (Table 2). In most cases, the Uniform model
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Fig. 1. Locations of Chinese white dolphin sighted in Xiamen waters in 2004.
Table 2.
Density, abundance and other associated parameters for different months in Xiamen
Time
Selected model
ESW (m)
ER (km1)
D (km2)
N
CV (%)
Single-boat survey February March April May July August October November–Decembera
Uniform/polynomial Neg Exp/cosine Uniform/polynomial Uniform/polynomial Uniform/hermite Uniform/polynomial Uniform/hermite Uniform/cosine
210 433 259 175 303 308 433 314
0.0123 0.0156 0.0114 0.0074 0.0117 0.0108 0.0132 0.0180
0.1408 0.1040 0.1296 0.1546 0.0929 0.0965 0.1019 0.1826
99 72 89 108 65 67 71 127
46.31 59.96 32.41 58.09 61.25 60.18 54.10 61.96
Average
Uniform/cosine
275
0.0135
0.1232
86
20.16
Four-boat survey March May November
Uniform/polynomial Uniform/polynomial Uniform/hermite
200 190 200
0.0148 0.0091 0.0122
0.1358 0.1587 0.0971
95 111 68
37.21 52.55 47.95
Average
Uniform/cosine
213
0.0146
0.1417
99
31.99
Combined data February–May July–August October–December
Uniform/cosine Uniform/polynomial Uniform/cosine
164 300 245
0.0110 0.0113 0.0122
0.1350 0.0963 0.1249
93 67 87
26.34 41.60 38.78
Average
Uniform/hermit
255
0.0135
0.1240
87
21.83
ESW, effective strip width, n, number of on-effort sightings, L, total length of transect surveyed, ER, encounter rate (n/L), D, estimated density, N, abundance, CV, coefficient of variation. a The December data were pooled with November data due to that only five single-boat surveys were conducted in this month.
was identified as the best one. The estimated effective strip width (ESW) ranged from 164 to 433 m. The highest value (0.018 sightings/km) of encounter rate
(n/L) was found in the single-boat surveys of November– December 2004, whereas the lowest one (0.0074 sightings/km) was in single-boat surveys of May.
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Estimates of abundance from single-boat survey data varied in months (Table 2), from 65 in July to 127 in November–December, with an average of 86. The multiple-boat survey generated abundance estimates of 95, 111 and 68, respectively, for March, May and November data, with an average of 99. In order to explore the seasonal change of abundance, the data of February–May, July–August, and October–November from single- and multipleboat surveys were pooled, respectively. The February– May data generated an estimate of 93 dolphins, whereas the July–August data resulted in a slightly less estimate of 67 dolphins and the estimate increased to 87 for October–December data. The average abundance estimate of 87 dolphins was obtained based on the combined data of single- and multiple-boat surveys.
The coefficients of variation of the estimates should be taken into account when evaluating abundance estimates (Jefferson 2000). An estimate with CVso20% represented relatively high levels of statistical precision, whereas the estimates with CVs ranged from 21% to 42% represented moderate levels of statistical precision (Jefferson 2000). In addition, the fit of detection function to the distance data should be also considered (Calambokidis and Barlow 2004; Slooten et al. 2004) (Fig. 2). According to these criterion, the averaged estimate of 86 dolphins for single-boat survey (CV ¼ 20.16%) (Fig. 2A) is regarded reliable and could serve as appropriate bases for the conservation and management of this population. Further, the seasonal abundance estimates ranged from 67 (July–August, CV ¼ 41.6%) to 93 (February–May, CV ¼ 26.34%, Fig. 2C) were considered moderately reliable.
Fig. 2. Best line-transect models (smoothed curves) fit to distributions of Chinese white dolphin perpendicular distances (histograms).
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Discussion Abundance estimate precision The variances in f(0), n/L and S unevenly contributed to the total variance of abundance estimates from singleboat survey (Table 3). Relative to variance of f(0), variances in n/L and S made more important contribution. For this reason, some more efforts should be made in the future to reduce the variances of n/L and S. Accuracy and precision of the estimates would be improved by more precise matching of survey effort to the dolphins’ distribution and counting for group size.
Distribution Sightings of Chinese white dolphin were recorded in all the Xiamen waters during our field surveys, Xigang and Jiyu, however, represented the major distribution areas (Fig. 1) considering 69.61% sightings were found in these areas. This may be resulted from freshwater input from the Jiulong River, which could lead to an increase in the level of biodiversity and especially the biomass of fishes in this area. In addition, dolphins’ prey species, e.g., reef-associated Nibea albiflora (Wang et al. 2003), mainly concentrate in the inshore and shallow rocky reefs in this area, which may increase the feeding opportunities for dolphins (Karczmarski et al. 2000b). Seasonal change in distribution was found significant. In spring, most dolphins (59.65%) occurred in Xigang whereas very few individuals were found in other waters. From summer to winter, the sightings in Xigang decreased to some degree, but still account for 31.11% of the total sightings. In contrast, the sightings in Jiyu, Dapan and Dadeng waters increased significantly in Table 3. Percentage contributions of parameters to estimate of variance in density Time Single-boat survey February March April May July August October November Multiple-boat survey March May November
f(0)
27.1
21.4
66.5 43.3 31.4
ER
S
73.1 47.2 87.6 66.2 55.6 59.7 34.6 63.8
26.9 25.7 12.4 33.8 44.4 40.3 44 36.2
5.5 22.9 40
28 33.8 28.6
f(0), probability density function at zero perpendicular distance, ER, encounter rate (n/L), S, unbiased mean group size.
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these seasons. The seasonal changes of distribution pattern suggested an outward movement from inside harbor to outside waters after spring. However, further surveys should be conducted to confirm this behavior and reveal its significance. Although the Baozhuyu Island presented a previous important distribution area of Chinese white dolphins (Wang 1965), very few dolphins were found in this area in the present study (Fig. 1). The decrease in sighting rate in this area might result from the more and more constructions of sea wall in the past decades and the presence of extensive shallow waters of less than two meters and oyster farms, etc. Based on Liu and Huang’s (2000) surveys, Tongan Bay was one of the two ‘major distribution areas’ of Chinese white dolphins in Xiamen, where dolphins occurred yearround at high density. However, in the present study, the sightings in Tongan Bay are much less than in other waters especially Xigang and Jiyu. Besides, most dolphins sighted in Tongan occurred in spring, whereas few in other seasons (Fig. 1). The extensive mariculture and pollutant release in this area might be the reason that caused habitat loss and water deterioration and then made this water unsuitable for the survival of dolphins. Although we conducted relatively fewer surveys in Dadeng waters due to special political reason, the encounter rate was relative high especially in autumn and winter. For example, the encounter rate in November, 2004 increased to 2 sightings per survey over the average value of 0.564. Fishermen interviewed in the questionnaire surveys also told of more sightings of dolphins in autumn and winter than in other seasons. This distribution pattern might relate with the better water quality and less disturbances in Dadeng. According to the report on marine environment quality of Xiamen by the Oceans and Fisheries Bureau of Xiamen, 2005, although most waters in Xiamen were classified as ‘contaminated area’ or even worse, water quality in Dadeng is relatively better than other waters in Xiamen. Although mariculture still existed in Dadeng, other human disturbances, which commonly happened in other waters, such as vessel traffic, coastal construction projects, etc., are very scarce in this area. For this reason, the Dadeng waters might be the better habitat for Chinese white dolphins and should be preserved as a ‘sanctuary’ for Xiamen population in the future. It is still unclear whether the Xiamen population is an ‘open’ or an ‘isolated’ population, or whether there is an exchange between dolphins in Xiamen and in other waters adjacent to Xiamen. Liu and Huang (2000) suggested that dolphins never move to outside Wuyu Island and Chinmen Island. However, this is not well supported by the present study. Some individuals, e.g., an identified individual of JY040222, was observed swimming out of Xiaodeng Island in November. Actually, some individuals were found to inhabit Shishi,
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Quanzhou where is about tens kilometers away from Xiamen. Considering the Chinese white dolphins might have a linear range of a few hundred kilometers as reported by Karczmarski (2000), dolphins in the above areas are obviously within the linear range of this species. Thus, dolphins distributed in Shishi, Quanzhou, and Xiamen might constitute a single population. Some further surveys should be conducted in the future to confirm this, in collaboration with local governments of above areas.
Population tendency of Chinese white dolphins in Xiamen The present abundance estimate of 86 dolphins is greater than previous estimate of 60 individuals by Liu and Huang (2000). However, this can not be explained with population increasing. The increase in abundance estimate relative to Liu and Huang (2000) was largely due to the difference in survey method, sighting effort, and analysis method. Liu and Huang (2000) made the estimate mainly based on the data collected from landbased observations. Only 84 boat surveys covering transect line of 2836 km were conducted. For this reason, it is not appropriate to make a direct comparison for both results. In addition, under the high death pressure as mentioned above, it is unlikely for the small population estimated by Liu and Huang (2000) to remain as current population size level. Further, it is worthy of noting that Jefferson and Hung (2004) mentioned a preliminary abundance estimate for Xiamen population by using line-transect sampling technique. They used the data collected in 1997–1998 with transect line of 1208 km and 28 groups of dolphins sighted to generate an abundance estimate of 80 dolphins in Xiamen. Although the information in Jefferson and Hung’s (2004) survey is relatively inadequate and not comparable to the present study, their result give some support for the present study. Of course, some more surveys should be conducted to monitor this population and accumulate data to get a more accurate estimate in the future. Further, some evidences in the decrease in encounter rate were found to support the population decline in this population. According to the field data provided by Liu and Huang (2000), it was easy to calculate that the encounter rates were 2.7 sightings/100 km and 16.4 individuals/100 km in 1994–1999, whereas both rates significantly decreased to 1.7 and 7.7, respectively, in the present surveys. Actually, many kinds of human activities were found in Xiamen, which imposed great impacts on the Chinese white dolphins distributed there. For example, the area of Xigang to Jiyu is the busiest area in the Xiamen harbor with a great deal of vessel traffics and other associated
human activities. Due to coastal harbor constructions, underwater blasting or dredging are very common in Xiamen waters especially in Xigang, Haicang, etc. Extensive mariculture was found in Tongan Bay and Dadeng, and oyster or laver farms were commonly found in Tongan Bay and Jiyu, respectively. Fishing activities were found in all the Xiamen waters. Besides, water contamination is another serious problem in Xiamen. Most waters in Xiamen were classified as ‘contaminated area’ or even worse. It is well known that the above mentioned human activities have led to habitat degradation, and the pressure on resident dolphins will be inevitable. These human activities, therefore, must be effectively reduced or managed in the near future if we want to prevent the Chinese white dolphin population from declining further.
Conservation considerations The Xigang and Tongan Bay were defined as respective west and east core areas when the Xiamen Nature Reserve for Chinese White Dolphin was established in 1997 (Fig. 3). The present study showed Xigang and Jiyu waters the major area of distribution, whereas Tongan Bay was mainly utilized in spring. In contrast to the few sightings and low encounter rate in Tongan Bay, the encounter rate in Dadeng which is adjacent to Tongan Bay was relatively high as revealed above. For this reason, we recommend to extend the previous east core area of Xiamen Nature Reserve to cover the Dadeng area in order to provide more and better habitat for Chinese white dolphins (Fig. 3). Although the status of the Xigang area except for the area from Xiamen Bridge to Haicang Bridge as the major habitat of Chinese white dolphins was further clarified in this study due to high sighting rate in various seasons, area of Jiyu to Wuyu was proved the major habitat for Chinese white dolphins especially in autumn and winter. Thus, the north borderline should be shifted from Xiamen Bridge southward to Haicang Bridge, and the west core area should be expanded to cover the Jiyu to Wuyu area. The redesigned core areas of Xiamen Nature Reserve were shown in Fig. 3. As discussed above, the Xiamen population of Chinese white dolphin is small in size and may be declining. To conserve this population, we recommend: (1) Underwater blasting operations in the Xiamen Harbor should be strictly managed and effectively controlled. The blasting power and its impact on the Chinese white dolphin should be monitored and evaluated. Some strategies should be taken to drive the dolphins from the blasting sites to the safe area. (2) In order to effectively reduce the impacts of vessel traffics on the Chinese white dolphins, some ‘go slow’ zones should be established especially in
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Fig. 3. The previous and redesigned core areas of Xiamen Nature Reserve for the Chinese White Dolphin.
the Xigang and Jiyu, where the maximum velocity of all kinds of vessels especially yachts should be set to 8–10 km/h. (3) Fishing activities, especially gillnetting and trawling, should be managed and controlled to recover the local fishery resources and improve the food supply for the Chinese white dolphins. The mariculture in Tongan Bay and laver farms around Jiyu should be reduced or banned to improve the habitat quality for dolphins. (4) Some more researches should be conducted on the population abundance, distribution, habitat selection, human impacts, social structure, genetic diversity, etc. The information will be valuable for the conservation of this population. (5) Stranding and incidental catch network should be established to monitor the human impacts on the Chinese white dolphins in Xiamen, to cure and release injured dolphins, and to collect samples from the individuals for the purpose of conservation and scientific researches. For doing so, it is urgent to train local fishermen and fishery related persons to improve their knowledge and techniques to deal with incidentally captured or killed, and stranded dolphins.
Acknowledgments This research was financially supported by the Oceans and Fisheries Bureau of Xiamen (OFBX), China. Xirong Zhang, Rongbiao Hong, Lifeng Zhang, and Bingyu Chen are greatly appreciated for providing
useful data and for their invaluable support throughout the study. We thank Yazhong Zhou, Shiqiang Zhou, Anda Chen, Huirong Wang, Jinlong Wu, Zhi Yang, Min Zhang, Sandong Hong and Huqiu Hong for their kind assistance in the field surveys.
Zusammenfassung Anzahl, Verbreitung und Schutz von chinesischen Su¨ßwasserdelphinen Seit Jahren ist das Verhalten der Menschen die gro¨ßte Bedrohung fu¨r die chinesischen Su¨ßwasserdelphine. Die immer steigende Sterbequote der Su¨ßwasserdelphine ist bereits im Fokus der regionalen Regierung, der Bevo¨lkerung sowie der Medien in Xiamen gewesen. Es ist von großer Bedeutung die derzeitige Situation der Su¨ßwasserdelphine in Xiamen zu erfassen, damit man sowohl die fru¨her ergriffenen Schutzmaßnahmen bewerten, als auch die fu¨r diese Art geeigneten Schutzmaßnahmen ergreifen kann. Diese Studie mit ‘‘Line-Transect’’Methodologie’’ ist eine fachliche Untersuchung fu¨r das Gewa¨sser von 700 Quadratkilometern in der Na¨he von Xiamen. Auf der 6157 km langen Linie wurden die chinesischen Su¨ßwasserdelphine 102 mal entdeckt. Die Menge betra¨gt 67 Tiere (CV ¼ 41.6%) bis 93 Tiere (CV ¼ 26.34%), im Durchschnitt 86 Tiere (CV ¼ 20.16%). Im Großen und Ganzen sind Xigang und Jiyu die Hauptverbreitungszonen der chinesischen Su¨ßwasserdelphine. Die Verbreitung a¨ndert sich mit der Jahreszeit. Im Fru¨hling konzentrieren sich die
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meisten Su¨ßwasserdelphine in Xigang, sehr wenige in anderen Gebieten. Wa¨hrend der anderen Jahreszeiten sind die Su¨ßwasserdelphine in Xigang nur wenig zu finden. Dafu¨r sind in Jiyu, Dapan und Dadeng entsprechend sehr viele anzutreffen. Das bedeutet, die chinesischen Su¨ßwasserdelphine verlagern sich nach dem Fru¨hling vom Hafen nach draußen.
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