( Neophocaena phocaenoides asiaeorientalis) m/ s, [ 49 (2) : , 2003 ]

Transcription

1 49 (2) : A cta Zoologica S inica 3 33 ( ) ( Neophocaena phocaenoides asiaeorientalis) : > > > ; m 8118 % 9 m 7313 % ; ( ) ; m/ s m ; 2 4 ; [ 49 (2) : ] Habitat use and preliminary evaluation of the habitat status of the Yangtze f inless porpoise ( Neophocaena phocaenoides asiaeorientalis) in the Balijiang section of the Yangtze River China 3 WEI Zhuo ZHAN G Xian2Feng WAN G Ke2Xiong ZHAO Qing2Zhong KUAN G Xin2An WAN G Xiao2Qiang WAN G Ding 33 ( Instit ute of Hydrobiology Chi nese Academy of Sciences W uhan Chi na) Abstract The only freshwater subspecies of finless porpoise ( Neophocaena phocaenoides) the Yangtze finless porpoise ( N. p. asiaeorientalis) is only found in the middle and lower reaches of the Yangtze River and the two connected Dongting and Poyang Lakes. Due to deterioration of the habitat quality of the Yangtze River the finless porpois popula2 tion has decreased markedly during the last ten years. In order to evaluate the habitat use and preferences of the species we carried out stationary and transect observations along the 20 km long Balijiang section of the Yangtze River ( E N) from 1996 to The surveys covered four different seasons with less effort in summer when the water level was high because of flooding. Two boats were engaged in each transect survey. During transect surveys both boats synchronously moved up or down along opposite banks of the river and in speeds of between 8-10 km/ hr the distance between them ranging from 400 to 800 m depending on the width of the river channel. Stationary observations were conducted from two boats anchored on either side of the river. Communication between the boats was maintained us2 ing V HF hand2held radios. Observers on each boat were responsible for observations in the half of the river nearest them ( KSCX221203) ( ) (220103) ( ) [ This study was funded by the Innovation Project ( No : KSCX221203) and Youth Scientist Group Project ( ) of the Chinese Academy of Sciences the Frontier Science Project Programme of the Institute of Hydrobiology CAS (No : ) and Wuhan Youth Sunlight Programme (No : ) ] 33 (Corresponding author) E2mail : ac. cn 35 E2mail : ac. cn ν 2003 Acta Zoologica Sinica

2 Data recorded included porpoise groups group sizes sectors in which they stayed the time they spent in different sec2 tors the distance from shore behavior and the duration of different behavior. The entire section of river was divided into m long sectors. Porpoise behavior was classified into four categories : feeding care2giving playing and resting. Environmental and behavioral determinants of the habitat use andpreferences of the animals were quantified using two in2 dices the coefficient of area use (AU) and activity index (AI). By definition AU = D/ T where D is the time spent by the animals in a particular sector and T is the total observation time on any one day. AI = B/ S where B is the time the animals were engaged in a particular behavior within a sector and S is the time spent by the animals in any one sector. Mean AI was calculated separately for each of the four categories of behavior. In total 25 transect and 6 stationary sur2 veys were carried out. Porpoises were sighted in 353 hours within 71 observation days with 529 porpoise groups observed and 467 behavioral records. Statistical analyses of the data show that 8118 % of the individuals were found within m of the riverπs banks and 7313 % in the areas where the water depth was less than 9 m. The small sized fish con2 sumed by this porpoise were more abundant in these shallow areas than in deeper water. The density of the animals de2 creased with increasing water depth the functional relationship between these two factors being Y = e X = depth Y = density). Water velocity and clarity of the sectors in which the animals stayed varied from 013 m/ s to 112 m/ s and 012 m to 018 m (Secchi disk reading) respectively. These ranges were similar to those recorded in the whole sec2 tion. Porpoises could be seen in any one sector but there were significant differences for AU ( t = n = 20 P < 0101) among the 20 sectors. More animals were found in sectors where there were confluences that were formed because the water current was divided into several parts by sand bars and beaches. In these sectors there was less boat traffic no pollution and more small sized fish. Mean AI values for the four categories of behavior in sequence are as follows : Feeding ( ) > Care2giving ( ) > Playing ( ) > Resting ( ). Feeding and Care2 giving were dominant behaviors for the animals staying in the section. Some behaviors might present more often in certain sectors. Based on these results we conclude that water depth and food availability are the main factors limiting the inshore distribution of this species. The porpoises much prefer to concentrate in confluences that are formed by the joining of sev2 eral currents. In these areas boat traffic is light and small sized fish prey are more abundant. Therefore such confluences are key habitat of primary importance for the Yangtze finless porpoise in this section of the river. However porpoises have no apparent preference for water clarity and water velocity in the section. Because the Balijiang section of the Yangtze possesses many such microhabitats it provides sufficient space and can satisfy the porpoises different requirements for feeding care2giving resting and playing. Compared with our survey results in other parts of the river it is concluded that the Balijiang section is one of the best finless porpoise habitats in the Yangtze Therefore this section of the river would be a good location in which to establish a reserve for the conservation of this endemic endangered species [ Acta Zo2 ologica Sinica 49 (2) : ]. Key words Yangtze finless porpoise ( Neophocaena phocaenoides asiaeorientalis) Habitat Coefficient of Area Use Ac2 tivity Index Evaluation ( X ( Karcz2 marski et al. 2000) Karczmarski et al. (2000) ( Sousa chinensis) (Algoa) (Jefferson et al. 1993) 400 m 15 m ( ; 1995) cm Leatherwood et al. (2000) ( Inia geof f rensis Sotalia f l uviatilis ) 11 6

3 2 : 165 ( 1993) ( 2002) ( Wang et al ; Zhou et al ; 2000 ; 2000 ; Wei et al ; 2002) d 12 d 20 d 18 d 71 d 6 10 d 08 : : 00 ( 300 m 3 ) h m ( E 116 ( 2002) N) 20 km : hp ( ) 2 ( 1) ( 120 hp) m ( 1 Fig. 1 Sketch map of the Balijiang section of the Yangtze River

4 ) 8 10 km/ h ; m ; ; ; ( (Care2giving) : ; ) ( Resting) : ( C21400L ) ( Playing) : ( ) ( Secchi disc) 20 ( 2) FCV m 50 m 113 ( Karczmarksi et al. 2 FM255 ( Feeding) : 2 ( ) ; ( Coefficient of area use AU) : 1999) AU = D/ 4 T D : ; T : 2 20 Fig. 2 Pattern of habitat use displayed by porpoises in the Balijiang section of the Yangtze River

5 2 : 167 (Activity index AI) : AI = B/ m S B : S : 8118 % ( n = 433) ( 3A) 9 m 7313 % ( n = 388) ( 3B) 350 m ( A) ( B) ( C) Fig. 3 Distribution of sightings of porpoises ( A = distance from bank B = water depth C = distance from the observation boat) recorded in Balijiang section from October 1966 to October 2000

6 % ( n = 469) ( 3C) 3 (B) 3 21 m 3 m 0101) AU 4 10 ( n = 52) ( n = 14) 17 ( n = 6) Y = e X ( n = 529 X : Y : ; 0 < X < 25) ( n = 76) m/ s m > > > 4 AU ( t = n = 20 P < ( n = 100) ( n = 91) ( n = 75) AU ( 6) AU Fig. 4 Mean coeff icient of area use of f inless porpoises in the Balijiang section of the Yangtze River from 1996 to 2000 ( Error bars indicate one standard deviation) Fig. 5 Mean activity index of f inless porpoises in the Balijiang section of the Yangtze River from 1996 to 2000 ( Error bars indicate one standard deviation)

7 2 : Fig. 6 Mean activity index values of the f inless porpoise in sectors of the Balijiang section of the Yangtze River with a high mean coeff icient of area use from 1996 to ( 1980) 20 km 15 km m/ s m ( 20 km ) ( ) 2 4 m ( Wang et al ; Wei et al. ( ) ) En Kawa Hirokazu Ichikawa Ko2

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