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2008b) and stationary platforms (Wang et al., 2005; Akamatsu et al., 2008a). An automatic
acoustic data-logger (A-tag, Marine Micro Technology, Saitama, Japan) system, which only
records the high-frequency sound events but not waveform (see below for details), has proven
powerful and convenient for acoustic observation of finless porpoises (Wang et al., 2005;
Akamatsu et al., 2008a, b).
In the present study, we applied the A-tag to observe the finless porpoises acoustically in
a boat-based stationary platform at Stations 0, 1, and 2, to document their presence pattern
among these stations, and a buoy-based stationary platform at Station C to document long-
term presence patterns (Figure 1). Thereafter, fragmented or isolated status, and potential
movement pattern of porpoises in this area is discussed, and factors that may affect the
presence and movement of animals are analyzed. Finally, some conservation measurements
are suggested.
M
ATERIALS AND
M
ETHODS
Study Site and Observation System
This study was performed in the mouth area of Poyang Lake, at its confluence point with
the river (Figure 1). The width of this water changes temporally and is hundreds of meters
during the low-water season (November to March of next year) and is several kilometers
during the high-water season (April to October).
Three stations, (station 0, 29
o
45'06‖ N, 116
o
12'41‖ E; station 1, 29
o
44'34‖ N,
116
o
12'10‖ E, and station 2, 29
o
44'02‖ N, 116
o
11'47‖ E), were selected for boat-based
stationary acoustic observation to document the spatial presence pattern of porpoises. The
acoustic observation was carried out during April 27-29, 2006 and May 9-10, 2007 at
Stations 1, 2 and Station 0, respectively (Figure 1). All three stations were along the north
shore of the shipping channel in the ―bottleneck‖ mouth area, with sandbank, shallow water,
and aquatic grass, which constitute the favorite habitat of porpoises (Chen et al., 1997). The
distances between Stations 0 and 1, and 1 and 2 were approximately 1300 m and 1200 m,
respectively. Station 2 was situated between two bridges (highway and railway bridges, see
Figure 1), approximately 300 m upstream from the highway bridge. During acoustic
observations, boats at each station were fixed by double anchors to minimize drifting. The
directions of the boats were relatively immovable and boat engines were completely stopped
during observation. Water depths were approximately 3 m at the three stations.
To document the temporal presence pattern of porpoises, Station C (29
o
42'43‖ N,
116
o
11'26‖ E), which was based on a buoy and approximately 300 m downstream from the
railway bridge, and 2,400 m upstream to Station 2 (Figure 1), was selected for long-term
acoustic observation since June 27, 2007. Station C is situated beside the deep channel along
the south shore and near the railway bridge. The water depth of this station is over 13 m
during high-water seasons, and over 1.5 m even during the low-water seasons. These depth
values justified station C as a suitable station for year-round underwater acoustic observation.
The buoy is held by only one anchor, and its direction was variable, changed by water
current, wind, water waves made by passing ships, etc.
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