Swimming speeds and buoyancy compensation of migrating adult chum salmon Oncorhynchus keta revealed by speed/depth/acceleration data logger
Hideji Tanaka*,1,
Yasuaki Takagi2 and
Yasuhiko Naito1
1 National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan and
2 Otsuchi Marine Research Center, Ocean Research Institute, the University of Tokyo, Akahama, Otsuchi, Iwate 028-1102, Japan
View larger version (32K):
[in a new window]
|
Fig. 1. Study site was off the Sanriku coast, Japan, in October 1997 and October 1999. Homing adult chum salmon were fished and released with loggers at the mouth of Otsuchi Bay. Filled squares indicate the sites where salmon were recovered. Unfortunately, the retrieval location of salmon 9902 was unknown. Numbers indicate salmon identification number, and numbers in parentheses correspond to the number of days before salmon were recovered. Lines show 100, 200 and 300 m contours.
|
|
View larger version (18K):
[in a new window]
|
Fig. 2. Schematic diagram showing the direction of surging and swaying accelerations recorded by a data logger placed on the left side of the body of a salmon, below the front edge of the dorsal fin (black bar). Data for surging acceleration were converted to body angles, as described in the text. Body angles while salmon were ascending are presented as positive values, and body angles while salmon were descending are presented as negative values.  , angle of ascent/descent.
|
|
View larger version (14K):
[in a new window]
|
Fig. 3. A swaying acceleration profile of a chum salmon swimming at a flow rate of 0.7 m s–1 in a chamber. Video recordings were used to confirm that each sharp peak in acceleration synchronized with one tail beat. When the salmon beat its caudal fin to the left, the acceleration reached a positive maximum value and vice versa. For the peaks indicated, the amplitude of the peak (H) was greater than 1.0 m s–2, and bottom–peak–bottom duration (T) was less than 1 s. These values were recorded and converted to tailbeat frequency.
|
|
View larger version (34K):
[in a new window]
|
Fig. 4. An excerpt from the recordings of swimming depth, swimming speed, body angle and swaying acceleration for salmon 9904, showing profiles typical of those during the coastal migration of chum salmon.
|
|
View larger version (16K):
[in a new window]
|
Fig. 5. Frequency distributions of swimming speeds for two homing chum salmon (salmon 9706 and 9709) for the entire recording period in October 1997. Salmon 9706 was recovered approximately 70 km away 3.1 days after release, and salmon 9709 was recovered approximately 7.9 km away 4.2 days after release.
|
|
View larger version (20K):
[in a new window]
|
Fig. 6. Frequency distribution of body angles for a chum salmon (9904) recorded simultaneously with swimming speeds higher than 0.3 m s–1. The mean body angle was 0.3±14.0°; that for salmon 9902 was –0.6±14.8° (not shown) (means ± S.D.., N=110 499).
|
|
View larger version (22K):
[in a new window]
|
Fig. 7. Mean values of vertical rate, swimming speed, body angle and tailbeat frequency per 1 m depth change for the initial, middle and final 5 m ranges of vertical movements whose total change of depth was greater than 25 m for salmon 9902 and 9904. Values are means ± S.E.M. The left panels shows descents (N=9) that started from the surface water ( 5 m deep) and the right panel shows ascents (N=13) that finished in the surface water. Apart from swimming speed, all behavioural variables changed significantly with respect to the change in the range of vertical travel (Friedman’s test).
|
|
© The Company of Biologists Ltd 2001
