. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 206 A. B. STEINBACH Marker bouy Area of transect Depth in meters. 20 FIGURE 3. Depth contours of the river bed inshore from the ship anchorage. The steep drop-off from 6 to about 15 meters and the drop at 20 meters are typical of the river as a whole; the irregularities shown indicate the rocky submerged point extending from the shore (the line of submerged trees is indicated by splotches). The path taken during the transects illustrated in Figure 4 is shaded. activity. The type of activity is indicated by a number (referrin
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 206 A. B. STEINBACH Marker bouy Area of transect Depth in meters. 20 FIGURE 3. Depth contours of the river bed inshore from the ship anchorage. The steep drop-off from 6 to about 15 meters and the drop at 20 meters are typical of the river as a whole; the irregularities shown indicate the rocky submerged point extending from the shore (the line of submerged trees is indicated by splotches). The path taken during the transects illustrated in Figure 4 is shaded. activity. The type of activity is indicated by a number (referring to the groups in Table I) below each trace. Artifacts (subscripted "A") resulted when the electrodes truck rocks. The lowest trace (heavy line) indicates depth along the transect. Practically all activity along the entire transect vanished during the night (compare the upper trace with others; the recording gain was about 10 times that used in the third trace, and 5 times that in the second and fourth traces). Thirteen other transects (not illustrated) along the lines shown in Figure 1 indicated that activity was restricted to patches, and was not distributed along the river bed at a constant depth or distance from shore. To determine the stability of the deep water activity, two anchored buoys (marked A and B in Figs. 1, 3 and 4) were placed over areas of high daytime activity, and integrated bottom activities below these buoys were determined at intervals (Fig. 5). During the day, activity at buoy A was emitted exclusively by group 2 fishes, while that at buoy B was a mixture of groups 1 and 3. On suc- cessive days, activity at buoy A was constant to within at least ±10%, while that at buoy B was slightly more variable, ±25%. Each aggregation was found to be about 3 m in radius. Between 1600 and 1800 hrs, as the sun set, activity began. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - co
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
