WUR8IG and WURSIG BEHAVIOR AND ECOLOGY OF TVRSIOPS TRrXCATLS 



TYPE OF MOVEMENT IN WATER 'lOm DEEP 



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a 



UJ 



o 4 

 2 



TYPE OF MOVEMENT IN WATER JlOm DEEP 



Figure 7. — Movement relative to depth contours In "parallel" 

 movement, dolphins stayed in the same depth between theodo- 

 lite readings, in "intermediate" movement they crossed contour 

 lines at an angle, and in "perpendicular" movement they moved 

 perpendicular to depth contours, and therefore changed depths 

 rapidly In shallow i <10 m) water, dolphins moved parallel to 

 depth lines I ±22.5) significantly more than they moved perpen- 

 dicular to them I ±22.5'.P<0.001,chi-squaregoodnessoffit testi 

 and in deeper 15^10 m) water this trend was weaker but still 

 present iP < 0.03. test as above! . The circles to the right show the 

 divisions of movement, where parallel lines indicate movement 

 parallel to depth lines, and an inverted T represents movement 

 perpendicular to them. Only one-half circle is shown for shallow 

 water because it is likely that animals near shore cannot travel 

 into shallower water. However, the expected percentages of 

 movement relative to depth contours remains the same in shal- 

 low and deep water. 



therefore after a while could be predicted. Near 

 camp there were three locations where subgroups 

 turned more often than expected if turns were 

 made at random (P<0.005, ehi-square goodness of 

 fit test). All three of these locations were marked 

 by rocks which were submerged during medium 

 and high tides. When the tide was low enough to 

 uncover these rocky areas, leaving only an even, 

 sandy bottom covered, the preference for turning 

 at those areas disappeared. It appears, therefore, 

 that the animals used these rocks as underwater 

 landmarks which, at least at times, stimulated 

 them to change direction. It is unlikely that the 

 dolphins turned at these locations simply to avoid 

 bumping into the rocks, since one of the three 

 areas was marked by rocks only 5-10 cm above the 

 sandy substrate. All three areas formed distinct 

 discontinuities in the bottom topography, how- 



CORRELATION 

 COEFFICIENT 

 t ) = 0.928 



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TIDE HEIGHT (m) 



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TIDE HEIGHT (m) 



Figure 8. — Average depth of water in which dolphins traveled 

 at different tide heights during a lowering lor ebbi tide (a). Bars 

 above and below points represent QS'^/r confidence limits. A 

 least-squares regression line through the means shows that dol- 

 phins were found in progressively shallower water as the tide 

 ebbed (correlation is statistically significant. P- 0.01 1. Average 

 depth of water in which dolphins traveled at different tide 

 heights during a rising (or flood) tide ib). The rising trend was 

 interrupted between tides 1 and 3 m by animals more often 

 moving into greater depth (shown by increase in mean depth and 

 by larger SS':? confidence limits, because variability increased!. 



ever, and may have served as cues to turn at the 

 boundary of the area traversed. 



The tongue of land called Los Conos i Figure 2 ), 6 

 km north of camp, appeared to be the northward 

 boundary of the present population's range. In 260 

 h of observation, dolphins were never observed 

 traveling north of this point. When they were lost 

 from sight, it was either due to bad visibility or 

 because the animals traveled out of range in the 

 southwest portion of the study area. In addition, 

 when the animals were first spotted coming into 

 the study area, they always came from the south- 

 west, never from the north. 



As was described earlier, bottlenose dolphins in 

 the present study exhibited two distinct move- 

 ments. Usually, they moved slowly and very close 

 to shore, in shallow (<10 m deep) water. They 

 moved for brief ( 16 min) periods, mainly during 

 midday in nonsummer seasons, into deeper ( >10 



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