FISHERY BULLETIN VOL 77. NO, 2 



to- 



1-5 b-IO 10-15 15-20 20-25 25-30 50- J5 



DEPTHS (m) 



FUU'RE 5- — Average speed of travel of bottlenose dolphins in 

 different depths of water. Numbers represent number of theodo- 

 lite readings per depth category for which speed information was 

 available. Shallow-water i-lO mi'speeds are significantly dif- 

 ferent from those in deeper water lP<0.01, Mann-Whitney 

 U-test. Sokal and Rohlf 19691. 



Movement of dolphins was also affected by tidal 

 fluctuations. Animals were found in progressively 

 shallower water as the tide ebbed. Thus, dolphins 

 tended to remain the same distance from the high 

 tide line. When the tide was 6 m above mean low 

 water, dolphins were found in 9 m depth. At mean 

 low water, they were found at a depth of 3 m 

 (Figure 8a). At low wateras the tide began to flood, 

 the dolphins remained in shallow water (3 m) but 

 as the tide continued to rise from 1 to 3 m, they 

 moved into deeper water. At a tide height of 4-7 m, 

 they moved into waters 5-10 m deep (Figure 8b). 

 Depths over which dolphins were when flood tide 

 was between 1 and 3 m were quite variable, indi- 

 cating that the animals moved in all depths near 

 shore at those times, and moved into deep water 

 more often than at other tide heights. Thus, on a 

 lowering tide, dolphins were found in progres- 

 sively shallower water, while on a rising tide the 

 reverse trend appeared, but with a dramatic inter- 

 ruption in this trend at tide heights of about 1-3 m. 

 At those heights, dolphins more often moved into 

 deep water for brief periods. 



Bottlenose dolphin subgroups often moved back 

 and forth longitudinally within a confined area 

 near shore, thus at times staying within sight of 

 our observation points all day. Within 0..5 km of 

 shore, they turned (changed direction by 

 180°±10") on the average every 673 m (SD = 980, 

 n =104), and farther than 0.5 km from shore they 

 turned every 1,382 m(SD = 1,094?; = 11). Despite 

 the large standard deviations in these readings, 

 dolphins farther from shore traveled significantly 

 longer distances before turning than when they 



lOr 

 8 

 6 



10 



E 8 



10 



8 10 12 14 16 18 20 



10 12 14 

 HOUR OF DAY 



20 



Figure 6. — Mean speed of travel at different times of day <ai 

 The numbers near points represent number of theodolite read- 

 ings with speed data gathered for that hour of day. The.se data 

 were divided into months (b. c). In July and October, dolphin.- 

 traveled faster at 1300 h than at other times, while in December 

 and January, they traveled faster in late afternoon iP- 0.01, 

 Kruskal-Wallis test in lieu of one-way ANOVA Sokal and Rohlf 

 19691. 



were within 0.5 km of shore iP<0.05, t-test). How- 

 ever, because they traveled faster when farther 

 from shore (and in generally deeper water, see 

 Figure 4), the time between turns was not sig- 

 nificantly longer (mean time <0.5 km from shore 

 = 8.8 min, >0.5 km = 10.0 min). Thus, dolphins 

 changed direction about every 9 or 10 min. The 

 increase in distance covered appeared to be a con- 

 sequence of the greater speed in deeper water. 



Changes in direction by 180'±10' were often 

 made at the same locations on different days, and 



404 



