WURSIG and WURSIG. BEHAVIOR AND ECOLOGY OF Tl'RSIOPS TRrXCATUS 



n 1 



LOS CONOS 



CAMP + 



TUR5IDP5 TRPEL FILE 13 10/24/75 0707. MI 



075G.I5 97 ENTRIES 



8000 



9000 



10000 



IIOOO 



12000 



13000 



Figure 2. — Depth contour map of one-fourth of the study area. Margin numbers represent meter distances relative to a zero location on 

 land. Crosses foiTn 1 km squares. "Cliff Hut" and "Camp" are the locations from which most observations were made. Depth contours are 

 in meters at mean low water (ML Wi. The usual distance for good observation of a moving dolphm group was at least 3 km. At a normal 

 tide height of 5 m above MLW. water depth of 40 m was 1 km from Cliff Hut, and thus clearly visible. The solid Ime above Cliff Hut 

 represents a sample track of a bottlenose dolphin group, and the printed information gives computer file location, date of track, time of 

 day, and number of theodolite entries. About 200 such tracks were obtained of bottlenose dolphins during the 21-mo study. The map is 

 from a larger area map which was by courtesy of Roger Payne, New York Zoological Society; Oliver Brazier. Woods Hole Oceanographic 

 Institute; and Russ Charif Harvard Universitv. 



Since dolphins often did not travel in straight 

 line, speed information from theodolite readings 

 separated by several minutes was lower than the 

 actual speed traveled. To minimize erroi's in speed 

 calculations, only readings made within 30 s of 

 each other were used. The accuracy of the transit 

 (±30" of arc) allowed for placement of position 

 within ±100 m at 5.5 km distance. 



RESULTS 



Preferred Depths 



To determine whether dolphins prefer a specific 

 depth of water, and to map their movement pat- 

 terns, theodolite readings were obtained 

 whenever bottlenose dolphins came within sight- 



ing range of shore ( 1-10 km, depending on visibil- 

 ity). Within that range, the depth of water varied 

 from 1 to 65 m. Bottlenose dolphins occurred 92% 

 of the time in water <10 m deep (2,655 of 2,883 

 theodolite readings), within 1 km of shore (Figure 

 3). None were ever sighted in water >39 m. Visi- 

 bility at almost all times extended to at least 3 km 

 from shore, where water depth was 45-50 m (see 

 Figure 1), and we consistently tracked dusky dol- 

 phins in much deeper water (Wiirsig and Wiirsig 

 see footnote 4). Furthermore, we traversed the 

 study area by boat in waters 1 to 10 km from shore 

 on 109 occasions and never saw bottlenose dol- 

 phins in water >39 m. For these reasons we be- 

 lieve that the data for shallow nearshore travel 

 are not biased by sighting error. In general, dol- 

 phins moved in shallow water in the morning and 



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