WURSIG and WURSIG: BEHAVIOR AND ECOLOGY OF TURSIOPS TRUSCATUS 



coastal dolphins at times rest close to shore (and 

 move slowly while resting) to avoid deeper water 

 predators such as sharks and killer whales i Norris 

 and Dohl see footnote 3; Wiirsig and Wiirsig see 

 footnote 4). They more often feed farther from 

 shore and in deeper water, and are more active at 

 that time. 



In this study there was evidence that bottlenose 

 dolphms near shore paid attention to bottom to- 

 pography. While they in general moved over con- 

 sistent water depth for brief periods, they often 

 moved back and forth over the same bottom topog- 

 raphy durmg a falling tide. As a result, they 

 traveled in progressively shallower water as the 

 tide receded. Furthermore, they changed direction 

 over particular underwater landmarks, usually 

 consistmg of groups of rocks. This type of move- 

 ment associated with bottom topography may be 

 strongest while the animals are searching for bot- 

 tom-dwelling prey. However, we do not know what 

 their food was at such times. The intertidal areas 

 in which they were traveling had abundant snails, 

 and part of the area was covered by mussels. Mus- 

 sels were especially abundant on the rocky out- 

 croppings where dolphins turned (and at times 

 milled or lingered for several minutes), but we 

 have no direct evidence for feeding on shellfish. 

 Norris and Prescott (1961) reported that Tursiops 

 in California waters feed at times on hermit crabs 

 and shellfish. Also present in and around rocks 

 were larger — up to 1 m long — fish. Pinguipet: fas- 

 ciatus. We observed individual dolphins shaking 

 these fish in their mouths and repeatedly tossing 

 them into the air on three separate occasions. Al- 

 though this behavior at first looked like "play" 

 before feeding on the fish, it is likely that the 

 dolphins were tossing and shaking them to soften 

 the fish and possibly to separate the head from the 

 edible body (as reported by Brown and Norris 

 1956). It thus appears that this fish constitutes a 

 nearshore prey item, and it may be part of the 

 reason that bottlenose dolphins often turned and 

 lingered near rocks. 



During intermediate flood tides dolphins trav- 

 eled more often into deep water than at other tide 

 stages. Since deepwater movement appeared cor- 

 related with group feeding on schooling fish, feed- 

 ing may have occurred more often during such 

 intermediate rising tides. We therefore suspect 

 that schooling fish were also more often present in 

 nearshore waters during rising tides, perhaps 

 brought into the area from deeper water by the 

 tidal currents. Although we have no evidence for 



this postulated movement of bottlenose dolphin 

 prey, it is a common behavior of many fish species 

 to come in with the tide, and thus a reasonable 

 possibility in the present case. Tide-related 

 movements ofTursiops sp. have been described by 

 McBride and Hebb (1948). Norris and Prescott 

 ( 1961 ). D. K. Caldwell and M. C. Caldwell ( 1972), 

 Irvine and Wells ( 1972 ), Shane ( 1977 ), and others. 

 Most of these descriptions involved the move- 

 ments of bottlenose dolphins into and out of coast- 

 al channels or canals and are therefore not strictly 

 comparable with the present study. However, dol- 

 phin movement appeared often to be food-related 

 in these studies. Saayman and Tayler (in press) 

 found a peak in Sousa sp. feeding 2 h before high 

 tide, presumably also because prey fish were 

 being brought into their study area by the tide. 



Near shore, dolphins changed direction by 180° 

 approximately once every 700 m. This was the 

 average distance between rocky outcroppings of 

 cliffs. The turns often tended to keep the animals 

 in a restricted area within sight of our observation 

 points for several hours. When farther than 0.5 km 

 from shore, dolphins traveled about twice the 

 nearshore distance before turning, possibly be- 

 cause they encountered no rocks or outjuttings of 

 cliffs in such deeper water. Nevertheless, because 

 travel in one direction lasted on the average only 9 

 or 10 min whether near or far from shore, deeper 

 water travel also usually kept the animals in a 

 particular area. 



Although we were able to describe the move- 

 ments of bottlenose dolphins in some detail within 

 an approximately 50 km^ area, we do not know- 

 where the dolphins went when they moved out of 

 our area. They did not travel beyond a certain 

 point (Los Conos. Figure 2) within the study area, 

 but at least once individuals traveled as far as 300 

 km away from the study site (Wiirsig and Wiirsig 

 1977; Wiirsig 1978). However, a more accurate 

 definition of range awaits further data. 



It was mentioned previously that slow move- 

 ment near shore may at times be associated with 

 feeding on large solitary fish as well as on smaller 

 bottom-dwelling organisms. Dolphins also en- 

 gaged in other activities while moving near shore. 

 During the morning, we observed very little aerial 

 behavior such as leaping, noseouts, belly-ups, and 

 kelp tossing. As a result it appeared that their 

 activity level was less during the morning than 

 during the afternoon, and that much of the time 

 the animals were resting as they moved back and 

 forth close to shore. A similar pattern of rest dur- 



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