BEHAVIOR 



The May 1993 survey was excluded due to its brevity. Behavioral budgets 

 are biased to an unknown extent by the behavior "feeding behind 

 shrimpboat" (FBS). The shrimp fishery operates predominantly on summer 

 mornings to early afternoons in the study area (Spencer Lynn, personal 

 observation), and trawling shrimpboats are reliable places to find dolphins 

 (Fertl 1994). Since the primary goal of our field effort subsequent to cessation 

 of radio-transmitters was to photo-identify individuals, effort was often 

 biased towards seeking out shrimpboats. 



Table 7 presents the proportion of behaviors seen overall and within each 

 habitat type. Travel represented 50.7% of sightings and feeding 28.4%. Most 

 behaviors were seen in all habitat types. Travel in "jetty" channels was 

 common, as was feeding at the ends of jetties and in "channels '. 



Dolphins displayed a variety of interesting feeding behaviors, including 

 individuals "herding" fish against cement walls and ship hulls. Most feeding 

 appeared to be at an individual level, though aggregations of dolphins 

 feeding in subgroups of about one to three could be large and spread out over 

 areas of 100 m^ or more. Several dolphins rapidly converging on one spot 

 could be evidence of coordinated feeding, or a simple strategy of "getting there 

 first". Some feeding was seen in very shallow water (> 0.5 m). On one 

 occasion we observed 4 dolphins "headstanding" in water approximately 1-m 

 deep. Their bodies and jDedundes were so far in the air that we believe they 

 may have been rooting in the bottom with their rostrums. Feeding was often 

 seen concurrently with travel. A typical sighting of travel-feed usually 

 involved groups of one to three dolphins traveling slowly in a channel. 

 Individual dolphins would occasionally stop traveling to apparently 

 investigate habitat structure such as channel walls and ships at dock. Often 

 evidence of feeding was then seen. Group mates often continued traveling 

 during the foraging attempt, performing similar activities. 



No strong seasonal or hourly trends in behavior or group size were found 

 (Fig. 11 and Fig. 12, respectively). More groups were encountered traveling in 

 July-August and September. Trends may be obscured by bias due to FBS in 

 the May and June surveys, and by spuriously low observations of feeding in 

 January (n = three feeding observations in January but n = 24 the previous 

 December). However, from August through December, a trend for increased 

 sightings of feeding groups is evident. Concomitant with increased feeding is 

 a trend for decreased social activity from May through January (Fig. 11a). 



18 



