Data Analysis 



Dorsal fin photographs were categorized by distinctive features such as 

 size, location and position of major notches, as well as by artificially-applied 

 marks (Wiirsig and Jefferson 1990). Sighting locations were plotted and 

 examined for patterns of range and site fidelity. 



Indices of association were calculated for freeze-branded dolphins or\ly by 

 use of the half-weight index of association (Dice 1945, Cairns and Schwager 

 1987): 



ab 



}i(N^^N^) 



where 



l^^ = the number of times individuals a and b were seen 

 together, 



^^ = the number of times individual a was seen, and 

 ^^ = the number of times individual b was seen. 



The half-weight index was chosen because it is commonly used, facilitating 

 comparison with other studies; and because it is least biased when 

 individuals of a pair are more likely to be seen separate than together, which 

 we believed to be a good assumption for the dolphin pairs examined in this 

 study (Cairns and Schwager 1987). 



A minimum of five sightings of an individual was chosen as a criterion 

 for inclusion in affiliation analyses. We believe that five sightings provide a 

 reasonable number of resightings from which to generalize, given the small 

 sample sizes, without limiting the number of individuals so much as to 

 preclude interesting comparisons. Multiple sightings of an individual in a 

 single day were counted as a single sighting. Numbers of affiliates were 

 examined for differences across sex, females with- and without-calf, pregnant 

 and non-pregnant females (Mann- Whitney U); and age, mean half- weight 

 index value, range size, mean group size, and number of sightings (simple 

 linear regression). Mean-index values were compared among dolphins 

 (Kruskal-Wallis) and between sexes (Mann-Whitney U). We examined an 

 individual's two "closest" (highest index value) associates for patterns of sex, 

 age, and reproductive condition. 



