While average index values for Matagorda Bay dolphins 

 (I = 0.119 ± 0.027 [SD]) were similar to overall average values in other 

 studies, the moderate and high values seen in Galveston, Sarasota, Shark Bay, 

 and San Diego for some non-mother /calf pairs and differences in these 

 values with age and sex were absent. By looking only at freeze-branded 

 dolphins, caught nearly at random with respect to each other, the present 

 study has examined affiliations between what constitutes a nearly random 

 sample of the local dolphin population. Other studies, however, have 

 examined indices of association among the subgroup of dolphins with the 

 highest sighting rates (e.g., all dolphins seen ^ five times). This latter method 

 is more likely to discover high-level associates since such pairs of individuals 

 v^rill have similar sighting frequencies, as they are often seen in the same 

 group. Clearly, close and long-term associations (indicated by coi\sistent high 

 index values) are not lacking among Matagorda Bay dolphins. Gruber (1981) 

 documented several, as did Shane (1977) in Aransas Bay, and Fertl (1994) and 

 Brager et al. (1994) in Galveston Bay. While we are unable to determine how 

 our examination of patterns among freeze-branded dolphins only has 

 influenced these results, we suspect that as data from naturally-marked 

 individuals is incorporated, Matagorda Bay, which already shares 

 characteristics of its habitat v^nth Sarasota Bay and other sheltered estuarine 

 study sites, will be seen to share life history characteristics of its dolphins as 

 well. 



Group composition was not static. Some individuals had as many as 

 10-13 freeze-branded affiliates over the course of the year. All but four non- 

 calves sighted ^ five times had > five freeze-branded affiliates, cmd a high 

 percentage of potential pairv^se combinations was seen. The low association 

 indices, high numbers of affiliates, and variable group sizes reveal a fluid 

 sodal structure for these resident dolphins. Confirmation of tendencies 

 awaits results from naturally marked individuals. Dolphins of the 

 Matagorda/Espiritu Santo/San Antonio Bay complex probably know each 

 other well, and often feed and socialize together. They may easily share 

 tainted prey, disease vectors, or exposure to anthropogenic toxins and 

 contaminants which could contribute to massive die-offs similar to that 

 which occurred in Spring 1992. Similarly, parasite occurrence may be quite 

 equally distributed among adults of the area. 



BEHAVIOR 



Other studies on the Texas coast consistently indicated high levels of 

 feeding in the morning, high levels of socializing in the afternoon, and more 

 time spent feeding with less socializing traveling in winter months (Shane 

 1977, Gruber 1981, Brager 1993). Increased feeding in colder seasons was 

 hypothesized to offset increased thermoregulatory demands (Brager 1993) or 



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