< 140cm). The proportion of stranded animals measuring < 140cm has been decreasing since 

 1986. 



Population Abundance and Trends 



Estimates of bottlenose dolphin abundance from large-scale aerial surveys of the Gulf 

 of Mexico (Scott et al. 1989) were compared with historical stranding data. The available 

 population abundance estimates for the northwestern Gulf of Mexico indicate that 

 abundance is lowest in the winter, increases during the spring, and remains at about the 

 spring level through the summer and fall. Strandings in the northwestern Gulf peak from 

 February-April; it appears that strandings in the northwestern Gulf peak during a period 

 when abundance is increasing. However, if only the nearshore and inshore £ireas (waters 

 < 18.3m) are considered, strandings peak when abundance is at intermediate levels and 

 declining. 



Available bottlenose dolphin abundance estimates for the northeastern Gulf of 

 Mexico indicate that the lowest abundance occurs during the summer, with the highest 

 abundance during the winter. Strandings for the northeastern Gulf peak diuing March and 

 April, which appears to be when abundance is declining. When only the nearshore and 

 inshore areas are considered, strandings peak when abundance appears to be declining. 



Aerial surveys of portions of the northwestern Gulf were conducted during March and 

 June, 1990. The results of these surveys indicate that there may have been more animals 

 present in the inshore areas (waters to 18.3m) and offshore areas (waters 18.3m to 183m) 

 during 1990 than the previous sampling period (1983-84). These results are similar to the 

 findings of nearshore surveys conducted prior to the 1987-88 east coast dolphin dieoff, but 

 differ from the results of offshore surveys conducted during the 1987-88 dieoff which 

 indicated there was a 60% chance of a decline in the offshore stock abundance (Scott and 

 Bum 1987). 



Age Structure of Stranded Animals 



The age structure of the bottlenose dolphins stranded along the Texas coast was 

 examined to determine if was different during 1990 as compared to previous years. The 

 available sample of teeth from animals stranded during January- June during 1983-90 were 

 aged using standard techniques for bottlenose dolphins (e.g., see Hohn et al 1989). The 

 available sample consisted of 195 animals, of which 70 were obtained in 1990. 



Comparison of the 1983-89 and 1990 aged samples indicated that the differences 

 observed were not statistically significant (Kolmogorov-Smimov two-sample test, DN=0.19, 

 p>0.10). However, further examination of the samples indicated that the 1983-89 aged 

 sampled was most likely biased, and that this likely bias resulted in under-representation of 



