Institution; Southeast U.S. Marine Mammal Stranding Network; Spring Hill College; Texas 

 A&M University; Texas Marine Mammal Stranding Network; US Coast Guard; and others. 



This report provides a background on bottlenose dolphin strandings in the Gulf and 

 the various research activities pursued during the investigation. Reports on several research 

 activities are included as separate sections. The rationale for the research directions taken 

 are discussed, as are the difficulties encountered in executing the investigation. The results 

 of each research activity are summarized and discussed, and, when appropriate, integrated 

 with other research results for further discussion. Reconmiendations are given for improving 

 the SEFC's stranding investigation capabihties, along with steps taken to implement these 

 recommendations. 



Stranding Rate and Trends 



The mortality event investigated occurred during January through May, 1990. 

 Strandings from January through June, 1986-89, were compared to the January through 

 June, 1990, strandings. Strandings during 1986-89 for these months ranged from 122-174; 

 strandings totaled 367 during the same months in 1990. Compared to the 1986-89 average, 

 during 1990 the largest increase in sfrandings was observed in Alabama (9.68 fold) and the 

 lowest in Texas (1.80 fold). For the U.S. Gulf as a whole, January-Jime 1990 strandings 

 were 2.62 times the 1986-89 average and 2.1 times the prior maximum recorded. 



The 1990 strandings generally followed the same seasonal pattern previously 

 observed, with a peak in sfrandings during March. The 1990 strandings during January- 

 March were from about 3 to 4 times greater than the 1986-89 averages. April 1990 

 strandings were about twice the prior 4-year average, and May and June 1990 strandings 

 were also about double, but were relatively low in number, 25 and 23, respectively. 

 Strandings throughout the Gulf during 1990 were the highest on record for all months except 

 August. 



The sex ratio of the Texas, January- June 1990 sfrandings, was compared to that of 

 1984-89 Texas strandings. The sex was recorded for 400 animals that stranded during 1984- 

 89, and the sex ratio was 1.00:0.67, males to females. The sex ratio for 1990 was 1.00:0.98, 

 which still falls within the yearly ranges observed (1.00:0.34 to 0.85:1.00). 



The length-frequency distribution of Texas, January-Jime 1990 strandings, was 

 compared to that of the Texas, January-June 1984-89, combined length frequency 

 distribution. Contingency table analysis indicated that the differences between the 1990 and 

 1984-89 distributions were statistically significant. The largest differences occurred in the 

 numbers of animals < 140cm, with proportionally half as many stranding during 1990 as 

 compared to 1984-89. About 30% of the January- June 1984-89 strandings were < 140cm; 

 during 1990 for these months only 15% were < 140cm. This is the lowest proportion 

 observed, except for 1985 (only 35 strandings were recovered during 1985, and only 4 were 



