796 



Fishery Bulletin 90(4). 1992 



Although Gunter found 12 species offish and 1 shrimp, 

 83% of fish consumed were Mugil cephalus. 



A significant difference between stranded (presum- 

 ably ill) and net-caught/capture-kiiled (presumably 

 healthy) dolphins is that stranded dolphins (Barros 

 1992, Barros and Odell 1990) have a high percentage 

 of empty stomachs (empty or < Ig, 32-54%) while net- 

 caught or captured dolphins (Cockcroft and Ross 1990, 

 Gunter 1942) have a very low percentage of empty 

 stomachs (<3%). The reason for this discrepancy is not 

 documented, but ill dolphins often have a decreased ap- 

 petite or may not be able to catch food. Another reason 

 for a high percentage of empty stomachs in the Bay 

 dolphins may be lack of food availability. Of 19 Bay 

 dolphins examined, 32% had empty stomachs and 37% 

 had only unidentifiable bones and scales (no flesh). 

 Gunter (1942) observed 34 killed specimens of T. trun- 

 catus; none of the stomachs were void of food. In addi- 

 tion, Gunter (1942) showed that the average number 

 of recognizable fish/stomach was 18, whereas the 15% 

 of EMB dolphins that had eaten recently had no more 

 than 2 recognizable fish/stomach. These data, along 

 with the Texas Parks & Wildlife fish freeze-kill and 

 biomass data, indicate that food was in short supply 

 for the Bay dolphins. I suspect that many of them might 

 have survived if they had sufficient nutrition. 



Ridgway and Fenner (1982) state that the blubber 

 may thin as weight loss progresses to emaciation, and 

 reduced blubber thickness at necropsy is one sign of 

 emaciation. Studies on healthy, well-fed dolphins at the 

 Naval Ocean Systems Center in San Diego show that 

 T. truncatus have thicker blubber as body weight in- 

 creases, and that T. truncatus may respond within 2 

 weeks to water-temperature changes by increasing or 

 decreasing blubber thickness for cooler or warmer 

 temperatures, respectively (William A. Friedl, NOSC, 

 Kaneohe, HI, pers. commun., Nov. 1990). Level of star- 

 vation may not be the only reason for differences in 

 blubber thickness between EMB and Texas coast 

 dolphins: the EMB dolphins might originally have had 

 thinner-than-normal blubber resulting from living in a 

 shallow bay with higher-than-average water tempera- 

 tures (29, 25, and 19°C monthly average water tem- 

 peratures in EMB for September, October, and 

 November 1989, respectively); or the normal prey field 

 in EMB might be limited compared with other areas. 

 Further work on blubber constituents and factors af- 

 fecting blubber thickness is needed to determine if blub- 

 ber thickness is an indicator of starvation as a cause 

 of death. 



The December 1989 EMB freeze, in which temper- 

 atures stayed near freezing for about 4 days, resulted 

 in devastation of the dolphins' most-likely major food 

 source, the striped mullet. The dolphins' emaciated 

 condition, the substantial reduction in their blubber 



thickness, lack of food in their stomachs, the assess- 

 ment that dolphins lived for 2 weeks following the 

 freeze, and the EMB fish freeze-kill and biomass data 

 suggest, in addition to any direct effects to the dolphins 

 of the extreme cold, that decimation of the food 

 resource contributed to this acute dolphin mortality 

 event. 



Acknowledgments 



I thank the following organizations and individuals for 

 their contributions that made this report possible: 

 Texas Marine Mammal Stranding Network (Dr. Ray- 

 mond Tarpley, founder of the TMMSN; Gina Barron, 

 for her untiring efforts and organizational skills; Elsa 

 Haubold and all the other members of the network who 

 have graciously devoted their time); Texas Parks and 

 Wildlife Department (Steve Marwitz and Lawrence 

 McEachron, Rockport, Texas); U.S. Coast Guard; 

 Houston Helicopter (Mike Boyaki and Dave Beard); Dr. 

 James Calvin, Department of Statistics, Texas A&M 

 University, College Station; and Naval Oceanographic 

 Command Detachment, Asheville, North Carolina. 

 Special thanks to Dr. Sam H. Ridgway (Naval Ocean 

 Systems Center) for his critique and support for this 

 work, and to F.G. Wood for his suggestions. Dr. Ray- 

 mond J. Tarpley (TMMSN and Texas A&M University), 

 provided NOSC with information on blubber measure- 

 ments taken from dolphins stranded on the Texas coast 

 from 1981 to June 1989. 



Citations 



Anonymous 



1986 Regional organization for the protection of the marine 

 environment, Report of the first meeting of e.xperts on mor- 

 tality of marine animals. Kuwait. Nov. 22-23. 1986. 

 Barros, N.B. 



1992 Food habits. In Hansen, L.J. (coordinator), Report on 

 investigation of 1990 GuK of Mexico bottlenose dolphin strand- 

 ings, p. 41-46. Contrib. MIA-9293, NMFS Southeast Fish. 

 Sci. Cent., Miami. 

 Barros, N.B., and D.K. Odell 



1990 Food habits of bottlenose dolphins in the southeastern 

 United States. In Leatherwood, S., and R.R. Reeves (eds.). 

 The bottlenose dolphin, p. 309-328. Academic Press, San 

 Diego. 

 Cockcroft, V.B., and G.J.B. Ross 



1990 Food and feeding of the Indian Ocean bottlenose dolphin 

 off southern Natal, South Africa. In Leatherwood, S., and 

 R.R. Reeves (eds.), The bottlenose dolphin, p. 295-308. Aca- 

 demic Press, San Diego. 



Dailey, J. A., J.C. Kana, and L.W. McEachron 



1991 Trends in relative abundance in size of selected finfish 

 and shellfish along the Texas coast: November 1975-December 

 1989. Manage. Data Ser. 53. Texas Parks Wildl. Dep., Fish. 

 Wildl. Div., Coastal Fish. Br., Austin, 241 p. 



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