An Investigation of Dolphin (Tursiops truncatus) Deaths in East Matagorda Bay, Texas in January 1990
IAAAM 1991
W. George Miller1, DVM, PhD; Raymond J. Tarpley2, DVM, PhD
1Naval Ocean System Center, San Diego, CA; 2Department of Veterinary Anatomy and Public Health, College of Veterinary Anatomy, Texas A&M University, College Station, TX

Acute mortality in localized bottlenose dolphin pods of 10 to 40 animals has likely occurred but at present there are no comprehensive documented reports of such events. In January 1990, the US Coast Guard Station at Freeport, Texas was notified by a helicopter pilot that he had sighted a total of 23 dead Bottlenose dolphins (Tursiops truncatus), on the shore or in the tidal flats of East Matagorda Bay (EMB), Texas and another 3 dead dolphins (Tursiops truncatus) on the shore of the Gulf of Mexico of East Matagorda Peninsula.

Each dead dolphin was identified with an ID number and its exact location noted as the animals were lifted from the beach. The carcasses were transported to Galveston, Texas for necropsy analysis at facilities provided by Texas A&M University for the Texas Marine Mammal Stranding Network. Major necropsy findings included an average 39% reduction in blubber thickness compared to similar aged dolphins stranded during winter months during the previous 8 years and a predominant lack of food material in the stomachs of dead dolphins.

Data was collected on the physical characteristics of EMB. The effect of weather on bay temperature, tidal changes, and resident animal populations was examined. The major food source for the dolphins, the striped mullet (Mugil cephalus) was devastated during the severe cold weather system that moved through the area in late December 1989. The mullet kill (2.75 million) in this small bay amounted to 42% of the total fish kill along the entire Texas coast for this time period. Average monthly temperatures of bay waters vary from about 12°C to 33°C; however, the water temperatures do drop to near 0°C for short periods during severe winter storms that hit the Texas coast as often as several times in a winter. In December 1989, water temperatures in this bay dropped to -1.36°C and stayed near 0°C for about 48 hours causing the bay to freeze over. The major reduction in blubber thickness suggests that decimation of the food resource in addition to any direct effects of the extreme cold contributed to this acute dolphin mortality.

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Raymond J. Tarpley, DVM, PhD

W. George Miller, DVM, PhD
San Diego, CA, USA

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