2008 Texas Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event

Bottlenose Dolphins (Tursiops truncatus) Photo: NMFS Southwest Fisheries Science Center

An increased number of bottlenose dolphins (Tursiops truncatus) stranded along the Texas coastline in February and March of 2008. The February strandings were spread out along the entire Texas coast, although Brazoria, Galveston and Nueces counties saw the most increase. On March 3rd, 21 dolphins washed ashore in Galveston and Jefferson counties in late stages of decomposition. Most animals showed evidence of severe scavenging from shark bites with only a partial carcass present. The dolphin strandings continued to occur in high numbers throughout March 2008.

The high numbers of strandings in March were limited to Matagorda, Brazoria, Galveston, and Jefferson counties with very few strandings (5 total) occurring along other areas of the Texas coastline. The total number of strandings recovered by the Texas Marine Mammal Stranding Network (TMMSN) in March was 78. In April, bottlenose dolphin strandings have decreased significantly with the total of 119 from February 1.

On March 18, 2008, a consultation was initiated with the Working Group on Marine Mammal Unusual Mortality Events following the procedures prescribed in 16 U.S.C. 1421(c), Section 404 of the Marine Mammal Protection Act to determine if an unusual mortality event was in progress and to solicit guidance on the investigation. The Working Group concluded at least two of the seven criteria established for designation of a UME had been met. These mortalities are unusual because: (1) there is a marked increase in the magnitude or a marked change in the nature of morbidity, mortality or strandings when compared with prior records (criteria number one); and (2) the species, age, or sex composition of the affected animals is different than that of animals that are normally affected (criteria number four).

The Harmful Algal Bloom (HAB) department for Texas Parks and Wildlife (TPWD) and the Louisiana Universities Marine Consortium (LUMCON) were immediately notified upon the increase in strandings and began reviewing water samples. The HAB department noted there was i ncreasing numbers of an alga called Dinophysis in samples collected in the Port Aransas area during February by TPWD. Water samples also tested positive for okadaic acid (a marine toxin produced by Dinophysis) in the area of Port Aransas. The area where the Dinophysis bloom was observed in February is approximately 250 miles south of the locations where the majority of strandings took place in March.

Coast Guard flights completed over the Gulf (offshore of Galveston and Jefferson Counties) during late March found no floating carcasses. Also, a notice to mariners was broadcast during late March for one week, asking that any floating carcasses be reported.

The investigation into this event is ongoing. The TMMSN is continuing to conduct beach-based surveys in Matagorda, Brazoria, Galveston and Jefferson counties through April. They are shipping tissue samples from the strandings to various researchers for analyses.