-
78. Mammals (Vertebrata: Mammalia) of the Gulf of Mexico
- Texas A&M University Press
- Chapter
- Additional Information
Because of their large body size and abundance, marine mammals are thought to have a major influence on the structure and function of marine communities (Bowen 1997). They are major consumers of production at most trophic levels, from primary production (manatees and baleen whales) to predatory fish (dolphins and toothed whales) and even to other marine mammals, such as the killer whale (Pittman, O’Sullivan, and Mase 2003). In the Gulf of Mexico, cetaceans (whales and dolphins) make up much of the diversity and abundance of upper-trophic level predators. Moreover, they are very mobile and can move tens of kilometers per day, and their physiological capabilities allow them to tolerate most of the environmental variations in the Gulf. It has only been toward the end of the 20th century, after the passage of the Marine Mammal Protection Act in 1972, that we have begun to gather systematic information about marine mammals in the Gulf. Prior to that time, our knowledge of their distribution and abundance was limited largely to reports of stranding and sightings documented by a small number of dedicated naturalists and scientists—people such as David and Melba Caldwell, Joe Moore, James Layne, George Lowery, and Gordon Gunter (the work of Würsig, Jefferson, and Schmidly 2000 has a detailed listing of the early literature). Most of these early observations were collected opportunistically, and in most cases, told us little more than the species composition for the Gulf. When Gordon Gunter (1954) published his account of the marine mammals in Fishery Bulletin 89, only 16 species of marine mammals were known from the Gulf. The only species that had been well studied in the Gulf of Mexico before the 1990s were 2 coastal ones, the common bottlenose dolphin (Tursiops truncatus) and the West Indian Manatee (Trichechus manatus). Coastal common bottlenose dolphins have been especially well studied by Randall Wells and colleagues in the eastern Gulf, the Sarasota-Bradenton area of west Florida, in the most long-term and detailed set of cetacean behavioral ecology investigations on Earth, in continuous fashion since the early 1970s (for example, Wells and Scott 2002). The other species occurred primarily offshore in relatively deep waters and received little attention prior to this time. Much of the information that has become available in the last few decades has come from the northern Gulf, with little known about the southern Gulf. The Southeastern United States Marine Mammal Stranding Network (SEUS MMSN) was established in 1977, and that marked the beginning of recording and archiving systematic stranding data for the Gulf. Schmidly 1343 78 Mammals (Vertebrata: Mammalia) of the Gulf of Mexico David J. Schmidly and Bernd Würsig Mammalia. After Smith 2002. 1344 ~ Mammals (Vertebrata: Mammalia) and was called the GulfCet surveys. The first part of the project (GulfCet I) was conducted from 1991 to 1995, and its main objective was to determine the distribution and abundance of cetaceans along the continental slope in the north-central and western Gulf, in areas that could be affected by future oil production (Davis and Fargion 1996). A continuation of the project (GulfCet II) ran from 1996 through 1998, with the main goal being to identify possible associations between cetacean high-use habitats and mesoscale environmental variability (Davis, Evans, and Würsig 2000, Davis et al. 2002). Collectively, this 6-year, 2-part study provided synoptic information on the distribution and abundance of cetaceans, using both visual and acoustic survey techniques (Jefferson 1995, Davis and Fargion 1996, Baumgartner 1997, Jefferson and Schiro 1997, Davis et al. 1998, Davis, Evans, and Würsig 2000, Würsig, Jefferson, and Schmidly 2000). Finally, between 1997 and 1999, opportunistic surveys were conducted during 6 oceanographic cruises aboard the B/O Justo Sierra in the southern Gulf and the Yucatán Channel , from Tuxpan, Veracruz, to Cozumel, Quintana Roo (Ortega-Ortiz 2002). A major development in marine mammalogy in the Gulf occurred in 1989, with the establishment of the first academic research and graduate education program in the region devoted solely to the study of marine mammals. The Marine Mammal Research and Graduate Education Program was developed as a partnership between the Department of Wildlife and Fisheries Sciences at Texas A&M University and the Department of Biology at Texas A&M at Galveston. Four marine mammalogists (Bernd Würsig, Randall Davis, Graham Worthy, and William Evans) were appointed to faculty positions, and they have been active with field and laboratory research programs involving graduate students in many aspects of the biology and natural history of marine...