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The objective of this thesis was to determine if there were any correlations in the distribution of cetaceans, especially sperm whales (Physeter macrocephalus), pantropical dolphins (Stenella attenuata), bottlenose dolphins (Tursiops truncatus), and Risso’s dolphins (Grampus griseus) in the northern Gulf of Mexico because of the influence of oil and gas production and exploration. This research is important because of the lack of knowledge about the impact of anthropogenic sounds from oil and gas exploration and production (E&P) on cetacean distribution in the Gulf of Mexico. I analyzed cetacean visual line-transect survey results from the Gulf of Mexico for period of 1992 – 2001. I divided this time span into an early period (1992 – 1997) and a late period (1998 – 2001). I overlayed the locations of cetacean sightings and the locations of oil and gas E&P platforms to demonstrate their close association in space, and tested a hypothesis that distribution would shift south correlated with changes in distribution of E&P. I compared the distributions of cetacean sightings in the entire Gulf of Mexico, and separated the Gulf of Mexico into east and west, between the early period and the late period. The east Gulf of Mexico represents an area without oil and gas E&P platforms and the west Gulf of Mexico is the area where oil and gas E&P platforms are located. The null hypothesis for these tests was that there was no difference in cetacean distribution between the early period and the late period. I also compared the distribution of sperm whales, pantropical dolphins, bottlenose dolphins, and Risso’s dolphins in the entire Gulf of Mexico, both east and west, between the early and late periods. I expect if distribution changes were correlated with changes in E&P distribution, then there will be a shift south in the western Gulf. Changes in distribution in the eastern Gulf would not be correlated with E&P. I found that the sightings per unit effort (SPUE) of all cetacean sightings in the entire Gulf of Mexico shifted to the south in the late period, as compared to the early period .The distribution of all cetacean sightings for the late period (1998-2001) was significantly different compared to the distributions of all cetacean sightings in the early period (1992-1997). The SPUE of sperm whale and bottlenose dolphin distributions were shifted to the north in the late period (1998-2001) compared to the early period (1992-1997). While pantropical dolphin distributions were significantly shifted to the south between the two time periods. I observed that the SPUE of all cetaceans sightings in the east Gulf of Mexico for the early period (1992-1997) were shifted to the south compared to the west, which were not different. The SPUE for sperm whales in the east for the early period were marginally shifted to the north in comparison to the west, which were also shifted further north. The SPUE for Risso’s dolphins in the east were shifted further north while in the west SPUE were shifted to the south. The SPUE for pantropical dolphin sightings were shifted to the north in both the east and west regions. While the SPUE for bottlenose dolphin sightings were shifted to the north in both the east and west Gulf of Mexico. My SPUE results suggest that pantropical dolphins, like the total cetaceans examined here, have shifted their distributions in the entire northern Gulf of Mexico to the south. However, in areas of high oil and gas E&P platforms the distributions of sperm whales and bottlenose dolphins did not shift their distributions from the early period to the late period to the south even though these E&P activities have shifted to the south over the past two decades as they expanded into the deeper waters of the northern Gulf of Mexico. Therefore, there is little evidence that large scale changes in the latitudinal distribution of marine mammals in the Northern Gulf have occurred as a result of greater offshore E&P activity.

Preservation of large tracts of habitat is often recommended for long-term population viability of area-sensitive species. Large tracts may not always be available. Smaller patches, though not able to contain a viable population individually, may contribute to overall regional population viability if within the small patches pairs could successfully reproduce. By definition, area-sensitive species should have a minimum patch size threshold of habitat below which they will not likely reproduce. Two potential causes for positive relationships between patch size and production are inverse relationships between patch size and brood parasitism and patch size and food availability. My objectives were (1) to determine the minimum patch size thresholds of reproductive success for golden-cheeked warblers (Dendroica chrysoparia), black-and-white warblers (Mniotilta varia), and white-eyed vireos (Vireo griseus); (2) to determine whether thresholds for occupancy, territory establishment by males, or pairing success were indicative of thresholds of reproduction; (3) to determine whether the proportion of pairs fledging brown-headed cowbird (Molothrus ater) young was related to patch size, and (4) to determine the affects of patch size on food availability (i.e., arthropod abundance). The Vickery index of reproductive activity was used to determine reproductive activity of each male or pair and to quantify parasitism occurrences. I collected arthropods using branch clipping to assess the relationship between patch size and arthropod abundance. I found minimum patch size thresholds of reproductive success for golden-cheeked and black-and-white warblers, but not for white-eyed vireos. Minimum patch size of reproductive success was between 15 and 20.1 ha. Minimum patch size thresholds for occupancy, territory establishment by males, and pair formation were not consistent with thresholds for reproductive success. I found no relationships between patch size and cowbird parasitism or patch size and arthropod biomass. Conservation practices for target species based on thresholds of occupancy, territory establishment, or pair formation may not address issues of reproduction. The ability to identify thresholds of reproductive success for target species could be useful in conservation and management in multiple ways including setting goals for retention and restoration of a target species’ habitat patch size.

Preservation of large tracts of habitat is often recommended for long-term population viability of area-sensitive species. Large tracts may not always be available. Smaller patches, though not able to contain a viable population individually, may contribute to overall regional population viability if within the small patches pairs could successfully reproduce. By definition, area-sensitive species should have a minimum patch size threshold of habitat below which they will not likely reproduce. Two potential causes for positive relationships between patch size and production are inverse relationships between patch size and brood parasitism and patch size and food availability. My objectives were (1) to determine the minimum patch size thresholds of reproductive success for golden-cheeked warblers (Dendroica chrysoparia), black-and-white warblers (Mniotilta varia), and white-eyed vireos (Vireo griseus); (2) to determine whether thresholds for occupancy, territory establishment by males, or pairing success were indicative of thresholds of reproduction; (3) to determine whether the proportion of pairs fledging brown-headed cowbird (Molothrus ater) young was related to patch size, and (4) to determine the affects of patch size on food availability (i.e., arthropod abundance). The Vickery index of reproductive activity was used to determine reproductive activity of each male or pair and to quantify parasitism occurrences. I collected arthropods using branch clipping to assess the relationship between patch size and arthropod abundance. I found minimum patch size thresholds of reproductive success for golden-cheeked and black-and-white warblers, but not for white-eyed vireos. Minimum patch size of reproductive success was between 15 and 20.1 ha. Minimum patch size thresholds for occupancy, territory establishment by males, and pair formation were not consistent with thresholds for reproductive success. I found no relationships between patch size and cowbird parasitism or patch size and arthropod biomass. Conservation practices for target species based on thresholds of occupancy, territory establishment, or pair formation may not address issues of reproduction. The ability to identify thresholds of reproductive success for target species could be useful in conservation and management in multiple ways including setting goals for retention and restoration of a target species’ habitat patch size.