Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1995. / Vita. Abstract. Includes bibliographical references (leaves 162-174). Also available via the Internet.

Piscivorous avian species are of particular importance in Mississippi due to their depredation of cultured catfish throughout the states aquaculture industry. The three most common of these species include the double-crested cormorant (Phalacrocorax auritus), great blue heron (Ardea herodias), and great egret (Ardea alba). Information on these species aquaculture use can aid in effective and ethical management while also providing insight into their foraging ecology and habitat use, which is particularly important given these species augment their nutritional requirements using man-made food sources. The objectives of this research were to explore numerous aspects of avian foraging ecology in relation to aquaculture at multiple spatial and temporal scales using historic and contemporary aerial survey data. First, we examined the distribution and abundance of species on aquaculture at both the farm and pond scale. Pond contents and characteristics influenced each species, including culture practices and surroundings. In all cases, the amount of aquaculture was positively related to species abundances. Pond and farm selection relationships were species-specific, illustrating inherent differences in their foraging ecology. Consequently, specific management actions will depend on the targeted species. We also found cormorant densities on aquaculture has not changed in the past 15 years, even though aquaculture has significantly declined. Second, we measured cormorant distribution between aquaculture and natural water bodies. The highest use of aquaculture occurred when producers were not allowed to use lethal control, whereas the lowest use occurred when producers could. This trend highlights the potential influence of mortality risk on cormorants' foraging distribution. Lastly, we examined cormorant dynamics at the regional scale using roosting data. We found the Midwest breeding population of cormorants has been increasing, but the abundance of cormorants wintering in Mississippi has been decreasing, suggesting aquaculture is the primary cause of inhabitation of the state. We also found the phenology of cormorant spring migration is occurring earlier each year. Aquaculture area had a positive influence on cormorant distribution at roosts particularly prior to migration. These findings suggest changes in agriculture, and potentially climate change, can influence phenology, distribution, and abundance of avian species at multiple scales.

Thesis (Ph.D. (Zoology)) -- University of the North, 1996 / Refer to document

The commercial production of channel catfish (Ictalurus punctatus) is major industry in Mississippi. Infections of channel catfish with the digenetic trematode Bolbophorus damnificus have often been associated with heavy economic losses in the industry. To efficiently control transmission of this trematode, the avian hosts need to be identified. In the first study, two American white pelicans, two double-crested cormorants, two great blue herons, and two great egrets were fed channel catfish infected with B. damnificus metacercariae. The presence of Bolbophorus damnificus ova in pelican feces at three days post infection (dpi) indicated the pelicans had patent infections. Mature B. damnificus were recovered from the intestines of both pelicans at 21 dpi. No B. damnificus infections were observed in the other bird species. In a second study, 33 American white pelicans, 34 double-crested cormorants, 35 great blue herons, and 32 great egrets were collected in the Mississippi Delta. The prevalence of B. damnificus in the American white pelican was 93.9%, with an average of 158 B. damnificus found per bird (range 0-681). Bolbophorus damnificus was not found in any of the other bird species. The results of these two studies confirm that the AWPE is the only proven natural host for B. damnificus. In a third study, two previously undescribed cercariae were found infecting rams-horn snails in commercial catfish ponds. In challenge studies, channel catfish were exposed to both cercariae types. Only one type of cercariae (type I) was infective to channel catfish. The first evidence of type I metacercariae was seen histologically at 14 dpi and grossly at 21 dpi. Development continued until 120 dpi, when both gross examination and histology suggested that the metacercariae were mature. The type I metacercariae appeared to cause little host damage. Molecular analysis of the 18S rRNA gene region indicated that the type I cercariae and metacercariae may be a species of Clinostomum. The data generated in these three studies provides additional information that can be used in the development of efficacious management schemes to control digenetic trematodes infecting commercial catfish.