We research and monitor the bottlenose dolphins of Galveston Bay, Texas primarily by carrying out monthly boat-based surveys. Using dorsal fin photo-identification methods, we are able to learn about individual dolphins. Additionally, we conduct exploratory surveys, remote biopsy sampling, and acoustic monitoring.
The core field program activity of the GDRP is monthly standardized boat-based surveys in upper Galveston Bay. Taking 2-3 days, the team surveys the entire primary study area to record dolphin sightings and environmental conditions. Observers take photographs of dolphins’ dorsal fins that facilitate individual identification. These data are analyzed to answer a variety of questions, including those pertaining to distribution, habitat use, demographics and skin lesions. The team also conducts opportunistic and exploratory surveys outside the primary study area.
Distribution and Habitat Preferences
A research priority since inception of the GDRP has been to determine when dolphins use upper Galveston and if they show habitat preferences within the estuary. By analyzing monthly encounter rates, we are exploring seasonal distribution patterns and evaluating if and when dolphins use nearshore, channel, and open bay habitats.
Individual bottlenose dolphins exhibit varying levels of site fidelity to our primary study area in upper Galveston Bay. To date, we have categorized individuals within the population as belonging to one of three groups depending on their affinity to upper Galveston Bay: year-round and seasonal residents (return annually), temporary residents, and transients (Fazioli et al. 2017). By collaborating with other photo-identification programs in Texas to compare individual dolphin ranging patterns and submitting our fin catalog to the Gulf of Mexico Dolphin Identification System (GoMDIS), we are working to broaden our understanding of how dolphins use Galveston Bay and the surrounding regions.
Texas estuary systems are highly influenced by freshwater runoff, and dolphins in Galveston Bay are exposed to prolonged low-salinity conditions. Bottlenose dolphins are physiologically adapted to inhabit waters with salinities that range from 18 – 35 ppt. They conserve freshwater through osmoregulation and are subject to negative health consequences and even death due to prolonged exposure to low salinity environments (< 10 ppt). In addition to electrolyte imbalances resulting in changes to blood chemistry, increased water absorption in low salinity environments may contribute to the development of “freshwater skin lesions” characterized by degradation and ulceration of the epidermis, often accompanied by secondary infections. The GDRP has documented the development of skin lesions following several freshwater inflow events since 2015. For example, dolphins utilizing upper Galveston Bay were exposed to very low salinity levels during the flood event associated with Hurricane Harvey in 2017; while some dolphins appeared to shift distribution following the hurricane, others remained in the area and exhibited extensive freshwater skin lesions (Fazioli and Mintzer 2020). Further understanding the consequences of freshwater exposure on dolphins in Galveston Bay remains a high priority.
Dolphins residing within industrial coastal regions carry increased toxin loads and are subject to adverse effects on reproduction, endocrine function, and immune function. Galveston Bay has a history of industrial contamination including polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides, and heavy metals. Seafood consumption advisories issued by the Department of State Health Services are currently in effect within the estuary. The San Jacinto River Waste Pits Superfund Site is implicated as a source of dioxins in upper GB. Analyses of remote biopsy tissue samples for persistent organic pollutants (POPs) are in progress in collaboration with the NOAA Marine Mammal Health and Stranding Response Program and plans for separate analyses for dioxins are underway.
Genetics and Stock Delineation
Data to support fine-scale characterization of most Texas bottlenose dolphin stocks remains insufficient to delineate biologically significant boundaries or to determine population abundance trends. Analyses of remote biopsy tissue samples from the Galveston Bay estuary for genetic markers are currently underway in collaboration with the NOAA Southeast Fisheries Science Center (SEFSC) Marine Mammal Genetics Program. Results will be compared to genetic samples collected in other parts of Texas.
One of the most important factors affecting bottlenose dolphin movement patterns and habitat preferences is the spatial and temporal distribution of prey resources. Survey data and stable isotope analysis of dolphins and fishes are being use to identify preferences in prey and foraging habitats.
Publications and Presentations
Mintzer, V. & Fazioli, K. Seasonal encounter rates of bottlenose dolphins (Tursiops truncatus) in upper Galveston Bay, TX. IN PREP
Fazioli, K. & Mintzer, V. (2020). Short-term Effects of Hurricane Harvey on Bottlenose Dolphins (Tursiops truncatus) in Upper Galveston Bay, TX. Estuaries and Coasts 43: 1013-1031. https://doi.org/10.1007/s12237-020-00751-y. https://rdcu.be/b4mY7
Fazioli, K., Mintzer, V., & Guillen, G. (2020). Monitoring bottlenose dolphins in Galveston Bay, Texas. Galveston Bay Estuary Program, State of the Bay Symposium, Galveston, TX. Presentation.
Fazioli, K., Mintzer, V., & Guillen, G. (2019). In the path of floodwaters: short-term effects of Hurricane Harvey on bottlenose dolphins (Tursiops truncatus) in upper Galveston Bay, Texas. World Marine Mammal Conference, Barcelona, Spain. Presentation.
Mintzer, V., Fazioli, K., & Guillen, G. (2018). Short-term effects of Hurricane Harvey on dolphins in the upper Galveston Bay Estuary. 9th National Summit on Coastal and Estuarine Restoration and Management, Long Beach, CA.
Fazioli, K., Mintzer, V., & Guillen, G. (2017). Site fidelity of bottlenose dolphins (Tursiops truncatus) in a highly-industrialized estuary. Society for Marine Mammalogy, 22nd Biennial Conference on the Biology of Marine Mammals, Halifax, NS, Canada.
Fazioli, K., Mintzer, V., Guillen, G., & Loe, S. (2016). Texas’ estuarine bottlenose dolphins: addressing knowledge gaps in Galveston Bay. In Restore America’s Estuaries, New Orleans, LA.
Fazioli, K., Mintzer, V., & Guillen, G. (2015). An apparent increase in bottlenose dolphins in upper Galveston Bay: city slickers or tourists? Gulf of Mexico Marine Mammal Research and Monitoring Meeting, New Orleans, LA.
Fazioli, K., Mintzer, V., & Guillen, G. (2015). Bottlenose dolphin activity in a highly industrialized region of Galveston Bay, Texas. Society for Marine Mammalogy, 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, CA.
Loe, S., Fazioli, K., & Guillen, G. (2015). Observations on the occurrence and distribution of bottlenose dolphins (Tursiops truncatus) in upper Galveston Bay. Texas Bays and Estuaries Meeting, Corpus Christi, TX.