Galveston Bay Dolphin Research Program
We conduct scientific research and monitoring of bottlenose dolphins in Galveston Bay, Texas. Using dorsal fin photo-identification methods during monthly boat-based surveys, we are able to learn about individual dolphins. Additionally, we conduct exploratory surveys, remote biopsy sampling, and acoustic monitoring to increase understanding of this population.
Long-Term Dolphin Population 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.
Current Research Projects/Questions
Distribution and Habitat Preferences
A research priority since inception of the GDRP has been to determine when dolphins use upper Galveston Bay and if they show habitat preferences within the estuary. By analyzing monthly encounter rates (Mintzer and Fazioli 2021), 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 (Mintzer et al. 2022). 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. McDaniel (2022) integrated survey data and stable isotope analysis of dolphins and fishes to identify preferences in prey and foraging habitats. Continued efforts to explore foraging ecology will focus on dolphin interactions with commercial shrimp trawlers in addition to distribution and movements of prey fish in the Galveston Bay estuary.
Mintzer, V. J., Quackenbush, A., & Fazioli, K. L. (2022). Site fidelity of common bottlenose dolphins (Tursiops truncatus) in a highly industrialized area of the Galveston Bay estuary. Marine Mammal Science, 1– 18. https://doi.org/10.1111/mms.12984
Mintzer, V. J. and K. L. Fazioli (2021). Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops truncatus) Encounter Rates in Upper Galveston Bay, Texas. Frontiers in Marine Science 8(1627). https://doi.org/10.3389/fmars.2021.754686
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. (2022). Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops Truncatus) Encounter Rates in Upper Galveston Bay, Texas. Society for Marine Mammalogy, 24th Biennial Conference on the Biology of Marine Mammals, Palm Beach, Florida. Poster.
Fazioli, K.L. and Mintzer, V.J. (2022). Effects of salinity on distribution and epidermal integrity of bottlenose dolphins (Tursiops truncatus) in Galveston Bay, Texas. Texas Academy of Science, 125th Annual Meeting, Houston, TX. Presentation.
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.
McDaniel, S. and Guillen, G.J. (2020). Foraging ecology of bottlenose dolphins (Tursiops truncatus) in Galveston Bay. Galveston Bay Estuary Program, State of the Bay Symposium, Galveston, TX. Poster.
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. Poster.
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. Poster.
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. Poster.
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. Poster.
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. Poster.
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. Poster.