Abstract:

This dataset contains the mean and 95% confidence limits for the proportion of dolphin diet made up of a variety of prey sources, including fish, cephalopods, and decapods. Results are presented separately for Barataria Bay, Louisiana, Sarasota Bay, Florida, and Dauphin Island/Mobile Bay, Alabama. The Stable Isotope Mixing Models in R (SIMMR) was used to determine the relative contribution of different prey species to the isotope signatures of northern Gulf of Mexico bottlenose dolphins (Tursiops truncatus). Skin samples were collected in 2018 from live dolphins in Barataria Bay, Louisiana, Sarasota Bay, Florida, and Dauphin Island, Alabama. They were also collected from dead, stranded dolphins near Barataria Bay, Louisiana (2011) and skin, muscle, and liver samples from dead, stranded dolphins near Mobile Bay, Alabama (2011, 2013-2015, 2017-2018). Prey samples (fish, crustaceans, cephalopods) were collected at each location and each year at sites from which dolphins were obtained (Barataria Bay: 2011, 2018; Mobile Bay: 2011, 2013-2015, 2017-2018). The isotope data from both the dolphin and prey tissues were used in the mixing models, and those data are available under GRIIDC Unique Dataset Identifier (UDI): R6.x809.000:0020 (DOI: 10.7266/n7-e5ry-ck72).

Suggested Citation:

Cloyed, Carl and Ruth Carmichael. 2021. Stable isotope mixing model estimates of common bottlenose dolphin (Tursiops truncatus) diets in the northern Gulf of Mexico from 2011 to 2018. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-4knr-kj95

Purpose:

To determine the relative contribution of different prey species to the isotope signatures of northern Gulf of Mexico bottlenose dolphins (Tursiops truncatus).

Data Parameters and Units:

Year [Year of capture or stranding]; Location [Capture or stranding location]; n_dolphins [Number of unique dolphins included in the analysis]; n_tracers [Number of isotopic tracers included in the analysis (3-carbon, nitrogen, sulfur; 2-carbon, nitrogen]; Tissue [Tissue that was sampled (skin, muscle, or liver)]; Status [Was dolphin sampled alive during a live capture-release health assessment, or were they sampled after stranding dead?]; Mean, low.Cl, and high. Cl [Proportion of diet made up by prey, according to mixing model results, Lower bound of the 95% credible interval for the proportion of the diet, and Upper bound of the 95% credible interval for the proportion of diet] for Anchovy, Ariidae (Barataria Bay only), Batrachoididae (Sarasota Bay only), Clupeidae (Mobile Bay only), Elopidae (Sarasota Bay only), Flounder (Barataria Bay only), Mugilidae (Sarasota Bay only), Perciformes, all fish, cephalopods, and decapods. Please note that the "Read.me" worksheet in the data file includes more detailed information, and ND means "No Data" and indicates those analyses were not performed. The samples were collected from the following locations: Dauphin Island, Alabama: 30.255508, -88.084946 Sarasota Bay, Florida: 27.3460, -82.5673 Barataria Bay, Louisiana: 29.3947, -89.9440

Methods:

The Stable Isotope Mixing Models in R (SIMMR package; Parnell A. 2016) was used to estimate the proportional dietary contributions for dolphins in Barataria Bay, Louisiana, Dauphin Island, Alabama, and Sarasota Bay, Florida. Carbon, nitrogen, and in some cases sulfur were estimated in these mixing models. These mixing models include isotope values from prey samples, which were obtained at each site. Trophic discrimination factors for skin were averaged from literature (Wilson et al., 2014; Giménez et al., 2017). Trophic discrimination factors for muscle and liver were taken from fin whales (Balaenoptera physalus), which was the phylogenetically and ecologically most similar species to common bottlenose dolphins for which this information was available (Borrell, Gómez-Campos & Aguilar 2016). We iterated the mixing model 20,000 times with a burn-in of 2,000.

Provenance and Historical References:

Borrell, A., Gómez-Campos, E., & Aguilar, A. (2016). Influence of Reproduction on Stable-Isotope Ratios: Nitrogen and Carbon Isotope Discrimination between Mothers, Fetuses, and Milk in the Fin Whale, a Capital Breeder. Physiological and Biochemical Zoology, 89(1), 41–50. doi:10.1086/684632 Giménez, J., Ramírez, F., Forero, M. G., Almunia, J., de Stephanis, R., & Navarro, J. (2017). Lipid effects on isotopic values in bottlenose dolphins (Tursiops truncatus) and their prey with implications for diet assessment. Marine Biology, 164(6). doi:10.1007/s00227-017-3154-5 Parnell, A. (2016). SIMMR, A Stable Isotope Mixing Model. R package Version 0.3. Available online at: https://cran.r-project.org/web/packages/simmr/ Wilson, R. M., Chanton, J. P., Balmer, B. C., & Nowacek, D. P. (2013). An evaluation of lipid extraction techniques for interpretation of carbon and nitrogen isotope values in bottlenose dolphin (Tursiops truncatus) skin tissue. Marine Mammal Science, 30(1), 85–103. doi:10.1111/mms.12018

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