Stable isotope ratios from northern Gulf of Mexico bottlenose dolphins (stranded and capture-release animals) and their prey (fish and crustaceans) from 2011-2018
Funded By:
Gulf of Mexico Research Initiative
Funding Cycle:
RFP-VI
Research Group:
Consortium for Advanced Research on Marine Mammal Health Assessment (CARMMHA)
Ryan Takeshita
National Marine Mammal Foundation
ryan.takeshita@nmmpfoundation.org
common bottlenose dolphin, Tursiops truncatus, stable isotopes, prey, Farfantepenaeus aztecus, Anchoa mitchilli, Micropogonias undulatus, Brevoortia patronus, Lolliguncula brevis, CN ratios, skin, muscle, liver
Abstract:
We compared dolphin skin stable isotope ratios and dolphin prey stable isotope ratios. In parallel with bottlenose dolphin capture-release health assessments, we used otter trawls in Barataria Bay, LA and Mobile Bay, AL and seine netting in Sarasota Bay, FL to catch bottlenose dolphin fish and crustacean prey. We also aggregated historical samples from 2011-2018 of stranded dolphins and previous trawling efforts for fish and crustaceans. Dolphin samples included skin for live captured animals and liver, skin, and muscle for stranded animals; fish samples included muscle; crustaceans included tissue slurries or just tissue. We used these data to run stable isotope analyses comparing isotopic ratios in dolphins over time to determine if and how their diets may have shifted in relation to the DWH oil spill. Update 01202021: We added two new worksheets to this dataset that includes stable carbon and nitrogen isotopes of dolphin skin samples from several sites in Florida (Dolphin.samples.FL) that were collected between 2004 and 2008 and from Barataria Bay, LA in 2011 and 2013 and Mississippi Sound, MS in 2011 as part of a National Resource Damage Assessment after the DWH oil spill (Dolphin.samples.NRDA).
Suggested Citation:
Carl Cloyed, Brian Balmer, Lori Schwacke, Teresa Rowles, Randall Wells, Cynthia Smith, Mandy Tumlin, Eric Zolman, and Ruth Carmichael. 2021. Stable isotope ratios from northern Gulf of Mexico bottlenose dolphins (stranded and capture-release animals) and their prey (fish and crustaceans) from 2011-2018. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-e5ry-ck72
Purpose:
We used these data to run stable isotope analyses comparing isotopic ratios in dolphins over time to determine if and how their diets may have shifted in relation to the DWH oil spill.
Data Parameters and Units:
Worksheet Column.header Description Dolphin.samples.FL ID Unique identifier for each dolphin sampled from Florida locations Dolphin.samples.FL Location Capture location Dolphin.samples.FL Sub.location The area within the above location where dolphin was captured Dolphin.samples.FL Date Date dolphin was captured Dolphin.samples.FL Year Year of capture Dolphin.samples.FL Condition Dolphins were either sampled during a capture-release health assessment (Alive) Dolphin.samples.FL Tissue What tissue was sampled? (skin) Dolphin.samples.FL d13C delta carbon-13 isotopic value (the ratio between 13C:12C in parts per thousand) Dolphin.samples.FL d15N delta nitrogen-15 isotopic value (the ratio between 15N:14N in parts per thousand) Dolphin.samples.NRDA ID Unique identifier for each dolphin sampled from Barataria Bay, LA or Mississippi Sound, MS in 2011 and 2013 Dolphin.samples.NRDA Location Capture location (Barataria Bay, LA or Mississippi, MS) Dolphin.samples.NRDA Sub.location The area within the above location where dolphin was captured Dolphin.samples.NRDA Year Year of capture Dolphin.samples.NRDA Condition Dolphins were either sampled during a capture-release health assessment (Alive) Dolphin.samples.NRDA Tissue What tissue was sampled? (skin) Dolphin.samples.NRDA d13C delta carbon-13 isotopic value (the ratio between 13C:12C in parts per thousand) Dolphin.samples.NRDA d15N delta nitrogen-15 isotopic value (the ratio between 15N:14N in parts per thousand) Dolphin.samples.CARMMHA ID Unique identifier for each dolphin sample in either Barataria Bay, LA or Mobile Bay, AL Dolphin.samples.CARMMHA Location Capture or stranding location (Barataria Bay, LA or Mobile Bay, AL) Dolphin.samples.CARMMHA Date Date dolphin was captured or found stranded Dolphin.samples.CARMMHA Year Year of capture or stranding Dolphin.samples.CARMMHA Condition Dolphins were either sampled during a capture-release health assessment (Alive) or dolphins were sampled after stranding (Dead) Dolphin.samples.CARMMHA Tissue What tissue was sampled? (skin, muscle, or liver) Dolphin.samples.CARMMHA d13C delta carbon-13 isotopic value (the ratio between 13C:12C in parts per thousand) Dolphin.samples.CARMMHA C_Amount Amount of carbon in sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer (µg) Dolphin.samples.CARMMHA d15N delta nitrogen-15 isotopic value (the ratio between 15N:14N in parts per thousand) Dolphin.samples.CARMMHA N_Amount Amount of nitrogen in sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer (µg) Dolphin.samples.CARMMHA CN_Ratio Ratio between C_Amount:N_Amount (carbon:nitrogen) Dolphin.samples.CARMMHA d34S delta sulfur-34 isotopic value (the ratio between 34S:33S in parts per thousand) Dolphin.samples.CARMMHA per_S Percent of sulfur in sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer (µg) Prey.samples ID Unique identifier for each prey sample Prey.samples Species Scientific name of fish, crustacean, or cephalopod Prey.samples Common_name Common name of fish, crustacean, or cephalopod Prey.samples Year Year sample was collected Prey.samples Month Month sample was collected Prey.samples Date Date sample was collected (m/d/y) Prey.samples Lat Latitude of sampling location Prey.samples Long Longitude of sampling location Prey.samples Region Region where sample was collected (MB: Mobile Bay, BB: Barataria Bay, SB: Sarasota Bay) Prey.samples Site Trawl location descriptor within region Prey.samples Number_ind Number of individuals pooled for the sample Prey.samples d13C delta carbon-13 isotopic value (the ratio between 13C:12C in parts per thousand) Prey.samples C_Amount Amount of carbon in sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer (µg) Prey.samples d15N delta nitrogen-15 isotopic value (the ratio between 15N:14N in parts per thousand) Prey.samples N_Amount Amount of nitrogen in sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer (µg) Prey.samples CN_Ratio Ratio between C_Amount:N_Amount (carbon:nitrogen) Prey.samples d34S delta sulfur-34 isotopic value (the ratio between 34S:33S in parts per thousand) Prey.samples per_S Percent sulfur in the sample. Calculated with a PDZ Europa ANCA-GSL elemental analyzer
Methods:
We collected dolphin skin samples for stable isotope analysis during dolphin health assessments at Sarasota Bay, Florida in June 2018, Barataria Bay, LA in July 2018, and Dauphin Island in September 2018. Skin samples were obtained using 8 mm coring tool from the dorsal fin or as part of a surgical biopsy wedge from each captured dolphin. Samples were stored at -20 C prior to sample processing. We also examined multiple tissues (liver, skin, muscle) from dolphins that stranded dead along the Alabama coast from the Alabama Marine Mammal Stranding Network. We randomly selected 30 dolphins that had stranded in 2011, 2013 – 2015, and 2017 – 2018 (n = 5 from each year): 2011 (all tissues n = 5), 2013 (liver: n = 4; skin: n = 5; muscle: n = 3), 2014 (liver: n = 2; skin: n = 5; muscle: n = 5), 2015, 2017, and 2018 (all tissues = 5). We randomly selected archived skin samples from dolphins that stranded in Barataria Bay in 2011 (n = 4), 2013 (n = 5), and 2014 (n = 5) that we obtained from the Louisiana Department of Wildlife and Fisheries. We also randomly selected archived skin samples of dolphins that had been dart-biopsied in Barataria Bay in 2011 (n = 6), 2013 (n = 6), 2014 (n = 6), and 2017 (n = 12) that we obtained from the National Institute of Standards and Technology (NIST). We collected prey samples (fish, decapods, cephalopods) at all three northern GoM study sites (Sarasota Bay, FL, Barataria Bay, LA, and Dauphin Island, AL). We collected prey samples in Barataria Bay during July 2018 from four locations using an otter trawl (4.6 m wide, 3.8 cm mesh). In Dauphin Island we collected prey samples from two locations during July 2011, 2013 – 2015, and 2017 – 2018 using an otter trawl (7.6 m long, 3.8 cm mesh). We also trawled around Dauphin Island during October 2018 at four locations using an otter trawl (4.9 m wide, 3.8 cm mesh). Trawls from both Barataria Bay and Dauphin Island were pulled at ~2 km h-1 for 20 minutes and if insufficient amount of prey were captured, the trawl was repeated. Prey samples in Sarasota Bay were collected during July 2018 from 10 locations by purse seine (183 m x 6.6 m). Dolphin and prey samples were both prepped before stable isotope analysis. For all dolphin skin samples, we separated blubber from the skin. All dolphin tissues (liver, muscle, and skin) were rinsed in UP water prior to lipid extraction (Cloyed et al. in press), using a Folch technique (Sweeting, Polunin & Jennings 2006). Samples were placed in 2 mL UP water and homogenized with a handheld rotor-stator. 6 mL of 2:1 chloroform:methanol solution were then added, the samples were sonicated for 5 mins, and centrifuged for 10 mins at 3353 g0. The supernatant was removed, and the process was repeated until the supernatant was clear (2-4 repetitions). Samples were dried at 60 C for 48 hrs and packed into tin capsules for isotope analysis. For prey samples, we dissected muscle from fish and decapods, and mantle tissue from cephalopods. All prey samples were rinsed with UP water, dried at 60 C for 48 hrs, homogenized with mortar and pestle, and packed into tin capsules for isotope analysis. Carbon and nitrogen analyses were performed at the Stable Isotope Facility of University of California at Davis, and sulfur analyses were performed at the Stable Isotope Core Laboratory, Washington State University. Isotopic values were expressed using the standard delta notation in parts per thousand (‰) calculated by (Rsample / Rstandard – 1) x 1,000, with Rsample and Rstandard representing the molar ratios of C13/C12, N15/N14, and S34/S33 of the sample and standard reference material, respectively. The reference material was Vienna-Pee Dee belemnite for carbon, atmospheric N2 for nitrogen, and Vienna Cañon Diablo trolite for sulfur. Repeated analysis of in-house reference materials (bovine liver, glutamic acid, and nylon 6 for C and N; repeated analyses of identical samples for S) showed that precision (SD) was 0.08‰, 0.07‰, and 0.15‰ for carbon, nitrogen, and sulfur, respectively.
Provenance and Historical References:
Cloyed, C.S., DaCosta, K.P., Hodanbosi, M.R. & Carmichael, R.H. (2020) The effects of lipid extraction on δ13C and δ15N values and use of lipid-correction models across tissues, taxa, and trophic groups. Methods in Ecology and Evolution, n/a. Sweeting, C., Polunin, N. & Jennings, S. (2006) Effects of chemical lipid extraction and arithmetic lipid correction on stable isotope ratios of fish tissues. Rapid Communications in Mass Spectrometry: An International Journal Devoted to the Rapid Dissemination of Up‐to‐the‐Minute Research in Mass Spectrometry, 20, 595-601.
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