Dataset: Stable isotope compositions (carbon, nitrogen, and sulfur) of muscle tissue in three species of fish from the Matagorda Bay region of Texas in the northwestern Gulf of Mexico from 2021 to 2023

Fish collection locations and associated information are found in an accompanying dataset for this project: https://www.bco-dmo.org/dataset/916418.

Fish carcasses were obtained from anglers at boat docks, fish cleaning stations, or other locations in the region. Fish were also obtained from bait shops where the proprietors verified the fish were sourced from the Matagorda Bay study region. These fish will be dissected to subsample white muscle tissue from each fish (skin and scales removed). Fish muscle tissue was dehydrated, pulverized to a fine powder, and packed into individual tin capsules for stable isotope analyses. All isotope analyses were conducted at the University of California, Davis Stable Isotope Facility. Analytical methods follow those described by Walther & Torrance (2024) and Valenza et al. (2025).

Additional text describing methods below are from https://stableisotopefacility.ucdavis.edu/

Samples were analyzed for 13C and 15N isotopes using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). Samples are combusted at 1000 degrees Celsius (°C) in a reactor packed with chromium oxide and silvered copper oxide. Following combustion, oxides are removed in a reduction reactor (reduced copper at 650°C). The helium carrier then flows through a water trap (magnesium perchlorate and phosphorous pentoxide). N2 and CO2 are separated on a Carbosieve GC column (65°C, 65 milliliters per minute (mL/min)) before entering the IRMS. During analysis, samples are interspersed with several replicates of at least four different laboratory reference materials. The long-term standard deviation is 0.2 ‰ for 13C and 0.3 ‰ for 15N. The final delta values, delivered to the customer, are expressed relative to international standards VPDB (Vienna Pee Dee Belemnite) and Air for carbon and nitrogen, respectively.

Stable isotope ratios of 34S in solid samples are measured using an Elementar vario ISOTOPE cube interfaced to an Isoprime PrecisION IRMS (Cheadle Hume, Stockport, UK). Samples are combusted at 1000°C in a reactor packed with tungsten oxide and elemental copper. Immediately following combustion, sample gases are reduced with elemental copper at 900°C and subsequently pass through a buffering reactor filled with quartz chips held at 900°C. SO2 and CO2 are then separated by purge and trap, allowing for full separation and peak focusing. Following separation, the SO2 adsorption trap is heated and the sample SO2 passes directly to the IRMS for measurement.

During analysis, samples are interspersed with replicates of several laboratory reference materials to monitor and allow for correction of any potential variation in drift and linearity. Final 34S delta values are obtained after adjusting the provisional measurements such that correct 34S delta values for laboratory quality assurance materials are obtained. The long-term reproducibility of this method is ± 0.4 ‰.