Quantifying euryhaline histories in red drum Sciaenops ocellatus: otolith chemistry and muscle isotope ratios

The combined use of otolith chemistry and tissue isotopes has the potential to reveal movements, habitat associations and food web interactions at a variety of spatial and temporal scales. Here, a combination of otolith Ba:Ca life-history transects with muscle tissue δ¹³C and δ¹⁵N values has been used to assess habitat use and oligohaline residence in red drum Sciaenops ocellatus in subtropical estuaries in the north-western Gulf of Mexico. Tissue isotopes were distinct among capture locations, particularly between bays with differing proximities to freshwater inflow sources. Otolith edge Ba:Ca values and tissue δ¹³C values were not correlated. These results indicated that fish were neither residing in nor feeding in oligohaline waters for significant periods of time within the tissue turnover window of several months prior to capture. Nonetheless, spatial differences in tissue isotope values indicated limited mixing among bays and relatively high site fidelity during estuarine occupancy. Lifetime otolith Ba:Ca transects revealed individual variability in the magnitude of residence in oligohaline waters. Using a mean oligohaline occupancy threshold, an estimated 82% of individuals used oligohaline waters at some point in their life. Nonetheless, 66% of individuals spent <20% of their life histories in oligohaline waters, suggesting intermittent and infrequent excursions into low salinity waters. Finally, a literature survey identified 56 peer-reviewed publications using combinations of otolith chemistry and tissue stable isotope ratios with a wide range of marker pairings and study aims. The diversity of ecological questions that can be asked with the combined use of these two approaches will provide valuable insight into fish ecology.