Nonlethal Fin Clip Model Validation for Stable Isotope Analysis of Spotted Gar and Alligator Gar

Stable isotope analysis (SIA) can be a powerful tool for investigating trophic ecology and energy fluxes through an ecosystem. In fish, muscle tissue is generally preferred for SIA due to its intermediate turnover rate, even though sampling muscle is often lethal. Here, we evaluated the feasibility of a fin clip model using fin tissue as a nonlethal alternative to using muscle tissue for SIA (nitrogen, δ¹⁵N and carbon, δ¹³C) in Spotted Gar Lepisosteus oculatus and Alligator Gar Atractosteus spatula. We also investigated the effects of locality, age, and size of Spotted Gars on the robustness of the fin clip model. Muscle tissue plugs and fin tissue clips were collected from Spotted Gars (n = 104) and Alligator Gars (n = 16) at four localities in southeastern Louisiana in 2019. Both Spotted Gars and Alligator Gars showed strong positive Pearson’s correlations in δ¹⁵N and δ¹³C between the fin and muscle tissues, and a linear regression analysis confirmed that the correlations were significant (Spotted Gar; δ¹⁵N: R² = 0.88; δ¹³C: R² = 0.95, P < 0.001; Alligator Gar; δ¹⁵N: R² = 0.74; δ¹³C: R² = 0.94, P < 0.001). The fin clip model for Spotted Gar was affected by locality but not by size or age. Overall, our results suggest that fin tissue can be used as a nonlethal surrogate for muscle tissue for SIA for both Spotted Gars and Alligator Gars.