Swimming energetics and thermal ecology of adult bonefish (Albula vulpes): a combined laboratory and field study in Eleuthera, The Bahamas

Knowledge of the swimming energetics and thermal ecology of sub-tropical and tropical coastal species is extremely limited, yet this information is critical for understanding animal–environment relationships in the face of climate change. Using the ecologically and economically important sportfish, bonefish (Albula vulpes), we determined the critical swimming speed (U_crit), metabolic rates (Formula presented.), scope for activity, and cost of transport (COT_net) across a range of temperatures using a swim tunnel. For both critical swimming speed and scope for activity, optimal (T_opt) and critical (T_crit) temperatures were determined. The optimal temperature for U_crit (96 cm/s) was 28.0 °C and the optimal temperature for scope for activity (7.5 mgO₂/min/kg) was 26.7 °C. We also estimated the thermal profile of bonefish in the wild using surgically implanted thermal loggers. Of the 138 implanted fish, eight were recaptured with functional loggers. After 220 days more than 55 % of recaptured tagged fish had expelled their thermal loggers. Thermal profiles revealed that bonefish did not exceed laboratory-determined critical temperatures (i.e., 14.5 °C minima and 37.9 °C maxima) and spent the majority of their time at their critical swimming speed optimal temperature. Nonetheless, fish experienced wide variation in daily temperature—both through time (up to 8 °C diel fluctuation and 14 °C seasonally) and among individuals. Collectively, laboratory and field data suggest that bonefish occupy habitats that approach, but rarely exceed (0.51 % of the time) their T_crit. Bonefish routinely experienced water temperatures in the field that exceeded their T_opt (~54 % of the time). Even minor increases in temperature (e.g., 1 °C) in tidal creeks will lead to greater exceedances of T_opt and T_crit or potentially reduce access of bonefish to essential feeding areas.