Behavioral Release Condition Score of Bull and Bonnethead Sharks as a Coarse Indicator of Stress

Capture and handling stress can induce acidosis and sometimes mortality in sharks. To approximate physiological condition after capture, fisheries researchers may use a behavioral health assessment at release. The goal of this study was to assess the efficacy of the behavioral release condition score (BRCS) in estimating the physiological stress response. The score was tested against changes in acid-base, blood gas, and metabolite analytes (pH, partial pressure of CO2, and lactate) and factors known to influence those analytes (species, capture and handing time, and water temperature) among wild-caught bull (Carcharhinus leucas) and bonnethead (Sphyrna tiburo) sharks. After gill net capture, sharks were processed for tagging, morphometrics, and blood sampling. Blood was sampled immediately before release. At release, a BRCS was assigned as good, fair, poor, or moribund. BRCS was modeled as a response to changes in blood analytes and putative stressors using ordinal logistic regression (OLR). Effects of significant main factors were further explored graphically and in chi-square tests or (multivariate) analyses of variance (MANOVAs/ANOVAs). Linear discriminant analyses with cross-validation were used to assess the ability of those factors to discriminate among BRCS on a case-by-case basis. The OLR models suggest that BRCS responds in species-specific ways to all three blood analytes and putative stressors. However, the broad overlaps in ranges of these parameters among BRCS lend prediction of BRCS by either of these two sets of predictors to be challenging to utilize. Given the coarse relationship of BRCS to acid base status in these species, further investigation of this and other behavioral assessment methods is recommended.