Talking to the dead: using Post-mortem data in the assessment of stress in tiger sharks (Galeocerdo cuvier) (Péron and Lesueur, 1822)

Abstract

Sharks are very sensitive to stress and prone to a high mortality rate after capture. Since approximately 50 million of sharks are caught as bycatch every year, and current recommendations to reduce the impact of commercial fishing strongly support immediate release, it is imperative to better understand post-release mortality caused by the stress of capture and handling. Blood samples allow the assessment of stress levels which are valuable tools to reduce mortality in commercial, recreational and scientific fishing, being essential for the improvement in those conservation measures. Biochemical analyses are widely used for sharks as stress indicators, with secondary plasma parameters (lactate, glucose and ions) being the most often employed assays. However, it is virtually impossible to determine baseline plasma parameters in free-ranging sharks, since blood withdrawal involves animal capture and restrain, which are stressful procedures. This study aims at analyzing secondary parameters of five healthy tiger sharks captured with circular hooks and handlines in Fernando de Noronha (Northeastern Brazil) and comparing them with secondary parameters of three dead tiger sharks caught off Recife (also Northeastern Brazil). The results showed that the analysis of some plasma constituents in dead animals may be an efficient tool to assess stress and lethality. However, traditional parameters such as glucose and calcium, need to be used with caution. The results also demonstrated the extreme importance of urea and phosphorus for assessing stress response and mortality in tiger sharks, both parameters frequently neglected and of utmost importance for shark's homeostasis.

Impacts of fisheries on elasmobranch reproduction: high rates of abortion and subsequent maternal mortality in the shortnose guitarfish

“…The comparison between groups (live females outside the reproductive period vs. females that survived after consecutive abortions vs. females that died after consecutive abortions) demonstrated that plasma urea, lactate, potassium, phosphorus and pH have significant alterations in the females that died. These results are consistent with loss of allostatic balance in elasmobranchs, condition closely related to stressful/lethal events (Brooks et al, 2012;Gallagher et al, 2014;Wosnick et al, 2017). Despite the changes in plasma concentrations of urea and lactate in the females that survived abortion when compared to the control group, it is probable that the allostatic balance was quickly reestablished or not even lost, allowing recovery even against such physical trauma.…”

“…Since post-mortem analysis can indicate when animals are reaching alarming conditions that may seriously compromise the ability for recovery (Wosnick et al, 2017), comparing females that aborted and survived with females that died after the phenomenon, may help to elucidate some of the physiological paths that are impaired during the stress caused by commercial capture and abortion. The comparison between groups (live females outside the reproductive period vs. females that survived after consecutive abortions vs. females that died after consecutive abortions) demonstrated that plasma urea, lactate, potassium, phosphorus and pH have significant alterations in the females that died.…”

“…To test for their physiological conditions, blood samples (0.5 mL) were obtained by caudal venipuncture using preheparinized syringes fitted with 26.5G needles from: (1) females that died after abortions in the laboratory along 48 h of monitoring (1 h after death to standardize blood collection), (2) females that survived after consecutive abortions in the laboratory along 48 h of monitoring, and (3) non-pregnant females also held for 48 h. To reduce handling stress that could lead to an even greater increase in mortality, only six females that survived after consecutive abortions had their blood collected. The post-mortem approach used in the present study aimed to set data from death animals as putative control/reference groups (Manire et al, 2001;Moyes et al, 2006;Wosnick et al, 2017). For statistical reasons, the same sample size was then established for both dead pregnant females and non-pregnant females (control group), totaling 18 animals sampled.…”

“…Consequently, even minor stressful stimuli may have inherent unpayable metabolic costs, as the resources allocated to fight stress reduce reproductive investment (Johnstone et al, 2000;French et al, 2007). Additionally, disturbances in the allostatic profile are closely related to high mortality rates and the inability to recover after facing stressful situations (Wosnick et al, 2017), which further reduces the chances of survival of bycatch species.…”

Challenges, pitfalls and surprises: development and validation of a monoclonal antibody for enzyme immunoassay of the steroid 1α-hydroxycorticosterone in elasmobranch species

“…Immediately prior to this exam, this female had a recent medical history (3 days), loss of appetite, lethargy and other behavior changes. Illness and injury can produce a state of altered homeostasis or allostatic load that has been associated with changes in glucocorticoids (see Romero 2004; Romero et al, 2009; Sapolsky et al, 2000 for a review), thus this sample was used as a high serum control or “reference sample” (Wosnick et al, 2017) in subsequent tests.…”