Pass the salt: physiological consequences of ecologically relevant hyposmotic exposure in juvenile gummy sharks (Mustelus antarcticus) and school sharks (Galeorhinus galeus)

Abstract

Estuaries are critical nursery grounds for juvenile sharks; however these shallow waters are susceptible to extreme fluctuations in salinity. We investigated the physiological effects of an ecologically relevant low saline exposure on two inshore juvenile shark species. School sharks had a more dramatic response, possibly influencing their distribution and abundance.

Influence of female reproductive state and of fishing‐capture stress on the oxygen uptake rate of a viviparous elasmobranch

“…Moreover, a reduced investment in maintenance of pregnancy might reduce the quality of the uterine environment due to the accumulation of toxic metabolites produced by the embryos that the mother cannot remove (Hamlett et al, 2005; Thibault & Schultz, 1978; Webb & Brett, 1972). We did not investigate recovery, but metabolic decline persisted for up to 24 h after osmotic stress in M. antarcticus and school sharks ( Galeorhinus galeus ; Morash et al, 2016; Tunnah et al, 2016) and up to 7 days after capture stress in C. milii (Finotto, 2021). Given the rapid development of T. dumerilii embryos (Marshall et al, 2007), even short‐term maternal energetic disruptions potentially severely impact embryonic development.…”

“…These animals realistically had enough time to recover from the mild stress associated with the additional respirometry confinement and this unlikely biased our results. To reduce the influence of food processing and digestion on animals' energetic load (Sims & Davies, 1994), ṀO 2 was measured at least 48 h after the last feeding event (Morash et al, 2016;Tunnah et al, 2016).…”

“…Pregnant females can survive severe capture stress (Finotto et al, 2021; Guida et al, 2017), but given the aforementioned maternal and neonatal consequences (Finotto et al, 2021; Guida et al, 2017), further investigations are needed. In the present study, we measured oxygen uptake rate ( Ṁ O 2 ), a proxy for aerobic energetic consumption (Bouyoucos et al, 2017, 2018; Clark et al, 2013; Cooke et al, 2014; Morash et al, 2016; Tunnah et al, 2016), to: (1) investigate the energetic impact of trawling‐capture simulation and air exposure on pregnant T. dumerili , verifying whether Ṁ O 2 measured in minimally stressed females differed from Ṁ O 2 measured in the same females immediately after capture stress; (2) estimate the oxygen requirements of sustaining late‐term pregnancy and embryonic respiration comparing the Ṁ O 2 measured in pregnant females with the Ṁ O 2 measured postpartum; (3) assess the energetic impact of capture stress in the context of the energetic requirements of pregnancy maintenance. Given the large energetic investment associated with pregnancy maintenance (Carrier et al, 2004; Hamlett et al, 2005; Parker et al, 1972; Trinnie et al, 2012), we expected to measure a significant decline in Ṁ O 2 after parturition.…”

Exercise intensity while hooked is associated with physiological status of longline-captured sharks

“…Gummy sharks were documented to remain stationary for ~90% of a longline capture event, such that blood pH (among other metrics) was not influenced by capture duration (Guida et al , 2016). The presence or absence of an effect of capture duration on blood pH in two sharks that rest during capture could be related to differences in metabolic rates; nurse sharks are estimated to have lower metabolic rates than gummy sharks at comparable temperatures (Skomal and Mandelman, 2012; Morash et al , 2016; Whitney et al , 2016). Therefore, nurse sharks appear to be quite resilient to stress.…”

Analysing tropical elasmobranch blood samples in the field: blood stability during storage and validation of the HemoCue® haemoglobin analyser

“…The HemoCue haemoglobin analyser has been used in studies spanning an array of fish species (e.g. Arnold, 2005; Clark et al, 2010; Raby et al, 2015; Ekström et al, 2016; Morash et al, 2016) and has been calibrated for use in teleost blood (Clark et al, 2008; Andrewartha et al, 2016), but has not yet been validated for use with elasmobranch blood. The HemoCue uses cuvettes coated with sodium deoxycholate, which lyses the RBCs, and sodium nitrite, which converts the haemoglobin to methaemoglobin.…”