Many conservation-minded fisheries management policies seek to reduce the number of landed individuals. While these regulations have the potential to be extremely effective, they can also result in the release of many individuals, some of which later succumb to the stress of capture. Evaluating and understanding the drivers of post-release mortality is of particular importance in elasmobranch species due to their general vulnerability to fishing pressure. High levels of plasma potassium (hyperkalemia) and acidosis following capture are often thought to be indicative of post-release mortality. However, while hyperkalemia is known to disrupt cardiac function in other vertebrates, this has yet to be evaluated in elasmobranch fishes. To investigate this link, isolated cardiac strip performance was measured under hyperkalemic (7.4 mM K+), acidotic (a pH decline of 0.26 units), hypoxic, and acute temperature (+/- 5° C) challenges. The ability of adrenaline to ameliorate negative effects of simulated capture stress was also assessed. Cardiac strips were harvested from three phylogenetically disparate (but sympatric) species from the coastal Mid-Atlantic: clearnose skate (Rostraja eglanteria), smooth dogfish (Mustelus canis), and sandbar shark (Carcharhinus plumbeus). Our data demonstrate hyperkalemia has a detrimental impact on cardiac function in elasmobranchs, which likely impairs cardiac function post-capture when high cardiac output is necessary. Our results also imply that future work attempting to use at-vessel blood chemistry measurements to assess post-release mortality should consider the ability of individual species to invoke an adrenaline response before assuming hyperkalemia alone is indicative of mortality.
Gail Schwieterman is originally from the United States, where she obtained a Bachelor’s degree in Biology from Oberlin College. After working as a contractor for Mote Marine Laboratory in Sarasota, FL, she started her PhD at the Virginia Institute of Marine Science where she is currently working with Dr. Richard Brill on the physiological impacts of multivariate stressors. She is a National Science Foundation Graduate Research Fellow, and is active in her institution’s Academic Council and the Diversity and Inclusion Committee. She is currently working in the Rummer Lab to understand the mechanisms of red blood cell swelling in elasmobranch fishes.