Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

The impacts of climate change on the physiology of school sharks in Southeast Tasmania (#8)

Katherine M Ollerhead 1 , David A Moreno 1 , Tyson J MacCormack 2 , Andrea J Morash 3 , Jayson M Semmens 1
  1. Institute for Marine and Antarctic Studies, University of Tasmania, Taroona, TAS, Australia
  2. Chemistry and Biochemistry, Mount Allison University, Sackville, New Brunswick, Canada
  3. Department of Biology, Mount Allison University, Sackville, New Brunswick, Canada

Due to strengthening wind systems that have driven the East Australian Current farther south, Tasmania is a climate change hotspot and is one of the world’s fastest warming marine regions. The Pittwater Estuary in the state’s southeast is part of a designated shark refuge area and the largest known Australian nursery for the ‘critically endangered’ school shark (Galeorhinus galeus), providing for high survival and growth of neonates before migration into deeper waters. However, the estuary experiences regular acute environmental variations during the summer/autumn period when sharks inhabit the area. This research aims to understand how acute changes in temperature and salinity impact the physiology of neonatal and juvenile school sharks, given that more-frequent extreme weather events are predicted under climate change scenarios. Captive animals were exposed for 48 h to conditions simulating both a hot/dry (22°C and 40‰) and a cold/wet (14°C and 25 ‰ salinity) summer/autumn followed by 24 h recovery. Blood samples were collected every 24 hours and haematocrit, haemoglobin, lactate and glucose, and plasma osmolality were measured. Oxygen consumption was also measured prior to experimentation, after 48 hours of acute exposure, and during recovery. Both simulated acute changes to hot/dry and cold/wet weather conditions elicited a physiological response for both life stages, with neonates generally more tolerant to the changes than juveniles. This suggests that neonates may have specialisations for inhabiting the estuary from birth until migration into deeper waters, which juveniles no longer possess. However, if these extreme events become more regular, as predicted, neonates may not be able to continue to tolerate the highly variable conditions, which may outweigh the benefits provided by the nursery. This could result in under-developed neonates moving into unprotected waters, which could have major implications for early life stage mortality and impact the recovery of this conservation dependant species.