Oral Presentation Australian Society of Fish Biology and Oceania Chondrichthyan Society Conference 2016

Too hot to handle? The use of movement by a benthic elasmobranch species, Hemiscyllium ocellatum, to aleviate effects of elevated temperature. (#117)

Connor Gervais 1 2 , Tiffany Nay 1 3 , Gillian Renshaw 4 , John Steffensen 5 , Jacob Johansen 6 , Jodie Rummer 1 3
  1. ARC Center of Excellence, James Cook University, Townsville, QLD, Australia
  2. Macquarie University, Sydney, NSW, Australia
  3. College of Marine and Environmental Sciences, James Cook University, Townsville, QLD, Australia
  4. Griffith University, Nathan, QLD, Australia
  5. University of Copenhagen, Helsingor, Denmark
  6. Department of Marine Science, University of Texas, Port Aransas, Texas, United States

Epaulette sharks, Hemiscyllium ocellatum, occupy shallow reef flats that can experience relatively large variations in daily and seasonal temperatures. For example, some coral reef flats can experience temperatures that are 3-4°C warmer than surrounding habitats on a daily basis. However, epaulette sharks may have evolved behavioural and/or physiological strategies to mitigate the effects of elevated temperatures, which will be important to their survival with climate change projections. We used a shuttle-box system to examine whether juvenile sharks that are exposed to current day summer and winter temperatures as well as predicted end-of-century temperatures use movement to maintain their body temperatures. We also examined the influence of temperature on growth and food consumption. We found that juvenile epaulette sharks showed a seasonally-dependent tendency to thermoregulate. During winter, when maximal habitat temperatures are far below lethal limits, individuals showed no thermoregulatory behaviour. However, during summer, when maximum temperatures may approach lethal limits, juveniles actively sought to limit thermal exposure to 30.7± 1.04°C during the day and 28.54± 0.75°C at night. Similarly, individuals acclimated to predicted end-of-century conditions (32°C), actively sought out 32.94± 0.46°C during the day and 30.74± 0.68°C at night. Regardless of acclimation temperature, juveniles maintained the same food consumption rates (5% of their body mass), but this resulted in decreased growth rates (mass and total length) in sharks living at 32°C. Although behavioural thermoregulation may be a trait with some capacity for acclimation, overall, this species experienced a clear reduction in growth and eventual mortality at temperatures just +3°C above summer averages. Within one generation, physiological and biochemical acclimation may be more costly than movement, and therefore the latter may be a valid strategy for this species to avoid extreme temperatures during summer months. As water temperatures continue to rise, it is important to consider that the distribution and abundance patterns for epaulette sharks and many other coral reef species may change.