Seasonally acclimated metabolic Q10 of the California horn shark, Heterodontus francisci

Dynamic environmental thermal conditions are known to affect physiological processes in ectothermic organisms that may influence movement, distribution and energetic costs. A better understanding of their metabolic Q10, temperature sensitivity, is needed in order to make realistic predictions about how some nearshore populations may respond to changing oceanographic conditions. Oxygen consumption was used as a proxy to measure acclimated standard metabolic rates (SMR) of the California horn shark (Heterodontus francisci) at four temperatures (14°, 16°, 20° and 22 °C) typically experienced throughout an annual cycle. Sharks were acclimated in a large holding tank at each of the desired temperatures for at least two weeks prior to the trial. All individuals tested were juveniles, ranging in size from 37 to 48 cm TL and weights of 0.41-0.94 kg. Respirometry trials ranged in length from 6 to 14 h. The estimated (±SE) resting ṀO2 (mg O2 kg−1 h−1) of the CA horn shark at each temperature treatment was 30.6 ± 3.4 (14°, n = 4), 33.9 ± 2.3 (16°, n = 10), 44.9 ± 2.4 (20°; n = 9) and 57.9 ± 2.7 (22 °C; n = 3). The metabolic Q10 of the CA horn shark from 14° to 22 °C is 2.01, providing a metric to generate predictive models to estimate minimum metabolic costs associated with changing thermal regimes and global sea temperature rise. Predictions from our model indicate during years 2012 to 2016, rising sea surface temperature associated with a strong El Niño Southern Oscillation (ENSO) event resulted in a 23% increase in minimum metabolic costs for the CA horn shark. The results from our model suggest the CA horn shark may need to adapt compensatory behaviors (e.g., behavioral thermoregulation) to cope with ENSO events and climate change.