Impact of conspecific necromones on the oxygen uptake rates of a benthic elasmobranch

Abstract

Given the vulnerability of early life stages to predation, many species elicit antipredator responses to predator-associated cues (e.g. alarm cues, necromones). However, the response used may vary between predatory stimuli. Antipredator responses, while ostensibly enhancing survival, are costly, either resulting in missed opportunities (e.g. foraging) through decreased activity and crypsis strategies (i.e. predator avoidance) or incurring high energetic costs through the use of generalized stress responses and increased activity (i.e. predator evasion). Juvenile Port Jackson sharks, Heterodontus portusjacksoni, were exposed to the scent of dead conspecifics (conspecific necromones) coupled with a simulated predator chase to determine the energetic effects of a predator ‘attack’. When exposed to necromone cues alone, juvenile sharks depressed their oxygen uptake rates for up to 3 h following exposure, indicating that they used crypsis to avoid detection by predators. However, when forced to swim and evade a predator, sharks increased their oxygen uptake rates, regardless of whether or not they were exposed to predatory cues. Juvenile sharks exposed to conspecific necromones may primarily rely on strategies that depress activity to avoid detection by predators; however, if forced to evade capture they use energetically costly escape strategies similar to typical ‘fight or flight’ responses.