Embryonic sharks grow within external cases that are often translucent. In response to signs of predators, the embryos of several shark species become motionless (or “freeze”). The amount of time that they can remain still is limited by their need for oxygen exchange stimulated by their movement. Ripley et al. exposed small-spotted catshark embryos to water at 15° and 20°C, and found that the time they could remain motionless was reduced by sevenfold at the higher temperature. Although the precise mechanism was not clear, the authors conclude that this was in part a result of higher metabolic requirements at higher temperatures. Thus, the ability to “freeze” at higher temperatures may be compromised, leading to higher rates of predation in warmer oceans.
Conserv. Physiol. 9, coab045 (2021).