I read recently that turtles were being 鈥渃old-stunned鈥� and sharks were freezing to death in the ocean off the north-eastern US coast. This was due to a cold spell with air temperatures of -12掳C, rather than the average 1掳C. Is this particularly cold or within the normal winter range, and how is it possible for animals to be affected in these ways? Also, why do we not see mass freezing of land animals before sea animals are affected, given the relative stability of ocean temperatures?
鈥� Sharks and turtles weren鈥檛 really freezing to death in January 2018 when an 鈥淎rctic outbreak鈥� of frigid air produced very low but not record-setting temperatures in the north-eastern US. For sharks to freeze, the coastal waters would have had to freeze too, and they didn鈥檛.
However, a few sharks and sea turtles were 鈥渃old-stunned鈥� because they apparently remained too long in quickly cooling near-shore waters that had no layer of warmer water below them to buffer the rapid temperature drop.
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鈥淔or sharks and turtles to actually freeze, the coastal waters would have to freeze too鈥�
They, along with most other fish, reptiles and amphibians, are ectotherms, animals whose body temperature closely follows the normal seasonal range of the water or air temperatures in which they live. Their metabolism is programmed to operate within this range, but if body temperature falls below it, some of the enzymes that control metabolic rate become inactive, partially stunning the animals.
However, if a shark or sea turtle can still breath and avoid predation or beaching during such an activity slump, normal metabolism and behaviour will soon return as the water temperature rises.
Mass freezing of land animals rarely occurs because any ectotherms will retreat to burrows, deep rock crevices or caves where temperatures never fall below freezing.
Endothermic animals such as birds and mammals, whose metabolic rate supports their relatively constant body temperature, have a different problem. They usually require a constant food supply to drive their metabolism. If food becomes scarce in the winter habitats of large grazing mammals, their body temperature drops and mass freezing of entire herds may occur.
Sam McGinnis, Professor Emeritus, Department of Biology, California State University, US
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