Children in the sea off Hawaii. Many fish and marine mammals are expected to fall into deeper waters from warm surfaces, but the surrounding temperature is only a few degrees higher than the ice point, and therefore they have to face the challenge of low temperatures. They need to ensure that new generations are sufficiently active for hunting. At cold ocean depths, a “mild hunter” is a good way of stopping the use of oxygen and thus preserving heat. Two sides have evolved into a unique abili...