Studying Sleep Patterns is not that easy

How do organisms living in a fluid medium sleep? A little thought to the question, and you no doubt realize the astounding luck we have as terrestrial mammals, who can rely on the convenient immobility of our sleeping quarts – we remain in approximately the same position all night long. For marine mammals and some birds, there is no such luxury, and nature had to devise various means to give their brains their due rest. The way these animals do it may seem uncomfortable to us……For example, Swifts (the most aerial of birds) sleep while in the air. Spinner Dolphins (Stenella longirostris), our research subjects, have a complex sleeping pattern which involves changes in geography, oceanographic parameters and social organization. Spinners are most active at night, hunting in large pods in deep waters. They tend to come inshore during the day to rest. Here they gather into tight groups that sink to the bottom and rise to the surface in synchronized patterns.

The problem is, our local Maui County group of Spinners is rarely seen doing anything remotely akin to resting; instead it is always seen splashing, leaping and spinning in the delightful feats of acrobatic prowess which earned them their namesake. Part of the problem may be that we haven’t yet found their preferred sleeping spot, or perhaps local boat traffic (and perhaps even our own research platform) rouses them from sleep before we can actually observe it.

Our latest cruise was somewhat successful (finally!) in encountering the characteristic down-up synchronized pattern. We were ecstatic! They do sleep! It is a wondrous pleasure to behold a pod of nearly one-hundred large wild organisms suddenly all disappear at once. Such coordination is mesmerizing.

But once they are gone, they’re not observable. With elated hearts we realized it is back to the drawing boards for our research protocol: how do we study something we can’t see?  Marine mammals are notoriously difficult to study, even with a dedicated research vessel and talented crew. 

Right now we are recording their energy levels, which are gleaned from watching the number of spins, leaps and slaps they perform in relation to time of day, location, presence/absence of boats, and other factors. This is only one of the parameters we collect data on, but it is the easiest one by far as long as you pay constant attention to the school of dolphins and follow it for hours at a time at a respectful distance.

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