Anatomy of a tuna’s internal compass

Southern blue-fin tuna. (Image from http://www.thewe.cc)

I was very intrigued by a research brief that recently ran in New Scientist magazine on the cause for  daily deep-diving behavior in southern blue-fin tuna. According to the un-bylined brief, these top-predator fish descend deeply like clock-work, penetrating the depths at almost exactly 30 minutes before sunrise and again 30 minutes after sunset.  Apparently scientists differ over the reasons behind this behavior. Some say that the tuna make rapid descents to keep track of their prey.  Others suggest diving rids the fish of pesky parasites. But a recent study interprets their behavior more complexly. A researcher from the University of Tasmania in Australia is lead author to a paper published in Behavioral Ecology and Sociobiology that concludes the tuna dive regularly to calibrate and fine-tune their internal compasses at the precise time of day when they can get the clearest reading possible.

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Forget megafauna, let’s talk magnetic fauna

Loggerhead turtles use the earth's magnetic field to navigate. Click to visit the Lohmann Lab at UNC to learn more.

When I first heard the term “biomagnetism” it captured an obscure fantastical corner of my imagination. But the reality of magnetic sensing in all sorts of animals — from butterflies to sea turtles to whales — and the ways they use it is the sort of science that rivals the most brightly colored dreams of sci-fi writers.  About two weeks back, I mused on the mechanism driving the earth’s magnetic field and what causes magnetic field reversals. When these flipping events occur, the earth’s magnetic field wans in intensity. Periods of declining magnetism are born out for hundreds to thousands of years, with sometimes wild fluctuations in the magnetic field lines. But what effect does declining or fluctuating magnetism have on species that rely on the earth’s magnetosphere like a global positioning system device? And how do they sense magentic fields anyways?

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