Figure 2.

a Narwhal at surfacing recording from crittercam. Narwhal starting the blow prior to surfacing at a normal position with the blowhole oriented towards the surface. Note the mirror effect of the water surface. Picture captured from Crittercam footage (see online electronic supplement, additional file 1). b Narwhal upside-down swimming along the inlet's bottom. Narwhal swimming upside-down (dark back oriented towards the bottom and the white belly oriented upwards) along the inlet's bottom accompanied by two other narwhals from the same group displaying identical behaviour. Picture captured from Crittercam footage (see online electronic supplement, additonal file 2). Photograph and footage courtesy of National Geographic Remote Imaging.