Special Senses

Like their otariid cousins, the special sensory organs in phocids include the eyes, ears, nose, and vibrissae (whiskers). Like all marine mammals, phocids have quite a challenge to overcome because they have to function in air, in water, in bright light, and in low light.

The physical properties of air and water are very different and the sensory organs must have special adaptations for functioning in these different media. Sound, for example, travels 4-5 times faster in seawater than in air but light actually travels slower in water than in air, a property described by the refractive index.

In addition to the adaptations of the eye discussed for pinnipeds in general, phocids in particular tend to have large eyes which allows them to see in lower light conditions (e.g. at greater depths). Of the two species that we highlight here, the Northern elephant seal and the harbor seal, elephant seals are able to see in the dimmest lighting conditions as a result of a large papillary area and the fact that their pupils don’t dilate to their to their maximum (e.g. letting in the most light) until the light conditions are very dim.

Like many other marine mammals, phocids are able to close their nostrils while diving. During necropsy, the nasal passages should be examined for presence of parasites including mites. In phocids, mites are usually of the Halarachne genus.

Research on the whiskers (vibrissae) of phocid seals has revealed them to be highly sensitive tactile structures capable of detecting the size and shape of objects as well as vibrations in the water column. Whiskers have also been increasingly used to investigate the diets of animals using stable isotope analysis. During necropsy you may have requests for whiskers from various species. In the images below, you can see an example of how to collect whiskers. It is usually important to ensure that the entire structure is plucked, rather than cut, so that the root of the whisker remains attached. This ensures that as the researcher analyzes the composition of the whisker, there is a consistent starting point marking the point in time when the whisker began growing out from the face.

During necropsy, you should examine the eyes, ears, nose and whiskers for any abnormalities. If the eyes are to be fixed, check in with your pathologist or the specific researcher to see how he or she would like the eye preserved. A common technique is to remove the eye whole and then cut a slice in the side of the sclera (the white part of the eyeball) and store in 10% buffered formalin. This allows the fixative to enter the eye and fix the entire organ. Several changes of the formalin may be required to fully fix the eye if this technique is used.

Additional information on pinnipeds sensory systems can be found in Mass and Supin, 2007 (eyes), Dehnhardt et al., 1998 (vibrissae), Miersch et al., 2011 (vibrissae), and Reichmuth (2012) and Waterzok and Ketton (1999) (Reynolds, and Rommel, eds).

 Detailed annotated images of the special senses in two phocids, the harbor seal and elephant seal, are shown below.  CLICK on an image to see an enlarged view.