Special Senses

The special sensory organs in pinnipeds include the eyes, ears, nose, and vibrissae. Marine mammals, especially pinnipeds, 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. You have no doubt experienced how the refractive index varies in air and water if you have ever tried to open your eyes in a swimming pool!

Pinnipeds spend part of their time on land and part of their time in water and thus must be able to function well in these two very different media. To cope with these differences, pinniped eyes have a flattened portion of the cornea which allows them to sea clearly in both air and water. Many species, especially deep diving species, have large eyes with pupils that can close very small (in bright light) but expand to a very large size (in low light) to allow them to see under a wide range of lighting conditions. Pinnipeds can close their nostrils completely to prevent water from entering the nasal cavity while diving and they also have very sensitive whiskers, or vibrissae, which allow them to detect fine scale changes in water movement. Pinnipeds can also hear well in both air and water though hearing is a very active area of research.

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 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. You should also be sure to check the nasal passages for nasal mites and note the extent of the infection if present.

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 (hearing).

Detailed annotated images of the special sensory structures in a California Sea Lion are shown below.  CLICK on an image to see an enlarged view.