A. Hearing.
1. Harbor seals have a well-developed sense of hearing, especially in the water.
2. Research shows that under water, harbor seals respond to sounds from 1 to 180 kHz with a peak sensitivity of 32 kHz.
3. In the air, hearing ability is greatly reduced; harbor seals respond to sounds from 1 to 22.5 kHz, with a peak sensitivity of 12 kHz. (The average hearing range for humans is 0.02 to 20 kHz.)
B. Eyesight.
1. Harbor seals have large eyes. Their vision underwater is better than a human's, but inferior on land. Lenses are enlarged and almost round, adapted for focusing on light that is refracted upon entering water. The lenses are not as well-adapted for sight in air.
2. Harbor seals' eyes are adapted for sight in dark and murky water.
a. Like the eyes of other pinnipeds, harbor seals' eyes contain high numbers of rod cells—photoreceptor cells that are sensitive to low light levels.
b. Harbor seals have a well-developed tapetum lucidum, a layer of reflecting plates behind the retina. These plates act as mirrors to reflect light back through the retina a second time, increasing the light-gathering ability of the rod cells. (The tapetum lucidum is the same structure that makes a cat's eyes appear to "glow" when reflecting light at night.)
c. Under water, the pupils dilate (expand) into a wide circle to let in as much light as possible. In bright light, the pupils constrict to a slit.
3. Mucus continually washes over the eyes to protect them. Unlike most land mammals, pinnipeds lack a duct for draining eye fluids into the nasal passages. When a harbor seal is out of the water, mucus surrounding the eyes gives them a wet, "tear-rimmed" look.
Harbor seals' eyes are adapted for seeing in dark and murky water.
4. Good vision does not seem to be essential to harbor seal survival; scientists have found blind but otherwise healthy individuals, including mothers with pups, at sea.
5. Harbor seals probably do not have color vision.
C. Tactile.
1. A harbor seal uses its sensitive vibrissae to find food, especially in dark, deep waters or at night. A substantial nerve system transmits tactile information from the vibrissae to the brain.
2. Each vibrissa can move independently. Under water, a harbor seal thrusts its vibrissae to and fro in a sweeping movement by pushing its mobile upper lip in and out.
3. Prey moving under water creates vibrations that the seal may detect with its vibrissae.
The vibrissae are attached to a substantial nerve network. Tactile
information is transmitted from the vibrissae to the brain.
D. Taste.
Little is known about a harbor seal's sense of taste.
E. Smell.
Researchers believe that harbor seals have an acute sense of smell on land. This sense may be important for mothers identifying their pups.
Adaptations for an Aquatic Environment
SeaWorld/Busch Gardens Animal Information Database
www.seaworld.org / www.buschgardens.org
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