A whale’s eye is designed to tolerate mechanical, chemical, optical, and osmotic water conditions while also allowing them to have increased visibility in the ocean and has thickness for protection from damage when diving with temperature changes in the ocean (Rodrigues et al, 2014).
In addition, the eye enables detection and capture of food, identification of other whales and guides them when migrating to other areas (Rodigues et al, 2014).
A whale uses its eye primarily to detect light instead of focusing and it is suggested to be retractable to endure the high pressures of the deep sea (Alstrup et al, 2017).
The retinas of both toothed whales and baleen whales is similar (Berta et al, 2015). Blue whale eyes have rods to see in dim light, but they do not have cones which are for color detection; therefore, they see color as grey shades (De luliis and Haddrath, 2017).
Dorsal view of the tympanic bone and ossicles from Tursiops truncatus. This view is also a particularly good vantage point from which to view the structures that receive the dorsal branch of the mandibular fat body. Subtle, but potentially important, landmarks are: two very thin bony locations marked by the prominent red and blue circles. The S-shaped black dotted-line marks the mallear ridge. The shorter black dotted line marks the ridge along the accessory ossicle. The small red dotted-line marks the sulcus for the chorda tympani. The tympanic bone is colored cyan, and the ossicles are colored as follows: malleus = yellow, incus = magenta, stapes = green. Credit: Cranford et al, 2010
Whales rely on sound to hear with toothed whales using a biosonar system for hearing called echolocation to observe their ocean environment (Yamato, et al, 2014) which is likely the reason this species has obtain evolutionary success and allows beaked whales and sperm whales into low visibility waters of great depths (Lambert, 2016).
Whales ears are narrow and sometimes have a discontinuous channel outside of the skull in the “tympano‐periotic complex” (TPC) which reduces bone conduction to aid them in directional hearing ability (Yamato, et al, 2014).
The TPC has bones of differing thicknesses, joints and soft tissues, allowing for complex vibrational states of sound that reach the TPC through a pathway in the throat (Cranford et al, 2010).
Most toothed whales ears are separated from the skull by ligamentous fibers to acoustically isolate the TPC from skull vibration noises; however, in sperm whales and beaked whales there is a bony connection to the skull suggesting the bone may be a conduction mechanism in these species (Schnitzler et al, 2017).
While sperm whales have a consolidated TPC bone, most toothed whale’s TPC is in two parts (Schnitzler et al, 2017).
Schnitzler et al (2017) further suggest sperm whales have exceptional frequency discrimination ability with a range from 5 to 20 kHz.
The structure of the cochlea in the ears of toothed whales and baleen whales differ significantly making:
- toothed whales sensitive to high frequency and ultrasonic sound vibrations
- baleen whales sensitive to low frequency and infrasonic noise (Ekdale, 2016).
Both species have fatty tissues in their ear systems for aquatic sound reception for their auditory ability (Yamato et al, 2014). “Acoustic fats” in the fatty melon of toothed whales’ foreheads remains stable despite body condition (Yamato et al, 2014).
Baleen whales do not use echolocation, instead they rely on sounds of low frequency which can carry over long distances in the water to communicate with potential mates (Yamato, et al, 2014).
Unique analysis of the vibratory complexity of the bony TPC. Unique motions of the head of the stapes in Cuvier's Beaked Whale (Ziphius cavirostris). Vector arrows show the relative magnitude and direction of motions at the head of the stapes for each natural mode of vibration or resonant frequency (the frequency is indicated by the numbers at each arrowhead). The Z axis runs through the head of the stapes and is more or less perpendicular to the footplate, which is in the XY plane. Colors code for frequencies: cold colors are low-frequency and the warm colors are high-frequency. The numbers associated with the arrows indicate the corresponding frequency. Vibrational analysis produces results from calculations based on structure. Credit: Cranford et al, 2010