Rss

Efficient Feeding Adaptation

Bowheads are continuous filter feeders that feed on zooplankton as tiny as 1mm (Berta et al., 2005, Werth, 2013, Werth, 2004). They have an adapted oral cavity morphology which increases filtering efficiency at low speeds (3km/h) throughout the water column including the surface and bottom (Werth, 2004, Würsig et al., 1989). The oral cavity and the curved cross-sectional baleen plate shape (Figure 14) are designed in such a way that feeding is powered by hydraulic and hydrodynamic pressures, which create a unidirectional flow along the baleen and prevent the formation of the bow wave, therefore prey are unable to escape (Lambertsen et al., 2005, Werth, 2004). The baleen are long, thin and highly mobile when water flows over them, they interlock crating a dense filtration mat (Werth, 2013). These adaptation of mouth morphology and baleen structure resulting in very high filtering efficiency (Lambertsen et al., 2005, Simon et al., 2009, Werth, 2013, Werth, 2004).

Schematic diagrams showing external (a) internal (b), and (c) morphology of the oral region and associated structures in a bowhead whale, Balaena mysticetus. At lower left (b) is a frontal section (anterior at top) and at lower right (c) a transverse section (dorsal at top), each at the level of the dashed horizontal line intersecting the other diagram. Prey-laden water enters the mouth anteriorly through a subrostral cleft (between baleen racks) and flows through and around the baleen plates and fringes, exiting, after prey have been removed, behind the lips.  By http://www.hindawi.com/journals/ijecol/2012/208913/fig1/

Figure 14: Schematic diagrams showing external (a) internal (b), and (c) morphology of the oral region and associated structures in a bowhead whale, Balaena mysticetus. At lower left (b) is a frontal section (anterior at top) and at lower right (c) a transverse section (dorsal at top), each at the level of the dashed horizontal line intersecting the other diagram. Prey-laden water enters the mouth anteriorly through a subrostral cleft (between baleen racks) and flows through and around the baleen plates and fringes, exiting, after prey have been removed, behind the lips.
(Source: http://www.hindawi.com/journals/ijecol/2012/208913/fig1/)

Bowheads have  retained their olfactory bulbs (0.13% of brain size compared to humans 0.008%), which is the rostral part of the brain (telencephalon). Olfactory bulbs result in a sense of smell (in air) as it relays smell cues between the sensory neuron and the higher part of the brain (Thewissen et al., 2011). Bowheads have not developed underwater chemoreception thus have no sense of waterborne chemical stimuli . The suggested reason for this adaptation selection pressure is possibly due to bowheads detecting highly dense kill clouds through the krill’s peculiar odour (dimethylsulfide and pyradines) or the olfaction bulb could play a role in mate detection (Thewissen et al., 2011).

 

Leave a Reply