100
Marine Mammal Physiology: Requisites for Ocean Living
balaenopterids have largely flaccid tongues for inversion and expansion of the large ventral pouch. Balaenids swim at slow, steady speeds (<1 m/s) to continuously drive water
into the mouth (Simon et al. 2009). Such a strategy may be required to efficiently filter water
with an enlarged mouth aperture that should incur significant drag and thus large energy
costs (Werth 2004). Despite this large anterior opening, there are two much smaller posterior openings of the mouth where water is thought to exit the mouth after being filtered
through the baleen (Werth 2004). The difference in area between the anterior and posterior
openings creates a Venturi effect, or suction, in front of the mouth that should help reduce
a bow wave from forming that would deflect prey away from the mouth (Werth 2004).
In addition, perioral structures such as the subrostral gap, orolabial sulcus, curvature of
baleen, mandibular rotation, and lingual mobility also permit the steady flow of water
through the baleen that improves the efficiency of filtration.
In contrast, Balaenopterids (rorquals) exhibit a dynamic process that involves a lunge,
or a rapid acceleration to high speed (Goldbogen et al. 2006; Simon et al. 2012; Kot et al.
2014), and the subsequent engulfment of a large volume of prey-laden water (Orton and
Brodie 1987). After the target volume of prey and water is engulfed, the mouth closes just
enough to leave the baleen exposed for filtration and this so-called lunge filter feeding
mechanism is enabled by an integrated suite. The engulfed water is then driven past the
baleen plates through the contraction of the expanded ventral pouch. This so-called lunge
filter feeding mechanism is enabled by a integrated suite of morphological and mechanical adaptations that facilitates the lunge feeding process: hyper-expandable ventral groove
blubber (Shadwick et al. 2013), elongate and curved jaws (Goldbogen et al. 2010; Pyenson
et al. 2013), and a sensory organ in the un-fused mandibular symphysis (Pyenson et al.
2012). In many large-bodied rorqual species, the size of the engulfed volume is commensurate with the whale’s body size (Goldbogen et al. 2007). This is due in large part to the
positive allometry of the skull and ventral pouch, whereby large whales exhibit relatively
larger oropharyngeal cavities. The positive allometry of the engulfment apparatus is
accompanied by the negative allometry of the caudal peduncle. As a result, larger rorquals
have big heads and short tails, which may reflect that whales are investing growth in the
anterior region at the expense of the posterior region (Goldbogen et al. 2010). The scaling of
pouch allometry appears to have important consequences for rorqual diving physiology,
feeding performance, and ecological niche (Goldbogen et al. 2012).
5.2.2 Order Sirenia: Manatees and dugongs
Sirenians were among the first mammal lineages to return to aquatic habitats. The earliest sirenians appear in the fossil record ~50 Ma in the middle to late Eocene (Savage
et al. 1994; Domning 2001) and our modern dugongs and manatees first appeared in the
middle Eocene and Oligocene, respectively. Our modern assemblage includes three manatee species with the Family Trichechidae: West Indian manatees (Trichechus manatus),
West African manatees (Trichechus senegalensis), Amazonian manatees (Trichechus inunguis), and two species within the Family Dugongidae, dugongs (Dugong dugon) and the
recently extinct Steller’s sea cow (Hydrodamalis gigas). Sirenians are distinct among marine
mammals in that they are herbivorous and possess many adaptations for grasping, excavating, and processing aquatic plants. Although sirenians may be superficially similar
in both morphology and diet, they are quite different in that manatees are considered to
be generalists, whereas dugongs are benthic specialists. There are several overarching
functional themes in sirenian feeding mechanisms that include the degree of deflection
of the rostrum, tooth replacement, the vibrissal-muscular complex. Among all sirenians,
Marine Mammal Physiology: Requisites for Ocean Living
balaenopterids have largely flaccid tongues for inversion and expansion of the large ventral pouch. Balaenids swim at slow, steady speeds (<1 m/s) to continuously drive water
into the mouth (Simon et al. 2009). Such a strategy may be required to efficiently filter water
with an enlarged mouth aperture that should incur significant drag and thus large energy
costs (Werth 2004). Despite this large anterior opening, there are two much smaller posterior openings of the mouth where water is thought to exit the mouth after being filtered
through the baleen (Werth 2004). The difference in area between the anterior and posterior
openings creates a Venturi effect, or suction, in front of the mouth that should help reduce
a bow wave from forming that would deflect prey away from the mouth (Werth 2004).
In addition, perioral structures such as the subrostral gap, orolabial sulcus, curvature of
baleen, mandibular rotation, and lingual mobility also permit the steady flow of water
through the baleen that improves the efficiency of filtration.
In contrast, Balaenopterids (rorquals) exhibit a dynamic process that involves a lunge,
or a rapid acceleration to high speed (Goldbogen et al. 2006; Simon et al. 2012; Kot et al.
2014), and the subsequent engulfment of a large volume of prey-laden water (Orton and
Brodie 1987). After the target volume of prey and water is engulfed, the mouth closes just
enough to leave the baleen exposed for filtration and this so-called lunge filter feeding
mechanism is enabled by an integrated suite. The engulfed water is then driven past the
baleen plates through the contraction of the expanded ventral pouch. This so-called lunge
filter feeding mechanism is enabled by a integrated suite of morphological and mechanical adaptations that facilitates the lunge feeding process: hyper-expandable ventral groove
blubber (Shadwick et al. 2013), elongate and curved jaws (Goldbogen et al. 2010; Pyenson
et al. 2013), and a sensory organ in the un-fused mandibular symphysis (Pyenson et al.
2012). In many large-bodied rorqual species, the size of the engulfed volume is commensurate with the whale’s body size (Goldbogen et al. 2007). This is due in large part to the
positive allometry of the skull and ventral pouch, whereby large whales exhibit relatively
larger oropharyngeal cavities. The positive allometry of the engulfment apparatus is
accompanied by the negative allometry of the caudal peduncle. As a result, larger rorquals
have big heads and short tails, which may reflect that whales are investing growth in the
anterior region at the expense of the posterior region (Goldbogen et al. 2010). The scaling of
pouch allometry appears to have important consequences for rorqual diving physiology,
feeding performance, and ecological niche (Goldbogen et al. 2012).
5.2.2 Order Sirenia: Manatees and dugongs
Sirenians were among the first mammal lineages to return to aquatic habitats. The earliest sirenians appear in the fossil record ~50 Ma in the middle to late Eocene (Savage
et al. 1994; Domning 2001) and our modern dugongs and manatees first appeared in the
middle Eocene and Oligocene, respectively. Our modern assemblage includes three manatee species with the Family Trichechidae: West Indian manatees (Trichechus manatus),
West African manatees (Trichechus senegalensis), Amazonian manatees (Trichechus inunguis), and two species within the Family Dugongidae, dugongs (Dugong dugon) and the
recently extinct Steller’s sea cow (Hydrodamalis gigas). Sirenians are distinct among marine
mammals in that they are herbivorous and possess many adaptations for grasping, excavating, and processing aquatic plants. Although sirenians may be superficially similar
in both morphology and diet, they are quite different in that manatees are considered to
be generalists, whereas dugongs are benthic specialists. There are several overarching
functional themes in sirenian feeding mechanisms that include the degree of deflection
of the rostrum, tooth replacement, the vibrissal-muscular complex. Among all sirenians,