106
Marine Mammal Physiology: Requisites for Ocean Living
be advantageous for suction feeding if other morphological adaptations are also present.
Indeed, new evidence from captive performance studies suggests that suction is widespread across most pinniped groups (Kastelein et al. 1994; Marshall et al. 2008; Hocking
et al. 2013; Marshall et al. 2014, in press) and indirect evidence suggests many more
species use suction (King 1983; Adam and Berta 2002; Hocking et al. 2013). Pinnipeds
that are presumed, or known, to employ suction feeding tend to have short, wide rostra with jaws that have scoop-like anterior ends, and a long mandibular symphysis,
or a mandible in which the ventral borders are angled toward the oral cavity. There
is also a trend toward simplification of tooth morphology and reduced functionality,
lost functionality, or loss of certain classes of teeth. The post-canine teeth of walruses,
bearded seals, and elephant seals are simple oval peg-like teeth with simple cusps that
are quickly worn flat with age, with little-to-no occlusal surface cusps or patterns (Fay
1982; King 1983; Unger 2010). These teeth may not be functional, or limited in function,
in adults. Monk seals depart from this pattern. Although no specific functional feeding
studies of monk seals have been conducted, animal-borne camera studies of feeding
(Parrish et al. 2002), as well as anecdotal evidence strongly support a suction capability
in these species (Monachus sp.). Their broad, robust teeth with heavy rugosities suggest
these shallow water foragers crush many prey items. The biomechanics and shape of
mandibles differ among pinnipeds (Jones et al. 2013). The shape of pinniped mandibles
appears to separate due to phylogenetic relatedness and each family displays distinct
morphologies. In addition, there are fundamental differences in jaw adductor muscular arrangement of otariids and the jaws of otariids are relatively longer than those of
phocids. However, male–male combat and the influence of mating strategies appear to
also act as a strong evolutionary driver in pinniped mandibular function (Jones et al.
2013) (Figure 5.2).
A feeding performance study of harbor seals (Phoca vitulina) (Marshall et al. 2014)
suggests that suction may be widespread among phocids. Harbor seals are the ultimate generalists among pinnipeds (Figure 5.2). They are the most widely distributed
phocid, and despite some disparity, there are up to five subspecies recognized (Rice
1998; Burns 2009). Harbor seals are opportunistic foragers that exhibit a generalized
feeding ecology. For example, harbor seals feed upon a wide diversity of small- to
medium-sized fish that include herring, anchovy, cod, hake, trout, smelt, shad, scorpionfish, rockfish, prickleback, greenling, sculpin, capelin, sandlance, salmon, flatfish, a
variety cephalopods, and invertebrates that are mostly crab and shrimp species, but
also include mollusks (Bigg 1981; Hoover 1988; Sharples et al. 2009; Kavanagh et al.
2010; Thomas et al. 2011; Brown et al. 2012; Bromaghin et al. 2013). Therefore, harbor
seals are ideal candidates to test hypotheses regarding feeding performance and the
ubiquity of suction feeding among phocids and all pinnipeds. In fact, animal-borne
cameras attached to harbor seals provide convincing evidence that they likely use several feeding modes ( suction and biting) (Bowen et al. 2002). The maximum hydraulic
jetting force recorded was 53.9 kPa. As found with most marine mammal performance
studies, suction and biting feeding modes were kinematically distinct. Suction was
characterized by a significantly smaller gape and gape angle, pursing of the rostral
lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape.
Biting was characterized by a large gape and gape angle and lip curling to expose
teeth. Harbor seals displayed a wide repertoire of behaviorally flexible feeding strategies, which likely forms the basis of their opportunistic, generalized feeding ecology
and concomitant breadth of diet. It is suggested that most pinnipeds will fall into this
behavioral pattern and suction capability.
Marine Mammal Physiology: Requisites for Ocean Living
be advantageous for suction feeding if other morphological adaptations are also present.
Indeed, new evidence from captive performance studies suggests that suction is widespread across most pinniped groups (Kastelein et al. 1994; Marshall et al. 2008; Hocking
et al. 2013; Marshall et al. 2014, in press) and indirect evidence suggests many more
species use suction (King 1983; Adam and Berta 2002; Hocking et al. 2013). Pinnipeds
that are presumed, or known, to employ suction feeding tend to have short, wide rostra with jaws that have scoop-like anterior ends, and a long mandibular symphysis,
or a mandible in which the ventral borders are angled toward the oral cavity. There
is also a trend toward simplification of tooth morphology and reduced functionality,
lost functionality, or loss of certain classes of teeth. The post-canine teeth of walruses,
bearded seals, and elephant seals are simple oval peg-like teeth with simple cusps that
are quickly worn flat with age, with little-to-no occlusal surface cusps or patterns (Fay
1982; King 1983; Unger 2010). These teeth may not be functional, or limited in function,
in adults. Monk seals depart from this pattern. Although no specific functional feeding
studies of monk seals have been conducted, animal-borne camera studies of feeding
(Parrish et al. 2002), as well as anecdotal evidence strongly support a suction capability
in these species (Monachus sp.). Their broad, robust teeth with heavy rugosities suggest
these shallow water foragers crush many prey items. The biomechanics and shape of
mandibles differ among pinnipeds (Jones et al. 2013). The shape of pinniped mandibles
appears to separate due to phylogenetic relatedness and each family displays distinct
morphologies. In addition, there are fundamental differences in jaw adductor muscular arrangement of otariids and the jaws of otariids are relatively longer than those of
phocids. However, male–male combat and the influence of mating strategies appear to
also act as a strong evolutionary driver in pinniped mandibular function (Jones et al.
2013) (Figure 5.2).
A feeding performance study of harbor seals (Phoca vitulina) (Marshall et al. 2014)
suggests that suction may be widespread among phocids. Harbor seals are the ultimate generalists among pinnipeds (Figure 5.2). They are the most widely distributed
phocid, and despite some disparity, there are up to five subspecies recognized (Rice
1998; Burns 2009). Harbor seals are opportunistic foragers that exhibit a generalized
feeding ecology. For example, harbor seals feed upon a wide diversity of small- to
medium-sized fish that include herring, anchovy, cod, hake, trout, smelt, shad, scorpionfish, rockfish, prickleback, greenling, sculpin, capelin, sandlance, salmon, flatfish, a
variety cephalopods, and invertebrates that are mostly crab and shrimp species, but
also include mollusks (Bigg 1981; Hoover 1988; Sharples et al. 2009; Kavanagh et al.
2010; Thomas et al. 2011; Brown et al. 2012; Bromaghin et al. 2013). Therefore, harbor
seals are ideal candidates to test hypotheses regarding feeding performance and the
ubiquity of suction feeding among phocids and all pinnipeds. In fact, animal-borne
cameras attached to harbor seals provide convincing evidence that they likely use several feeding modes ( suction and biting) (Bowen et al. 2002). The maximum hydraulic
jetting force recorded was 53.9 kPa. As found with most marine mammal performance
studies, suction and biting feeding modes were kinematically distinct. Suction was
characterized by a significantly smaller gape and gape angle, pursing of the rostral
lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape.
Biting was characterized by a large gape and gape angle and lip curling to expose
teeth. Harbor seals displayed a wide repertoire of behaviorally flexible feeding strategies, which likely forms the basis of their opportunistic, generalized feeding ecology
and concomitant breadth of diet. It is suggested that most pinnipeds will fall into this
behavioral pattern and suction capability.