126
Marine Mammal Physiology: Requisites for Ocean Living
Other invertebrates, however, are important to several pinniped species. Euphausiids
(krill) are an important part of the diet of crabeater seals, leopard seals, and Antarctic fur
seals in the Antarctic (Doidge and Croxall 1985), and may also be an important part of the
diet of southern elephant seal pups (Walters et al. 2014). In the Arctic, it is documented
that harp seals (Pagophilus groenlandicus) to some extent feed on crustaceans (krill, pelagic
amphipods), particularly pups and immature males (Sivertsen 1941; Sergeant 1973; Nilssen
et al. 1992). Other phocid species found in the Arctic, such as bearded seals (Erignathus
barbatus) are primarily benthic feeders, eating a variety of invertebrate prey (polychaetes,
crustaceans, and mollusks) in addition to pelagic fish and a few species of octopods (Pauly
et al. 1998; Hjelset et al. 1999; Hindell et al. 2012). The diet of walruses, which predominantly feed in shallow Arctic waters (typically less than 100 m deep), also consists largely of
benthic invertebrate prey, including bivalves, gastropods, and polychaete worms (Sheffield
and Grebmeier 2009), although larger prey (adult seals) are also taken.
Killer whales and leopard seals are two examples of top predator species which feed
on a wide variety of prey. Killer whales feed on cetaceans, seals, seabirds, sea otters,
dugongs, fish, and cephalopods. In the Northeast Pacific and Antarctica, populations of
up to three sympatric ecotypes have been found to feed on different prey types. In the
Northeast Pacific, “transient” killer whales feed mainly on marine mammals (especially
harbor seals, Phoca vitulina), while “resident” forms feed primarily on fish, with salmon
being particularly important in the diet of whales in British Columbia waters (Ford et al.
1998; Baird 2000; Pitman and Ensor 2003). The diet of a third ecotype (“offshores”) that
spends a limited time in coastal areas is less well-known but is thought to include fish
(Jones 2006). In Antarctica, the leopard seal inhabits coastal areas of the Antarctic continent where it feeds on a range of prey types from small invertebrates to larger mammals.
In the Antarctic Peninsula, the summer diet of the species includes Antarctic fur seals,
gentoo (Pygoscelis papua), macaroni penguins (Eudyptes chrysolophus), fish, squid, and krill
(e.g., Stone and Meier 1981), but mainly fish and krill during the winter (Lowry et al. 1988).
While in Prydz Bay, east Antarctica, Adelie penguins (Pygoscelis adeliae) are an important
prey item for seals during the summer, together with crabeater seals, benthic and pelagic
fish, and to a lesser extent amphipods and krill (Hall-Aspland and Rogers 2004). Predation
on southern elephant seal pups by this species has also been recorded at the Heard and
Kerguelen Islands in the southern Indian Ocean sector (e.g., Borsa 1990).
6.3.3 Suction feeding
A number of species have evolved other novel feeding strategies (Klages and Cockcroft
1990; Adam and Berta 2002). In the Arctic, specialized suction feeding on bivalve mollusks is
found in walrus and in bearded seals (Kastelein 1994; Adam and Berta 2002; Marshall et al.
2008). In the walrus and bearded seal, soft-bodied mollusks are removed from their shells
by powerful suction forces created by the rapid retraction of the tongue (Kastelein 1994).
6.3.4 Herbivory
The only marine mammals that are exclusively herbivorous are the sirenians (manatees and dugongs), which have a very different phylogenetic origin to the cetaceans and
pinnipeds.
Manatees (Trichecus spp.) and dugongs (Dugong dugong) feed on tropical grasses, roots,
and rhizomes in nearshore areas in saline environments and on water hyacinths, water lilies, and other vegetation in rivers and lakes. The very high degree of dietary specialization
Marine Mammal Physiology: Requisites for Ocean Living
Other invertebrates, however, are important to several pinniped species. Euphausiids
(krill) are an important part of the diet of crabeater seals, leopard seals, and Antarctic fur
seals in the Antarctic (Doidge and Croxall 1985), and may also be an important part of the
diet of southern elephant seal pups (Walters et al. 2014). In the Arctic, it is documented
that harp seals (Pagophilus groenlandicus) to some extent feed on crustaceans (krill, pelagic
amphipods), particularly pups and immature males (Sivertsen 1941; Sergeant 1973; Nilssen
et al. 1992). Other phocid species found in the Arctic, such as bearded seals (Erignathus
barbatus) are primarily benthic feeders, eating a variety of invertebrate prey (polychaetes,
crustaceans, and mollusks) in addition to pelagic fish and a few species of octopods (Pauly
et al. 1998; Hjelset et al. 1999; Hindell et al. 2012). The diet of walruses, which predominantly feed in shallow Arctic waters (typically less than 100 m deep), also consists largely of
benthic invertebrate prey, including bivalves, gastropods, and polychaete worms (Sheffield
and Grebmeier 2009), although larger prey (adult seals) are also taken.
Killer whales and leopard seals are two examples of top predator species which feed
on a wide variety of prey. Killer whales feed on cetaceans, seals, seabirds, sea otters,
dugongs, fish, and cephalopods. In the Northeast Pacific and Antarctica, populations of
up to three sympatric ecotypes have been found to feed on different prey types. In the
Northeast Pacific, “transient” killer whales feed mainly on marine mammals (especially
harbor seals, Phoca vitulina), while “resident” forms feed primarily on fish, with salmon
being particularly important in the diet of whales in British Columbia waters (Ford et al.
1998; Baird 2000; Pitman and Ensor 2003). The diet of a third ecotype (“offshores”) that
spends a limited time in coastal areas is less well-known but is thought to include fish
(Jones 2006). In Antarctica, the leopard seal inhabits coastal areas of the Antarctic continent where it feeds on a range of prey types from small invertebrates to larger mammals.
In the Antarctic Peninsula, the summer diet of the species includes Antarctic fur seals,
gentoo (Pygoscelis papua), macaroni penguins (Eudyptes chrysolophus), fish, squid, and krill
(e.g., Stone and Meier 1981), but mainly fish and krill during the winter (Lowry et al. 1988).
While in Prydz Bay, east Antarctica, Adelie penguins (Pygoscelis adeliae) are an important
prey item for seals during the summer, together with crabeater seals, benthic and pelagic
fish, and to a lesser extent amphipods and krill (Hall-Aspland and Rogers 2004). Predation
on southern elephant seal pups by this species has also been recorded at the Heard and
Kerguelen Islands in the southern Indian Ocean sector (e.g., Borsa 1990).
6.3.3 Suction feeding
A number of species have evolved other novel feeding strategies (Klages and Cockcroft
1990; Adam and Berta 2002). In the Arctic, specialized suction feeding on bivalve mollusks is
found in walrus and in bearded seals (Kastelein 1994; Adam and Berta 2002; Marshall et al.
2008). In the walrus and bearded seal, soft-bodied mollusks are removed from their shells
by powerful suction forces created by the rapid retraction of the tongue (Kastelein 1994).
6.3.4 Herbivory
The only marine mammals that are exclusively herbivorous are the sirenians (manatees and dugongs), which have a very different phylogenetic origin to the cetaceans and
pinnipeds.
Manatees (Trichecus spp.) and dugongs (Dugong dugong) feed on tropical grasses, roots,
and rhizomes in nearshore areas in saline environments and on water hyacinths, water lilies, and other vegetation in rivers and lakes. The very high degree of dietary specialization