Otariidae Eared Seals

The fur seals and sea lions (family Otariidae) have resolved the conflict between marine foraging and terrestrial nursing in a strikingly different manner. Although mothers initially haul out onto land to give birth and remain ashore for 1 1.5 weeks, they then begin a series of periodic foraging trips to sea interspersed with 1 4-day nursing periods ashore. Depending on species and pupping site, the foraging trips may be of remarkable length, from less than 1 day to more than 20 days.[1,2] The mother accumulates high-fat (30 55%) milk in her mammaries while at sea,[1,8] but the pup remains at the breeding colony initially digesting milk (from the prior nursing bout) and then fasting. It is not known how lactating otariids manage to sustain milk secretion without either a suckling stimulus or milk removal during these prolonged foraging trips. The fact that otariid species with longer foraging trips produce milks higher in fat[10] suggests that mammary storage volume may be limiting. Upon the mother's return, the pup ingests large quantities of milk over several days, equivalent to 50% of body weight in some species. However, as these nursing bouts are interspersed with periods of fasting, the average daily milk energy intake by otariid pups is lower, growth is slower, and lactation is of much longer duration than in the phocids (Table 1). Across both phocids and otariids, the intensity of lactation, expressed as milk-energy output per maternal metabolic size per day, is inversely related to the duration of lactation, ranging from 0.36 MJ/kg075/d in the California sea lion to 4.0 MJ/kg075/d in the hooded seal (Table 1).

Table 1 Milk and energy outputs at midlactation in marine mammalsa

Study

EO per

EO per

Lactation

Body

period

Milk

Energy output,

maternal

offspring

length

mass

(d after

yield

EO

MBSc

MBSc

Speciesb

(d)

(kg)

birth)

N

(kg/d)

(MJ/d)

(MJ/kg075/d)

(MJ/kg083/d)

Cetacea Odontoceti

Common dolphin

~ 540

112

~ 90

0.42

6.0

0.17

0.6

Great sperm whale

~ 740

13500

~ 180

9.0

12

0.09

0.3

Cetacea Mysticeti

Fin whale

210

65000

~ 180

160

2500

0.62

1.1

Blue whale

210

100000

~ 180

220

4000

0.72

1.3

Pinnipedia Otariidae

California sea lion

330

88

30 60

13

0.73

10.2

0.36

1.3

Australian fur seal

330

80

125 147

10

0.70

13.9

0.52

1.3

Northern fur seal

120

38

~85 105

23

0.72

16.8

1.1

1.9

Antarctic fur seal

115

41

84 98

13

0.70

12.5

0.82

2.1

Pinnipedia Phocidae

Weddell seal

45

342

8 38

9

3.5

75

0.94

2.2

N. elephant seal

27

402

0 24

6

5.5

91

1.0

2.3

Grey seal

17

173

0 14

9

3.0

69

1.4

4.0

Harp seal

12

113

4 11

4

3.6

75

2.2

4.3

Hooded seal

4

166

04

7

7.5

187

4.0

14.0

"Measured values except those in italics, which were estimated from growth rate and mammary mass. All species have only one young. (From Refs. 1 8.)

bScientific binomials provided in Refs. 1, 2, 4, and 7.

cMBS metabolic body size (mass0 75 in adults; mass0 83 in sucking young). (From Refs. 6 and 7.)

"Measured values except those in italics, which were estimated from growth rate and mammary mass. All species have only one young. (From Refs. 1 8.)

bScientific binomials provided in Refs. 1, 2, 4, and 7.

cMBS metabolic body size (mass0 75 in adults; mass0 83 in sucking young). (From Refs. 6 and 7.)

Pregnancy And Childbirth

Pregnancy And Childbirth

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