Ai. Boltnev et al., NORTHERN FUR-SEAL YOUNG - INTERRELATIONSHIPS AMONG BIRTH SIZE, GROWTH, AND SURVIVAL, Canadian journal of zoology, 76(5), 1998, pp. 843-854
We investigated size at birth, growth, and early survival of northern
fur seals (Callorhinus ursinus) from birth to weaning at Bering Island
, Russia, over 8 breeding seasons from 1982 to 1989. One thousand and
thirteen fur seals (565 males and 448 females) were measured in a long
itudinal study and an additional 2697 animals were measured at birth.
At birth, female pups were about 10% lighter and about 3% shorter than
male pups. The coefficients of variation of mass (12.5 and 12.8%) and
length (4.5 and 4.7%) were similar for the two sexes. We partitioned
the lactation period into four time periods: 1, the perinatal period (
ages 0-10 days); 2, the early development period (ages 11-40 days); 3,
the period of intensive molting (ages 41-80 days); and 4, the prewean
ing period (ages 81-140 days). We investigated four measures of growth
: absolute growth in mass (AGM) in grams per day, absolute growth in l
ength (AGL) in millimetres per day, relative growth in mass (RGM) as a
percentage per day, and relative growth in length (RGL) as a percenta
ge per day. For both sexes, AGM was highest during period 4 (mean = 12
4.8 g/day, SE = 7.4 g/day, and mean = 109.6 g/day, SE = 6.8 g/day for
males and females, respectively) and AGL was highest during period 2 (
mean = 3.74 mm/day, SE = 0.18 mm/day, and mean = 3.42 mm/day, SE = 0.2
1 mm/day for males and females, respectively). RGM (mean = 1.06%, SE =
0.09%, and mean = 1.02%, SE = 0.11% for males and females, respective
ly) and RGL (mean = 0.53%, SE = 0.03%, and mean = 0.50%, SE = 0.03% fo
r males and females, respectively) were highest during period 2 for bo
th sexes. For both sexes, growth rates were slowest during the molting
period. Sexual differences were detected in AGM in period 4 and for t
he combined data over periods 1-3. Sexual differences in AGL were dete
cted for the combined data over periods 1 3, and 4 only. No sexual dif
ferences in relative growth were found. Subsequent growth in mass and
length was correlated with birth size. We found the greatest annual va
riation during the periods when growth was fastest. Condition indices
were calculated using the allometric relationship between length and m
ass separately for neonates and pups older than 5 days. The condition
indices at birth varied significantly annually. The condition index wa
s lowest during the molting period (3). Animals that survived for at l
east 40 days were larger at birth and had a higher condition index tha
n those that did not survive. In years of moderate or high pup surviva
l rates, survival rates were higher in animals born later in the breed
ing season.