Part I: Seals teeth and whales ears - Scott Polar Research Institute ...

Estimates of total biomass at birth by sex were 2.7 million kg for males and 2.15
million kg for females. The curves for both sexes reached a peak of respectively 11.0
million kg and 9.4 million kg at weaning, 23 days later. These and other seasonal
fluctuations are not shown in the figure and the curves take their origin at an age of
about two weeks. Similar calculations were made for subsequent age classes. In the
female there was a steady decline in biomass after the first year; in the male it
declined to 3 yrs and then rose to a peak at 6 yrs, after which it declined again. This
reflected the male growth spurt in body length and weight. The estimated weight of
the catch in each harvested age group is also shown in [fig 12]. It totalled 10.44
million kg and appeared to be equivalent to taking no animals less than 8-year–old
and then taking the entire 8-yr–old year class, leaving no escapement. A catch about
17% heavier should result if it were possible to take the entire 6-year-old class. But it
isn’t possible to confine the catch to a single year class in this way, and for
reproductive success an adequate stock of breeding bulls must be present on the
beaches. Furthermore, in order to obtain this increased yield a large increase in effort
would have been needed, for instead of 5437 8-year-olds, 7922 6-year-olds would
have had to be taken. There would be operational/financial penalties of this 45%
increase in the actual numbers taken.
The calculations were necessarily crude approximations, but despite this it would
appear that the 1958 size and age composition of the catch came close to fulfilling the
conditions necessary for obtaining the maximum sustained yield of males. An
estimate of the total year-round standing stock of the herd, from these calculations,
was about 169 million kg. An annual male catch of 10.44 million kg would be about
6% gross of the total standing stock if the whole carcass could be utilised. In terms of
blubber only it is only 2.4%, because blubber and skin equal 0.4 x body weight.
Some results of implementing the new regulations
Catch per unit effort. A sharp rise in the CPUE after the new regulations had been
introduced in 1952, with a catch quota of 6,000, looked promising. It rose from 27.6
seals/CDW in the period 1949-52, to 34.3 seals/CDW in 1955-58 - that was by 26.1% -
and appeared to reversing the trend. In 1957 and 1958 sealing operations were
hampered by exceptionally bad weather and the full quota wasn’t attained. Then
unfortunately there was a change in the catching effort, which meant that the
measure of CDW had changed substantially, so I was not able to extend this analysis.
(Vessels changed; the larger Petrel, 245 grt, replaced the older, smaller Lille Karl, 77
grt. Two sealing captains of twenty years experience (Edgardo Lees and Thorlief
Hammerstad) retired and were replaced of by Gunnar Virik Nilsen and Arne Bogen)
in 1957).
Oil yield. Figure 7 also shows that the date of mid season became earlier, by about
two weeks, on the introduction of the new regulations and smaller quota. This
would be expected to be associated with a higher oil yield per seal, because the
depletion of their blubber due to fasting and aggression, would not have advanced
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