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Antarctic krill being closer inshore and adults occurring over deep water. The
amount of krill that must have been consumed by baleen whales in the years before
commercial whaling took its toll was prodigious
-
some estimates put it as high as
200million tonnes a year
and this still left enough food available for large
populations of seabirds, seals and
-
sh.
Whilst all populations were reduced by whaling in the twentieth century, the
suspension of commercial whaling in the Southern Ocean since 1984 has given some
species an opportunity to recover. Some populations of humpbacks are certainly
recovering as apparently are southern right whales, but the information for
n
whales is presently too poor to say with any certainty what their population
trend is. Minke whales have remained present in considerable numbers and are
now the main target for Japanese scienti
c whaling, with a catch of a few
Box 6.5
The astounding productivity of blue whales
The blue whale is the largest animal that has ever lived and can grow to a weight
of 140 tonnes and a length of 35m. Blue whales reach maturity at 5 years, they
have a 10
3
years. All of this is supported on a diet of pure krill, and during the Antarctic
summer an individual blue whale may eat 40million krill a day (around
3.6 tonnes). This makes them especially vulnerable to any direct effects of climate
change on krill availability. In comparison, the largest land animal, the African
elephant, which can weigh 12 tonnes, reaches maturity at 9
-
12month gestation period and produce a 2.5 tonne calf every 2
-
12 years, has a
22month gestation period and produces a 120 kg calf every 5 years. The
prodigious productivity of blue whales is even more amazing because they are
generally thought to con
-
8months of the year when
they are in the Southern Ocean. Obviously, the pre-human-era food web of the
Antarctic region was suf
ne their feeding to the 6
-
cient to support not only the huge populations of blue
whales that existed before exploitation but also large populations of other krill-
feeding whales such as
fin, humpback and minke, and enormous populations
of krill-dependent seals, seabirds and
fish. About 1.3million whales were killed
during the years of commercial whaling in the Antarctic, including 350 000 blues;
the blue whale population remains below 15% of its pre-exploitation level,
despite 40 years of protection, and their numbers are so low that it is dif
cult to
estimate a population size. Scientists are still debating the effect on the ecosystem
of the removal of such a high proportion of the baleen whales and whether they
will ever be able to recover. Some even speculate that the ecosystem may have
changed forever and there will be no return to the days when
backs and
beaks were seen at close intervals quite near the ship, and from horizon to
horizon ... The sea was swarming with Euphausia
'
Whales
'
'
(Bruce, 1915).
 
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