Note on a Minke Whale Kept Alive in Aquarium
By
SEIJI KIMURA and T AKAHISA NEMOTO
Mito Aquarium, in the suburbs of Numazu city, Sizuoka prefecture,
is famous in having a special pool to keep some large fish or dolphinsin the utmost part of a small inlet. Striped porpoises (Lagenorhynchus
obliquidens Gill) and bottle-nosed dolphins (Tursiops truncatus truncatus(Montague)) are now favourites in the pool.
Recently, a minke whale (Balaenoptera acutorostrata Lacepede) had
been kept for about a month in this aquarium. ·As the keeping ofbaleen whale in an aquarium is very rare, we would like to report ashort note on this whale with some records of observations made by
us and submarine photographs taken by the Mainichi Press Co.
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Fig. 1.

Location of Mito Aquarium

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Fig. 2.

----jPlan of the keeping
pool.

The minke whale was caught by Osiki-ami (a kind of fixed net forfish) placed at 2 km. in front of the aquarium on November 26th 1955.
The whale was brought to the pool, hanged between two boats,
after being wrapped up in nets, and towed by a motor boat. It took
about an hour to take the whale to the aquarium and the whale is said
as very gentle during the time of transportation. As shown in fig. 2,
the pool is square in its shape (one side about 70 m. long), three sides
are surrounded by land and the one, facing to the sea, is blocked withnets of synthetic fibres, through which the sea water circulates. A
breakwater has been built in front of the pool in order to prevent thenets from any damage caused by waves. The deepest point of the pool is
12 m. deep, and the shallowest point is 4 m. at high tide, 1 m. at low tide.
Thus the minke whale was brought to the same pool, where two
striped porpoises had already been kept. The minke whale was estimatedto be about 20 feet long and its sex could not be determined. It had

182

s. KIMURA and T. NEMOTO

been very gentle and swam generally anti-clockwise along the circle
shown in fig. 2 until finally escaped from the pool after about a month.
The whale seemed very healthy, showing no sign of wound or desease.
Its dorsal fin inclined slightly to left side of the body.
Mr. Hanajima, in charge of that aquarium, had tried in vain to
feed the whale with flesh of anchovy every day, but it was often
observed that many small mackerels kept in the pool gathered in themiddle part of the pool and bounded up in the morning, suggestingthat they had been attacked by the whale as in the case of otherbaleen whales. Some decreased number of mackerels observed might
be attributable to whale's consumption.
Some observations on respiration were made of this whale consecutively through a day in December 1955. The whale was swimming,
usually following the same route of anti-clockwise in the deepest partof the pool (A in fig. 2), repeating respirations always at about thepoint C shown in fig. 2 after 2 or 3 run. Such regularity in the placeof respiration may partly be attributed to the bottom condition of thepool. The whale had repeated somewhat rhythmical respirations, though
no conspicuous periodicity had been observed. Intervals between respirations became shorter after a long dive, and vice versa.
The intervals between respirations decreased gradually as night
comes, but increased again after midnight. The peak was observed at
one o'clock (fig. 4). However, we can not draw any difinite conclusionfrom this fact whether this is really due to the whale's relaxation. We
had never observed any other sign of the relaxation of porpoises inswimming, though they were seemed slightly inactive through themidnight. Our observation was endorsed by the members attending
there and we are of the opinion that the whale had never breaked theswimming for sleeping throughout the period of the keeping, contrary
to some other dolphins observed in Marine Studios, Marineland, Florida.
Towards the end of December three bottle-nosed dolphins werebrought to the same pool. A few days after, to our regrets, theminke whale has escaped from the aquarium, breaking the nets at theposition B shown in fig. 2 at a time before dawn on January 2nd of
this year and no body noticed it until the morning. We wonder if theescape of the minke be attributable to the nuisance caused by thedolphins. It is informed, however, that no change had been observedin the behavior of the minke even after the arrival of the dolphins.
Thus, the minke whale was kept alive for 37 days in that aquarium.
This is not the first experience for the aquarium, because they alreadyhad two similar cases before. The first minke whale was kept about
20 years ago for nearly three months, and in the latter half of that

Note on a Minke Whale Kept Alive in Aquarium
around 17: 00

around 20: 30

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Fig. 3.

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TimeFig. 4.

Change of mean interval time between respiration according
to the time of a day.

184s. KIMURA and T. NEMOTO

term it is said that the minke had fed on food. The second minke
whale, a calf of several weeks old, had been kept in May 1954 until
died after 2 weeks.
We wish to express our thanks to Mr. Jisaku Hanajima, the managerof Mito Aquarium, who accorded many facilities to us. We are alsoindebted to the Mainichi Press Company for the splendid submarine
photographs shown in plates III-V.

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