THE OCEAN FOOD-SUPPLY 481 
When trawling in McMurdo Sound it was a conunou 
occurrence to find that nearly lialf the catch consisted of 
dead animals. 
From an examination of the summer temperatures at 
various depths in several parts of the Ross Sea it was 
found that a temperature of -fro'^ Centigrade was hardly 
ever reached. The usual temperature was slightly below 
0° Centigrade. 
At these low temperatures bacterial decomposition is at 
a minimum, and the food supply of the ocean remains in 
cold storage. However, a small amount of decomposition 
must take place to allow of tlie production of nitrates for 
the plants. 
The abundance of plankton in Antarctic waters is shown 
by a brownish discolouration of the sea produced by tlie 
diatoms. 
Another indication is given by large numbers of 
whalebone whales, which feed upon tlie plankton. 
It is true that only about three species of wlialebone 
whales were recognised south of the pack, but the number 
of individuals seen daily around the ship was very great. 
The two commonest species seen were Balanoptera 
Sibbaldi^ the Blue Whale, and Balcenoptera rostrata, the 
Pike Whale. 
The large schools of killer whales, Orca gladiator^ are an 
indirect indication of a plenteous food supply, because they 
feed upon seals and penguins, which in their turn live 
upon the plankton. 
If it was fully realised by whalers that there is a natural 
reason for the abundance of whales in the cohl waters of 
VOL. XI. 2 I 
