RESPIRATION I23 



we do not know whether in fact such large quanthies of mucus are 

 produced, and until the foam has actually been isolated in the blow 

 itself, it would be safer to work on the orthodox explanation, though it is 

 quite possible that even very small quantities of mucus may act as con- 

 densation nuclei, in much the same way that impurities in the air cause 

 London fog. 



So much for the blow. What of the dive? We might have wondered 

 how deep the animals go down, and why they 'sound' in the first place. 

 \Villiam Scoresby studied this problem during the nineteenth century, 

 and by running out a harpoon line he concluded that the whale could 

 dive to a depth of more than 50 fathoms, and modern whalei's would 

 agree with him. The harpoon lines, of which every catcher boat carries 

 two, are as a rule i km (3,280 feet) long, to allow for the fact that trapped 

 whales never dive down vertically but try to get as far away from the boat 

 as possible. Moreover, the line must be paid out carefully if it is not to 

 break. 



For inore precise information we must turn to P. F. Scholander, a 

 Norwegian physiologist. In 1940, working from Steinshamn, a Norwegian 

 whaling station, he attached manometers to harpoons used for shooting 

 Fin Whales, and from their maximum pressure determined the maximum 

 depth. Discarding data of whales which came up dead, he found figures of 

 46, 57, 74, 126 and 194 fathoms. (The record for a skin diver is about 

 60 fathoms.) Experts, however, think that vminjured whales do not usually 

 descend to more than about 25-50 fathoms, though, if need be, they can 

 dive down 200-250 fathoms without any adverse effects, for some of 

 Scholander's Wliales continued to behave quite normally and had to be 

 finished off with a second harpoon. Actually most animals are capable of 

 exceptional spurts of effort when they are vmder stress. Thus a normally 

 placid Zebu cow is capable of clearing a 6-foot hedge from a standing 

 start, and captive animals have often astonished spectators in zoological 

 gardens by their vmsuspected athletic prowess. 



Even so, it seems odd that Rorquals should want to go down to a depth 

 of 50 fathoms, when krill, their main food, is predominantly found in the 

 first 5 fathoms of the sea. This was established by the very comprehensive 

 investigations carried out by J. W. S. Marr (National Institute of Oceano- 

 graphy, Wormley) who showed that, though krill can be found as deep 

 as 500 fathoms, it is most highly concentrated near the top. However, 

 Rorquals, like humans, may grow tired of their monotonous diet, and 

 since it is known that their food is not exclusively restricted to krill, this 

 may well be the explanation for their deep dive. 



Much more is known about the feeding habits of Sperm and Bottlenose 

 Whales. These animals feed principally on cuttlefish, different species of 



