SUMMARIZED CONCLUSIONS 281 



after mid-season. They tend to replace the larger individuals which move farther south 

 at this time. 



The numerical data for the three seasons during which diatom infection was studied 

 at South Georgia are given in summarized form. The catch has been divided into month 

 groups, and the percentage of various classes of whales showing infection, thick film, 

 spore formation, etc., has been calculated. Brief mention of two small series of observa- 

 tions in other localities has also been made. 



In the following sections the seasonal variation in percentage infection and per- 

 centage with thick film are considered, and it is shown that the diatom data bear out 

 the general idea of whale movement derived from other lines of enquiry. The incidence 

 of the invasion of immature whales about mid-season is normally reflected in a temporary 

 falling off in percentage infection, but some of the later arrivals are already infected, 

 and probably come from the westward. Blue whales on their way north at the end of 

 the season showed the highest percentage infection of all, in accordance with ex- 

 pectation. In general there is a steady increase in the proportion of infected whales 

 throughout the season. 



On the South Georgian grounds, Fin whales were found to be more liable to diatom 

 infection than Blue whales, with the exception above mentioned. Scrapings collected on 

 the ice-edge to the south of Africa indicate that farther south Blue whales are infected just 

 as often. The conclusion is reached that during the seasons studied, the majority of the 

 Blue whales taken were on passage to and from other feeding grounds farther south. Male 

 Fin whales seem to be more often infected than the females, which is perhaps correlated 

 with greater development of the schooling habit, particularly among the immature 

 individuals. All these considerations point to the conclusion that the migratory move- 

 ments of Blue whales are more regular and more extensive than those of Fin whales, 

 mainly owing to their greater southerly range, amply demonstrated of recent years by 

 the catches of the pelagic whaling fleet. 



It has been possible to demonstrate the early observation of Bennett, that whales with 

 heavy diatom film are in better condition than those without, by plotting the mean 

 fatness of heavily infected Fin whales against that of the total Fin whales, for each month 

 during the first two seasons studied at South Georgia. The heavily infected whales were 

 appreciably fatter in ten out of the twelve month groups. The two exceptions occurred 

 during the early part of each season, and were probably due to the nucleus of whales 

 that remained south during the winter. Two other interesting points are well brought 

 out by the fatness figures: the general improvement in the condition of the whales 

 throughout the season, and a temporary decrease due to the invasion of immature whales 

 at mid-season in 1928-9. They also afford concrete proof of another important early 

 observation by Bennett, that the condition of Fin whales tends to be poorer in big " Fin 

 whale years". The season 1929-30 was a big Fin whale year at South Georgia, and the 

 marked inferiority in condition of the whales, as compared with that of those captured 

 during the previous season, is very well brought out by the two graphs. 



The general conclusion is reached that diatom data may be a valuable aid to other 



