286 DISCOVERY REPORTS 



catching hake off Patagonia, and direct comparison of the two sets of length frequencies seems highly 



instructive. 



These data of Hickling's are given in the form of percentage length frequencies for each month, 

 irrespective of sex, over a period of more than two years. To facilitate direct comparison with our 

 southern data the results have been recalculated to exclude the very small number of fish less than 

 20-0 cm. long, and then meaned. For the southern species we have 4704 measurements of hake 

 caught with a commercial trawl at all seasons, between 42 and 53° S, the latter probably being the 

 normal southern limit of the species. In addition to the calculation of the mean, standard deviation, etc. , 

 by the long method, they have been secondarily grouped into 5-0 cm. length classes, and the percentage 

 length frequencies computed, so that curves could be drawn for direct comparison with Hickling's 

 data. 



-1 



30 



so 60 70 

 LENGTH _ CMS 



u In IbtItI ytIyhImiI kIx Ixr Ixnl 



YEAR CLASSES 



Fig. 20. Percentage length frequencies, and a partial life curve, for Merluccius merhicciiis. From 



Hickling, 1933, table IX a. 



Before this comparison is made, it is necessary to make clear one most important difference between 

 the two stocks : the males of the Patagonian hake are relatively much smaller than those of the European 

 hake. It will be shown that Patagonian hake are some 5-0 cm. smaller than European hake, on the 

 average, when the sexes are lumped together; but although directly comparable data for the separate 

 sexes are not available, it can be shown that males of the Patagonian stock are relatively much smaller 

 than this difference would indicate. Means for each sex of European hake may be obtained from 

 Hickling's table IX a. While the means for the Patagonian stock are not directly comparable with 

 these, the difference between the mean lengths for each sex, in each set of data, may readily be com- 

 puted; and the difference between these differences is probably significant, though this cannot be 

 established statistically. For Patagonian hake the difference is 49-9 cm. for females less 36-4 cm. for 

 males, i.e. 13-5 cm. For European hake, with data including a much higher proportion of the smaller 

 individuals of both sexes, it was 34-9 cm. for females less 31-0 cm. for males, i.e. 3-9 cm. Moreover, 

 if we take the largest decile of the 1396 Patagonian males, we find that they show a mean length of 

 46-1 cm., the largest individual was 64 cm. long, and only i % of the total of 50-0 cm. and over. The 

 largest decile of the European males has a mean length of 56-1 cm., while the largest individual age 

 group had a mean length of 767 cm. ; and some 7% of the total were 50-0 cm. long and over, in spite 

 of the much greater proportion of small individuals in this series of measurements. 



