157 



mature.'' 2 were taken within the limits of the spawning season ; 1, measuring 

 33-5-38-5 cm., was caught in March 1914, 30 miles to the westward ; the other, 

 measuring 38-40"8 cm., was recaptured near Aberdeen, in February 1913, at a 

 distance of 47 miles. 



EXPERIMENT IV. 



12^^ June 1913. 



In this experiment, 119 plaice were marked and Uberated, consisting of 36 

 males, 82 females, and 1 whose sex was not ascertained. The sizes of the males 

 varied from 27 to 45 cm., and 11 were under adult size (33 cm.). Of the females, 

 the sizes were from 24"5 to 56'5 cm., and 25 were under adult size (38 cm.). The 

 numbers liberated and recaptured, arranged in 5-cm. groups, are shown in the 

 following table : — 



* One at 24'5 cm. 



The fish were caught at the place where they were liberated, viz. 40 miles east 

 of the Isle of May. 



The number recaptured was 54, or 45'4 per cent., viz. 16 males (44*4 per cent.) 

 and 38 females (46-3 per cent.). Thirteen of the males were over adult size on 

 recapture, ranging from 36"5-44'7 cm., with an average of 39*9 cm., compared 

 V ith a range of 30-42*5 cm., and an average of 37*3 cm. on liberation ; they were 

 at hberty for from 53 to 993 days, the mean being 335 days ; they migrated distances 

 of from 10^ to 149 miles, the mean being 64*5 miles, and the average rate of move- 

 ment 1-9 miles per 10 days. Three of the males were under adult size, the average 

 being 28'8 cm., compared with 28*3 cm. on hberation ; they were free for a mean 

 period of 76 days, and travelled an average distance of 23*5 miles, at a mean rate 

 of 3" 1 miles. Thirty-four of the females were of adult size on recapture, the average 

 being 44*9 cm., and the range from 38'8 to 55'3 cm., compared with an average of 

 42'6 cm., and a range of 29 to 56*5 cm. on hberation ; the periods of freedom 

 varied from 29 to 989 days, the mean being 290 days ; the distances travelled 

 varied from 11 to 141 miles, the average being 36-5 miles, and the mean rate 1-35 

 miles. Four were under adult size, the mean being 33*9 cm., as compared \vith 

 32-7 cm. on hberation ; they were at hberty for an average of 147 days, and 

 travelled a mean distance of 32-2 miles, at an average rate of 2*2 miles. 



The Extent and Direction of Migration. 



First Quarter. — None of the fish was recovered in June. In July, 6 were taken, 

 1 male and 5 females. The male was caught off St. Abb's Head, after 29 days, a 

 distance of 26 miles to the south and west. A female, of 34-34 cm., was taken 

 5 miles to the south and west, after 30 days ; another, of 42-5-42-5 cm., was caught 

 19 miles to the south and east, after 34 days ; a third, of 56-5-55"3 cm., was taken, 

 after 44 days, 21 mileS to the north and east ; a fourth, of 53-52-7 cm., and 

 described as "spent," was caught, after 29 days, in the same locahty, a little farther 

 to the west, at a distance of 21 miles ; the fifth female, of 39-5-38-8 em., was 

 recaptured, after 43 days, south-east of Aberdeen, at a distance of 36 miles. 



Eight were recaptured in August, 3 males and 5 females. All the males were 

 taken to the south and west ; 1, of 42-5-42 cm., after 53 days, lOJ miles distant ; 

 another, of 30-5-30 cm., after 72 days, 17 miles in the same direction, to the north- 

 east of St. Abb's Head ; the third, measuring 37-38-2 cm., after 68 days, to the 

 east of the Isle of May, at a distance of 24 miles. One of the females, of 51-50-9 

 cm., and described as "spent," was taken, after 70 days, 23 miles to the south- 

 west, north-east of Longstone Light ; the other 4 females went to the northwards • 



