75 



EXPERIMENT X. 



26th March 1913. 



The number of plaice marked and liberated in this experiment was 100, 28 

 being males, 71 females, and 1 whose sex was not ascertained. The males ranged 

 in size from 30 to 39 cm., and 5 wore inider the adult size (33 ("in.) ; the sizes of 

 the females were from 31 to 59*5 cm., and 33 were under the adult siz • (38 cm.). 

 Tn the following table they are arranged in 5-cm. groups : — 



The fish used were taken by the " Groldseeker " at Station VI., in the Firth of 

 Forth, off St. Monans, on the 26th March, and were Mberated, all in good condition, 

 after being in the tanks of running water for two hours and twenty minutes. 



The number recaptured was 56, or 56 per cent., viz. 20 males, or 71*4 per cent., 

 and 36 females, or 50*7 per cent. 



Nineteen of the males were of adult size on recapture, namely, from 33 to 42 cm., 

 with an average of 37*8 cm., as compared with a range of 30' 5 to 39 cm., and an 

 average of 34'8 cm. on hberation ; they were at Uberty for from 5 to 474 days, 

 the mean being 216 days ; the distances migrated varied from 2^ to 301 miles, 

 the mean being 74-7 miles, and the mean rate of movement 3*6 miles per 10 days. 



Of the females, 33 were of adult size on recapture, ranging from 38'4 to 61*9 cm., 

 with a mean of 42"9 cm., as compared with 31 to 59*5 cm. and an average of 38"6 

 cm. on liberation ; the periods of freedom varied from 54 to 634 days, the average 

 being 283 days ; the distances migrated ranged from 5 to 185 miles, with an average 

 of 7r4 miles, and a mean rate of travel of 2*5 miles per 10 days. Three of the 

 females were under the adult size, the average being 36-6 cm., as compared with 

 36 cm. on liberation ; the average period of freedom was 60 days, and the mean 

 distance travelled 11" 8 miles, with a mean rate of 1'9 miles. 



The Extent and Direction of Migration. 



First Quarter. — Li this period is included the remainder of the month of March, 

 in which 2 males were recaptured, both in the Firth of Forth, and both " immature " 

 1, of 33-32' 9 cm., was taken, after 2 days, off Largo, at a distance of 6 miles; 

 the other, of 35"5-35"5 cm., was caught, after 5 days, off Pittenweem, at a distance 

 of 6 miles. 



Four were caught in April, 3 males and 1 female, all within the Firth of Forth, 

 and all " immature." The female, which measured 37-37*2 cm., was taken off 

 Largo, at a distance of 6 miles, after 30 days ; all the males were recaptured off 

 Pittenweem, at a distance of 4| miles, after 13, 14, and 16 days ; they measured 

 36-5-36-4 cm., 35-5-35-7 cm., and 37-37 cm., and were thus above the size of 

 33 cm., assigned as the minimum size of the adult males. 



Six were recaptured in May, 2 males and 4 females, all " immature." One of 

 the males, measuring 345-35-2 cm., was taken near Elie, in the Firth of Forth, 

 after 54 days, at a distance of 2| miles ; the other male was caught to the east of 

 the Isle of May, at a distance of 24|- miles, after 46 days ; it meastsed 32-5-33 cm. 

 Two of the females were found in the same direction as the last male, 1, measuring 

 39-5-39-2 cm., at a distance of 16i miles, after 54 days, the other, measuring 35-5- 

 35 cm., at a distance of 2f miles, after 36 days ; the third female was got north- 

 east of the Bell Rock, at a distance of 39 miles, after 61 days ; it measured 37-5- 

 38-4 cm. ; the remaining female, of 39-39-3 cm., was taken, after 58 days, near 

 Buchanness, at a distance of 86 miles. 



