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Part ILL — Eleventh Annual Report 



the size at which the male fish may be regarded as reaching maturity ; 

 and only nineteen were above 15 inches (four of these being 17 inches 

 long), and this is the size about which the female attains maturity. 

 The figures given refer to the size of the fish when returned to the 

 sea; and they must be kept in view in considering the movements of 

 the fish. The Table shows that only twenty-one specimens of 1 2 inches 

 or above that size were recovered, and of these only one was above 15 

 inches in length. These experiments may therefore be said broadly to 

 deal with the migratory movements of immature plaice. The period 

 which elapsed between the liberation and re-capture of the fish varied in 

 different cases from 2 days to 819 days (or 2 years and 3 months) ; 

 the average being 239*6 days, or 8 months. It will be seen at once, 

 by a glance at the Table, that the extent of the movement does not corre- 

 spond to the length of time the fish was free in the water. In assigning 

 a certain number of miles * as the 1 distance travelled,' I have measured 

 the distance between the place of liberation and the place of recovery in 

 a straight line, or one as direct as possible. It is of course obvious that 

 the fish may in the interval have travelled much further; indeed, it 

 may be said that this must almost always have occurred, but there is 

 nothing to show the extent of this movement. One point comes out 

 clearly in contrasting the tabulated results of the experiments on the cod 

 and common dab with those on the plaice, namely, the comparative 

 stationariness of the latter. The number of miles between the points of 

 liberation and re-capture in the case of the plaice varies from practically 

 nil to 28. The average for all the cases in which the distance is 

 given is 6*15 miles, and the mean period of freedom was, as we have 

 seen, 239*6 days. But certain of the records of the distance travelled by 

 fish captured by trawlers must be regarded with doubt. The seven cap- 

 tured by trawlers, of which particulars are given, are represented to have 

 travelled from 5 to 28 miles; the average distance being 16*6 miles, 

 and the average period of immersion 265*9 days. Some of these records 

 referring to fish at or above the size at which sexual maturity is reached 

 are probably approximately correct ; but others are, I think, erroneous, 

 such, for iiistance, as the case where a plaice of 1 1 inches long is said 

 to have gone offshore 28 miles in 71 days. From the fact that beam- 

 trawling is prohibited under penalties in the waters where most of the 

 fish were liberated, it may have been thought desirable to represent 

 them as having been captured further from the boundary of the closed 

 waters than was actually the case ; and if the few plaice caught by trawl 

 are disregarded, we find the mean distance travelled by the others is 5*1 

 miles in an average period of 241 days. As is shown below, the range of 

 movement of another flat-fish, the common dab, is very much greater, the 

 average distance travelled by the marked specimens of this fish having 

 been 14*5 miles in a mean period of 178*3 days. 



Some of the results may be referred to in detail. One plaice, 10 J inches 

 in length, liberated in the Firth of Forth, at Station VI., opposite Pitten- 

 weem, on 7th November 1889, was re-captured on Abertay Bank at the 

 mouth of the Tay on 26th March. 1891, after the lapse of 504 days, having 

 travelled probably along the coast, from the Firth of Forth and across 

 St Andrews Bay, a distance of at least 19 miles. Another, 14 \ inches in 

 length, was liberated at Station V., near the Isle of May, on 20th October 

 1890, and was re-canght half-a-mile east from Granton Harbour on 27th 

 October in the following year ; it was therefore free for 372 days, and had 

 gone 20 miles. Two specimens, 8J and 9 -J inches long, set free together 

 off Fiddra, on 17th July 1891, were taken at the same place, half-a-mile 

 off Lehh, one on the 27th May, and the other on 7th June 1892, each 

 * The miles are geographical miles. 



