— 2;{ - LATER STAGES: PLEURONECTIDS 



Plaice of Groups I and II in West Bay (English Channel) were found to be considerably 

 larger (on an average) than plaice of approximately the same age anywhere off the coast 

 of Holland, England or Denmark (North Sea?). The otoliths of these English Channel 

 fish are shown to be readily distinguishable by the greater breadth of the rings showing 

 a more rapid growth. This direct proof that the growth rate may vary considerably in 

 different regions is important as the inference to the same effect often made from comparison 

 of average lengths on different grounds is open to great uncertainty. Other differences 

 in average length of plaice of the same age are shown to exist. Thus at the same age 

 and the same distance from shore the plaice of the Horn Reef (Danish) are smaller than 

 those off the Texel (Dutch). The author suggests at least two possible explanations of 

 this phenomenon, both based upon the greater density of population in the Horn Reef 

 area, namely, more rapid migration offshore and slower rate of growth. In a previous 

 report I have drawn the inference that whilst the II group is only found comparatively 

 near the Danish shore the III group is found uninterruptedly seawards over the whole 

 area to beyond the Dogger Bank, a distance of perhaps 150 miles. In the case of the 

 Texel, the present work seems to show that the migration of plaice extends at most to 

 about 70 miles, when the influence of the English nurseries appears to commence, as 

 shown by a rise in the density of each age-group. 



In all attempts to translate average lengths into growth-rates one is confronted with 

 this same difficulty, which is discussed by the author. If the III group, for example, 

 becomes distributed from Danish waters to the Dogger then the IV group found on any 

 ground, e. g. the Dogger, is a complex of those of the III group which have grown for 

 a year on that ground and obtained the benefit of its high feeding capacity, and those 

 of the IV group, presumably the largest, which have migrated from grounds lying 

 shorewards. The high average length of plaice of any year-group on an offshore ground 

 may be due to all or any of three causes (l) the high average length of the earliest of an 

 age-group reaching the ground, (2) the rapid growth of these fish upon the ground and 

 (3) the high average length of the migrants of subsequent years. So far as the Southern 

 Bight is concerned considerable progress has been made towards a more reliable estimate 

 of the growth-rate. This more or less self-contained area has been sampled by four 

 continuous series of hauls, the results of which are deserving of closer study. 



The author employs the data of the Texel-Leman section for comparison with those 

 of the Scheveningen-to-Southem Deep Water Section. They are shown to be in close 

 agreement and the inference is drawn that the estimates of average yearly growth in this 

 region of the Southern Bight are established on a satisfactory basis, so tar as the higher 

 age groups are concerned. 



The results are as follows : — 



