19 - 



APPENDIX B : HEINCKE 



Otherwise, the plaice of the older years (6 and over) are relatively, and indeed 

 absolutely, more numerous beyond than within the 40 m. line. 



The two sexes of the plaice. Commencement of maturity. We have 

 determined the sex of very numerous plaice and found, (from 43,500 specimens in round 

 numbers), that in every 100, about 53 are males and 47 females on the average. Within 

 our region of observation the females are, on an average, somewhat larger than the males 

 at the same age; how much larger they are, cannot as yet be exactly determined. 



So far as the age is concerned, at which the plaice becomes mature, i. e. spawns 

 for the first time, we have not found a single female which did not possess at least 4 

 white otolith rings and had therefore completed 4 full years, amongst the plaice which 

 were undoubtedly ripe and whose otoliths were examined. On the other hand, we found 

 several males which 



were ripe after 3 full -^"'^ Distance from W in sm. 40 m. Line 



years. The average size 

 of the plaice at first- 

 maturity in the Ger- 

 man Bight of the North 

 Sea is for the males, 

 about 30 to 35 cm., 

 for the females 35 to 

 40 cm. 



The yearly in- 

 crease of growth 

 in the plaice is 

 greatest in the 2'^'' to 

 the 4* year, especially 

 in the 3"''^, according 

 to our investigations; 

 after the attainment of 

 maturity , the yearly 

 growth gradually be- 

 comes less and is very small in the older stages. We have examined some large plaice of 

 66 to 70 cm., which were certainly 20 years old and over that, and had consequently 

 spawned 15 times and more. Unfortunately, we have caught relatively few large plaice, as 

 yet, of over 55 cm. in length, probably because we have made relatively few hauls in the 

 open North Sea and it appears from our observations already mentioned, that the largest 

 and oldest plaice are caught furthest out in the sea. 



We have not been able, as yet, to determine from our own observations, at what parts 

 of the North Sea the spawning or fully-ripe plaice collect together in large shoals. The 

 spawning time must occur between January and April, with the maximum probably in 

 February, but hitherto, we could only begin our investigations as a rule in March. A 

 moderate number of large ripe plaice was twice taken in this month, 30 sea-miles N.W. 

 from Heligoland and on the Oyster Bank; a smaller quantity was found c. 65 sea-miles 

 N.W. on the 40 m. line, in the so-called Clay Deep, the southern mud bank on the 

 southern part of the Jutland Bank. These discoveries of spawning plaice were made in 



Pig. 3. Distribution of the plaice caught in the 7 hauls mentioned, graded 

 according to depth, distance of the fishing-ground from land, and their 



average size. 



