5 - 



APPENDIX H': REDEKE 



themselves to the cooler water of the true "Wattenmeer", i. e. the waters around and 

 between the Frisian Islands. 



The chief resort of the smallest plaice of this year is in the "Wattenmeer" on the 

 shallow sand-banks moderately warmed in summer. Thus, they are found in great abund- 

 ance on the shallowest parts just below low-water mark along the whole Dutch coast. 

 Finally, they have been found to occur in the Oosterschelde where similar conditions 

 prevail as in the "Wattenmeer". 



In April, the little fish of the Scheldt had a length of 14 to 30 mm., in June from 

 22 to 76 mm. In July, 94 plaice of the O-group taken at Helder measured 35 to 69 mm. 

 (M. = 50), the majority 47—53 mm.; at other places, they had a length of 50 to 85 mm. 

 In September they had grown to 54 to m mm. (M. = 65) and in October to 55 to 

 114 mm. (M. = 76). In the following February, these small plaice had grown to 8 — 9 cm. ; 

 but they are now of the I-group and no longer of the O-group. 



The plaice of this group, now in their second year, are found in the shallow water '^^^ p'"'''* °^ 



. 1 t 1 r 1 r the second year 



durmg summer and autumn together with those of the previous year, but more fre- 

 quently on somewhat deeper grounds in the neighbourhood of the coast; in spring, 

 they are as close to the coast as 10 to 15 m., in autumn and winter they are tolerably 

 far out to sea, about the 20 m. line. 



They seem to grow but moderately in the spring : from January to June only about 

 2 cm., as their length in the latter month only reaches 10 to 11 cm. on an average. 



In June and July, as soon as the water of the Wattenmeer and shallow coastal zone 

 of the North Sea begins to be greatly warmed, the I-group travels back into deeper water. 

 The majority of these plaice, especially the largest, have now left the Wattenmeer and 

 moved into the open sea, where they dwell in the coastal edge down to depths of about 

 20 m. They grow better here, as their length, which is about 1 1 cm. on an average in 

 July, reaches to 15 cm. on an average in September. 



Again, it is very striking, that plaice of the same age taken in the Zuydersee at the 

 same time show a length of only 11 cm. on the average, thus considerably less. A good haul 

 of young plaice (240 specimens) was made in the Zuydersee on the 17"' of September- 

 It consisted of specimens of the O- and I-groups, as was proved by investigation of the 

 otoliths and can be seen from the accompanying percentage frequency-polygon (p. 6 fig. i.) 



The continuous line refers to this haul, the broken line to a haul with the otter- 

 trawl covered by finer netting (647 specimens), which was made in the North Sea at 

 the island of Vlieland on the 20''' of September, thus 3 days later. 



The difference in size mentioned can be clearly seen from the curs^es without further 

 explanation. 



The plaice of the I-group seem also to grow little in winter, as we found the 

 average length at Vlieland to be always 15 to 16 cm. from November to March, and at 

 other places, at Egmont, 14 cm. This was in March: they were thus no longer of the 

 I-group but belonged to the Il-group, i. e. they were at the beginning of their third year. 



The plaice of the Il-group frequent the coast to about the 20 m. line in spring; up The plaice ot 



T.I , 1 , , , , r ^ A the third year 



to July, they grow about 2 to 3 cm. and have then an average length or 16 to 17 cm. At 

 this time, they occur though rarely on the true fishing-grounds in greater depths. In 

 summer, however, they move in great shoals from the coast into the deeper water, and 

 from this time onwards are found in numbers on the grounds just mentioned, their 



