368 



Part III. — Fifteenth Annual Report 



the movement of the water ; in the case of flat-fishes, the young then 

 settle on the bottom, and have completed their pelagic life. 



The period during which the young fish is subject to the movement 

 of the current must vary considerably in different species, but, except in 

 a few cases, we do not yet possess exact information as to the duration 

 of the post-larval stage. It has, however, to be noted in this connec- 

 tion that, while the pelagic eggs are almost always confined to the 

 surface wators, the larval and post-larval fishes become more abundant 

 in the intermediate layers and towards the bottom. As a rule, the 

 surface tow-net takes eggs and the bottom tow-net takes larval and post- 

 larval fishes. Owing, therefore, to the sinking of the young fishes from 

 the surface layers, they will not be so liable to be carried by the current, 

 unless the latter also equally involves the bottom layers. 



Both the pelagic eggs and the larvae that issue from them are very 

 small, as may be seen from the following table comprising some of the 

 chief forms, and which gives measurements in fractions of an inch : — 



of egg. 1 " } A A A A A A A A A A A A 

 L T^vi ?} * * * ••• i A - * * * * * A 



It will be evident that these tiny fishes, the longest of which on emerg- 

 ing from the egg is only about Jth of an inch in length, could in any 

 case have but a feeble power of contending with the current. 



It is of great importance, in dealing with the question of the transport 

 of pelagic eggs and larvae, to consider the position of the places where 

 the various species spawn — the location of their breeding-grounds — and 

 also the time during which the spawning occurs, or the spawning season. 

 The importance of the latter point chiefly relates to the duration of the 

 period of development within the egg, for in summer, when the tempera- 

 ture of the water is higher, the pelagic eggs hatch much more rapidly 

 than in the winter or spring. The investigations made by the ' Garland ' 

 have thrown a great deal of light on both these questions. It has been 

 shown that the important food-fishes, such as cod, plaice, haddock, ling, 

 saithe, turbot, halibut, sole, lemon sole, do not spawn within the terri- 

 torial waters on the East Coast ; and this has been subsequently confirmed 

 in other places where the physical conditions are similar, and especially 

 when the depth of the water is not great. * There is little doubt that 

 around the whole of the North Sea, with the exception of the deep 

 waters off the Norwegian coast, the fishes named do not spawn within 

 the three-mile limit, but further out from shore. On the West Coast, 

 on the other hand, where the physical conditions are different and deep 

 water extends close to the shore, spawning fishes may be found within 

 the territorial zone. Fishes that do spawn within the three-mile limit 

 on the East Coast, as well as further off, are the dabs, the flounder, the 

 sprat, and the gurnard ; and while the great majority of whiting spawn 

 beyond the limit, a few spawn on the borders or within the limits. The 

 dabs also spawn chiefly offshore, and the only species which appear to 

 shed their eggs rather more within than without the limit are the flounder 

 and the sprat. 



The fact just stated, that the valuable food-fishes do not spawn within 

 the territorial waters in the North Sea, is one of great importance. The 



* See my papers, 'The Spawning and Spawning Places of Marine Food Fishes,' 

 Eighth Ann. Report, Part III. p. 257 (1890); 'Observations on the Reproduction, 

 Maturity, and Sexual Relations of the Food Fishes,' Tenth Ann. Report, Part III, 

 p. 235 (1892). 



Cod - clock! W ing. Saithe " Lill S- Turbot - Bri11 - Sole - PIaice - L |Se n Flouuder - Dab - 



