304 



Part III. — Twenty-fourth Annual Report 



the spring herrings spawn when the bottom water is the coldest of the 

 year and the autumn spawners when it is the warmest of the year. 



The effect of the difference on the rate of development in the eggs must 

 be considerable. From the Table given above it may be inferred that the 

 eggs of the spring fish take from about 25 to 30 days to hatch in 

 February and March, while the eggs of the autumn spawners hatch in 9 

 or 10 days, or approximately in a third of the time. One must therefore 

 add these numbers to the date fixed for the maximum spawning in order 

 to determine the period when most of the larval herrings appear in the 

 water. In the case of the spring fish the period is about the middle of 

 April, and in the case of the autumn fish it is about the second week of 

 September. 



The advantage to the autumn herring in respect of the quicker develop- 

 ment in the egg is, however, compensated by the difference in the tem- 

 perature to which the young growing herrings are soon exposed. With the 

 spring fish the temperature is a rising one, favourable to growth, for many 

 subsequent months, while with those hatched in autumn, the temperature 

 is a falling one, especially at the surface, and thus less favourable to 

 growth 



How long it may take in some instances for the young of the spring 

 herring to reach even a small size is shown by an experiment of Mr. 

 Harald Dannevig. On 13th- 14th March he fertilised some herring eggs 

 and brought them to the Marine Laboratory at Aberdeen, where they 

 hatched on 9th April, after an " incubation " period of 26 or 27 days. 

 The larvae then measured 8mm. in length. The yolk was not absorbed 

 until 9 days later, and 23 days after hatching the post-larvae measured 

 only 10mm. In this case 49 or 50 days elapsed (viz., 13th-14th March- 

 2nd May) before the young herring measured f-ths of an inch, thus 

 offering a great contrast to the results of Meyer, but in the latter case the 

 temperature during the experiment was not the same as at Aberdeen. 

 Much stress cannot be put upon the experiment, but Mr. Dannevig 

 is skilful in rearing post-larval fishes, as his success with the plaice 

 shows. 



The difference in temperature between the bottom and surface water, 

 above shown, no doubt explains the fact that the larva? in spring soon 

 seek the upper layers, while in autumn they do this to a very small 

 extent, the later larvae, as Masterman says, appearing never to leave the 

 bottom, but to migrate shorewards at once, without an intermediate 

 journey through the mid-water and surface layers. 



The young herring when it is hatched is of a length ranging from 

 5'2mm. to 8"8mm. inch), and the yolk disappears in from three or 

 four days to a week ; traces may be found in larvae measuring over 9mm. 



It may be mentioned that the larva of the sprat is 3-3*7mm. when 

 hatched, and, according to Ehrenbaum, the length when the yolk is 

 absorbed (in about a week) is 4'7mm. They may thus be easily 

 separated in some collections. 



6.— A Criticism of Meyer's Conclusions and Observations. 



Before dealing with the collections of herrings given in the Tables 

 appended to this report, it may be well to consider some general results 

 as to the growth of fishes deduced from my researches with a number of 

 other species, and how they bear upon the statements concerning the 

 growth of the herring above quoted, and more especially those of Meyer 

 and Jenkins. 



