16 Fishery Board for Scotland. 



The more complete table for the Dornoch Firth shows that even 

 within a spawning area of limited extent, there are very marked 

 variations in the frequencies of the eggs on the same day at points 

 relatively near to each other. Surface collections which were taken 

 on 27th February 1906 have frequencies of 797, 1370, and 397 respect- 

 ively. The relative proportions of the eggs in the different stages of 

 development are practically identical, so that in all probability these 

 eggs had the same origin. The Dornoch Firth is a shallow inshore 

 area, and it is probable that the tides, carrying the eggs backwards and 

 forwards once in twelve hours within the area, may vitiate deductions 

 from single observations. 



In 1908 the locality was visited in January, February, and March. 

 The frequencies for these months are very high in comparison with 

 those found in spawning season 1904-1905. Probably spawning plaice 

 were more numerous during the season 1907-1908 than during the 

 season 1904-1905. The frequencies of newly spawned eggs are ex- 

 tremely high in February, and although there is a decline in March there 

 are still many newly spawned eggs within the area. On the other hand, 

 on 11th January 1908 almost twenty per cent, of the eggs had already 

 passed beyond the first stages of development, so that it is reasonable 

 to assume that spawning had already begun in the first days of 

 December 1907. 



So far the records of collections from the different water layers 



have not been considered in any detail, although the percentages of 



eggs at the different stages of development are taken from the total 



number of eggs captured at a particular station. The number of eggs 



got in the vertical nets is so small that the results cannot be used with 



any degree of accuracy to compare the frequencies of eggs in the 



difierent water layers. We are thus forced back on the records of the 



horizontal hauls taken with non-closing nets at different depths. 



The cheese-cloth nets used in the observations are attached at definite 



intervals to a vertical loaded line which is towed very slowly behind the 



ship. The net which fishes at the bottom is attached to the vertical 



line quite close to the weight, the other nets are attached at the required 



distances along the line. Such a series of nets takes some time both 



to shoot and to haul, and as the bottom net is put away first and hauled 



in last it is necessarily a longer time in the water than the surface net. 



If these nets fish not only when they are being towed but also when 



they are being hauled the frequencies obtained must be higher than 



those which would be got from closing nets. The nets are towed for 



the same length of time, so that the catches from the nets below the 



surface should theoretically be equal to a horizontal haul and two 



vertical hauls, one at shooting and one at hauling. That is to say, if 



the eggs are uniformly distributed throughout the different water 



layers the number of eggs from the bottom tow-net should not exceed 



the number got in the surface-haul by more than twice the number got 



in the vertical haul. If the following table be considered from this 



point of view, the eggs in the Dornoch Firth were somewhat uniformly 



distributed throughout the different water-layers in January 1905. 



There are only minor differences between the numbers captured at the 



different depths. The table also shows that the vertical distribution 



in January 1908 was obviously very unequal, for most of the eggs were 



found in the surface layers. It should be noted that the frequencies 



