SEA-FISHERIES LABORATORY. 131 



continuous one, that representing the age is discontinuous. 

 It is sometimes difficult, at particular seasons in the year, 

 to be sure of the number of rings of growth in the 

 otolith. A faint marking on the margin may be the 

 beginning of another opaque ring, but the appearance 

 may also be only the effect of refraction. A week or so later 

 it might have been possible to ascertain with certainty 

 the age of the otolith in question; but there would be a 

 difference of a whole year in the recorded age of the fish, 

 while the length of the latter would hardly have changed. 

 Obviously the " lumping " together of catches consisting 

 of plaice which were passing through this transition 

 stage, and others taken before or after the cessation of 

 growth, would produce discordant results. 



The plaice examined in 1909 are therefore grouped 

 according to the precise fishing ground and the month of 

 capture. The disadvantage inherent in this classification 

 of the results is that small numbers of fish must, of 

 necessity, be considered. It would, of course, be possible 

 to examine, say, 1,000 plaice from each fishing ground 

 during three or four sample months of the year, but the 

 practical difficulties of investigation on such a scale are 

 very obvious. On the whole it is better to deal with 

 small numbers of fish taken under precisely similar 

 conditions, and trust that the summation of the results 

 of several years' investigation may afford accurate data 

 for age-determinations. 



The tables on pp. 172-178 include the results of all 

 the measurements made in 1909, and are summarised in 

 the table on p. 180. It will be seen, by inspection 

 of the latter, that there are gaps in the series representing 

 each fishing-ground; and these gaps are due partly to 

 the fact that plaice are not present on each ground to 

 abundance throughout the year, and partly to the not 



