166 Part III. — Sixteenth Annual Report 



shows that their movements are more or less erratic. On February 14, 

 1890, Euphausiidse are recorded as "common" in a bottom tow-net 

 gathering at Station V., but at Station VII., a little to the south of 

 Station V., trawled the previous day, they are described as " very rare," 

 while, on the other hand, the Mysidse were more common, and in much 

 greater variety, at this station. Moreover, at Station I., which is in line 

 with Station V., but a little farther west, and also at Stations II., III., 

 and IV., which were all tow-netted within a few days of each other, 

 Euphausiidse are either altogether absent from the tow-net lists or they 

 are described as " rare." These Schizopods were again present in the 

 Forth in considerable numbers in the following March; they were 

 common at Stations I., III., IV, VIII. , and IX., but few or rare at 

 Stations II., V., VI., and VII. During the following summer 

 Euphausiidse were entirely absent from, or were very scarce in, the 

 tow-net gatherings which were then collected ; but the records for the 

 ensuing month of October describe these organisms as frequent at some 

 of the stations during that month, and they continue to be represented 

 in the tow-net gatherings in varying numbers, from one or other of the 

 stations, all through the winter and on to the spring of 1891. During 

 the summer and winter months of that year comparatively few records of 

 the Euphausiidse occur in the lists of tow-net gatherings, and not till the 

 beginning of 1892 is there much increase in the number of the records; 

 but, though in February and March there is a decided increase, the 

 captures of them even then are usually described as " few " or " rare." 

 With one or two exceptions, Schizopods continued to be scarce in the 

 tow-net gatherings till the winter of 1893-94, when they appear to have 

 become more than usually numerous, and, in a considerable proportion of 

 the gatherings collected during December and January of that winter, 

 they are referred to as " common " or " frequent." With the advent of 

 summer, however, and from that time on into 1895, the numbers of these 

 crustaceans are again considerably reduced. From a study of all the 

 facts at our disposal in the published records in the Fishery Board's 

 Annual Reports for 1889 to 1896, there seems to be a fair amount of 

 evidence tending to show the existence of a more or less regular yearly 

 increase and decrease in the numbers of Schizopoda present in the estuary 

 of the Forth, but the reason of this increase and decrease is not sufficiently 

 clear to permit at present of a satisfactory explanation. 



Besides this apparent yearly variation referred to, there also appears 

 to be a fluctuation, which may or may not be regular, that extends over 

 a longer time. I refer to the presence of Schizopoda in considerable 

 numbers in the winter of 1889-90, and again in the winter of 1893-94 ; 

 but to ascertain whether this variation is merely accidental or not would 

 have required the investigations to be carried on over a much longer 

 period than they have been. In considering this question of the seasonal 

 variations of the Schizopoda, I have dealt mainly with the Euphausiidse, 

 because this family is the one most numerously represented in the Firth 

 of Forth, and the one which has shown the greatest tendency to a regular 

 periodic increase and decrease. The Mysidse, also, to some extent show a 

 similar tendency to variation, but the variation is scarcely so well marked 

 as in the case of Euphausiidse. 



