COD EGGS IN MASSACHUSETTS BAY, 1924-1925 



291 



SIZE OF COD EGGS 



In the course of the investigation many interesting observations were made on 

 allied problems, which, for the most part, will have to be treated separately later. 

 However, because of its possible application in future surveys of this type, it may 

 be well to include a brief report on the effect of temperature on the size of cod eggs. 



In making a study of production centers where the local stock is supplemented 

 each year by contributions in the form of eggs and pelagic fry from other sources it 

 will be highly desirable if one can determine in any one area the quantity of eggs 

 supplied from other spawning centers and their relative importance compared with 

 local production. If the temperature at the time of fertilization affects the size of 

 cod eggs, and if the physical conditions in two spawning centers are sufficiently 

 different, then it is quite probable that locally spawned eggs in one of these 

 two areas may be distinguished by measurement from immigrants from the other. 

 For example, on the Grand Banks the cod spawn in summer at a time when the 

 temperature of the shallow banks water has risen considerably above that of the 

 Labrador current. If eggs produced farther north and carried south to the banks can 

 be distinguished, through their size, it may throw important light on the problem 

 of whether the cod stock of the Grand Banks is self-supporting or, if not, to what 

 extent it is dependent upon contributions from other sources. 



I first noticed the variation in cod eggs collected in the region of the Grand 

 Banks on June 5 to 17, 1924. There was a veiy striking difference between those 

 from the warm, shallow water over the bank and those from the cold Arctic current. 

 The average size of the banks eggs, based on measurements of about 500 eggs, was 

 1.28 millimeters, while at station 3, in the Labrador current, the average was 1.42 

 millimeters. The following table gives the results for each station: 



Table 13 



Date, J924 



Station 



Average 



Smallest 



Largest 



Number 

 measured 



June 5 - 



1 

 2 

 3 

 4 



5 

 6 

 7 

 8 



Millimeters 

 1.31 

 1.27 

 1.42 

 1.27 

 1.24 

 1.28 

 1.29 

 1. 30 



Millimeters 

 1. 10 

 1. 17 

 1. 35 

 1.20 

 1.20 

 1. 15 

 1. 17 

 1. 19 



Millimeters 

 1.38 

 1. 32 

 1. 55 

 1.50 

 1.27 

 1.40 

 1. 40 

 1.40 



240 

 5 

 16 

 9 

 7 

 65 

 107 

 66 



June 7 - 



Do 



June 12. 





June 15 . — 



June 16 



June 17 





The eggs were found to average between 1.2 millimeters and 1.3 millimeters 

 everywhere except at No. 3, the most northerly station (approximately 390 miles 

 north of the tip of the Grand Banks), where the surprising average of 1.42 milli- 

 meters was found, no eggs being less than 1.35 millimeters. The total absence of 

 cleavage stages at this station (the earliest eggs having the embryo well developed) 

 indicates that they may have been carried for a long distance and belong to an 

 entirely different race of fish, although I do not think the latter condition probable. 

 The rate of flow of the Labrador current at this point, the low temperature, and the 

 number of planktonic forms occurring here and at no other station, tend to sub- 

 stantiate the former possibility. Metridia longa and Calanus hyperboreas, true arctic 



