BIOLOGY OF THE ATLANTIC MACKEREL 



181 



9, it is seen that logarithmic curves with a change in slope at 30 days of age, or length 

 of 19.5 mm., fit the points as well or better than does the straight line in the lower part 

 of figure 9. 



The observations on haddock (Walford, 1938, p. 68-69) were taken in a manner 

 similar to those on mackerel. In fact, the material consisted mainly of haddock larvae 

 caught on our mackerel cruises. Walford summarized these by months, giving 

 frequency distributions for each of the four months: April, May, June, and July. 

 From these polymodal frequency distributions, he selected modes that he considered 

 to be homologous, recognizing three such series. Taking his middle series as perhaps 

 the most typical, the modal values, as nearly as can be read from his figure 50, were 



- - 4 



0.4 



50 



40 

 30 



20 i 



10 5 



6 -> 



10 20 30 40 50 60 70 60 90 100 

 AGE, DAYS 



Fioori 10.— Growth of haddock during early lite. Data from Walford, 1938. 



3, 3.5, 18, and 43 mm. on the mid-dates, April 11, May 15, June 17, and July 17, 

 respectively. According to Walford, the 3 mm. mode of the first cruise consisted 

 of recently hatched individuals. Assuming this size to be zero days old, the logarithms 

 of the modal sizes were plotted against age in figure 10, whence it is apparent that the 

 growth of the haddock was logarithmic as in the mackerel. 12 



Data on the northern pike (Embody, 1910) consisted of the average length in 

 samples of two or more specimens drawn from a population reared in the laboratory 

 at water temperatures of 65° to 72° F. Since the data are not readily accessible, they 

 are repeated below : 13 



Age iu days after hatching: 







2 



3 



4 



Total length in 

 \miltimcters 



7 



9. 25 



10. 5 



11.5 



. Total length in 



Age in days after hatching: mllllmeteu 



5 13 



7 '14 



9 15.25 



11 16 



! Sac absorbed. 



» Another of the series of modes selected by Walford also becomes logarithmic with slight re-interpretation of his fig. 49. The 

 new interpretation involves the assumption that the group in question was under-represented in the April sample, an assumption 

 that is reasonable in view of the fact that his samples for this month were from a more easterly area than that subsequently sampled. 

 (This is true also of the central mode, above discussed, but the group forming this mode could have drifted into the area subsequently 

 sampled, whereas the time sequences were such that the group here under consideration in all probability could not have so drifted) . 

 It further involves taking the mode for May at 12 instead of 17 mm. and for June at 30 instead oi 33 mm. These selections are 01 

 prominences on the curve, which are equal to those selected by Walford, and by reason of parallelism with the middle group, seem 

 more reasonable than the points given in Walford's figures 49 and 60. Walford's third series obviously consists of a younger group 

 not present enough months to repay study. 



11 1 am grateful to the late Professor Embody for communicating these data to me by letter. 



