MIGRATIONS OF COD 79 
Table 31 . — Various water temperatures, selected to show the wide difference between Nantucket Shoals 
and the Chatham-South Channel region, particularly in summer — Continued 
Refer- 
ence 
No. 
Station 
Date 
Position 
Locality 
X Depth ij 
Temperature 
Meters 
Fath- 
oms 
0 C. 
0 F. 
Chatham grounds — Continued 
30 
July 19,1928 
41 
35 N. 
12 miles NE. true from Round Shoal buoy 
0 
0 
15.8 
CO. 5 
69 
32 W. 
11 
6 
15.4 
59.8 
16 
9 
13. 6 
56. 5 
18 
10 
10. 8 
51. 5 
22 
12 
9. 5 
49. 1 
44 
24 
6. 6 
44. 0 
31 
Q 10085 
Aug. 4, 1913 
41 
39 N. 
12 miles E. from Chatham Light 
0 
0 
17. 5 
63.5 
69 
42 W. 
18 
10 
6.4 
43.6 
48 
26 
5.8 
42. 4 
32 
G 10257 
Aug. 24, 1914 
41 
39 N. 
6 miles E. from Chatham Light.. 
0 
0 
20.0 
68.0 
69 
49 W. 
25 
14 
6.8 
44.2 
South Channel 
33 
A 20345 
July 16, 1928 
41 
16 N. 
19 miles SE. by E. true from Round Shoal buoy .. . 
0 
0 
11.6 
52.8 
69 
23 W. 
20 
11 
7.0 
44.6 
45 
24 
5.3 
41. 5 
34 
G 10354 
July 25,1916 
40 
26 N. 
57 miles SSE. true from Sankaty Head, Nantucket 
0 
0 
13. 6 
56.5 
69 
24 W. 
30 
16 
8.7 
47. 7 
70 
39 
6. 1 
43.0 
Georges Bank ( western part) 
35 
G 10059 
July 9, 1913 
41 
06 N. 
68 miles SE. by EH E. true from Chatham Light 
0 
0 
13.3 
56.0 
68 
42 W. 
27 
14 
12. 6 
54.6 
55 
30 
12. 6 
54. 6 
36 
G 10347 
July 23,1916 
41 
06 N. 
64 miles SE. by E. true from Chatham Light 
0 
0 
11.4 
52. 5 
68 
51 W. 
30 
16 
10.9 
51.6 
60 
32 
9.6 
49.3 
37 
G 10348 
do__ 
40 
49 N. 
90 miles SE. by E. true from Chatham Light 
0 
0 
11. 7 
53. 0 
68 
21 W. 
25 
14 
11.3 
52.4 
50 
27 
11. 2 
52. 2 
38 
A 20212 
Sept. 5, 1920 
41 
12 N. 
68 miles SE. by E. true from Chatham Light.. 
0 
0 
13.9 
57 
68 
35 W. 
13 
7 
14.8 
58. 6 
53 
29 
13.7 
56.6 
It can be seen from Table 31 that there is a striking difference in the summer 
temperature on bottom between Nantucket Shoals and the Chatham-South Channel 
region, the latter being much the cooler. If then cod on the shoals wish to avoid the 
relatively warm water (50° to 60° F.) that obtains there in summer they need migrate 
eastward only 10 to 15 miles to find an environment of about 40° to 45° F., and 
even a shorter distance to find intermediate temperatures. Yet, only a small part 
of the Nantucket cod population at times make this summer emigration, for it was 
only the years from 1923 to 1925 during this investigation that the number was at 
all appreciable, as only stragglers journeyed eastward from 1926 to 1928. 
If a good series of temperatures had been obtained for each of these years some 
correlation between the warmth of the water and the tendency of cod to emigrate 
eastward from the shoals might have been found. But our records are too incom- 
plete for such an analysis. It was found, however, that during 1925, which was the 
warmest year of the six, considerably more cod did move eastward into cooler water 
than during any of the other years of record. (See Table 20, p. 36.) But in spite of 
this result we have no substantial proof based on temperature alone that Nantucket 
cod shift ground to avoid warm water in summer. 
So far as the tendency for cod to seek cooler water is concerned, the small dif- 
ferences that exist in the maximum temperatures on the shoals each summer appear 
to be of less importance than the average size of the adult and near-adult cod which 
make up the population there. For example, if the lengths of the cod caught by 
the Halcyon and the Albatross II are averaged for the three years from 1923 to 1925, 
when a perceptible emigration of Nantucket cod occurred to the eastward, and for 
105919—30 6 
