488 
BULLETIN OF THE BUREAU OF FISHERIES 
the two groups is 36.5 percent, indicating that the earlier shells had lost one-third of 
their efficiency as spat collectors in 9 days, even during the time when the bay water 
was most free from fouling materials and organisms. The shells in wire bags are less 
subject to fouling than those thrown directly upon the grounds, for they are well 
supported above the silt of the bottom and tidal flow serves to keep them clean. 
The depreciation in effectiveness of shells thrown on the grounds is probably very 
rapid, particularly during early summer when there is still considerable silt. An 
understanding of the setting periods should serve to make it possible to eliminate 
much of the loss due to fouling of cultch. 
It was noted that setting periods appeared to be approximately 2, 4, or 6 weeks 
apart, rather definitely spaced, suggesting that tidal periodicity might be concerned. 
By plotting the daily range of tide throughout each setting season (fig. 23 to 27) this 
suggestion was shown to be well founded. In almost every case the time of maximum 
frequency of setting is near to tbe time of greatest tidal range; and in many cases it 
may be observed that during neap tides, when the range of tide is small, the frequency 
of setting is also low. In some of the series in which 7-day bags were used it is difficult 
to decide from tbe graphs the exact dates of maximum frequency of setting. To 
throw more light upon the nature of the periodicity and the possible relation to tidal 
conditions a series of bags of shells was tested in one dike in 1935 in such a manner 
that each bag generally remained in the water onty 2 or 3 days. 
Table 33. — -Number of spat caught on bags of shells planted at frequent intervals in Oyster Bay, dike 5, 
1935 
Date 
planted 
Date 
removed 
Number 
of days 
Total number 
of spat 
Number of spat 
daily 
Date 
planted 
Date 
removed 
Number 
of days 
Total number 
of spat 
Number of 
spat daily 
June 18 
June 20 
2 
1,120 
554 
July 23 
July 25 
2 
4,786 
2, 393 
June 19 
June 21 
2 
1, S40 
920 
July 24 
July 26 
2 
2, 788 
1,394 
June 20 
June 22 
2 
4. 123 
2, 061 
July 25 
July 27 
2 
2, 851 
1,425 
June 21 
June 24 
3 
6, 909 
2,303 
July 26 
July 29. 
3 
3, 231 
1,077 
June 24 
June 25 
1 
5, 471 
5, 471 
July 27 
-__do — 
2 
883 
441 
June 22 
June 24 
2 
3, 226 
1,613 
Do— 
July 30 
3 
1, 220 
407 
June 25 
June 26 
1 
1, 186 
1,186 
July 29 
July 31 
2 
177 
88 
June 20 
Juno 27 
1 
4, 131 
4, 131 
July 30 
Aug. 1 
2 
88 
44 
June 27 
June 28 
1 
8, 703 
8, 703 
July 31 
Aug. 2 
2 
37 
18 
June 28 
July 1 
3 
8,211 
2, 737 
Aug. 1 
Aug. 3 
2 
83 
41 
June 29 
--.do 
2 
37, 704 
18, 852 
Aug. 2 
Aug. 5 
3 
122 
41 
Do... 
July 2 
3 
10, 157 
3, 386 
Aug. 3 
Aug. 6 
3 
191 
64 
July 1 
July 3 
2 
24. 120 
12, 060 
Do-.. 
Aug. 5 
2 
57 
28 
July 2 
July 4 
2 
29, 149 
14, 574 
Aug. 5 
Aug. 7 
2 
60 
30 
July 3 
J uly 5 
2 
31,043 
15, 021 
Aug. 6 
Aug. 8 
2 
34 
17 
July 4 
July 6 
2 
20, 360 
10, 180 
Aug. 7 
Aug. 9 
2 
57 
28 
July 5 
July 8 
3 
16, 640 
5, 547 
Aug. 8 
Aug. 10 
2 
191 
95 
July 0 
...do 
2 
7,500 
3, 750 
Aug. 9 
Aug. 12 
3 
1, 200 
400 
Do... 
July 9 
3 
8, 805 
2, 935 
Aug. 10 
-_-do 
2 
360 
180 
July 8 
July 10 
2 
2,914 
1, 457 
Do... 
Aug. 17 
7 
45,314 
6, 473 
July 10 
July 12 
2 
1, OSO 
540 
Aug. 12 
__.do 
5 
47, 968 
9, 593 
July 11 
July 13 
2 
622 
311 
Aug. 17 
Aug. 19 
2 
17, 126 
8, 563 
July 12 
July 15 
3 
3,162 
1, 054 
Do-.. 
Aug. 20 
3 
19, 571 
6, 524 
July 13 
___do 
2 
4, 520 
2, 260 
Aug. 19 
Aug. 21 
2 
9,694 
4, 847 
Do.. 
July 16 
3 
6, 168 
2,056 
Aug. 22 
Aug. 24 
2 
4, 351 
2, 175 
July 15 
July 17 
2 
4, 617 
2, 308 
Aug. 23 
Aug. 26 
3 
4,783 
1,594 
July 10 
July 18 
2 
4, 445 
2, 222 
Aug. 24 
Aug. 27 
3 
9, 434 
3, 145 
July 17 
July 19 
2 
4,200 
2, 100 
Aug. 26 
Aug. 28 
2 
4, 662 
2, 331 
July 18 
July 20 
2 
4, 831 
2, 415 
Aug. 27 
Aug. 29 
2 
6, 225 
3,112 
July 19 
July 22 
3 
10, 460 
3, 487 
Aug. 28 
Aug. 30 
2 
3, 663 
1,831 
July 20 
July 23 
3 
5, 723 
1, 908 
Aug. 29 
Aug. 31 
2 
2, 757 
1, 378 
Do-.. 
July 22 
2 
3, 448 
1,724 
Aug. 30 
Sept. 2 
3 
5, 794 
1,931 
July 22 
July 24 
2 
2, 843 
1,421 
Aug. 31 
Sept. 3 
3 
6, 791 
2, 263 
Smaller units make the graph (fig. 33) more complete and permit a more certain 
statement of the correlation between frequency of setting and tidal periods. The 
results of the counts are given in detail in table 33. On the graph the daily range of 
tide is also plotted, and it may readily be seen that the maximum of the first setting 
period is centered almost exactly during a period of extreme, or spring, tides. Setting 
started on June 17, at the time of maximum range of the preceding tidal period, and 
