312 
BULLETIN OP THE BUREAU OP FISHERIES 
We have encountered one or more centers of abundance for S. elegans on every 
cruise, and on such occasions the numbers actually present in the water may be 
very great (for so large an animal) , as illustrated by the following examples : 
Date 
Station 
Approxi- 
mate 
number 
of S. 
elegans 
per 
square 
meter 
Date 
Station 
Approxi- 
mate 
number 
of S. 
elegans 
per 
square 
meter 
July 19, 1916 
Do 
July 23, 1916 
10341, Massachusetts Bay... 
10342, Massachusetts Bay... 
10347, Georges Bank 
2,500 
1, 750 
2, 500 
July 25, 1916 
July 23, 1914. 
July 25, 1914 
10354, ofi Nantucket 
10224, Georges Bank.. 
10330, near Cape Sable 
5. 000 
2.000 
2,140 
In every case, however, we have found these swarms limited to areas so small 
that the neighboring stations have yielded only a fraction as many Sagittse. Thus, 
in July, 1913, hauls off northern Cape Cod and on the western end of Georges Bank 
each yielded upwards of 1,000 large S. elegans, but an intermediate station of about 
the same temperature and salinity yielded only 28, while a month later the Sagitta 
stock at the first of these localities had dwindled nearly to the vanishing point 
(Bigelow, 1915, p. 298). Variations in the local abundance of this species were no 
less striking on August 15 of the same year, when we found it abundant off Cape 
Elizabeth and near the Isles of Shoals but extremely rare at a station halfway 
between those two localities. Again, on July 23, 1914, we found the waters over the 
northeast edge of Georges Bank (station 10224) alive with S. elegans, though there 
were very few at a neighboring station (10223) on the bank to the south or over 
the deep a few miles to the north. Similarly, S. elegans swarmed a couple of days 
later near Cape Sable and in the Northern Channel (stations 10229 and 10230), 
but was so rare over Browns Bank (station 10228) that our tow nettings yielded 
only one or two examples; and in July, 1916, we found S. elegans in multitudes in 
Massachusetts Bay on the 19th (station 10342) but much less common off Cape 
Cod only a few miles away (station 10344). 
The data gathered on the spring cruises of 1913 and 1920 show that S. elegans , 
like most other large planktonic animals, becomes very scarce in most parts of the 
Gulf in early spring shortly after the water has cooled to its winter minimum, and 
falls to its lowest numerical ebb during the vernal flowering period of the diatoms. 
Thus in Massachusetts Bay in 1913 S. elegans dominated the tow in mid-February, 
with a catch of about 125 cubic centimeters in the horizontal haul on the 13th (Bige- 
low, 1914a, p. 405); but it had become so scarce by March 4 that the total catch in 
the large net (half hour’s haul) was only 12 individuals, and no Sagittse at all were 
taken on April 3, when diatoms were swarming. In 1920 S. elegans persisted in some 
numbers in the bay until the diatom flowerings were well advanced, vertical hauls 
on April 6 and 9 (stations 20089 and 20090) still yielding Sagittse at the rates of 10 
and 40 specimens, respectively, per square meter; but shortly thereafter they became 
so scarce in that general region that none were taken in the vertical haul and only 
occasional specimens in the horizontals on May 4 (station 20120). In this respect 
