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BULLETIN OF THE BUREAU OF FISHERIES 



We have encountered one or more centers of abundance for Si 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: 



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 £. elegans, but an intermediate station of about 

 the same temperature and salinity yielded only 2S, 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 Sagitta? 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 



