318 BULLETIN OF THE BUKEAU OF FISHERIES 



level, 69 but the numbers caught at the surface were usually small compared to the 

 deep hauls. The two stations at which moderately rich surface catches were made 

 were both occupied after dark; at one of them (20049) there were nearly as many 

 S. elegans on the surface as in the 240-0 meter haul, while at the other (20066) 

 swarms of this chretognath dominated the water at the time, but the deep haul cap- 

 tured upwards of a liter of them and the surface net but about half as many. On 

 the whole, these stations suggest that the sagitta population was sparser above than 

 below, say, 10 meters depth in March, but below that depth they afford no evidence 

 of concentration at any level down to the deepest stratum of the gulf. 



S. elegans occurred as regularly at the surface in April, 1920 (18 stations out of 

 a possible 22), as in March; usually, however, in small numbers, except that the 

 notable swarm which we had encountered on the eastern part of Georges Bank the 

 month before, just mentioned (station 20066), still dominated the water there on 

 April 16, at the surface as well as at 50 meters depth. S. elegans was also taken on 

 the surface, though in small numbers, at all our stations in the western side of the 

 gulf during the first half of May in 1920, by which time the surface temperature 

 had risen to 6° to 9.7°. In summer, however, we have usually found few or no S. 

 elegans at the surface, even at localities where it has been plentiful at some lower 

 level, and the zone between 40 and 100 meters has generally proved the most pro- 

 ductive of the large adult S. elegans, though they have been taken in sufficient num- 

 bers in the deeper hauls to establish their presence, though in diminishing number, 

 right down to the bottom of the deep basins. Perhaps the most instructive example 

 of this vertical stratification which has come to our notice was in the Massachusetts 

 Bay region on July 19, 1916, when there were few or no S. elegans at the surface 

 and relatively few (compared to the copepods) at 30 to 40 meters, but swarms 

 at 80 to 90 meters. Similarly, the surface haul took no Sagitta? and the 30-meter 

 haul but few off Cape Cod on July S, 1913, although the net from 60 meters brought 

 back an abundance of them (Bigelow, 1915, p. 267). In the eastern corner of the 

 basin of the gulf, off the mouth of the Bay of Fundy (station 10246), on August 12, 

 1914, oidy one S. elegans was taken on the surface, many in the 50-0-meter haul, 

 and few at 150-0 meters. No S. elegans were taken on the surface on July 23, 1914 

 (station 10224), on the eastern part of Georges Bank, where it was plentiful at 40 

 meters, and other instances of this same sort might be mentioned. 



Although our surface tows usually have yielded no S. elegans or only a scattering 

 of them in summer, we have occasionally taken it in abundance right on the sur- 

 face in July and August. This, for instance, was the case near Mount Desert Rock 

 on August 16, 1912 (station 10032), south of Nantucket Shoals, July 9, 1913 

 (station 10060), and in the Northern Channel, July 25, 1914 (station 10229), while 

 Huntsman (1919, p. 464) records it at the surface at one station in the Bay of 

 Fundy in mid-September. 



The large-sized individuals of 8. elegans were relatively as scarce at the surface 

 in the western half of the gulf at the end of October and during the first days of 

 November in 1 91 6, 70 when the surface temperature had fallen to 8.3° to 10.2°, as they 



'• S. elegant taken in 20 surface tows out of a possible 27. 



~° No large ones takon in the surface hauls, stations 10399 to 10404. 



