PLANKTON OF THE GULF OF MAINE 27 



euphausiids and hyperiids, but only a few Sagittae; the haul from 60-odd meters 

 contained almost no euphausiids, hyperiids, or pteropods, but yielded large numbers 

 of Sagittae, and Euchosta was taken in it alone. Thus, the Calanus, euphausiids, and 

 pteropods were mostly above 30-50 meters, the Euchaeta and Sagittae below that 

 depth, with Beroe, Pleurobrachia, and Stephanomia more evenly distributed (Bigelow, 

 1915, p. 267). 



A similar bathymetric segregation as between the copepods and the large adult 

 Sagittae prevailed in Massachusetts Bay on July 19, 1916 (station 10341; figs. 12 and 

 13), when the haul at 30 meters yielded a practically pure Calanus plankton with 

 many larval fishes and some young euphausiids but very few Sagittae, whereas 

 the net working at SO meters captured a swarm of large S. elegans but not nearly so 

 many Calanus as the shoaler haul. This condition must have been general over a 

 considerable area at the time, for we had much the same experience two days later off 

 Cape Cod (station 10344), where Calanus and young silver hake were extraordinarily 

 abundant at 40 meters (the largest catch of young fishes we have ever made — Bigelow 

 and Welsh, 1925, p. 394), but evidently concentrated in a narrow depth zone centering 

 at about that level, for both were practically absent on the surface, on the one hand, 

 and very much less numerous in the 90-0 meter catch, on the other, whereas Sagittas, 

 equally absent from the surface, were scarce in the 40-meter hauls but abundant in 

 the catch from 90 meters. 



A depth relationship of the same sort (between copepods and euphausiids) obtained 

 on August 9, 1913, off Cape Ann (station 100S7), where the 30-0 meter haul brought 

 back a rich gathering of the former (chiefly Calanus, with many Pseudocalanus) and 

 manj- larval rosefish, but only an occasional euphausiid, whereas we captured a con- 

 siderable number of the latter (small Thysancessa) at 80-0 meters, but only a fraction 

 as many copepods as at 30 meters, and an occasional Sebastes. On the other hand, lest 

 the reader conclude that the Sagittae and the euphausiids invariably congregate 

 below the densest shoals of copepods when stratification occurs between these 

 groups, I may point out that we found the 40-0 meter haul on the northwest slope of 

 Georges Bank, July 20, 1914 (station 10215), practically monopolized by S. elegans 

 and Limacina retroversa, with very few copepods, whereas a rather rich haul from 

 70-0 meters brought in about as great a bulk of copepods (about equal numbers of 

 Calanus and Pseudocalanus) as Sagittae, but no Limacina at all. Similarly, there 

 were about sLx times as many Calanus and Pseudocalanus at 110-0 meters as at 40-0 

 meters off Cape Ann on August 31, 1915 (station 10306), with just the reverse holding 

 in these same hauls for Euthemisto and for young euphausiids. The latter, indeed, 

 were almost wholly confined to the shoaler level, where they about equaled the 

 copepods in bulk if not in numbers. The copepod plankton of the western basin must 

 also have been much denser below than above 100 meters on May 5, 1915 (station 

 10267), when the vertical haul from 250-0 meters yielded great numbers, whereas 

 the catch of the horizontal net working at 85 meters and up to the surface was 

 scanty (total catch less than % liter). 



As still another instance of vertical stratification in summer, I may mention our 

 station of August 12, 1914, on German Bank (10244), where the surface water con- 

 tained an abundance of small Euthemisto but only a few Calanus (besides the Pleuro- 



