PLANKTON OF THE GULF OF MAINE 
27 
euphausiids and hyperiids, but only a few Sagittse; the haul from 60-odd meters 
contained almost no euphausiids, hyperiids, or pteropods, but yielded large numbers 
of Sagittse, and Euchseta was taken in it alone. Thus, the Calanus, euphausiids, and 
pteropods were mostly above 30-50 meters, the Euchseta and Sagittse 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 
Sagittse 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 Sagittse, whereas 
the net working at 80 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 Sagittse, 
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 10087), where the 30-0 meter haul brought 
"back a rich gathering of the former (chiefly Calanus, with many Pseudocalanus) and 
many larval rosefish, but only an occasional euphausiid, whereas we captured a con- 
siderable number of the latter (small Thysanoessa) 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 Sagittse 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 Sagittse, but no Limacina at all. Similarly, there 
were about six 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 34 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- 
