PLANKTON OF THE GULF OF MAINE 45 



sizing this depth limit for reasons which will appear presently) of the offshore parts 

 of the gulf is the most monotonous. 



Although our records for this season are not all that might be desired, it seems 

 certain that copepods (Calanus in particular) reach their high-water mark early in 

 June, the exact date varying locally and with the forwardness of the season. So 

 completely did the calanoids (chiefly ft finmarchicus) monopolize the upper strata 

 of water right across from Cape Cod to Cape Sable during May, 1915, that the only 

 other animals to be found among a liter of copepods off Cape Ann on May 4 

 (station 10266) were a few Sagitta eltgans, one young fish, two tiny Euthemisto, a 

 few euphausiid larvae, and a few fish eggs, with the zooplankton of the western basin 

 (station 10267), where diatoms were still swarming, so monotonous that a haul from 

 S5 meters yielded nothing but copepods and one Tomopteris. Nor was the catch 

 more varied in the central deep (station 10269), only one euphausiid, one Euthemisto, 

 six or seven large Clione, and an occasional Limacina being detected among the 

 copepods in the 85-meter tow on May 6, while we found only a few Euthemisto, 

 euphausiids, and Sagitta?, with an arctic planktonic element to be discussed else- 

 where (p. 59), among swarms of copepods in the eastern basin on that same day 

 (station 10270). 



In that year (which was apparently a typical one) the plankton of the upper 

 100 meters was as monotonously calanoid in June as it had been in May. In the 

 Grand Manan Channel, for example, on the 4th (station 10281), the 50-meter catch 

 consisted of copepods varied only by 1 Euthemisto, 2 Clione, 1 Aglantha, 1 young fish, 

 1 fish egg, 2 Sagitta elegans, and a single specimen of Tomopteris. Much the same 

 condition prevailed in the Fundy Deep on the 10th (station 10282); likewise near 

 Mount Desert Island on the 11th (station 10284), when a cursory examination of more 

 than 2 liters of Calanus and other copepods in the 70-0 meter haul revealed only 

 one Clione and a single Sagitta as the sole variants. On the 26th of June, too, the 

 upper strata of the western basin were similarly occupied by a calanoid plankton 

 in extraordinary abundance (about 40,000 large Calanus per square meter). 



In the western and northern parts of the gulf, where copepods monopolize the 

 water more completely at their peak season than they do the deep basin offshore, 

 it is an unusual event for Sagitta?, amphipods, euphausiids, or pteropods, etc., to 

 be of any importance in the plankton in spring or early summer, with the notable 

 exceptions of the swarms of the euphausiid shrimp Thysanoessa raschii near the 

 Isles of Shoals in April and May, 1913, and (with its relative, Th. inermis) on April 

 9, 1920 (station20093) , described below (p. 145) ; with the exception, too, of Meganycti- 

 phanes, which is so plentiful in the northeast corner of the trough off Grand Manan 

 that we captured no less than 1J^ liters there on June 10, 1915 (station 10283), in 

 half an hour's haul at 100-0 meters, and of Pleurobrachia, which swarms on German 

 Bank in May and June just as it does in summer (p. 19). Even where copepods so 

 dominate the contents of the net, however, that nothing else strikes the eye at the 

 first glance, a more careful examination of the catch will reveal some few amphipods, 

 euphausiids, Sagitta?, etc. 



June 19 is the earliest date on which we found large Euthemisto in any abundance 

 in 1915 (eastern basin, haul from 85-0 meters, station 10288). The interesting 



