30 BULLETIN OF THE BUREAU OF FISHERIES 



hence, except for that one instance, the catches in the deep summer hauls have all 

 been contaminated by the Calanus community captured by the open nets on their 

 journeys up and down. For this reason I can not claim that the Euchasta, Eukrok- 

 nia, etc., taken at any given station necessarily came from the deepest levels. But 

 the Euchasta community has been consistently represented in our midsummer hauls 

 below 100 meters, no matter in what part of the basin of the gulf these have been 

 made (see the following tables, pp. 40 and 50), and as we have never found it in any 

 abundance in hauls shoaler than 100 meters it would be merely academic to dispute 

 the general thesis that it is actually characteristic of the deepest stratum of the Gulf 

 of Maine. 



Whether the occasional excursions of Eukrohnia and Euchseta to the surface, 

 such as I have just mentioned (p. 29) and discuss at greater length elsewhere 

 (pp. 235, 328), are sporadic events induced bysome temporarily or locally active vertical 

 circulation, or whether they are mqre regular concomitants of regularly recurrent 

 physical states than now appears probable, the fact remains that it is only below 

 100 meters — that is, in the saltest water of the trough of the gulf, which is never 

 very cold — that the Euchseta community occurs regularly. 15 The Euchasta com- 

 munity similarly characterizes the corresponding level along the continental slope 

 abreast of the gulf. 



The use of the closing net is requisite to show in what relative amounts these deep- 

 water animals are mingled with Calanus and its companions in the deeper strata 

 of the inner parts of the gulf. In one such haul just mentioned (off Cape Cod, 

 August 29, 1912, station 10043) at a station where Calanus outnumbered Euchseta 

 at least 2,000 to 1 in the 20-0 meter haul (Bigelow, 1914, p. 116), these two copepods 

 were about equally numerous at 125 to 120 meters, with Euchasta bulking the larger, 

 thanks to its great size. The total volume of the catch was small, however (less than 

 one-half liter), and we have never found the deep-water Euchseta community 

 even approaching the swarms of Calanus of the upper 100 meters, or so, in volume of 

 plankton present in the water. Unfortunately we lack precise data on this point. 



To recapitulate, three chief bathymetric pelagic communities of animals can be 

 distinguished in the Gulf of Maine in summer, not, of course, sharply outlined, but 

 still sufficiently so to be recognizable. First is that of the surface, with its juveniles, 

 small copepods, etc., which receives accessions of large copepods, Sagittse, euphausiids, 

 etc., by night and rarely by day; second, the general boreal community of the upper 

 and mid depths, with Calanus, Metridia, and Pseudocalanus, Euthemisto, Thysa- 

 noessa, and Sagitta elegans as its index species; third, the Euchseta community of the 

 deepest waters of the gulf. The distinctions between these communities, and espe- 

 cially between the last two, are greatest when and where the water is most stratified 

 in density and temperature — that is, in the southwestern part of the gulf in mid- 

 summer — least when and where the water is most uniform vertically. This is the case 

 in all parts of the gulf during late winter and early spring; and throughout the year 

 in regions of very active vertical circulation, such as the neighborhood of Eastport, 

 the St. Andrews region at the mouth of the Bay of Fundy, and locally on the offshore 

 banks. 



11 See p. 236 (or precise temperatures and salinities. 



