28 BULLETIN OF THE BUREAU OF FISHERIES 



brachia so common there, p. 19), whereas the haul from 40 meters yielded copepods 

 chiefly, with only occasional Euthemisto. 



No doubt a more intensive examination of the zooplankton of the Gulf of Maine 

 will multiply such instances indefinitely, but enough have been mentioned to show 

 that a definite vertical segregation may occur at certain times and places between 

 animals having the same faunal status. On other occasions the contents of hauls 

 at different depth levels, between, say, 10 and 100 meters, are often almost precisely 

 alike, as was the case near Lurcher Shoal on August 15, 1912 (station 10031), when 

 copepods, euphausiids, Sagittse, Staurophora, Euthemisto, and even Salpse (p. 56) 

 occurred in proportions so similar in hauls from 50-0 and from 100-0 meters that it 

 would have been difficult to distinguish samples of the one catch from the other had 

 it not been for the presence of the large copepod Euchseta in the deeper one. Many 

 other instances of this same sort might be mentioned also. 



Our experience has been that young and larval forms of all sorts, from fish eggs to 

 copepod nauplii, are usually most plentiful at or very near the surface. For example, 

 in May, 1920, which is the season of their greatest abundance, nauplii were far more 

 abundant in the surface catch and in closing-net hauls from 10-15 meters in Massa- 

 chusetts Bay (stations 20120, 20121, and 20124) and off the Merrimac River 

 (station 20122) than in the deeper catches. It is safe to say that the great majority 

 of the copepods breeding in the Gulf of Maine pass through their early stages in the 

 upper 40 meters of water. Similarly, the nauplius and cyprid larva? of the common 

 barnacle, so prominent in the plankton for a brief period in spring (p. 43), are usually 

 condensed at and near the surface, rarely at some lower level (station 20105, figs. 23 

 and 24). Larval and even half -grown euphausiids are also far more plentiful above 

 than below 50 meters; and this is even more true of larval amphipods (Euthemisto), 

 which live close to the surface at first (p. 163), to sink to deeper levels with advancing 

 age; likewise of young S. elegans, as described elsewhere (p. 316). Since most of the 

 fish produced in the gulf live in this same zone during their first weeks, it may, 

 not inaptly, be named the nursery of the gulf. 



Certain conspicuous adult animals are also as typically characteristic of the sur- 

 face of the gulf as are the innumerable, larval forms. Such, for instance, is the large 

 blue copepod Anomalocera which may often be seen darting to and fro in the sun- 

 light immediately in the surface film and which seldom sinks more than a few 

 fathoms. The small brown copepod Temora longicornis likewise occurs in greatest 

 numbers near the surface; for instance, a surface tow near Nantucket Lightship, 

 on July 9, 1913 (station 10060), "yielded thousands, while the haul from 20 fathoms 

 caught only 25 specimens, and it was not taken at all in hauls from depths greater 

 than 23 fathoms" during that summer (Bigelow, 1915, p. 294). Much the same 

 rule holds for the little copepod Centropages typicus, of which "the surface haul at 

 station 10088 yielded ten times as many specimens as the haul from 80 fathoms, 

 though made with a net of only one-sixth the mouth area" (Bigelow, 1915, p. 293), 

 and which we twice found common at the surface during August, 1914, but not at 

 all in the catches at 25 meters and deeper (Bigelow, 1917, p. 291). It is our surface 

 hauls, too, that most often yield Evadne and appendicularians; indeed, we question 

 whether the latter ever sinks to any great depth in the Gulf of Maine. One of the 



