PLANKTON OF THE GULF OF MAINE 151 



of our stations in the western side of the basin of the gulf, except on May 5 and 

 June 26, 1915 (stations 10267 and 10299). 



The triangular extremity of the deep trough north of latitude 44° is the only 

 offshore locality in the gulf where we have found it constantly abundant. Moderate 

 catches of Meganyctiphanes were also made on Browns Bank on July 24, 1914 

 (though our hauls at about this same location just one month earlier in 1915 yielded 

 none), in the Fundy Deep on March 22, 1920 (station 20079), in the center of the 

 gulf on April 17 of that year (station 20113), and it has been found swarming in 

 Massachusetts Bay at least once in the past (Hansen, 1915). However, we have 

 never taken more than a few specimens at any station there in all our cruising; and 

 the fact that, with the exceptions just recorded, our hauls in other localities have 

 usually yielded only from one or two to a couple of dozens of these shrimps is evidence 

 that Meganyctiphanes seldom swarms anywhere in the gulf except in the northeastern 

 part. 



It is not possible to estimate the actual numerical strength of Meganyctiphanes 

 at any of our stations, because the small nets that have been used for the vertical 

 tows in the Gulf of Maine do not yield reliable data for so active an animal and one 

 which so commonly occurs in shoals. Two stations occupied by the Albatross in 

 the center of abundance for this shrimp off Grand Manan during the spring of 1920 

 illustrate this imperfection of the record, for the vertical haul of April 12 (station 

 20100) did not yield a single specimen — that is, missed the school of shrimps alto- 

 gether — although the catch of the horizontal haul — about 50 specimens — was about 

 the same as on March 23 (station 20081), when the vertical haul indicated a 

 Meganyctiphanes population of about 275 below each square meter of sea surface. 



Although Meganyctiphanes is not neritic (for it is not dependent on the bottom 

 at any stage in development or associated with the coast line in its distribution), 

 it is a creature of the banks water on both sides of the Atlantic and is not oceanic 

 in the typical sense, finding the high temperatures and sahnities outside the edge 

 of the continent an absolute barrier to its offshore dispersal along the American 

 littoral. At one place and season or another Meganyctiphanes occurs over a very 

 wide range of temperature in the Gulf of Maine, certainly from upward of 15° to 

 as low as 2 to 3°, and possibly even colder; but it was rare at the coldest stations 

 (0.5 to 2.5°) during March and April, 1920, with only three records from water as 

 cold as 2°, s0 the temperature being higher than 3° and in most cases as warm as 4° 

 to 5° at the five localities and at the deeper levels where it was most abundant during 

 those months, although the surface strata might be colder. 81 It follows that almost 

 the entire local stock of the species was then living in tempeartures of 3.5 to 5°. 

 Therefore 3 to 4° may be set tentatively as the coldest favorable for the existence 

 of Meganyctiphanes in the Gulf of Maine, a thesis corroborated by its absence from 

 Ipswich Bay on April 9, 1920 (station 20092), when the temperature at 20 to 30 meters 

 was still only 2.5°, coupled with its presence there on May 8 (station 20122), by 

 which date the temperature had risen to 3 to 4° at that level. 



» One specimen at station 20054, 100-0 meters, temperature 1.7 to 2.5°; occasional examples at station 20056, whole column of 

 water, 0.5 to 1.9°; 3 specimens at station 20057, whole column of water, 1.9 to 2.2°. 



" Station 20079, 180 meters, about 4°; station 20031, 140 meters, 4.5°; station 20100, 100-0 meters, about 4.5°; station 20113, 

 surface, 3.3, and 4.5° at about 130 meters; station 20114, 110 meters, about 4°. 



