260 BULLETIN OF THE BXJBEAU OF FISHERIES 



nearly 6,000, and M. lucens averaged about 8,000 per square meter at two stations at 

 the mouth of Massachusetts Bay on October 27 (stations 10338 and 10339). 



The count off Penobscott Bay rose similarly from 590 per square meter on Sep- 

 tember 16 (station 10318) to 12,250 per square meter on October 9 (station 10329), 

 and from none at all off Machias, Me., on September 11 (station 10316) to 7,687 per 

 square meter on October 9 (station 10327). In no case did we find the numbers of 

 M. lucens decrease from September to October at any given locality. Though the 

 evidence just detailed is not precise, with each example being explicable as the re- 

 sult of chance, when all are taken together they point to a more or less definite autum- 

 nal maximum for M. lucens within the Gulf of Maine. 



The scarcity of M. Iwens in the Woods Hole region in summer, deducible from the 

 fact that the only specimen which Wheeler (1901) saw there was taken in December, 

 contrasted with large catches of 11,700 and 16,300 per square meter made close in to 

 Marthas Vineyard and offshore on this line on October 21, 1915 (stations 10331 and 

 10333), suggests a similar autumnal augmentation for the species as far west and 

 south as it regularly inhabits the shoal waters over the inner part of the continental 

 shelf. 



Unfortunately no vertical hauls were made, and consequently the numbers per 

 square meter can not be stated for the later autumn or until February in any year; 

 but it is probable that the numbers existing over the Gulf of Maine as a whole suffer a 

 sharp drop in November because the catches of copepods in the horizontal hauls 

 during the midwinter of 1920-21 were uniformly very scanty, M. lucens averaging 

 only about 8 per cent of them. 



Vertical distribution. — In other seas M. lucens has been found from the surface 

 down to 2,000 meters. In the North Atlantic it is, on the whole, most abundant 

 between 50 and 100 meters, with a decided tendency to swim up to the surface at 

 night and to sink again by day (Farran, 1910) ; but in the San Diego region on the 

 Pacific coast of the United States, where Esterly (1912, p. 301) describes it as "over- 

 whelmingly more abundant and frequent on the surface between 10 p. m. and 2 

 a. m." and "practically absent from the surface between 8 a. m. and 8 p. m.," its 

 daytime plurimum is much deeper — 200 to 300 fathoms. 



In the gulf of Maine it is decidedly more numerous at some little depth than 

 at the surface, and the frequency of its presence at the top of the water is apparently 

 a factor of the time of year, to some extent, as well as of the time of day. Thus, 

 during the spring of 1920 it was recognized in 24 surface hauls (table, p. 303), wide- 

 spread over the gulf, and in 62 verticals. It has been listed only five times at the 

 surface in July and August — twice in 1912 (Bigelow, 1914, table, p. 115), three 

 times in 1914 (Bigelow, 1917, table, p. 290), and not at all in 1913, although this was 

 a summer when it was nearly universal east and north of Cape Cod. No data are 

 available for 1915. As regards the time of day, sixteen of the spring records for it 

 at the surface were from between 6 p. m. and 8 a. m., and eight between 8 a. m. and 

 6 p. m. All but one of the summer records were between sunset and sunrise, the single 

 exception (station 10245, August 12, 1914) being for 10.30 a. m., but at a locality near 

 Lurcher Shoal where considerable vertical stirring of the water by tidal currents is to 

 be looked for. Thus, in the Gulf of Maine M. lucens is more apt to come to the surface 



