348 
BULLETIN OF THE BUREAU OF FISHERIES 
species especially, Acartia clausii, which Wilson has singled out as of much biological 
and economic importance in the bay, owing to its abundance at times and constant 
presence during our cruises, deserves some attention. The catches of this copepod 
have been studied by Wilson, and his findings bear out the statements of Farran 
(1910, p. 77), Willey (1920, p. 201 and 1921, p. 187), and Bigelow (1926, p. 171) with 
respect to the neritic character of this species. Its occurrence in Chesapeake Bay 
during the cruises of July, August, October, December, 1920, and January, March- 
April, and May-June, 1921, in rather large numbers at practically all areas, the pres- 
ence of egg-bearing females and larval stages at certain times, the high percentage of 
this species in the copepod catches, and its comparative scarcity in oceanic waters 
indicate that this form is one of the shallower, neritic waters and that it is endemic in 
Chesapeake Bay. 
This form has been found along our coasts as far north as the Arctic Circle by 
Willey (1920, p. 20 K), in the St. Lawrence River 90 miles from Quebec by Herdman, 
Thompson, and Scott (1898, p. 76), in the Gulf of St. Lawrence by Scott (1907, p. 49), 
in Narragansett Bay by Williams (1906, p. 648), in the Gulf of Maine by Bigelow 
(1926, p. 171), in Woods Hole by Fish (1925, p. 145), and by our survey in and imme- 
diately outside of Chesapeake Bay. The data are not sufficient as yet to tell whether 
it belongs primarily to the northern or southern regions of our Atlantic coast. Bige- 
low’s cruises from Cape Cod to Chesapeake Bay in 1913 and 1916 did not bring it 
to light, but it was found in small numbers outside of the mouth of Chesapeake Bay 
on our August, 1920, cruise and at the same time much more abundantly at nearly 
all of the areas in Chesapeake Bay. 
Wilson, from an examination of the females of Acartia clausii (and A. longiremis 
as well) found that during the July, 1920, cruise these forms were carrying eggs, and 
that the same was true on the January, 1921, cruise. This indicates, as he states, 
that there are two breeding seasons for these species in Chesapeake Bay — one during 
the summer and the other in the late winter. Correlated with these two breeding 
seasons one would expect maximum numbers of individuals to appear some time 
after. Judging from the catches made during the March-April, 1921, cruise, con- 
spicuously large numbers occurred at that time, since the counts at several of the 
areas visited were very much higher than those of any other cruises. It should be 
mentioned, however, that towings were made only in the upper part of the bay — areas 
R, R', S, T, V, W, Y, and Z — on that cruise. The indications are that the March- 
April cruise was taken at a time which was close to the spring maximum. It is more 
difficult to detect a well-defined autumnal increase corresponding to the summer 
breeding season from a study of the catches, but there was undoubtedly a general 
increase in numbers during the October, December, 1920, and January, 1921, cruises, 
so that the seasonal abundance in the upper part of Chesapeake Bay at least cor- 
responds rather closely to the seasonal occurrence found by Fish (1925, p. 145) at 
Woods Hole during the period from June, 1922, to May, 1923. The counts made of 
the catches of the summer cruises were the lowest of the year. 
Little can be said of the vertical distribution of Acartia clausii in the bay, owing 
to the methods employed in making the towings, but it is clear that large numbers 
of this species may occur at the surface in the daytime; and it is probable, as Wilson 
states, that they may be distributed in various proportions from the surface to the 
bottom. Bigelow (1926, p. 175) has found this species more abundant at the surface 
at times but also repeatedly more plentiful at some deeper level in the Gulf of Maine. 
