Observations on the biology of Microsetcllu norvcKicu 



243 



However in certain localities north of Cape Cod it is at times very numerous. For 

 example, in Frenchman's Bay it was found by the author to be the dominant species 

 during two months of weekly observations in July and August 1930, when adults and 

 young often comprised over 90% by number of the total zooplankton population. 

 Again in 1931 in the same region 17,907 adults per cubic metre were taken in the upper 

 50 metres near Monhegan Island on August 21. 



To determine its importance elsewhere in the Gulf of Maine and Bay of Fundy, 

 an analysis has been made of collections obtained between July 28, 193 1 , and September 

 29, 1932. The area covered, location of stations and methods have been described 

 in a previous report (Fish, 1936 a). 



Fig. 1. Distribution of adult Microsetella nonegica in April 1932. Number per minute of towing 



REGIONAL DISTRIBUTION OF THE ADULT STOCK* 

 In the western Atlantic M. norvegica ranges from Arctic waters (76° 02' N, Jesper- 

 SEN, 1923) at least as far south as Chesapeake Bay where it was found by Wilson 

 (1932) in December 1920 and January 1921. At Woods Hole it appeared m late 

 March and early April 1923 (Fish, 1925), in Narragansett Bay in March 1906 (Sharpf. 

 1910) and in Block Island Sound in October and December 1949 (Dlevev. 1952). 

 These records indicate that, like most boreo-arctic plankton anmials, M. norvegica 

 extends its range southward along the coast during the winter months. 



North of Cape Cod it is widespread in the Gulf of Maine and Bay ot Fundy, xs.ih 

 a tendency to form local concentrations of limited area (Fig. 1). When hrst observed 

 * Mature individuals and late copepodite stages have been combined in the counts. 



