294 BULLETIN OF THE BUREAU OF FISHERIES 



Tortanus discaudatus (Thompson and Scott) 



This species has so far been found only off the Pacific and Atlantic coasts'of 

 North America, either close to land or in partially inclosed waters. On the west 

 coast it is reported from Puget Sound (Thompson and Scott, 1S98) and from Bering 

 Sea and Alaska (Willey, 1920). The Atlantic records are from the Gulf of St. Law- 

 rence, whence it was first described (Thompson and Scott, 1898) and where it has 

 since been found widespread and in abundance in the shoaler parts (T. Scott, 1905; 

 Willey, 1919), and recently at Woods Hole (Fish, 1925). The Canadian fisheries 

 expedition had it outside Cabot Strait and at two stations close to the outer coast of 

 Nova Scotia (Willey, 1919). Wright (1907) records it from Canso, Nova Scotia, 

 Willey (1921) has stated that it is plentiful at St. Andrews, and there are other 

 Gulf of Maine records, as below. It has been found in considerable numbers at 

 Woods Hole in July and occasionally in December and May (Wheeler, 1901 ; Sharpe, 

 1911; Sumner, Osburne, and Cole, 1913a), but it has not been found further south. 



Gulf of Maine. — At St. Andrews this is one of the most frequent and abundant 

 copepods. It appeared in about half the hauls from mid-May through June in 

 Doctor McMurrich's plankton lists for 1915 and 1916, rising to its maximum during 

 July, August, and September, for which quarter it is listed in almost every haul. 

 In October and November it was much less constant (only about 50 per cent of the 

 hauls), and when taken it was less abundant. In December Tortanus occurred in 

 only about 25 per cent of the hauls, in January only once, and not at all in February, 

 March, or April. During the late autumn and winter of 1916-17, Tortanus formed 

 46 per cent of the copepods in a gathering at St. Andrews on November 2, 9 per cent 

 on December 8, 4 per cent on February 23, and was not detected at all on April 7, 

 May 1, or May 17 (Willey, 1921). It is likewise plentiful in summer at Canso, 

 Nova Scotia (Wright, 1907), and in the Gulf of St. Lawrence, Willey (1920, p. 22) 

 describing it as composing "50 to 75 per cent of the summer copepod plankton off 

 Souris, Prince Edward Island." On the whole, therefore, it may be classed as a 

 summer species along the northeastern coast of America. A periodicity of this sort 

 indicates one breeding period yearly, probably extending from early summer until 

 early autumn, with little or no reproduction taking place in late autumn, winter, or 

 early spring. 



The abundance and frequency of Tortanus at St. Andrews, with its presence 

 in Portland Harbor in July (Bigelow, 1914) and at Woods Hole, as just noted, 

 suggest that it occurs in estuarine and inclosed waters all around the coast line of 

 the gulf; but it is so closely confined to such situations that we have taken it only 

 four times in the open gulf in all our towing — twice in Massachusetts Bay during the 

 winter season of 1912-1913 (station 10048, November 20, and station 10053, Febru- 

 ary 12), once on German Bank (April 15, 1920, station 20103), and once in the 

 northeastern corner of the basin off the mouth of the Bay of Fundy (January 5. 1921, 

 station 10502). Not only is Tortanus extremely infrequent outside the outer head- 

 lands in the Gulf of Maine, but it is among the scarcest of copepods there, in numbers, 

 the first three of the records just listed being based on one or two specimens each. 



