PLANKTON OF THE GULF OF MAINE 293 



seasonal periodicity, both in the gulf and in the seas of northern Europe (p. 291), 

 points to a wave of reproduction in the rising temperature of late spring or early 

 summer, very little production taking place during the coldest months of the year; 

 but with Temora occupying so broad a range in latitude and living under physical 

 conditions so various, it is not likely that the precise temperature governs its periods 

 of reproduction. Even in an area as confined as the Gulf of Maine there may be re- 

 gional differences in this respect, for the comparatively large catches made at two 

 stations in the eastern side of the gulf on May 6 to 10, 1915 (stations 10270 and 

 10272), at temperatures of 3° to 4°, point to reproduction in even colder water shortly 

 previous, whereas Doctor McMurrich did not begin to find Temora a constant ele- 

 ment in the tow at St. Andrews until the temperature of the water was near its annual 

 maximum of 12° to 13° in September. It is questionable, however, whether it 

 breeds successfully in temperatures higher than 15° to 16°. 



Economic importance. — Wherever Temora abounds in northern seas it is one of 

 the most important articles in the diet of herring (it is described by Willey (1921, p. 

 187) as "herring food par excellence"), of mackerel, and probably of other plankton- 

 eating fishes. Lebour (1920) found it one of the copepods most commonly eaten by 

 young fishes at Plymouth, England. Except for Willey's (1921) suggestion that 

 fluctuations in the abundance of this and of other copepods may possibly be corre- 

 lated with the weir catches of young herring ("sardines") in the Bay of Fundy, 

 I know of nothing published on Temora as food for fishes in the Gulf of Maine. 

 Certainly it can not rival Calanus finmarchicus in that respect in the open gulf, 

 but on the occasions when it swarms any schooling fish in the vicinity would no 

 doubt gorge on it, and large mackerel opened by Doctor W. C. Kendall off the north- 

 west slope of Georges Bank on August 23, 1896, were full of these "small brown 

 copepods" and of red feed (Calanus). 



The frequency and comparative abundance of Temora at St. Andrews from 

 September on suggests greater economic importance for it there than in other parts 

 of the gulf. 



Temora turbinata (Dana) 



This form is very closely allied to T. longicornis but is recognizable by a uniform 

 and well-defined difference in the size and structure of the fifth legs of both male and 

 female, a difference which Dr. C. B. Wilson writes he has been able to substantiate 

 on a very large number of specimens from Chesapeake Bay. There are differences, 

 also, in the relative length of the last two segments of the abdomen and in the struc- 

 ture of the two terminal setae of the furca, as described by Giesbrecht (1892). 



T. turbinata is a more southern copepod than T. longicornis, previously published 

 records for it including the tropical Pacific, Sulu Sea, China Sea, New Zealand, 

 Malay Archipelago, and Gulf of Guinea. It has not been reported from the North 

 Atlantic, but Dr. C. B. Wilson contributes the note that it "is present in great 

 abundance in the plankton of Chesapeake Bay and vicinity," and he detected a 

 scattering of T. turbinata at three Gulf of Maine stations in the spring of 1920 — 

 viz, off the continental slope of Georges Bank on February 22 and April 16 (stations 

 20045 and 20109) and in Massachusetts Bay near Boston Harbor on April 9 (station 

 200S9). In the Gulf of Maine it is evidently a very rare stray from the south. 



