292 BULLETIN OF THE BUKEAU OF FISHERIES 



in the gulf within this depth zone, but at one of Doctor Kendall's stations off Nan- 

 tucket shoals (September 2, 1896), when there was a difference of less than one 

 degree of temperature between the surface (14.2°) and the 20-meter level (13.6°), 

 the catch of "small brown copepods" in 5-minute tows at 10 meters, 20 meters, and 

 30 meters was roughly proportionate to the depth — that is, to the length of the 

 column of water fished through — indicating that Temora was comparatively uni- 

 formly distributed down to that depth. 



Temperature and salinity. — -The distribution of T. longicornis in other seas proves 

 it tolerant of a wide range in its physical surroundings from salinities as low as 6.54 

 per mille in the inner Baltic to upward of 35 per mille in the open Atlantic, in tem- 

 peratures as low as about 2° and upwards of 20°. Its tendency to congregate near 

 the surface makes it subject to a wide seasonal variation in temperature in many 

 seas. Thus, at St. Andrews it survives temperatures as low as —1° to 0° in mid- 

 winter; at Woods Hole also. At the other extreme, one of our largest catches of 

 Temora (station 10260, surface) was from water of 16°. 



The highest temperature at which it has been definitely recorded in North 

 American waters is 20.5° on the surface at a July station off New York (station 

 10066; Bigelow, 1915, p. 294), where sinking to a depth of only 30 meters would 

 have lowered the temperature by 10°. But there is some reason to believe that it 

 finds somewhere between 15° and 20° the upper limit of favorable temperature, for 

 it was fairly well represented in the hauls from 25 and 10 meters, at another station 

 off New York on August 1, 1916 (station 10362), levels at which the temperature was, 

 respectively, about 12° and 16°, but was wanting at the surface in 21.1°. Within the 

 Gulf of Maine any planktonic animal can always reach water cooler than 15° by 

 sinking down less than 20 meters even at the warmest season and in the warmest 

 region, but there is no direct evidence that Temora tends to sink below the warmest 

 zone. The fact that Doctor Kendall, in his notes for August and September, 1896, 

 records "small brown copepods" (in all probability T. longicornis) in several surface 

 tows off the northwestern slope of Georges Bank and in the neighboring parts of the 

 basin at temperatures of 17.5° to 20°, as well as repeatedly in 13° to 15° on the bank 

 itself, makes it more likely that temperatures as high as 18° to 20° do not hinder 

 its existence or growth. 



It is not likely that differences in salinity within the limits prevailing in the Gulf 

 of Maine affect the distribution of this copepod, but the high salinities of the oceanic 

 basin, per se, or in conjunction with high temperature, may be the effective barrier 

 which confines it to the banks water inside the inner edge of the Gulf Stream off 

 the North American coast. 



Why Temora (and this applies to many other neritic members of the plankton) 

 should be so closely confined to comparatively shoal regions, irrespective of the 

 physical state of the water within wide limits, when it has no connection with the 

 bottom at any stage in its existence but is pelagic throughout its life, is a question 

 to which no answer can yet be given. 



Breeding. — No direct observations have been made on the breeding of Temora 

 in the Gulf of Maine nor have its larval stages been detected there, but its distribution, 

 regional and seasonal, is such as to leave no doubt that it is regularly endemic. Its 



