PLANKTON OF THE GULF OF MAINE 291 



anywhere at that season; but that as the existing stock, which has carried over the 

 winter, dies out entirely in some localities between April and August, active multi- 

 plication takes place locally, which under exceptionally favorable circumstances may 

 build up the shoals previously alluded to(p.290)and which in any case raises thegcneral 

 averago of abundance to several times its early spring level. It is not possible to 

 set a definite date when this multiplication begins. In 1915 catches as large as 1,100 

 to 8,200 per square meter were made in the eastern side of the gulf by May 6 to 10 

 (stations 10270 and 10272; table, p. 297), but we found only 140 to 420 Temora per 

 square meter at stations in the western side from the 4th to the 17th of the month 

 in 1920. Probably the schedule varies over a period of several weeks from year to 

 year, as do most periodic changes in northern seas, but it agrees essentially with the 

 seasonal periodicity of the species in the Irish Sea, where it is most plentiful in 

 summer, 59 and in the Baltic generally, where it is scarce in February, most common in 

 August and November, and scarce or common in May, depending on the locality 

 (Farran, 1910). 



Comparison of the data just outlined for the open Gulf of Maine with Doctor 

 McMurrich's plankton lists brings out the interesting difference that Temora com- 

 mences to multiply three months or more earlier in the season out at sea than in 

 the inclosed waters at St. Andrews, a difference which may be correlated with tem- 

 perature. 



Vertical distribution. — Obviously a species having its center of distribution 

 within the 100-meter contour must be most plentiful above that level, and Temora 

 has been found most numerous close to the surface. For example, the swarm off 

 Nantucket of July 9, 1913 (station 10060), was so closely confined to the uppermost 

 stratum that while the surface haul with a small net yielded thousands the haul 

 from 40 meters with a large net caught only 25 specimens (Bigelow, 1915, p. 294). 

 The Massachusetts Bay swarm of October 31, 1916, was likewise on the surface, 

 with Calanus, not Temora, dominating the catch from 60 meters. Doctor McMur- 

 rich's St. Andrews records were all from within 7 meters of the surface, and many of 

 them were immediately at the surface irrespective of season. Dr. W. C. Kendall also 

 took it repeatedly in surface tows on Georges Bank in August and September, 1896. 

 In the spring of 1920 the surface tows (table, p. 303) yielded it with about as groat 

 frequency and in about as great numbers as the vertical hauls, and as an extra- 

 limital instance of the same sort in neighboring American waters Temora longlcornis 

 dominated the surface tow between Block Island and Marthas Vineyard on November 

 10, 1916 (station 10405). It is plentiful in very shoal water at Woods Hole, and Willey 

 (1919) found it regularly on the surface in the Gulf of St. Lawrence and about a3 

 often in surface as in vertical hauls on the Nova Scotian shelf. Herdman, Thompson, 

 and Scott's (1898) records in the North Atlantic were all from within a couple of 

 fathoms of the surface, and this copepod has repeatedly been taken in abundance at 

 the surface in north European waters. 



No direct evidence is available as to how deep Temora descends in the Gulf of 

 Maine, but apparently the zone of greatest abundance for it hardly extends below 

 about 50 meters. No attention has been paid to possible stratification of Temora 



" This appears in the counts of copepods given by Herdman (1908 and 1919). 



