OF DIATOMS AND COPEPODA IN THE IRISH SEA. 



113 



Calanus. 



Calanus finmarchicus (Gunner) * is present throughout the year in the 

 Irish Sea, and may be taken in small quantities at almost any time and in 

 larger numbers on different occasions in different years. In 1907 it was 

 fairly abundant (a few thousands in a haul) in April, and again at the end of 

 July and the beginning of August, and in October. In 1908, on the other 

 hand, the thousands per haul were not reached until later in the year, and 

 the numbers remained relatively high from September to December (2,850 

 on December 23rd). In 1909, in addition to occasional thousands in May, 



Fig. 12.— Curves of Calanus for three years (1907-9) at Port Erin, showing 

 successive waves of invasion, 2 or 3 in each summer. 



June, July, and October, we have evidence of an unusually large swarm that 

 entered the bay on July 17th and 19th, when hauls estimated at 20,000 each 

 were obtained. The average for these three years shows maxima in July 

 and October (see fig. 12). 



In 1910 there were no very large hauls, and the thousands were only 

 reached at the end of July and the beginning of August — perhaps the most 

 usual time for swarms to appear in the bay. 



In 1911 the numbers in general were low, but two of the customary large 

 swarms appeared in summer, one on July 4th and the other on Julv 18th. 



In 1912 the numbers were higher again, and thousands 



occurred on 



various dates from April to October. The very high record of 50,720 was 

 obtained on May 17th, unusually early for such a large swarm. 



* I use this older specific name as I am inclined to agree with "Wolfenden, Esterly and 

 others that the characters used in the attempt to separate "finmarchicus" and "helgolandicus'' 

 as species are too slight and inconstant to be relied upon. 



9* 



