1 92 1.] Fauna of the Chilka Lake : Polychaeta. 569 



channel is separated from the sea by a narrow spit of sand. The inner part of the 

 channel has a bottom of mud and sand, whilst the outer part is clean sand, and has 

 an extensive oyster bed at Manikpatna. The dominating feature, at any rate in the 

 channel, is the great seasonal change in the salinity of the water. All the main rivers 

 enter the lake at the northern end. In the rainy season an enormous amount of 

 fresh water enters this part of the lake, and gradually expels the salt water, so that 

 from the middle of August to the middle of October, the northern half of the lake 

 and the whole of the channel are occupied by water which is quite fresh. In the 

 dry season the volume of water in the lake is reduced by evaporation, and salt- 

 water from the Bay of Bengal enters the channel, and occupies it entirely as far as the 

 inner entrance to the main area. Here the transition to water only slightly brackish 

 occurs in a small space, and the main area is filled with water of low salinity. The 

 southern half of the lake receives no large rivers, and throughout the year contains 

 water only slightly brackish, varying between the limits sp. gr. i - ooi-i - oi5. The 

 variation at any particular spot in this part of the lake is not more than - oio, and is 

 usually less, or one- third to one-fifth of that in the channel, where the sp. gr. ranges 

 from 1 -ooo-i ' 0270. The level of the water in the lake is 5 or 6 feet higher in the 

 freshwater season (August to December) than in the salt-water season (December to 

 August) . 



The following table shows the distribution of the various species in the lake, the 

 date of capture (salt or freshwater season), the specific gravity of the water where they 

 were found, and the extreme observed range of the specific gravity they would have 

 to endure if they lived there throughout the year. The true range is probably greater, 

 as the limits represent observations made only in February and March (salt-water 

 season) and in September (freshwater season) in 1914 (Annandale and Kemp, 1915, 

 p. 6). The majority of captures at the south-west end of the lake were made during the 

 salt-water season, but this is largely due to the lower level of the water at that period 

 rendering it easier to reach the habitat of the various mud- and sand-dwelling species. 

 In the outer channel the bulk of the records were made in the fresh-water period, 

 because it was only at that time that the launch used for dredging and trawling, 

 could cross the shallow bar which separates the main area from the outer channel, at 

 Mugger-Mukh. These circumstances limit to some extent the conclusions which 

 might be drawn from the distribution of species as known at present. 



