igi5.] Fauna of the Chilka Lake : Introduction. 5 



The main area of the Chilka Lake is exceedingly shallow. In the dry season, 



when the water-level is at its lowest, the depth rarely 

 Depths . r J 



exceeds 8 ft. at the southern end ; while over an immense 



area towards the northern extremity it nowhere reaches 4 ft. The deepest sounding 



we obtained at this season was 10 ft., at a point close to the eastern end of Kalidai 



Id., whence a comparatively deep trough extends towards the shores of Parikudh. 



At many places we found it impossible to approach within a mile of the shore even 



in a small row-boat. 



We have already referred to the shallowness of the water at Mugger-Mukh and to 

 the depth of the outer channel at this season. The deepest water is said to be 

 situated off Arakhuda and our boatmen talked of five fathoms ; but the deepest 

 soundings we ourselves obtained did not exceed 20 ft. 



In the flood-season all depths are increased by 5 or 6 ft., the exact amount 

 probably varying from year to year. 



It is evident that the differences in depth, relatively great though they may be, 

 are actually insufficient to produce any appreciable effect on the fauna of different 

 parts of the lake, except in so far as they imply a great rise of temperature in 

 extremely shallow water. 



The origin of the Chilka Lake was thus explained by the late Dr. W. T. Blanford 



Origin of the lake. in his "Sketch of the Geology of Orissa " ' : — 



"The lake itself is a part of the sea first rendered shallow by deposits from the mouths of the 

 Mahanaddi and from silt carried up the bay round the hills near Ganjam by the violent southerly winds 

 of the monsoon, and then entirely cut off by a spit, formed, by the same agency, of sand drifted along 

 the coast. Near the south-western extremity of this spit there is a considerable deposit of estuarine 

 shells, at a height of 20 to 30 feet above the present flood level of the Chilka." 



For our special purpose it is unnecessary to elaborate this concise statement, 

 with which we are in general agreement. 1 We may point out, however, that even 

 stronger evidence for the belief that the lake was once an open bay than that 

 adduced in the passage quoted, is to be found in the occurrence on the rocks at 

 the base Ganta Sila of the remains of solitary corals, organisms that flourish only 

 in a pure, sea-water. The beds of dead P lacuna-shells to which we have alread}^ 

 alluded provide evidence less strong, for Placuna flourishes in the Tampalakaman 

 (Tamblegam) Lake 3 on the coast of Ceylon, in which conditions are not very 

 dissimilar to those of the Chilka Lake. 



Hydrography op the Lake. 



Of the varied elements that compose the physical environment of the fauna of 

 the lake by far the most noteworthy is the great periodic change in salinity to which 



1 Rec. Gsol. Surv. India, V, p. 56 (1872). 



1 Hunter, in his ''Orissa'''' (p. 25; 1872) cites a legend which implies that the bed of the lake 

 was dry land as late as the 4th century A.D. 



3 Hornell, "Report on the Placuna Placenta Pearl Fishery of Lake Tampalakainatn " : Rep. 

 Ceylon Marine Biol. Lab., I, p. 41 (1906). 



