XIV. NOTES ON THE FAUNA OF THE 

 jMATLAH river IN THE GANGETIC 



DEIvTA. 



By Stanley Kemp, B.A., Superintendent , Zoological Survey 



of India. 



In December 1915, thanks to the kindness of Mr. T. South- 

 well, Deputy Director of Fisheries, Bengal and Bihar, I was able 

 to visit certain parts of the Gangetic delta in the SX- " Kitt}'," 

 a launch recently built by Government for fishery investigation. 

 The area examined comprises the Matlah River and the channels 

 in its vicinity, and extends from Port Canning in the north to the 

 junction of the Matlah and Biddah rivers in the south, a distance of 

 about 30 miles. The following note deals only with the bottom 

 fauna of this area. 



The Matlah river is one of the largest of the numerous water- 

 ways thai; traverse the Gangetic delta and is navigable for ships of 

 large tonnage as far as Port Canning. It varies in depth, but in 

 the main channel there is nowhere less than 4-| fathoms at low 

 spring tides ; over considerable areas the water exceeds 8 fathoms 

 and the chart published in 1855 shows that still deeper pockets 

 exist, soundings at a point some yh; miles below Port Canning 

 reaching a maximum of 27 fathoms. 



The level of the water varies greatly according to tide; there 

 is as a general rule a difference of about 10 feet between high and 

 low water, a figure that may rise to as much as 15 feet at spring 

 tides. Towards the close of the monsoon the average level is 

 raised by floods and at such times the uncultivated islands (that 

 is to say, those that are not surrounded by an embankment) are 

 almost wholly submerged at high tide. The water is nearly always 

 heavily laden with silt and doubtless shows great seasonal varia- 

 tion in salinity. On the occasion of my visit the specific gravity 

 (corrected to a standard temperature of I5°C.) varied from i'00375 

 to i'oio75,' Higher readings would almost certainly be found im- 

 mediately prior to the monsoon, when the land drainage is at its 

 minimum, and during the flood season the water at certain states 

 of the tide is probably almost fresh. 



In the area examined the river bottom appears to be composed 

 of very finely divided mud, in character considerably softer than 

 I have seen in any other locality. On the banks at low water a 

 person of average weight will sometimes sink to a depth of two 

 feet and, unless active, may require assistance to extricate himself. 



^ The specific gravity of the sea on the Orissa coast of the Bay of Bengal is 

 much greater than the highest of these readings, varying from about roi; at the 

 close of the monsoon to i'028o in earlv spring. 



