296 THE FAUNA OF THE EXE ESTUARY. 



respects. Looking at tlie two faunas as a whole, it must he noted 

 that that of the Exe estuary is very much more limited in number of 

 species than that of Salcombe. This is particularly obvious when we 

 exclude from the list of Exe species those which were obtained on the 

 seaward side of the Polesands, a region which is really outside the 

 estuary. 



This limitation in the number of species living in the Exe estuary 

 seems to a large extent to be due to the following causes. In the 

 first place, the banks uncovered in the Exmouth estuary are left 

 dry for a very long time between two tides, and in most parts of the 

 estuary there is little difference in the area uncovered by the spring 

 and neap tides. The banks of the low-water stream are generally 

 steep, especially in the lower parts of the estuary, and the spring tides 

 merely uncover a few additional feet of these steep banks. Hence it 

 follows that the banks uncovered at Exmouth must really be regarded 

 as belonging to a higher tidal level than the rich low-water banks 

 exposed at spring tides in such harbours as Salcombe and Plymouth. 

 When this is borne in mind the differences in fauna become far 

 less striking, as these higher tidal levels are nowhere very rich in 

 number of species. The actual rise and fall of tide at Exmouth is 

 also less than at either Salcombe or Plymouth. The following figures 

 are from King's Pilot's Handboolc for the English Channel (12th 

 edition) : — 



Exmouth. Springs rise 12^ feet, neaps S| feet, and neaps range 

 5 feet. 



Salcombe.* Springs rise 15 feet, neaps IH feet, and neaps range 

 6 1 feet. 



The second point of importance is the very great strength of the 

 tidal stream at Exmouth, both when it is running over the banks 

 and to a still greater extent in the main channel when the banks are 

 uncovered. The evidences of the great scour produced by the tide 

 are numerous, and the soil of the banks is in many cases subject to 

 such great disturbance that it is rendered practically barren so far 

 as animal life is concerned. 



A third point which requires consideration is the quantity of fresh 

 water which enters the estuary. A proper knowledge of this question 

 could only be arrived at by systematic observations carried out during 

 the entire year, and more especially during the more rainy parts of 

 the year. The following information, however, supplied to us by 



• The figures for heights of tides given in the " Report on the Fauna of the Salcombe 

 Estuary" (this Journal, vol. vi. p. 151) were taken from the Plymouth Tide Table, as 

 information gathered locally led to the conclusion that the maxinuini rise inside the 

 estuary was about 17 feet, which is practically tlie same as at Plymouth. 



