124 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



from month to month, in the modal size of the small 

 plaice taken in the shrimp trawl : this varies from about 

 T to 1\ cms., with corresponding values of frequency of 

 about 60 per cent, to TO per cent. That is the proportion 

 of the whole catch which is at and over the mean modal 

 length ( = about 7'3 cms.) is about 67 per cent. At the 

 beginning and end of the year the curves are apparently 

 simple, but at most other times there are two modes, the 



f Inches 



Fig. 15. Percentages of plaice at and above each unit of length, caught 

 in the Mersey area in certain months in 1909. 



lesser being due to immigration of larger fish at the 

 beginning of the year, and to the growth of the small 

 fish at the latter end of the year. The mean proportion 

 of the total catch which consists of plaice between 5 and 

 9 cms. in length is very nearly 66 per cent. That is to 

 say, a shrimp trawl-net of 25 feet beam and \ inch mesh 

 catches a certain number of young plaice,* and about 



* Average values for the numbers of small plaice taken are given 

 by Dr. Jenkins and mvself in Ann. Rept. Lancashire Sea-Fish. Laby. 

 for 1900, p. 39, 1901. 



