SEA-FISHERIES LABORATORY. 147 



ON PERIODICITY IN THE ABUNDANCE OF PLAICE 

 OFF THE MERSEY ESTUARY. 



By R. J. Daniel, B.Sc. 



In the report for 1917 of the Lancashire Sea Fisheries 

 Laboratory (pp. 60-68) reference was made to a series of 

 experimental hauls made by trawl nets having meshes of 

 \ and \\ inch (measured from knot to knot). These experi- 

 ments were made by the local fisheries officer, Mr. G. Eccles, 

 a highly experienced fisherman, during the years 1892 to the 

 present time. They are strictly comparable with each other, 

 having all been made by the same person, and in the same 

 way, and they form a very interesting series of data. In the 

 present paper the results are considered more fully, and the 

 years 1918 and 1919 are included. 



Unfortunately, the records for the three years 1898-1900 

 for the fish trawl experiments have been lost ; there is, how- 

 ever, no doubt as to the tendency of the data during the period 

 in question. 



Table I gives the actual data relating to the fish trawl 

 experiments, every haul being recorded in the order in which 

 it was made. The column " plaice per haul " gives the actual 

 numbers caught during the time (" hours ") stated in the 

 adjoining column. Thus for the year 1892, plaice were 

 caught in a haul of 1 hour's duration, 88 in a haul of J hour, 

 20 plaice in a haul of £ hour, and so on. At the foot of each 

 column is given the total number of plaice caught in all the 

 hauls made during the year, the total number of hours spent 

 in making the hauls, and the average catch of plaice pel 

 hour's fishing. 



Table II is arranged in a similar way, and gives the 

 records for the experimental hauls made with the shrimp 

 trawl, that is with the mesh of \ inch. 



