56 



the fish-measurers to go to sea with them and make records of 

 the fish caught. Still in no case were we in control aud fully 

 able to choose the grounds and times for the hauls. Scientific 

 work on board the police vessels had, of course, to be dependent 

 on the nature of the official duties tliat were to be performed. 

 In the circumstances the results that were obtained are very 

 satisfactory. 



One can, of course, make certain conclusions of value 

 merely by comparing average catches taken at different times, 

 and on different grounds, with each other. No doubt these 

 experiments do give us rough general pictures of the abundance 

 of fish from time to time and, so far as they go, they must 

 represent the experience that an observant fisherman would 

 acquire. Thus the tables on pp. 46-7, giving the relative 

 abundance of the different species of fish on the various 

 grounds, are certainly to be regarded as representing the 

 natural conditions in an approximate manner. So also, the 

 series of hauls made in the Mersey by Capt. G. Eccles, give 

 some very valuable information. Too much, however, must 

 not be made of the ordinary periodic trawlings on which the 

 present report is based, as representing variations in abundance 

 from year to year. 



What has been done has been to seek to get the information 

 we require by a study of the measurements of the fish them- 

 selves, rather than by mere counts of the numbers taken per 

 haul. These relative lengths, ages, etc., are independent of 

 the actual numbers of fish taken. It will be seen that they do 

 give us valuable and, we believe, reliable data. Combined with 

 the results of the fish-marking experiments and the information 

 given by the official statistics, they enable us to deduce 

 conclusions that are of value for the administrators. 



The statistical 7nethods employed. 



When the measurements of the fish sampled are arranged 

 as follows : — 



