SEA-FISHERIES LABORATORY. 177 



obtained by averaging all the hauls taken in the season 

 in question and reducing to average catch per hour. As 

 the figures are too irregular for it to be possible to form 

 any idea of variation directly from the tables, curves were 

 drawn through points representing the values to be 

 examined. Fig. 4 is a curve drawn through points 

 corresponding to the average catch per hour with shank- 

 net of dabs in the four seasons. To eliminate the small 

 yearly difference in this variation, the whole period of 

 fifteen years was considered. Fig. 3 is the curve of the 

 same values for the shrimp-trawl. These show that the 

 maximum catches of dabs are made in the winter, from 

 November to February, and the minimum catches in the 

 summer, from May to July. The very low position of the 

 curves in June and July should not be taken as repre- 

 senting the actual values, but as indicating the probability 

 that if an average were obtainable for the catches taken 

 at this time, it would be lower than the averages for 

 catches either before or after it, Figs. 1 and 2 are 

 the curves for yearly variation in number of plaice caught 

 per hour on the ground with shrimp-trawl and shank-net 

 respectively, each curve representing the same season 

 throughout the fifteen years considered. The curves have 

 not been drawn through the points representing the actual 

 values, but have been smoothed in the same way as were 

 the monthly averages for the Mersey Banks (see page 179), 

 so that irregular variations are disregarded and the 

 general tendency of the figures shown. Both sets of curves 

 show a marked decrease in the number of plaice taken per 

 hour on the Closed Ground since 1892. This decrease is 

 least visible in the curve for April to June. Other curves 

 have been drawn, but are not included, as they show littli 

 sign of any regular variation. Thus, the curves for hourly 

 catch of shrimps are so irregular that no deductions could 



