YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



195 



Table 19. — Estimated weight, by quarters, of yellowtail of 

 each length group in the landings from the southern New 

 England stock, during 1943 



[In pounds] 



CALCULATING NUMBERS OF FISH LANDED 



In many of the later computations, it will be 

 desirable to deal in numbers rather than pounds 

 of fish to avoid a constant accounting for change 

 due to growth. 



The landings, given by quarters in thousands 

 of pounds in table 7, may be converted to numbers 

 of fish if we know the average weight of the fish. 

 The average weight, W (table 20), is estimated 

 by summing the weights of the fish measured for 

 length as follows : 



. 1N L W L 



W=- 



Ni 



N L = number in each length group (appendix 

 tables C-14 and C-lo, pp. 244-5), ll r z. = average 

 weight of yellowtail of the corresponding length 

 in that quarter (table 19), yV r =total number 

 measured during the quarter. After determining 

 the average weight of the fish, the landings in 

 thousands of pounds are converted to number of 

 fish (table 21). 



CATCH PER UNIT OF EFFORT 



We determined the catch per unit-of-effort to 

 obtain an estimate of the relative size of the popu- 



lation or the equivalent as defined by Marr (1951), 

 the relative apparent abundance. 6 



Table 20. — Average weight of yellowtail, by quarters, landed 

 from the southern New England stock, 191,2-1,7 



Table 21. — Number of yellowtail, by quarters, landed from 

 the southern New England stock, 1942-1,7 



[In thousands of fish] 



In developing this measure of abundance, we 

 sought one that would be stable, continuous, and 

 representative of the fleet's activities. We desired 

 a figure that would not vary with changes in the 

 composition of the fleet, with seasonal changes in 

 the weather, or with changes in the relative at- 

 tractiveness to the fishermen of yellowtail and 

 other species. Of course, this measure should be 

 continuous and uninterrupted in order to provide 

 data in all seasons of all the years under study. 

 Finally, since vessels seeking yellowtail fish as a 

 fleet and freely exchange information by radio 

 and in port, they naturally concentrate where the 

 fish are concentrated. Their fishing is far from 

 randomly distributed. They avoid for months, or 

 even years, areas wdiere yellowtail are judged to 

 be scattered and the risk of an unproductive trip 

 is too great. There appears to be no possibility 

 of obtaining a measure of abundance from this 

 fishing activity that would be based on fishing 

 effort distributed over the range of the stock. We, 

 therefore, considered as an alternative obtaining 

 a measure representative of the activities of the 

 entire fleet. 



"We shall use the terms In the sense defined by Marr as 

 follows : Abundance, the absolute number of Individuals in the 

 population ; availability, the degree or percentage to which a 

 population is accessible to the fishery ; apparent abundance, 

 abundance as affected by availability; and catch per unit of 

 effort, an index number related to the apparent abundance. 



