The question then is whether or not these 

 changes reflect the abundance of the total 

 population or of the individual year classes 

 which comprised the catch. This question 

 may be answered by studying i^fi size and 

 age compt»3ition of the catches. To do this 

 the population was sampled as follows: Random 

 samples of about 100 fish per catch were 

 measured from as many catches as possible 

 throughout the season. These measurements, 

 when tabulated, fell into certain size groups 

 that were indicative of age, at least to the 

 fourth summer. Because of the overlapping 

 of measurements of the older and larger fish, 

 lengths of fish five summers and older were 

 grouped and treated as a single unit. This 

 appeared permissible since the life span of 

 the scup in the commercial fishery is rela- 

 tively short, the greater part of the catch 

 being composed of 2- to 4-year-old fish in 

 varying proportions, while fish over 5 years 

 of age composed relatively less of the catch. 



To insure reliability in interpretation of 

 age by this method, it is necessary that there 

 be a fairly continuous series of measure- 

 ments of fish from postlarval sizes to the 

 largest size present in the commercial fish- 

 ery. Fishermen discard fish less than about 

 7 inches in length, so special arrangements 

 were made to obtain fish below this limit. 

 For sizes immediately below the legal or 

 market limit, samples were obtained from 

 the commercial catches before discarding 

 took place or from 1- or 2-bushel lots of 

 unsorted fish brought in at various times by 

 cooperative fishermen. 



Samples of fish from the smallest sizes 

 (approximately 11 cm. or 4.5 inches) caught 

 by pound nets down to and including postlarval 

 sizes were obtained by dip nets in the vicinity 

 of pound nets during June and July, when 

 spawning scup constitute a large part of the 

 catch. Along the Middle Atlantic and southern 

 New England coast, spawning occurs mainly 

 in May and June and part of July according 

 to Bigelow and Welsh (1925). Small-mesh 

 seines and otter trawls were used along the 

 beach and in the deeper water of small inlets 

 from middle of July to end of October. The 

 smallest fish were caught with these gears 

 in July 1929 when the length mode of scup 



caught with dip net was 1 cm. Others caught 

 with beach seines averaged about 4.5 cm. 

 (fig. 5, table 5). The difference in sizes caught 

 by these gears may reflect the efficiency of 

 capture by each type of gear. The two sizes 

 begin to merge in August, and during Sep- 

 tember when captures were made by seine 

 only, the fish caught had grown to an average 



24 • aiOIZMI*!* 2022 242* M30 32MM3*i 



LENGTH (CENTIMETERS) 



I 2. » A S « r • (lOil 121314 19 

 LENGTH (INCHES) 



/beach SEINE, / DIP NET, / POUNDNET. 



Figure 5. --Length composition in percent of scup caught 

 by experimental and commercial gear, 1928-31. 



15 



