Table 18. — Length of scup in the catch of the winter trawl fishery landed at Virginia ports, 

 1931-35, weighted according to the quantities landed 



[Numbers of fish, in thousands] 



•"• Fish helow 17.0 cm. (approximately) were discarded by dealers as unsaleable. 



in yield were changes in abundance, it would 

 be expected that the changes in size com- 

 position would involve principally changes 

 in the relative importance of the annual 

 increments of young fish as was the case 

 in the summer fishery. The best catches of 

 the winter fishery, however, were in years 

 when the large fish were relatively more 

 important (1931, 1934, 1935, figure 9); and 

 further, that the relative importance of the 

 several size groups that composed the catch 

 not only differed when one winter was com- 

 pared to another, but underwent erratic changes 

 even within a season. The latter, in particular, 

 suggests that fluctuations in the catch re- 

 sulted from changes in availability rather 

 than changes in abundance. 



Hydrography 



The principal causes of the changes in 

 availability of scup in the winter fishery 

 may be found in the hydrographic studies 

 of the winter trawl fishing area. It is not 

 surprising to expect that differences in water 

 temperature should affect the movements and 

 behavior of fish in the winter trawl fishery, 

 since their seasonal migrations appear to 

 be closely related to temperature changes. 

 With the chilling of the inshore waters in fall, 

 the fish leave their summer grounds and 

 migrate to winter regions where temperatures 

 are about as high as the lowest found in the 

 summer fishing grounds along the inshore 

 coastal waters. Likewise, with the warming 



37 



