Bottom Trawl Survey Results 



The cumulative spring and autumn distributions over the time series are 

 shown in Figures 10.1 and 10.2. These plots accurately and dramatically 

 depict the seasonal extremes of mackerel migration. If the spring data were 

 gathered synoptical ly, the northern and inshore occurrences would not be 

 seen. In Figure 10.3, data from all cruises prior to 1976 have been deleted, 

 and a more representative picture of spring (March to April) distribution 

 results. Once mackerel begin moving onto the shelf in the spring, the 

 rapidity of their movement is evident (compare Figures 10.1 and 10.3). The 

 autumn distribution plot shows some occurrences in northern portions of the 

 area; these are all young-of-the-year (Y0Y) which frequently inhabit these 

 waters during the summer. The autumn catches near the North Carolina-Virginia 

 border were probably chub mackerel {Seombev japoniaue) , a smaller species that 

 frequents warmer southern areas and is often confused with Atlantic mackerel. 



The graphs of mean weight and number per tow (Figures 10.4-10.7) do not 

 present a very definitive picture. However, the declining population size 

 during the mid-70's and the beginning of a recovery during 1973 and 1979 are 

 apparent. 



Length frequencies for six strata sets, arranged by season, are shown in 

 Figures 10.8-10.18. These graphs support the earlier description concerning 

 the occurrence of Y0Y during autumn. There is no plot for autumn offshore 

 strata set 5 because no fish were caught in that area. 



Figures 10.19 and 10.20 show the percentage occurrence by stratum of Y0Y; 

 cutoff sizes were 17 and 18 cm, respectively, for spring and fall series. 

 Once again it is apparent that the autumn catches consisted mostly of Y0Y. 



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