FISHERY BULLETIN: VOL. 70, NO. 3 



summarized these data for the years 1955-59. 

 There has been no further elucidation of the 

 schooling dynamics of this fish. This study pur- 

 sues that objective. 



SOURCES AND TREATMENT 

 OF DATA 



The basic data consisted of fishing logbooks 

 maintained aboard menhaden vessels for use by 

 the National Marine Fisheries Service and re- 

 duction plant records of daily vessel landings 

 from 1955 to 1962. Of the single-set catches 

 recorded in the logbooks, only those for which 

 the "hailed" catch was within 10^/r of the plant 

 weights were used in the analyses. Vessel land- 

 ings at the reduction plants were converted to 

 metric tons. 



I assumed that each purse-seine set during 

 the "summer fishery" (April-September) was 

 made on a discrete school of Atlantic menhaden. 

 Sets made on large aggregations of fish that ap- 

 peared off" Long Island in late September or early 

 October (June and Nicholson, 1964) and off 

 North Carolina in November and December were 

 considered separately. 



Despite the rigorous screening of fishing log- 

 books, several sources of error may have been 

 involved in the identification of single-school 

 catches and estimates of school size. Foremost 

 of these are (1) a portion of a school may have 

 escaped during capture, (2) a variable loss in 

 weight from decomposition may have occurred 

 within single-school catches of the same initial 

 size (such losses would be proportionately great- 

 er during warmer weather and in catches made 

 at the beginning of the fishing day), and (3) a 

 single recorded set may have actually included 

 more than one set. Items (1) and (3) would 

 have a greater effect on the catch estimates, but 

 there is no way of determining the extent of 

 these sources of error in this study; item (2) 

 must be considered a random factor. 



Catch samples, which provided measures of 

 fish size, were taken from daily vessel landings 

 at reduction plants along the Atlantic coast (Fig- 

 ure 1) as part of a routine catch-sampling pro- 

 gram begun in 1955 (June and Reintjes, 1959). 

 Fish lengths were grouped in '/2-cni classes. The 



mean length, variance, and standard deviation 

 and the mean weight, in grams, of fish in each 

 catch sample were computed. 



The number of fish within a single-set catch 

 was determined by dividing the weight of the 

 catch by the mean weight of the fish in the catch 

 sample, A catch sample was obtained from 275 

 single-school catches during the summer fishery 

 and from an additional 64 single-set catches from 

 the large fall aggregations of fish off Long Island 

 (23 sets) and North Carolina (41 sets). 



Detailed logbook information and accompany- 

 ing plant weights were available for 2,643 single- 

 school summer catches and an additional 286 

 single-set fall catches off Long Island (138 sets) 

 and North Carolina (248 sets). The number of 

 single-school summer catches for which there 

 were data constituted about 1 % of an estimated 

 240,000 purse-seine sets made during the 8 sea- 

 sons. Except for 1961 and 1962, when a com- 

 bined total of only four single-school summer 

 catches were recorded for the South Atlantic 

 Area, single-set catches were taken throughout 

 the range and period of fishing and are there- 

 fore believed to be representative of the schools 

 or larger aggregations of fish into which the pop- 

 ulation was divided. 



SEASONAL GROUPINGS OF THE FISH 



Examination of 2,643 single-school summer 

 catches indicated wide variation in school size 

 (weight). A plot of the combined frequencies 

 of single-school catches for the 8 seasons, by 3- 

 ton size classes (upper panel. Figure 2) , shows a 

 pronounced skewness in the distribution toward 

 smaller catches, with the mode occurring in the 

 4- to 6-ton size class. Single-school catches 

 ranged from 0.3 to 103 tons. The grand mean 

 for the 8 seasons was 16.6 tons, with a standard 

 deviation of 12.25 tons. The size-frequency dis- 

 tributions of single-school catches in individual 

 seasons (lower panels, Figure 2) also were asym- 

 metrical and, without exception, similar in shape 

 to that of the combined data. The maximum fre- 

 quency in every year fell in either the 4- to 6-ton 

 or the 7- to 9-ton size classes. 



Although there were exceptions in some years, 

 larger schools were generally found in the north- 



700 



