VARIATIONS IN SIZE AND LENGTH COMPOSITION OF 

 ATLANTIC MENHADEN GROUPINGS 



Fred C. June' 



ABSTRACT 



This paper gives estimates of size (weight) and length composition of summer schools 

 and fall school-aggregations of Atlantic menhaden based on single-set purse-seine catches 

 and accompanying catch samples obtained in 1955-62. The data show that the fish school 

 by length and the average size of summer schools decreases as the apparent abundance 

 of fish in a given area of the coast decreases. The significance of the school concept in 

 the study of the dynamics of the population and the effects of fishing upon it are discussed, 

 and additional avenues of research are suggested. 



The Atlantic menhaden, Brevoortia tyrannus, is 

 a schooling fish that occurs in the western At- 

 lantic Ocean from Nova Scotia to Florida and is 

 the object of a purse-seine fishery over most of 

 its range (Reintjes, 1969) . The fishery is based 

 on seasonal appearances of the fish schools in 

 shallow waters overlying the inner half of the 

 continental shelf (Roithmayr, 1963). Fisher- 

 men and aerial fish spotters, who locate and as- 

 sist in the capture of menhaden, have a working 

 knowledge of school size, composition, and be- 

 havior, but there exists little quantitative infor- 

 mation on these and other aspects of the school- 

 ing phenomenon. Of primary interest to the 

 fishery biologist are the degree to which the fish 

 school by size, the relationship between size of 

 schools and size of fish within schools, and the 

 variation in size of schools in relation to changes 

 in abundance of the fish and to fishing. These 

 aspects of Atlantic menhaden schooling are the 

 subject of this paper. 



The nature of density and fishery-related 

 changes in the schooling of various pelagic ma- 

 rine fishes is not well understood, but sufficient 

 evidence was put forward by diff"erent workers 

 to indicate insight into the importance of this be- 

 havioral phenomenon. The significance of the 



' Bureau of Sport Fisheries and Wildlife, North Cen- 

 tral Reservoir Investigations, P.O. Box 698, Pierre, SD 

 57501. 



school concept in the study of the dynamics of 

 an exploited fish population whose members are 

 grouped and difl"erentially distributed by size 

 was apparently first recognized by Thompson 

 (1926) and further elaborated by Sette (1943) 

 for the Pacific sardine (Sardinops sagax) . Much 

 of the quantitative information on fish schooling 

 dynamics has come from work on tunas. Schae- 

 fer (1948) and Brock (1954), for example, dis- 

 cussed some implications of observed variations 

 in the size of fish within and between schools in 

 the design of a sampling system for yellowfin 

 {Thunnus alhacares) and skipjack {Euthynnus 

 pelamis) tuna stocks, respectively. Orange, 

 Schaefer, and Larmie (1957) and Broadhead 

 and Orange (1960) off"ered evidence of fishery- 

 related changes in the schooling dynamics of 

 yellowfin tuna, while Brock (1962) considered 

 implications of the interrelationship between the 

 size and number of yellowfin tuna forming a 

 school and the success of longline fishing. June 

 and Reintjes (1959) established that the At- 

 lantic menhaden also schools by size, and they 

 concluded that the school is therefore the appro- 

 priate unit for sampling the size, age, and sex 

 composition of the population. They further 

 demonstrated seasonal and annual variations in 

 the estimated number and geographical distri- 

 bution of purse-seine sets on menhaden schools 

 in a series of reports beginning with 1955 (June 

 and Reintjes, 1959), and Roithmayr (1963) 



Manuscript accepted February 1972. 

 FISHERY BULLETIN: VOL. 70. NO. 3, 



1972. 



699 



