FISHERY BULLETIN: VOL. 75, NO. 1 



the mechanism by which temperature anomalies 

 influence the fishery. 



Cushing (1969) listed three sources of variation 

 which might affect recruitment: year-to-year 

 environmental changes, larger scale climatic 

 changes, and differences due to stock density. The 

 year-to-year effects were considered by Cushing to 

 be randomly distributed around the stock and 

 recruitment curve and not of major consequence in 

 the long-term regulation of fisheries. Over a 

 number of years, variations around a stock and 

 recruitment curve may tend to cancel one another 

 and the fishery may provide a relatively stable 

 yield. However, when a fishery is overexploited 

 and subjected to poor survival as a result of en- 

 vironmental conditions, stock size may be reduced 

 to a small fraction of that necessary to maintain a 

 maximum sustainable yield (MSY). Further, with 

 overcapitalization, fishing effort may remain 

 high, preventing a resurgence of the stocks by 

 maintaining a spawning stock too small to pro- 

 duce a large year class under favorable en- 

 vironmental conditions. From this standpoint, a 

 predictive capability, based on knowledge of 

 density-dependent and density-independent 

 recruitment could be vital to the maintenance of 

 adequate stock size through a reduction in effort, 

 or to the harvesting of surplus population beyond 

 that necessary to maintain the MSY. Fisheries, in 

 the generic sense, operate over long periods of 

 time. Fishermen, fish processors, and consumers 

 operate on a much shorter time scale and large, 

 unexpected, year-to-year fluctuations in stock size 

 have significant economic and social impact. 



The Atlantic menhaden, Brevoortia tyrannus, is 

 a species that has supported a significant fishery 

 since the middle of the 19th century (Reintjes 

 1969). Landings from the fishery have been 

 sampled extensively since 1955 and the major 

 characteristics of the stocks and the fishery have 

 been determined. Information for a variety of 

 stock sizes and from a range of environmentally 

 different years is available, and the stocks have 

 been subjected to heavy fishing pressure (Schaaf 

 and Huntsman 1972). 



A study of forecasting methods and the de- 

 velopment of a forecast for the Atlantic menhaden 

 fishery was carried out by the National Marine 

 Fisheries Service (Schaaf et al. 4 ). The manuscript 



points out that knowledge of the biology of re- 

 cruitment of the Atlantic menhaden is needed to 

 take advantage of strong year classes through the 

 development of short-term fishing strategies. 

 Knowledge of poor year classes would also be 

 beneficial from a standpoint of avoiding excessive 

 fishing pressure on the stocks. 



A single year class is harvested by industry over 

 a 4- to 5-yr period, and its failure could be masked 

 to some extent by overfishing of other year classes 

 taken concurrently, resulting in serious stock 

 depletion. Conversely, a large year class may lead 

 to a large increase in fishing effort which con- 

 tinues after the year class has been harvested, 

 leading to overcapitalization and overfishing in 

 subsequent years of reduced stock size. A large 

 year class, followed by several poor year classes is 

 potentially disastrous to the fishing industry and 

 to the stocks. Knowledge of the recruitment pro- 

 cess and the ability to predict year-class strength 

 is necessary if the fishery is to operate at the MSY 

 level. 



Detailed information on the composition of 

 Atlantic menhaden stocks obtained yearly since 

 1955 shows a range in numbers recruited into the 

 fishery of from 11.5 billion in 1958 to 0.9 billion in 

 1967. Although some of the variation in re- 

 cruitment can be attributed to fluctuations in the 

 size of the spawning stock (Schaaf and Huntsman 

 1972), the wide range of fluctuations between 

 years with similar spawning stock sizes suggests 

 that environmental factors are influencing the 

 survival of prerecruits. This study attempts to 

 identify those factors, determine their relative 

 influences, and develop a predictive model to 

 account for the variations between actual and 

 expected recruitment into the Atlantic menhaden 

 fishery. 



SPAWNING AND 

 LARVAL DISTRIBUTION 



Gravid or running-ripe Atlantic menhaden are 

 rarely caught and spawning has not been ob- 

 served. Without conclusive information, the time 

 and place of spawning has been inferred by the 

 relative ripeness of maturing ova, the occurrence 

 of partially spent ovaries, and the distribution and 

 occurrence of eggs and small larvae. 



Higham and Nicholson (1964:262) reported that 



"Schaaf, W. E., J. E. Sykes, and R. B. Chapoton. 1973. Forecast 

 of 1973 Atlantic and Gulf menhaden catches based on the histor- 

 ical relation of catch and fishing effort. Unpubl. manuscr., 22 p. 



Atlantic Estuarine Fisheries Center, National Marine Fisheries 

 Service, NO A A, Beaufort, NC 28516. 



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