Relation Between Spawning Stock 

 and Recruitment 



Unfortunately, it has not been possible with 

 menhaden to establish a reliable relation 

 between the spawning stock and subsequent 

 recruitment to the fishery. This has been 

 partially due to the fact that the menhaden 

 research program has never had funding for 

 oceanic studies during the time of menhaden 

 spawning. Consequently, little is known about 

 what is probably the most critical time in their 

 life history. 



Nevertheless, an examination of the data 

 from the Middle Atlantic area in relation to 

 spawning stock and resulting progeny is per- 

 haps indicative of possible adverse effects from 

 the present low population levels of Atlantic 

 menhaden. The catch-per-unit effort (SVD) for 

 the Middle Atlantic Area was used as a measure 

 of the spawning population, and the total catch 

 from each year class (Table 2) was used as a 

 measure of year-class abundance. If we assume 

 a reproduction curve of the type proposed by 

 Ricker (1958), i.e.. 



R 

 where 

 R 

 P 

 Pr 

 Pm 



p.^(PrP)/P,n 



Reproduction 

 Spawning stock 

 Stock size at which R = P 

 Stock size giving maximum reproduc- 

 tion in the absolute sense 

 the base of natural logarithm 

 (2.71828-^), 



the relations shown in Figures 39 and 40 can 

 be computed. 



It is apparent that the largest year classes 

 occurred when the catch-per-unit-effort in the 

 Middle Atlantic area was the highest, and that 

 current low catches per unit of effort in that 

 area are related to small year classes. A stock 

 size reflected by a catch-per-unit-effort of at 

 least 0.8 appears to be a desirable goal. The 

 theoretical maximum reproduction (Pm) would 

 be achieved at a catch-per-unit-effort of 

 1.08— considerably above present day levels. 

 The data again suggest the desirability of 

 increasing the escapement of Atlantic men- 

 haden into the Middle Atlantic Area. Since this 

 increased escapement would essentially be 



RELATIVE SIZE OF PARENTAL STOCK-CPU E (PI 



Figure 39.— Relation between relative size of the parent 

 stock, as measured by Middle Atlantic catch per unit 

 of effort, and the natural logarithm (In) of R/P where 

 R=year-class abundance and P=spawning stock (Num- 

 bers indicate year classes). 



9 80 - 



RELATIVE SIZE OF PARENTAL STOCK- CPUE (P) 



Figure 40.— Relation between relative size of the parent 

 stock, as measured by Middle Atlantic catch per unit 

 of effort and year-class abundance (Numbers indicate 

 year classes). 



mature fish, it would actually result in an 

 increase in the spawning population. 



There might be some question as to why the 

 catch-per-unit-effort for the Middle Atlantic 

 Area was used as a measure of the spawning 

 population. Catches in some of the other areas 

 consist of a large number of immature fish 

 (ages and 1), which do not contribute to 

 spawning success (Chesapeake Bay, South 

 Atlantic, and North Carolina fall fishery). The 

 age 2 fish, one of the most abundant age 

 groups in the spawning population, are not 

 fully recruited into the North Atlantic Area 

 fishery. Finally, the North Carolina fall fishery 

 is of short duration and can be seriously 

 affected by bad weather. Consequently, the 

 Middle Atlantic appears to be the area in which 



22 



