FISHERY BULLETIN: VOL. 75, NO. 1 



5Y, 5Ze, and 5Zw-SA 6, red hake in 5Ze and 

 5Zw-SA 6, yellowtail in 5Ze, 5Zw, and SA 6, and 

 herring in 5Y and 5Z-SA 6. (We considered the 

 remaining species and species groups indicated as 

 stocks for the purpose of this analysis.) Silver 

 hake, herring, and mackerel stock sizes were 

 available from virtual population analyses in 

 previous assessments (International Commission 

 for the Northwest Atlantic Fisheries 1974e, see 

 footnote 17; Anderson 19,20 ), while annual esti- 

 mates for haddock and red hake had also been 

 computed earlier (Hennemuth see footnote 5; 

 Anderson 21 ; Clark 22 ) using average weight or 

 mean weight at age data and the relationship: 



calculated stock size for each year using Equation 

 (3); 1964-66 stock sizes were then assumed to be 

 similar to the 1967-68 average as commercial 

 abundance indices were stable through this 

 period. We then obtained values for succeeding 

 years by adjusting the 1967-68 average by stock 

 abundance indices based on pre-recruit survey 

 catches (Brown and Hennemuth see footnote 6; 

 Parrack 23 ), i.e., 



Stock size in year i = Mean stock size for 1967-68 



Abundance index for year i 

 Mean abundance index for 1967-68 



(4) 



C t =N,F l /Z l (l - expt-ZJ) 



(3) 



where C t = landings (number) in year i, 



N t = stock size ( number) at the beginning of 



year i, 

 F- = instantaneous fishing mortality rate 



in year i, and 

 Z = instantaneous total mortality rate in 

 year i ( =F t + M, the instantaneous 

 natural mortality rate). 



Approximations of stock size for both long- 

 finned and short-finned squids are also available 

 for recent years ( International Commission for the 

 Northwest Atlantic Fisheries 1975c). We used 

 these approximations for all years in view of 

 uncertainty regarding stock size and historical 

 trends in abundance for these species (Interna- 

 tional Commission for the Northwest Atlantic 

 Fisheries 1975c). 



Stock size estimates for the remaining species 

 and species groups are currently unavailable, and 

 we computed estimates by a variety of procedures. 

 For yellowtail, we assumed an F value of 1.0 for 

 the southern New England (5Zw) stock in 1967-68 

 (M = 0.2 in all cases) based on earlier assessment 

 work (Brown and Hennemuth see footnote 6), and 



19 Anderson, E. D. 1975. Assessment of the ICNAF Division 5Y 

 silver hake stock. Int. Comm. Northwest Atl. Fish. Annu. Meet. 

 1975, Res. Doc. No. 62, Serial No. 3544 (mimeo.), 13 p. 



20 Anderson, E. D. 1975. Assessment of the ICNAF Subdivision 

 5Ze and Subdivision 5Zw-Statistical Area 6 silver hake stocks. 

 Int. Comm. Northwest Atl. Fish. Annu. Meet. 1975, Res. Doc. No. 

 94, Serial No. 3574 (mimeo.), 17 p. 



"Anderson, E. D. 1974. Assessment of red hake in ICNAF 

 Subarea 5 and Statistical Area 6. Int. Comm. Northwest Atl. 

 Fish. Annu. Meet. 1974, Res. Doc. No. 19, Serial No. 3165 

 (mimeo.), 27 p. 



22 Clark, S. 1975. Current status of the Georges Bank (5Ze) 

 haddock stock. Int. Comm. Northwest Atl Fish. Annu. Meet. 

 1975, Res. Doc. No. 48, Serial No. 3527 (mimeo.), 9 p. 



For an estimate of SA 6 stock size, we obtained 

 values for the 1963-66 period by multiplying the 

 computed average stock size value for southern 

 New England by the ratio between mean survey 

 abundance indices between the SA 6 and southern 

 New England stock areas and the ratio between 

 the actual bottom areas considered; we obtained 

 the remaining values using stock abundance 

 indices (Parrack see footnote 23) as above. For the 

 Georges Bank (5Ze) stock, we assumed an F value 

 of 0.8 in 1964 and 1965 (Brown and Hennemuth 

 see footnote 6), calculated stock sizes by Equation 

 (3), and averaged these values to obtain an initial 

 estimate; we then adjusted this value by means of 

 commercial abundance indices (Brown and 

 Hennemuth see footnote 6; Parrack see footnote 

 23) according to Equation (4) to obtain estimates 

 for later years. The Cape Cod yellowtail stock was 

 considered to have been relatively stable in recent 

 years; we computed an estimate for 1969 by 

 Equation (3) assuming an F value of 0.8 and added 

 the resulting value to each Georges Bank stock 

 size estimate to obtain combined estimates for the 

 Georges Bank area. 



We obtained stock size estimates for the re- 

 maining stocks from Equation (3) using available 

 estimates of F and M and historical catch data 

 (International Commission for the Northwest 

 Atlantic Fisheries 1965-1973, 1974c, 1975a, see 

 footnote 12). We computed an average stock size 

 for the entire 1965-75 period for 5Y cod using 

 mortality rates reported by Penttila and Gifford 24 , 



23 Parrack, M. L. 1974. Status review of ICNAF Subarea 5 and 

 Statistical Area 6 yellowtail flounder stocks. Int. Comm. 

 Northwest Atl. Fish. Annu. Meet. 1974, Res. Doc. No. 99, Serial 

 No. 3335 (mimeo.), 17 p. 



24 Penttila, J. A., and V. M. Gifford. 1975. Growth and mortal- 

 ity rates for cod from the Georges Bank and Gulf of Maine areas. 

 Int. Comm. Northwest Atl. Fish. Annu. Meet. 1975, Res. Doc. No. 

 46, Serial No. 3525 (mimeo.), 13 p. 



14 



