Lough and O'Brien: Life-stage recruitment models for Gadus morhua and Melanogrammus aeglefmus on Georges Bank 
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Figure 1 
(A) Map of the northeast coast of the United States showing the Georges Bank study 
area. ( B ) Generalized distribution of Atlantic cod ( Gadus morhua ) and haddock (Mela- 
nogrammus aeglefinus ) eggs (1), larvae (2, 3), and pelagic juveniles (4, 5) during their 
first 3-4 months of life in the clockwise circulation over Georges Bank. The shaded 
areas within the stage patches represent the areas of highest density. Cross-hatching 
indicates where the highest abundance of recently-settled, demersal juveniles (6) may 
be found in early-summer. The arrows represent the direction and relative speed of 
mean summer water column flow. A reference arrow of 5 cm/s in length is located on 
Nantucket Shoals. Figure is redrawn from Lough et al. (2005, fig. 1). Depth contours 
are given in meters (m). 
Larvae of both species take approximately 30 clays to 
grow to 10 mm standard length (SL) ( t 2 ). Pelagic cod 
juveniles take 90 and haddock juveniles take 70 days 
to reach 5 cm SL ( t 3 ). The demersal juvenile stage (t 4 ) 
for cod takes 241 days to reach 26 cm SL, and 210 days 
for haddock to reach 20 cm SL. January 1 is the date 
when fish are considered to be 1 year old. The demersal 
juvenile duration was estimated from the mid-date of 
the pelagic juvenile stage (Lough, 2010). Stage dura- 
tion specified above, which is dependent on growth and 
temperature, was not varied in this study. 
The initial recruitment predictions were based on es- 
timates of spawning and hatching abundances and life- 
stage mortality rates derived from the MARMAP and 
GLOBEC surveys (Tables 1 and 2). Revised hatching 
abundances for GLOBEC years were used so that the 
methods were the same as those used for the MARMAP 
years (Mountain and Kane, 2010). 
With this life-stage recruitment model, estimates of 
age-1 recruitment from the initial egg and hatching 
(larval) abundances were determined and correlated 
with the VPA-derived age-1 recruitment for Georges 
Bank cod and haddock. Simulations based on random- 
ization of parameters were not done for confidence lim- 
its of the age-1 recruits because the potential range of 
the parameters was so wide as to be meaningless. 
VPA-derived egg abundance 
Spawning stock biomass (SSB) and recruitment fR) 
for Georges Bank cod and haddock were obtained from 
assessments conducted by using the adaptive frame- 
work for the estimation of population size (ADAPT) 
virtual population analyses (VPA) calibration method 
(Parrack, 1986; Conser and Powers, 1990). The VPAs 
were calibrated with indices of abundance from spring 
and fall research bottom trawl surveys through 2005 
(O’Brien et al. 1 ; Brodziak et al. 2 ). SSB was estimated 
by using NOAA Fisheries Toolbox, Virtual Population 
Analysis, vers. 3.0 software (NOAA, 2008) as the prod- 
uct of the numbers of fish in the first year of the period 
in question, the mean weight at age (as determined from 
commercial fishery catch statistics), and the variable 
proportion of mature fish-at-age summed over all age 
classes. Maturation ogives were estimated with logistic 
regression of maturity data collected during NEFSC 
spring bottom trawl research surveys (O’Brien et al. 1 ; 
Brodziak et al. 2 ). 
