Lough and O'Brien: Life-stage recruitment models for Gadus morhua and Melcinogrammus aeg/efinus on Georges Bank 
133 
40 - 
30 - 
20 - 
10 - 
0 -■ 
1975 1980 1985 1990 1995 2000 2005 
Year 
Figure 7 
Yearly comparison of the various cod ( Gadus morhua ) life stage model 
predictions of recruitment (triangles) with the Georges Bank cod 
virtual population analysis (VPA) for age-1 recruitment (squares). 
Life-stage model predictions of recruitment start from the annual 
survey spawning abundance of eggs (A), the survey hatching abun- 
dance of larvae (B), and the abundance of eggs derived from the 
VPA spawning stock biomass method (C). Ichthyoplankton survey 
data were used from the Marine Resource Monitoring, Assessment, 
and Prediction (MARMAP) study (1977-87) and U.S. Global Ocean 
Ecosystems Dynamics (GLOBEC) study (1995-99); egg data were 
lost for the 1977-78 seasons. 
1978 recruitment from the VPA was 84xl0 6 
versus the predicted 15xl0 6 . There were no 
egg data available from the 1978 surveys, 
but the larval abundance was the highest 
of the time series 12,280 x 10 12 (see Table 
2), which would indicate that the VPA SSB 
derived egg production was significantly un- 
derestimated, or there was an unusual sur- 
vival of eggs. The 2003 VPA R was 789 xlO 6 
versus the predicted 192 xlO 6 . For this year 
class there was no egg or larval data avail- 
able to compare with the VPA SSB derived 
egg production estimate. 
With the use of these simple models with 
proxies, the results indicated that forecast- 
ing recruitment for individual years can best 
be made if there is good survey coverage of 
the larval stage as conducted for the GLO- 
BEC years. Forecasts would be poorer if only 
survey coverage of the egg stage or seasonal 
egg abundance derived from the VPA SSB 
were used. 
Discussion 
Cod recruitment had not fully recovered in 
recent years from the low recruitment of the 
1990s with only a moderate year class in 
2003 and weak year classes in 2000, 2002, 
and 2004 (O’Brien et al. 1 ; and see Lough et 
al., 2008, fig. 2). A relatively strong cod year 
class occurred in 1980 and more moderate 
year classes in 1985 and 1988. Older year 
classes (>age 5) were greatly reduced after 
the 1980s. Spawning stock biomass had only 
increased slightly since closure of the fishery 
in 1994. Environmental conditions may have 
been especially favorable for early survival 
of the 1985 and 2003 year classes according 
to the recruitment survival index ( R/SSB ). 
High haddock year classes occurred in 
1963, 1975, 1978, and 2003, generally from 
intermediate spawning stock biomasses (see 
Lough et al., 2008, fig. 3). After closure of 
the Georges Bank fishery in 1994, haddock 
SSB steadily recovered, and with older age 
classes entering the population, recruitment 
increased to moderate levels with the 1998 
and 2000 year classes. The 2003 year class 
of haddock was the highest recorded recruit- 
ment since 1963 (Brodziak et al. 2 ). The re- 
cruitment survival index generally followed 
the trend in recruitment (Friedland et al., 2008). 
Both estimates of egg and larval production and SSB 
and recruitment based on survey data are inherently 
imprecise. Coefficients of variation (CV) for the egg 
and larval abundance estimates from the MARMAP 
surveys ranged between 20 and 60% (Lough et al., 
2006). They are especially sensitive to the interval be- 
tween surveys in relation to the timing and duration of 
the egg and larval stages, and the number of samples 
within a cruise (Pennington and Berrien, 1984; Hauser 
and Sissenwine, 1991). The monthly GLOBEC egg and 
larval surveys provided the best abundance assess- 
ments, whereas the bimonthly MARMAP surveys were 
less definitive. VPA-derived recruitment abundance 
