123 
Life-stage recruitment models 
for Atlantic cod ( Gad us morhua ) 
and haddock ( Melanogrammus aeg/efinus ) 
on Georges Bank 
Email address for contact author: Gregory.Lough@noaa.gov 
Northeast Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
166 Water St. 
Woods Hole, Massachusetts 02543 
Abstract — Ichthyoplankton surveys 
have been used to provide an inde- 
pendent estimate of adult spawning 
biomass of commercially exploited spe- 
cies and to further our understanding 
of the recruitment processes in the 
early life stages. However, predicting 
recruitment has been difficult because 
of the complex interaction of physical 
and biological processes operating at 
different spatial and temporal scales 
that can occur at the different life 
stages. A model of first-year life-stage 
recruitment was applied to Georges 
Bank Atlantic cod ( Gadus morhua) 
and haddock ( Melanogrammus aeglefi- 
iiu s) stocks over the years 1977-2004 
by using environmental and density- 
dependent relationships. The best life- 
stage mortality relationships for eggs, 
larvae, pelagic juveniles, and demer- 
sal juveniles were first determined by 
hindcasting recruitment estimates 
based on egg and larva! abundance 
and mortality rates derived from two 
intensive sampling periods, 1977-87 
and 1995-99. A wind-driven egg 
mortality relationship was used to 
estimate losses due to transport off 
the bank, and a wind-stress larval 
mortality relationship was derived 
from feeding and survival studies. A 
simple metric for the density-depen- 
dent effects of Atlantic cod was used 
for both Atlantic cod and haddock. 
These life stage proxies were then 
applied to the virtual population 
analysis (VPA) derived annual egg 
abundances to predict age-1 recruit- 
ment. Best models were determined 
from the correlation of predicted and 
VPA-derived age-1 abundance. The 
larval stage was the most quantifiable 
of any stage from surveys, whereas 
abundance estimates of the demer- 
sal juvenile stage were not available 
because of undersampling. Attempts 
to forecast recruitment from spawn- 
ing stock biomass or egg abundance, 
however, will always be poor because 
of variable egg survival. 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Manuscript submitted 12 August 2010. 
Manuscript accepted 14 October 2011. 
Fish. Bull. 110:123-140 (2012). 
R. Gregory Lough (contact author) 
Loretta O'Brien 
Atlantic cod ( Gadus morhua) and had- 
dock (Melanogrammus aeglefinus ) co- 
occur in many regions of the North 
Atlantic and show moderate levels 
of synchrony in recruitment within 
regions, indicating that common 
environmental conditions affect both 
species (Fogarty et ah, 2001). Recruit- 
ment in these species is generally 
correlated with the abundance of 
the late larval stage and more so by 
age-0 juveniles. However, the large 
year classes of haddock on Georges 
Bank resulted from different early life 
history survival rates, indicating that 
they were driven by different causes 
(Rothschild et al., 2005). 
Although recruitment control of At- 
lantic cod (hereafter, cod) and had- 
dock has generally been believed to 
be set at the juvenile stage (Myers 
and Cadigan, 1993; Fogarty et ah, 
2001), the importance of the contri- 
bution of survivors from the egg and 
larval stages has been variable and 
uncertain. A recent review concluded 
that no life stage or process can be 
singled out as the primary contribu- 
tor for recruitment variability in ma- 
rine fish (Houde, 2009). Recruitment 
levels can be controlled by environ- 
mental factors on eggs and larvae 
in some species and years but are 
regulated on late-stage larvae and 
juveniles in other species and years. 
Recruitment is not necessarily set at 
a particular stage because it is an 
integrated, cumulative process. Fore- 
casting recruitment will depend on 
our knowledge of the process, mecha- 
nisms that regulate recruitment, and 
our ability to monitor these processes. 
Environmental variables have been 
incorporated into stock and recruit- 
ment models to help explain addition- 
al variability (e.g., Maunder and Wat- 
ters, 2003; Fogarty et ah 2008; Hare 
et ah, 2010; Mantzouni et ah, 2010). 
Individual based models (IBMs) with 
specific species early life-stage be- 
haviors have been embedded in hy- 
drodynamic models to simulate vari- 
ability in egg and larvae transport 
and survival (see Miller [2007] for 
review). Process-based forecasting 
models are needed to link adult egg 
production with juvenile stages. Re- 
cruitment can be viewed in terms of 
stage-specific contingency survival. 
Recent conceptual models of recruit- 
ment view the complex process as 
the interactions between small-scale 
activating factors and larger-scale 
constraining factors (Stenseth et ah, 
1999; Bailey et ah, 2005). Activat- 
ing factors are high-frequency (sto- 
chastic) events that affect larval sur- 
vival, the cumulative result of many 
episodic events such as early larval 
feeding in relation to wind-induced 
turbulence, and invertebrate preda- 
tion. Constraining factors tend to 
limit population size through low fre- 
quency events, physical barriers, and 
density-dependent processes, such 
as competition for prey and limited 
space, predation, and cannibalism. 
On Georges Bank, the lower re- 
cruitment variability of cod (stan- 
dard deviation [SD] of residuals of 
