7 62 
Abstract .—We examine the popu- 
lation to population variability of in- 
trinsic rate of natural increase, r m , of 
Atlantic cod, Gadus morhua. The in- 
trinsic rate of increase is positively re- 
lated to temperature, contrary to the 
expectation that r m might increase as 
the high and low temperature limits of 
habitability for cod are approached. For 
the parameter regime considered, r m 
has a simple dependence on age-at-ma- 
turity and the number of replacements 
each spawner can produce at low popu- 
lation densities (a). It is shown that a. 
has no significant temperature depen- 
dence, and thus the covariation of r m 
and temperature arises from the influ- 
ence of temperature on age-at-maturity. 
We demonstrate that our estimates of 
r m are robust and thus may be of use in 
estimating the recovery time of de- 
pleted populations. 
Manuscript accepted 25 March 1997. 
Fishery Bulletin 95:762-772 ( 1997). 
Maximum population growth rates and 
recovery times for Atlantic cod, 
Gadus morhua 
Ransom A. Myers* 
Gordon Mertz 
Science Branch 
Department of Fisheries and Oceans 
RO. Box 5667 
St John's, Newfoundland, Canada A1C 5X1 
* Present address: Department of Biology 
Dalhousie University 
Halifax, Nova Scotia, Canada B3H 4J1 
E-mail address (for R. Myers):Ransom.Myers@Dal.Ca 
P. Stacey Fowlow 
Seaborne Ltd. 
PO. Box 2035 
Station C, 200 White Hills Road 
St. John's, Newfoundland, Canada A I C 5R6 
Perhaps the most fundamental of 
all ecological parameters is the in- 
trinsic rate of natural increase, r 
(Cole, 1954; Pimm, 1991). High r m 
will be selected for in populations 
that experience frequent excursions 
to low density (Charlesworth, 1994). 
Populations subjected to strong en- 
vironmental variability should 
evolve toward high r m (Mac Arthur 
and Wilson, 1967), which will im- 
part resilience to the population. 
However, allometric (cross species) 
comparisons (Fenchel, 1974; Hen- 
nemann. 1983; Charnov, 1993) sug- 
gest that r m chiefly depends on 
metabolic rate or somatic growth 
rate. Perhaps, the influence of en- 
vironmental variability on r m can be 
more readily discerned in cross 
population comparisons for a single 
species. In this paper we examine 
20 populations of Atlantic cod, Ga- 
dus morhua , to determine their 
maximum growth rates. We also 
discuss how these estimates help 
predict the recovery times of se- 
verely overfished populations. 
Atlantic cod lends itself to a study 
of this nature because there is a 
wealth of good quality biological 
data collected for stock manage- 
ment purposes. Moreover, these cod 
populations occupy a broad span of 
latitudes, including regions that are 
thought to represent the northern 
and southern limits of habitability 
for cod, and there is evidence that 
population variability increases as 
these extremes are approached 
(Myers, 1991). The increase in popu- 
lation variability at the limits of the 
range of cod could impose con- 
straints on r that would mask the 
m 
simple dependence of r m on meta- 
bolic rate or somatic growth rate 
apparent in cross species compari- 
sons. In fact, we will show, in what 
we believe is an unanticipated re- 
sult, that even for a within-species 
comparison, there is strong coupling 
between r and metabolic rate or 
TYl 
somatic growth rate (as represented 
by age at maturity or temperature). 
Our results have implications for 
the recovery rates of a number of 
