Humborstad et al.: Reflex impairment as a measure of survival potential for Gadus morhua 
399 
sure experiments, whereas 94% mortality 
(delayed mortality) occurred within 1 day 
(16 fish) and one fish died after 6 days. 
Forcing cod to swim for 5, 10, or 15 min- 
utes at 20 cm/s in combination with net 
abrasion and air exposure did not increase 
reflex impairment or mortality above that 
associated with air exposure alone. Reflex 
impairment increased with increased ex- 
posure to a combination of swimming, net 
abrasion, and air, and this effect appeared 
to be associated primarily with increased 
duration in air (ANOVA, F' 55 = 28.82, 
P<0.001; Fig. 3). Likewise, mortality in- 
creased with increased exposure to these 
stressors, and mortality appeared to be 
primarily associated with air exposure 
(ANOVA, F 55 = 25.15, PcO.OOl; Fig. 3). Cod 
injury from net abrasion was not obvious, 
other than the presence of sloughed scales 
on the net. No immediate mortality was 
observed from any of the combined stress- 
ors, whereas 94% of observed delayed mor- 
tality occurred within 1 day (15 fish) and 
one fish died after 14 days. 
Step 3: RAMP curves 
Reflex impairment and mortality were 
correlated for individual cod exposed to 
air (Spearman rank correlation = 0.85, 
PcO.OOl, n=32) and when exposed to swim- 
ming, net abrasion, and air (Spearman 
rank correlation =0.85, PcO.OOl, n = 64). 
The relationship between reflex impair- 
ment and mortality was sigmoid (RAMP 
curve), initially showing increasing reflex 
impairment with no mortality, followed 
by a sharp increase in mortality at reflex 
impairment values > 0.6 (Fig. 4A). The 
relationship between reflex impairment 
and mortality calculated for cod in groups 
defined by experimental treatments that 
combined swimming, net abrasion, and 
air exposure (Fig. 4B) showed a simi- 
lar pattern to that shown by the RAMP 
curve for individual fish, indicating that 
reflex impairment could predict mortality 
in populations of cod, as well as in indi- 
vidual fish. 
Discussion 
10,5 5,10 15,10 
Swim time, air exposure time (min) 
Figure 3 
Atlantic cod ( Gadus morhua) mean proportion of reflex impairment (•) 
and mortality (A) for seven treatment groups (n = 8 fish per treatment 
group) increased with increased stressor intensity. Fish were exposed 
to combinations of swimming (5, 10, and 15 minutes), net abrasion 
(1 minute), and air (5, 10, and 15 minutes). There were two groups 
of mean (±1 standard error) values that were significantly different 
(indicated by a, b). 
Capture-based aquaculture (CBA) is a 
combination of capture by commercial 
fisheries and rearing by aquaculture. In this article 
we address key stressors associated with the capture 
portion of CBA. Stress and mortality in fish from com- 
mercial fisheries often result from several classes of 
interacting acute stressors. These classes include cap- 
ture stressors (net entrainment, mesh passage, crushing, 
wounding, sustained swimming until exhaustion, and 
pressure changes), fishing conditions (towing time, light 
