Humborstad et at: Reflex impairment as a measure of survival potential for Gadus morhua 
401 
posure. Sensitivity to air exposure has been shown to 
vary among species, with mortality occurring at 7 to 45 
minutes of exposure (Davis, 2002). Air exposure is often 
inevitable during sorting in live-capture operations, and 
duration in air can be reduced to safe levels, e.g., by the 
introduction of water-filled sorting tables. 
Increased temperature is another stressor that has 
been associated with mortality in captured fish and 
may become important if cod are captured or sorted 
at temperatures above 12°C (Davis, 2002; Sartoris et 
al., 2003; Brattey and Cadigan, 2004; Suuronen et al., 
2005). Increased temperature may also raise sensitiv- 
ity to air exposure (Davis and Parker, 2004; Davis 
and Schreck, 2005). Temperatures in deep (200 m) and 
shallow (surface) water peak in July and August (at 
~3 and ~8°C, respectively) in coastal areas suitable for 
CBA in northern Norway (Loeng, 1991). During spring 
months when capture for CBA purposes occurs, mixing 
in these areas is high, and temperatures remain around 
~3°C throughout the water column and air temperature 
only rarely raises above 12°C in May (data from The 
Norwegian Meteorological Institute, Blindern, Oslo). 
Temperature should thus not be a critical factor at the 
temporal and spatial scales of current CBA practices in 
Norway, and accordingly we did not include temperature 
as a variable in our study. However attempts to develop 
CBA outside this temporal and spatial window (e.g., 
North Sea during summer months), warrant a high 
vigilance of temperature effects. 
A likely effect of adding a stressor is that it may 
cause an increase in the overall stress response. How- 
ever, forcing cod to swim for 5, 10, or 15 minutes at 20 
cm/s in combination with net abrasion and air expo- 
sure did not increase reflex impairment or mortality 
above that associated with exposure to air alone. This 
result even indicated that swimming for 10 minutes 
may have enhanced resistance to air exposure, having 
a palliative effect on the induction of further stress. In 
a study of free swimming cod, oxygen consumption did 
not increase until fish were swimming at 30 cm/s or 
higher, indicating that at less than 30 cm/s cod would 
not be stressed (Claireaux et al., 1995). Although not 
directly relevant to this study, sustained slow swim- 
ming in rainbow trout ( Oncorhynchus mykiss) and coho 
salmon ( Oncorhynchus kisutch) has reduced the dura- 
tion of recovery from exhaustive exercise (Farrell et al., 
2001; Lee-Jenkins et al., 2007). Little is known about 
the palliative effects of low-intensity exercise in fish, 
either before or after exposure to stressors. Studies of 
the swimming performance of cod have been focused on 
measurements of endurance and burst swimming (40- 
130 cm/s) and have included an evaluation of changes 
in the scope for metabolic activity (Reidy et al., 2000). 
Further study of the interactive effects of low-intensity 
exercise, the perception of stressors by fish, and their 
management of stress may contribute to methods for 
the significant reduction of stress in captured, released, 
transported, and net-penned fish. 
Injury to cod from net abrasion was not obvious, other 
than the presence of sloughed scales on the net, and did 
not appear to contribute to delayed mortality or reflex 
impairment. Fish with obvious damage to the skin, fin 
erosion (split fins), cataracts or opaque eyes, resulting 
from severe abrasion from net material will not pass 
the sorting procedure in CBA. Therefore a moderate 
intensity of abrasion was administered in this experi- 
ment because these injuries are not likely to be detected 
during sorting and may increase the risk for infection, 
disease, and delayed mortality. Such effects of moder- 
ate net abrasion were, however, not demonstrated in 
our experiment. Mortality rarely occurred in cod that 
were injured by net abrasion when escaping from a 
demersal trawl (Soldal et al., 1993). Injury to cod from 
fishing gear can occur, however; Baltic cod have been 
observed with a high incidence (48%) of skin infection 
probably associated with escape from fishing gear, but 
associated mortality was not determined (Mellergaard 
and Bagge, 1998). In other studies of net abrasion and 
consequent mortality, some species (herring, [ Clupea 
harengus ], and walleye Pollock [ Theragra chalcogram- 
ma ] were sensitive to net abrasion and showed delayed 
mortality associated with skin infection (Suuronen et 
al., 1996; Davis and Ottmar, 2006), whereas other spe- 
cies (sablefish [Anoplopoma fimbria ] and Pacific hali- 
but [ Hippoglossus stenolepis ] were more resistant and 
mortality was not correlated with skin abrasion (Davis 
and Ottmar, 2006). 
Capture, transport, and holding of fish are often asso- 
ciated with induction of stress and reduction of vitality. 
Reflex impairment could be used to evaluate the role of 
different stressors at each stage of the live-fish fishery 
and to identify fish with the highest probability for sur- 
vival. Successful live-fish capture, transport, and rear- 
ing operations should aim to minimize stress, optimize 
water quality, and minimize the increase of metabolic 
wastes (Huntingford et al., 2006; Ashley, 2007). Water 
quality and temperature must be controlled through in- 
puts, tank and pen configurations, and flow rates. Food 
(e.g., Olsen et al., 2008) and stocking density (Staurnes 
et al., 1994) may be important factors because they 
control physiological and behavioral states of fish. The 
adjustments of wild fish to confinement and unnatural 
densities and how these short-term adjustments affect 
future performance and welfare are also important 
considerations. Reflex testing may be performed also in 
free-swimming fish (Davis and Ottmar, 2006; Stien et 
al., 2007), and monitoring reflex impairment in captive 
fish can be a rapid real-time method for identifying op- 
timal transport and rearing conditions and for tracking 
recovery in cod after live capture. 
Acknowledgments 
The authors are grateful to Anders Mangor- Jensen 
for organizing and providing facilities and fish at the 
Austevoll Research Station in Norway, and for assis- 
tance during experiments. Shale Rosen is thanked for 
assistance carrying out experiments. Anne-Britt Skaar 
Tysseland is thanked for calculations of swimming speed 
