Fisheries Behavioral Ecology - Abstracts
Ryer, C.H., M.L. Ottmar, and E.A. Sturm. 2004. Behavioral impairment after escape from trawl codends may not be limited to fragile fish species. Fisheries Research 66:261-269.
Abstract
Field studies indicate great variability between fish species in their susceptibility to direct mortality resulting from stress
incurred during entrainment and escape through trawl codends. Moreover, stressors that do not directly kill fish may still
cause indirect mortality, such as behavioral impairment leading to predation. However, it is unknown whether resistance to
direct mortality also imparts resistance to behavioral impairment. Juvenile sablefish Anoplopoma fimbria are more resistant to
direct mortality resulting from physical damage and stress than are walleye pollock Theragra chalcogramma. We measured
juvenile sablefish resistance to behavioral impairment resulting from simulated trawl passage and compared results to those
for walleye pollock, a species already studied. Juvenile sablefish (18–27 cm) were subjected to three levels of simulated
trawl/escape stressors in the laboratory: (1) control: no stressors; (2) swim: forced swimming for 90 min at 0.33 ms-1 in a
towed net, followed by escape through 8 cm square mesh; and (3) swim/pin: forced swimming for 60 min, then pinning against
net meshes for 30 min, followed by 3 min crowding prior to escape. Subsequently, we examined sablefish behavior in the
presence of a threatening but non-lethal predator (38–49 cm sablefish). In a second experiment, equal numbers of trawl-stressed
and control fish were mixed and exposed to predation by a lingcod Ophiodon elongatus (62–87 cm). The first experiment
demonstrated that sablefish suffered the same behavioral impairments as walleye pollock: stressed fish swam slower, shoaled
less cohesively and allowed the predator to approach closer than did controls. In the second experiment all three levels of trawl
stress caused fish to be consumed in greater numbers (by lingcod) than control fish, again, like walleye pollock. Therefore,
although differing in susceptibility to potentially lethal stressors, both species exhibited similar impairments in response to
sub-lethal stressors. This suggests that for numerous fish species, behaviorally impaired individuals escaping codends may
be consumed by predators, contributing to unobserved mortality.
Last updated
26 April, 2007
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