Underwood et al. : Behavior-dependent selectivity of Limanda ferrugmea in the mouth of a bottom trawl 
439 
Figure 4 
The behavioral responses of yellowtail flounder ( Limanda ferruginea) 
from analysis of video footage collected during 5 tows of a bottom 
trawl in June 2010 on the southern Grand Bank off eastern New- 
foundland. Each circle represents a single behavior with the initial 
and end counts of the number of individuals that exhibited that be- 
havior. The arrows indicate the direction and count of individuals 
that changed their behavior. The fish drawings indicate the position 
of each behavior in relation to the substrate. 
surface] flatfishes that swim close to the 
seabed may also require less energy ( Vi- 
deler, 1993; Webb and Gerstner, 2000) to 
keep distance from the threat and, there- 
fore, have more time to seek escapement. 
Finally, swimming at an angle to the 
seabed forces individuals to swim more 
rapidly, to use more energy (in order to 
maintain a distance over ground from the 
threat) and by contrast, to reduce their 
escapement time. 
The initial response also could be af- 
fected by previous gear encounters and, 
therefore, also would influence the prob- 
ability of capture. We observed that indi- 
viduals assumed to be previously herded 
had only a 24% probability of avoiding 
capture and were twice as likely to be 
caught. These individuals were oriented 
toward the opposite wing of the trawl. Be- 
cause most yellowtail generally swam in 
the direction in which they were oriented 
(also see Stickney et al. [1973]), these fish 
would hit the footgear and end by being 
captured. 
The consistency of a fish’s response de- 
pended on the initial behavioral decision. 
Fish that responded with a slope or rise 
behavior generally maintained this same 
behavior throughout the period of observa- 
tion, but about 40% of the yellowtail that 
exhibited a run response shifted to a slope 
or rise response. Such a change in behavior 
was always one-way, that is, no individu- 
als moved back toward the seabed after 
leaving it. If, however, the energetic cost 
of continuing a response increases to some threshold, 
presumably the point of fatigue, an animal would be 
expected to switch behavior (Ydenberg and Dill, 1986; 
Breen et al., 2004; Peake and Farrell, 2006; Winger et 
al., 2010). Although there was no influence of gait on 
change in response in our study, indicating that a fish 
did not reach the critical level of fatigue, the behavioral 
shifts that were observed indicate that there are cumu- 
lative energetic costs of swimming ahead of the footgear. 
In light of the findings from previous behav- 
ioral studies and our study, the combined effects of 
trawl gear components need to be studied further 
in a manner that makes fishes initially have a run 
response then a rise or slope response during the 
capture process. Further experiments should include 
different combinations of vessel speed, sweep angle, 
and gear visibility to stimulate the run response in 
flatfishes before their approach to the mouth of a 
trawl. Once in the mouth of the trawl, lights in the 
central part of the footgear may cause a startled re- 
sponse (Walsh and Hickey, 1993) and trigger flatfish- 
es to leave the seabed. Studying the effect of various 
light sources, like flashing or intermittent lights, on 
response to the footgear by different species of flat- 
fishes would be worthwhile. 
Acknowledgments 
We thank the captains and crew of the FV Aqviq for 
their assistance and hospitality while out at sea, as 
well as to S. Mahlum, C. Batten, and J. White for their 
technical assistance. We also thank D. Schneider at 
Memorial University of Newfoundland, M. Penning- 
ton at Institute of Marine Research, and N. Cadigan 
at Fisheries and Oceans Canada for their statistical 
advice. Lastly, we, thank S. Grant and the anonymous 
reviewers for their comments on earlier versions. 
Literature cited 
Albert, O. T., A. Harbitz, and A. S. Hoines. 
2003. Greenland halibut observed by video in front of 
survey trawl: behaviour, escapement, and spatial pat- 
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