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Fishery Bulletin 113(4) 
Table 4 
Summary by categorical variables determined from yellowtail flounder ( Limanda ferruginea) observed in analysis of video 
footage from 5 tows of a bottom trawl in June 2010 on the southern Grand Bank off eastern Newfoundland. Total numbers 
of individuals that escaped and those that were caught are in bold, with the total numbers broken down into trawl interac- 
tions (TI) in parentheses. Trawl interactions are actively escape/caught (A), over taken by the trawl (O), and collided with 
the gear (C). The start densities of flatfishes are provided below the categorical variables. The mean density at the start of 
an observation, as well as standard errors (SE), 95% confidence intervals (Cl), and ranges, are calculated for all observations 
(Overall) and for escaped and caught fishes. 
Category 
Number 
Escaped (TI) 
Caught (TI) 
Species 
Yellowtail 
150 
55 (A 40, O 12, C 3) 
95 (A70, 0 21, C4) 
Length 
Large 
94 
33 (A 26, 0 6, C 1) 
61 (A 548, O 10, C 3) 
Small 
56 
22 (A 14,0 16, C 2) 
34 (A 22, O 11, C 1) 
Gait 
Kick-swim 
73 
29 (A 20,0 8, C 1) 
44 (A 29, O 11, C4) 
Burst-and-coast 
77 
26 (A 20, O 4, C 2) 
51 (A 41,0 10) 
Initial herding response 
Rise 
9 
0 
9 (A 8, Cl) 
Run 
112 
54 (A 39, O 12, C 3) 
58 (A 39, O 18, C 1) 
Slope 
29 
1 (A 1) 
28 (A 23, O 3, C 2) 
Previous gear experience 
Herded 
38 
9 (A 6, O 2, C 1) 
29 (A 23, 0 5, C 1) 
Not herded 
112 
46 (A 34, O 10, C 2) 
66 (A 47, O 16, C 3) 
Overall 
Escaped 
Caught 
Start density 
N 
150 
55 
95 
Mean (SE) 
13.0 (0.48) 
13.0 (0.88) 
13.0 (0.57) 
95% Cl 
0.95 
1.76 
1.13 
Range 
2-30 
4-30 
2-27 
In contrast to findings in earlier flatfish studies 
(Walsh, 1992; Godp et ah, 1999; Gibson, 2005), results 
from our study indicate that neither fish size nor fish 
density in the trawl mouth influenced the response 
or capture of yellowtail. Walsh (1992) collected high 
numbers of small flatfishes (<31 cm) under the trawl 
with the use of bags. This outcome contrasts with our 
findings, but, as mentioned previously, we could not 
distinguish fish that were buried in the substrate, 
a circumstance that could explain the difference in 
these results. In Walsh’s (1992) study, the small flat- 
fishes may not have reacted to the footgear but could 
have reacted to the small bag itself after they passed 
under the footgear. The lack of a density effect in our 
study may be explained by density counts that were 
lower in our study than in the study by Godp et al. 
(1999). Furthermore, we modeled fish size and density 
along with other variables to establish which factors 
influenced herded individuals the most, and both fish 
size and density were not among those factors. 
As predicted, peripherally located fish in the cen- 
ter of the footgear were mostly oriented inward, in- 
dicating that most of these fish had been previously 
herded. More than 90% of these fish also reacted by 
swimming in the direction in which they were initially 
oriented. In contrast, centrally positioned fish were 
generally oriented away from the oncoming trawl — 
a result that is similar to the findings of both Walsh 
and Hickey (1993) and Albert et al. (2003). The gen- 
eral orientation away from the trawl is a likely initial 
response to the impending trawl because the orienta- 
tion of yellowtail was consistent despite the change 
in the direction of trawling for each haul. Vessel-ra- 
diating noise is expected to influence the orientation 
of flatfishes, and American plaice have been shown to 
react at considerable distances ahead of an approach- 
ing trawler (P. Winger and S. Walsh, unpubl. data). In 
comparison, fish in peripheral locations mainly were 
turned perpendicular to the trawl gear, indicating 
that earlier physical encounters with the sweeps and 
wings were the dominating influence for this type of 
movement. 
The initial response and previous gear experience 
each had a strong influence on the capture of yellow- 
tail in the central part of the trawl mouth. The ob- 
served rate of escapement (37%) was similar to that 
had been found for Greenland halibut (ReinharcLtius 
hippoglossoides) (Albert et al., 2003), but the actual 
escapement rate for yellowtail is presumably much 
higher because of unobserved fish that pass under the 
footgear (Ryer and Barnett, 2006). Individuals that ex- 
hibited a run response had a 52% probability of es- 
caping, but lifting from the bottom (slope and rise re- 
sponses) resulted in all fish being caught. Flatfishes 
that leave the seabed can no longer see the threat of 
the footgear below (Ryer, 2008), and, although they 
avoid the immediate threat of the footgear, they do 
not avoid the net and are captured (Ryer et al., 2010). 
Because of the “ground effect,” [term describing the 
change in performance of moving objects near a solid 
