Underwood et at: Behavior-dependent selectivity of Limanda ferruginea in the mouth of a bottom trawl 
431 
Table 1 
Date, location, start depth, vessel’s course over ground, percentage of yellowtail flounder (Limanda ferruginea), American 
plaice (Hippoglossoides platessoides ), and witch flounder ( Glyptocephalus cynoglossus), and the number of observations of 
yellowtail flounder made in analyses of video footage from 5 tows of a bottom trawl in June 2010 on the southern Grand 
Bank off eastern Newfoundland. 
Course 
Percentage of flatfishes in catch Observations 
Tow 
Date 
(m/d) 
latitude 
n 
longitude 
(°) 
depth 
(m) 
ground 
(°) 
size 
(kg) 
Yellowtail 
flounder 
American 
plaice 
Witch 
flounder 
Number of 
yellowtail 
1 
6/17 
45.463 
-51.871 
82.3 
162 
2875 
86 
14 
44 
2 
6/20 
45.438 
-52.219 
73.2 
20 
1725 
92 
8 
38 
3 
6/22 
45.430 
-51.871 
80.5 
270 
2944 
84 
15 
1 
27 
4 
6/23 
45.393 
-51.175 
69.5 
344 
2530 
92 
8 
46 
5 
6/24 
45.454 
-51.283 
69.5 
142 
2392 
90 
10 
35 
shape, exhibit a close association with the seabed. Their 
We anticipated that the orientation 
of a fish in 
strategy to avoid natural predators is a combination of 
burying themselves in sediment, cryptic coloration, and 
low activity, all of which minimize their detection (Gib- 
son, 2005). As a predator advances, a flatfish will either 
remain immobile or flee to a short distance to maintain 
distance from the predator, settling only when the en- 
counter ceases. Similar behavior in relation to trawls 
has been observed in other flatfishes (Main and Sang- 
ster, 1981; Bublitz, 1996; Ryer and Barnett, 2006; Ryer 
et ah, 2010), which react to a gear at short distances 
and commonly move at a 90° angle to the trawl. This 
response occurs multiple times along the sweeps un- 
til flatfishes congregate in the mouth of a trawl. Once 
they are in the trawl mouth, escapement under the 
footgear is a particular problem (Albert et ah, 2003; 
Ryer and Barnett, 2006). Consequently, the mouth of 
the trawl is a critically important area when consider- 
ing how to improve gear efficiency (Engas and Godp, 
1989; Walsh, 1992). 
As a first step to improve the efficiency of the yel- 
lowtail fishery, we developed a high-definition camera 
system (Underwood et ah, 2012) because flatfish spe- 
cies were not able to be easily distinguished in most 
previous studies (e.g., Beamish, 1966; 1969; Walsh and 
Hickey, 1993; Bublitz, 1996; Kim and Wardle, 2003; 
Chosid et ah, 2012; Bryan et ah, 2014). Then we ex- 
amined the behavior of yellowtail in the central part 
of the trawl mouth during commercial bottom trawl- 
ing operations. The influence of fish size (Walsh, 1992; 
Peake and Farrell, 2004), swimming endurance and 
gait (Winger et ah, 1999, 2004), orientation (Beamish, 
1966), and density (Godp et ah, 1999) on general flatfish 
behavior have been examined in these studies; how- 
ever, each factor was examined separately. In contrast, 
we conducted an in-depth, quantitative study and ap- 
plied statistical models to simultaneously assess all of 
the above factors and explain what drives the behavior 
of individual fish and overall outcome for yellowtail in 
the mouth of the trawl. 
on the substrate and that previous herding by sweeps 
(previous experience of fish with gear) would affect the 
probability of capture of individual yellowtail. A flatfish 
observed in a trawl mouth would be either a fish that 
had been lying in the path of the trawl and is encoun- 
tering the gear for the first time or a fish that had 
been herded previously by the sweeps. In contrast, fish 
observed along the periphery of the footgear of a trawl 
would be expected to have been herded previously by 
the sweeps and, therefore, more likely to orient toward 
the opposite side of the trawl. Because the morphologi- 
cal features of flatfishes make it difficult for them to 
turn left or right (Stickney et ah, 1973), most yellowtail 
would be expected to swim in the direction they are 
facing; therefore, fish oriented inward, if they swam on 
their current trajectory, would observe the trawl gear 
earlier in their field of view and hit the footgear, in- 
creasing their probability of being captured. Previously 
herded fish are also likely to be more fatigued than 
first-time herded fish (Winger et al., 1999) — a state 
that could affect their response to a trawl and deter- 
mine whether an individual fish is caught or not. 
Materials and methods 
Experiments were conducted during the first tow of 
a bottom trawl each afternoon in June 2010 onboard 
the FV Aqviq, a 49-m groundfish trawler (2450 bhp) 
of Ocean Choice International, 1 on the southern Grand 
Bank off eastern Newfoundland (Table 1). The gear 
used in these experiments was a 2-bridle, 2-seam 
bottom trawl (Fig. 1) that had a 4-m extended upper 
panel (square) and that was equipped with rockhop- 
per footgear (52.5-cm-diameter rubber discs with 20- 
cm spacers). Towing speeds varied from 1.5 to 1.7 m/s. 
1 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement. 
