More English sole respond early to the foot-rope in the dark (as opposed to letting the gear hit them or pass over then) than do English sole in the light. This suggest that English sole will tend to be more vulnerable to capture by trawl gear at night than during the day, a result that will need to be confirmed through field experimentation.

2002
Lewis Barnett
Oregon State University
Project: Effect of ambient illumination on the behavioral response of juvenile English sole to disturbance by a bottom trawl footrope
(Supervisor: Cliff Ryer, NOAA/NMFS Alaska Fisheries Science Center)

Quotas for commercially valuable fish species are often limited by "bycatch"; those fish which are inadvertently captured along with the target species. Understanding how fish respond to fishing gear under various conditions will aid in the design of fishing strategies and gears that reduce bycatch. In this study, an OSU intern, Lewis Barnett and his advisor, Clifford Ryer, eamine how the presence or absence of light effect the behavioral response of English sole Parophrys vetulus to bottom disturbance caused by an approaching (trawl) foot-rope.

Click to view MPG: A trawl foot-rope, propelled through a 40 ft seawater tank in the laboratory simulates the bottom disturbance created by a real trawl, allowing detailed examination of behavioral responses of fish using digital video. Measurements are made in the light and the dark (using infrared illumination, to which fish are insensitive).

Click to view MPG: Flatfish are herded by the foot-rope of a commercial trawl, eventually tire, then fall back to become part of the catch. (Video courtesy of Craig Rose, AFSC).