Optomotor response in Atlantic cod (Gadus morhua) – can it be elicited and manipulated by trawl netting?

Description

The optomotor response is when animals move with a moving visual pattern. It is well documented in a wide range of animal groups including fish and is believed to be a major behavioral mechanism of fish in the process of being captured by trawl. Thus, the response has the potential of being utilized to increase trawl selectivity. It is the steady swimming of fishes at the same speed of the moving trawl gear often observed in the front of the trawl mouth on structures inside thee trawl that has been interpreted as the optomotor response. The optomotor response is suggested elicited by the moving trawl netting. However, other confounding stimuli during trawling may be responsible for the observed steady swimming, for example the groundgear in the trawl mouth area, leading to other interpretations of the holding behavior, such as herding.
Movement with moving visual pattern is considered an innate behavior and compulsory to normally performing individuals. Thus, the optomotor response is commonly used in the laboratory to study a range of topics, such as various aspects of the visual systems of fishes, schooling behavior and effect of pollutants. However, the optomotor response has shown to vary between species, and too little is known about the optomotor response in trawls. This study investigated for the first time the optomotor response of wild Atlantic cod (Gadus morhua), an important commercial species in demersal fisheries, using a standard laboratory set-up consisting of a rotating drum with black and white vertical stripes placed outside circular transparent fish tank. Further-more, in the same set-up, the black and white stripes were replaced by five sets of standard polyethylene trawl netting with different visual appearances, which were tested for their ability to elicit, enhance, or break-up the optomotor response of cod in two ambient light levels. Cod behavior was observed using infrared light (940 nm). The results from the video analysis are presented and discussed in relation to trawl fishery and with focus on inter-individual variability.

Period	15 Feb 2023
Event title	ICES-FAO Working group on fishing technology and fish behaviour (WGFTFB)
Event type	Conference
Location	Kochi, IndiaShow on map
Degree of Recognition	International