The behavior of the Argentine shortfin squid (Illex argentinus) exposed to bottom trawl gear off southern Brazil
Alvarez Perez,José Angel
Yasunaka,Bruna Firmino de Oliveira
ABSTRACT: The behavior of the Argentine shortfin squid (Illex argentinus) in reaction to a trawl net is reported from images obtained during one fishing tow operated by a commercial trawler in May 2015 in slope grounds off southern Brazil (depth 370-361 m; 33°37’S, 50°49’W). Video analysis utilized criteria to classify the horizontal and vertical distribution of squid in the field of view of the camera, posture (pitch and yaw), squid color patterns, escape reaction, swimming time and use of the tail fin. The monitored bottom trawl operation intercepted dense and patchily distributed schools of I. argentinus that could be observed for brief periods of time swimming ahead of the mouth of the trawl. Individuals were evenly distributed in the water column but concentrated on the center and right sectors of the trawl mouth. Most squids in the path of a trawl tended to swim by jet-propulsion for 10-20 s, tail-first and with regularly spaced fin flaps. Estimated speed (1.24 m s-1) was higher than cruise speed recorded for other ommastrephid squids in nature (0.3 m s-1), possibly reflecting an emergency escape reaction. After a period of sustained swimming ahead of the trawl, squid reacted in different ways including: a) slowing down and swimming into the net tunnel, b) shifting directions to escape through the trawl mouth sides, and c) swimming up, trying to escape over the top trawl panel, sometimes turning around pointing the tail towards the trawl mouth.