Effects on catches of green and blue light emitting diodes at the frame lines of diurnally deployed estuarine penaeid trawls

Penaeid trawls are among the world’s least selective fishing gears. This characteristic has justified decadal attempts at resolution and most commonly via retroactively fitted ‘bycatch reduction devices’ in the posterior sections to promote fish escape. However, ideally unwanted species would never enter a trawl. This study sought to investigate if fish could be avoided in diurnally deployed estuarine penaeid trawls via light emitting diodes (LEDs) located at the frame lines (headline and footrope). The assumption of few confounding effects of attaching six inactive LEDs (i.e. structures) to the frame lines was validated (experiment 1) before separate experiments were done to assess the effects on catches due to six active blue or green LEDs on the footrope (experiment 2) and then on the headline (experiment 3). Catches of the targeted school prawns, Metapenaeus macleayi and some fish (across all sizes; 4–20 cm total lengths), including mulloway, Argyrosomus japonicus, southern herring, Herklotsichthys castelnaui, and painted stinkfish, Eocallionymus papilio were similarly and significantly lower in trawls with at least one active LED treatment, and with greater consistency when these were on the headline. Some loss of target catches would preclude the commercial use of LEDs on the frame lines of the tested trawls. However, evidence of strong responses among some fish and their known behavioural and swimming differences to penaeids might support testing LEDs at other locations, including inside trawls, to reduce bycatches while maintaining target catches.