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Exploiting the sensory biology of fishes to reduce bycatch in fisheries Mark Hoppner (24167949) PUREID: 518938323 Bycatch fisheries fisheries research fish vision sensory ecology artificial light fish behaviour Bycatch in fisheries, the unintentional capture of non-target species or size classes, is a global conservation problem with significant economic implications. It undermines sustainable fisheries management, negatively affects ecosystem health and functioning, and incurs considerable economic losses in the fisheries sector. Traditional means of reducing bycatch have relied on exploiting physical or behavioural differences between target and non-target species. However, sensory systems are critical to the capture process as they link information input and behavioural output. Thus, exploiting sensory systems represents a promising approach to reducing bycatch in fisheries. This thesis investigates four specific aspects: (i) interspecific differences in visual acuity in gadoids, (ii) the contrast of coloured netting in the visual systems of fish, (iii) the effect of artificial light on bycatch reduction in a bottom fishery, and (iv) differences in the magnitude of behavioural responses to artificial light in teleost fishes. In Chapter 2, I investigated the visual acuity and retinal topography of gadoids, revealing inter- specific differences in visual specialisations linked to ecological traits. For example, haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and poor cod (Trisopterus minutus) have horizontal visual streaks with multiple areas of acute vision that may enable them to detect components of fishing gear simultaneously from different directions. Chapter 3 determined the chromatic contrast of coloured netting to the underwater light background in fish vision systems. I found that different coloured netting exhibit different levels of chromatic contrast in the visual systems of fish, and the chromatic properties of coloured netting can be adapted to increase or decrease its detectability to fish depending on the spectral and transmissive properties of the underwater environment. Chapter 4 examined the impact of artificial light on fish bycatch in a bottom trawl fishery targeting Norway lobster (Nephrops norvegicus). Although I hypothesised that the addition of green LEDs to an escape panel would reduce bycatch, the results did not support this hypothesis for most species. The study also found an unexpected increase in whiting (M. merlangus) bycatch, and further research is needed to investigate the impact of artificial light on their behaviour and overall how light can affect bycatch in different fishery locations and environmental conditions. In Chapter 5, I performed a meta-analysis investigating the behavioural responses of teleost fishes to artificial light and found that all species responded to light, but the magnitude of the response varied across studies. The study also highlighted the role of phylogeny in shaping the behavioural responses of teleost fishes to artificial light, underscoring the importance of evolutionary history in modifying fish behaviour. 5 In conclusion, this thesis underscores the need to comprehensively examine the sensory characteristics of fish and the stimuli that elicit behavioural responses to reduce bycatch in fisheries. The findings of this thesis not only enhance our understanding of fish visual ecology, chromatic attributes of coloured netting, the influence of artificial light on fish bycatch in a bottom trawl fishery, and the behavioural reactions of teleost fish to artificial light, but also provide actionable recommendations for the future. Firstly, I advise that the chromatic attributes of coloured netting are modified to either increase or decrease its visibility to fish. Secondly, I recommended that experiments are conducted on fish behaviour utilising artificial light with varying characteristics and across a diverse range of species. Lastly, I recommend employing underwater cameras during artificial light fishing trials to meticulously observe fish behaviour, thereby augmenting our knowledge on the impact of light on their behaviour. By amplifying the breadth of experiments involving artificial light and directly observing its effects on fish, we can more accurately tailor future endeavours utilising this technology as a method to reduce bycatch. Ultimately, I consider these recommendations as steps towards enhancing bycatch reduction initiatives in fisheries, supporting sustainable fisheries management and the conservation of marine ecosystems. 2026-10-01T16:47:54Z Text Thesis 10.17034/32638014.v1 https://figshare.com/articles/thesis/Exploiting_the_sensory_biology_of_fishes_to_reduce_bycatch_in_fisheries/32638014 All Rights Reserved