Effects of illumination and pot design on catch and bycatch when targeting northern shrimp (Pandalus borealis) using white LED PotLights

Abstract

Bottom towed gears can have severe and long-lasting effects on sensitive marine habitats and species. Diversification of gear types in fisheries using bottom towed gears to encompass low environmental impact methods, such as static gear, is one way to reduce dependency on damaging fishing methods. Here we report on trials investigating how the use of white Light Emitting Diodes (LEDs; Fishtek Marine PotLights) affect catch rates of northern shrimp (Pandalus borealis; normally caught using trawls) across three different pot designs off the west coast of Scotland. We also caught the valuable Norway lobster (Nephrops norvegicus) and valueless poor cod (Trisopterus minutus) and considered occurrences and catch rates of these species. Illuminated pots resulted in significant increases in catch per unit effort (CPUE; ind. pot−1 24 h−1) of northern shrimp for all pot types up to maximum mean of 4.6 ± 4.5 shrimp pot−1 24 h−1 (illuminated shrimp tubes specifically designed to catch shrimp; range = <0.1–11.1). However, despite the substantial increase in CPUE of northern shrimp due to illumination, these quantities do not constitute commercially viable catch volumes. Furthermore, illuminated pots resulted in high juvenile poor cod bycatch (88 % increase in catch rates across all pot types) and reduced catches of Norway lobster (48 % reduction in catch rates across all pots). The high presence of poor cod in catches in response to illumination mirrors the response observed for the closely related cod (Gadus morhua) using the same methods elsewhere, adding evidence on how fishing with light propagates in ecosystems. Finally, to explain our results we propose an ”Attraction Cascade” hypothesis, as there is no documented evidence of phototactic behaviour. Taken together, these results suggest that, when pot type and fishing area are configured for specific target species, illumination may offer promise of increased CPUE and even baitless fishing in pot fisheries and an alternative to trawl fisheries for northern shrimp.