Bycatch in valuable NE Atlantic baited ‘pot’ fisheries for lobster Homarus gammarus and edible crab Cancer pagurus has not been well documented, potentially limiting evidence-based management. Using onboard observers supplemented by fishers’ ecological knowledge (FEK) we characterised bycatch of fish and larger invertebrates in 10,741 pot hauls around the coast of Wales, UK, over 4 years in all seasons. A total of 1529 fish from 30 species, and around 15 species of invertebrate, were recorded. Bycatch abundance varied seasonally and spatially and was dominated by eight common and widespread taxa comprising six ‘core’ fish (two catsharks: bullhuss (Scyliorhinus stellaris) and smallspotted catshark (S. canicula); ballan wrasse Labrus bergylta, sea scorpions (Myoxocephalus scorpius & Taurulus bubalis combined), three-bearded rockling Gaidropsarus vulgaris, conger eel Conger conger, together 86% of fish abundance), velvet swimming crab Necora puber and spider crab Maja brachydactyla. Commercially important fish species were only caught in low numbers (3.0% of all fish), with cod Gadus morhua the most frequent (1.8% of all fish). Only two species of conservation interest were recorded: the large catshark Scyliorhinus stellaris which is locally abundant (assessed by the IUCN Red List of Threatened Species as ‘Near Threatened’ and ‘Vulnerable to extinction’ at European and global scales respectively), and a single legally retained spiny lobster Palinurus elephas. Retention or live release status was recorded for nearly all (96%) of the core fish individuals and varied widely with taxa: sea scorpions (never retained), Scyliorhinus stellaris (13% retained), smallspotted catshark, three-bearded rockling, conger eel (44–59% retained), with ballan wrasse having the highest retention (90% of 242 individuals; average of 5.5 individuals retained per trip when present). Observed high spider crab abundance combined with FEK of previous absence or scarcity suggest that this species has increased in northwards range and abundance in recent decades, possibly because of warming seas. No incidents of in-pot mammal or bird entrapment were recorded. The retention of fish for bait is not currently acknowledged in consumer advice or landings data. Possible effects of bait retention on populations of data-poor species which may be vulnerable to overexploitation (e.g., long-lived ballan wrasse) and coastal ecosystems are unknown and warrant further research.