Insights from Fishery Discards: Age and Feeding Habits of Large-Scaled Gurnard (Lepidotrigla cavillone, Lacepède 1801) and Spiny Gurnard (Lepidotrigla dieuzeidei, Blanc & Hureau 1973) in the Gulf of Cádiz (SW Iberian Peninsula)

Abstract

Despite their ecological importance, discarded species with low commercial value are often overlooked in marine research. This study examined the age structure and feeding habits of the large-scaled gurnard (Lepidotrigla cavillone) and the spiny gurnard (Lepidotrigla dieuzeidei) in the Gulf of Cádiz (SW Iberian Peninsula). A total of 225 specimens were collected during 19 fishing trips at depths of 15–550 m. Ages were estimated from otolith readings, and stomach contents were analysed to describe diet composition, niche breadth, and overlap. Both species showed positive allometric growth, with the most frequent age class being 5+ in L. cavillone and 5+–6+ in L. dieuzeidei. Crustaceans dominated the diet, with mysids accounting for >80% of the index of relative importance (IRI) in L. cavillone, but L. dieuzeidei displayed a broader diet including mysids (45% IRI) and decapods (32% IRI). Feeding patterns varied with time of day, depth, and size, reflecting ontogenetic and environmental influences. Levin’s index indicated stronger specialization in L. cavillone (BA = 0.090) than in L. dieuzeidei (BA = 0.208), while the Schoener index (0.575) showed moderate overlap. These findings provide the first biological insights into these discarded species in Atlantic waters, contributing to ecosystem-based fisheries management.