On the occurrence of a tropical-affinity species Merluccius polli (Actinopterygii, Gadiformes, Merlucciidae) in the Gulf of Cádiz (SW Spain) and market-driven implications for the black hake fishery

The Benguela hake, Merluccius polli Cadenat, 1950, is a demersal species typically distributed along the Atlantic coast of Africa, ranging from Angola to Mauritania. This study reports the first confirmed records of M. polli in the Gulf of Cádiz (NE Atlantic), suggesting a northward expansion of this tropical-affinity species. Two specimens were caught by commercial trawlers in 2022: one (47 cm TL) on 17 February, and a second (62 cm TL) on 27 July. Both individuals were identified based on meristic characters and caudal fin pigmentation. To contextualize these findings, we analyzed fisheries auction data (IDAPES) from 2000 to 2024. While M. polli is a new occurrence in the local wild ichthyofauna, it is commercially abundant in the region because it is landed in Spanish ports by national vessels operating in Northwest African fishing grounds. Analysis of recent sales notes (2022–2024) confirms that M. polli constitutes the dominant fraction (>95%) of the “black hakes” caught in African fishing grounds, which were historically pooled with Merluccius senegalensis Cadenat, 1950 in fishery statistics. Economic analysis reveals that black hakes maintain a stable, lower-price market niche compared to the local European hake, Merluccius merluccius (Linnaeus, 1758). These findings support the trend of tropicalization in the Gulf of Cádiz and highlight the importance of accurate species identification in commercial landings.