Between prey and pressures: Factors shaping the nutritional condition of Merluccius hubbsi larvae in the Northern Patagonian frontal system

Early fish life stages are highly vulnerable to environmental fluctuations and pollution, with strong implications for recruitment success. The Argentine hake, Merluccius hubbsi , is one of the most important fishery resources in the Argentine Sea. The main spawning area of the Patagonian stock is associated with the North Patagonian Frontal System (NPFS), a retention area considered essential for larval survival and feeding. However, recent studies have also reported high concentrations of anthropogenic microfibres (AMFs) in this system. Due to their size and characteristics, AMFs may overlap with larval prey and be incidentally ingested, potentially affecting larval nutritional condition (NC). This study evaluated the influence of oceanographic, biological, and anthropogenic variables, particularly AMFs, on the NC of M. hubbsi larvae. The standardized RNA/DNA ratio (RDs) was measured in 283 larvae collected during a spawning survey in January 2024. NC increased with larval length, with the probability of presenting good NC approaching 100% at approximately 8 mm. Good NC was negatively associated with water column stratification, larval density, and AMFs content per larva, but positively related to AMFs abundance in the environment, a variable positively correlated with prey availability. These results suggest that the oceanographic conditions favouring prey accumulation may also promote the retention and concentration of anthropogenic particles within the NPFS. This study provides the first evidence of a negative association between AMFs ingestion and larval NC in M. hubbsi , highlighting the dual ecological role of the NPFS as both a favourable nursery area and a potential ecological trap.