Evaluating non-stationary impacts of climate and environmental conditions on Argentine shortfin squid (Illex argentinus) in the southwest Atlantic Ocean

Growing evidence highlights non-stationarity in climate-ecosystem relationships, suggesting that traditional analyses assuming stationarity may inadequately capture the dynamic responses of marine species to climate change. The Argentine shortfin squid (Illex argentinus), a key economic species in the southwest Atlantic Ocean (SWAO), is highly sensitive to environmental variability. This study investigated the changes in I. argentinus catch in the Patagonian Shelf region of the SWAO in response to climate variability and characterized its non-stationary features. We used a Threshold Generalized Additive Model (TGAM) and key environmental and climate variables to identify threshold years in the climate-catch relationship for I. argentinus. Results revealed significant non-stationarity with two critical thresholds: 1990/1991 and 2015/2016. In the late 1980s, the climate-regulated Weddell Sea Ice Extent (WSIE) underwent a regime shift, concurrently with long-term average states of its associated Southern Ocean environmental variables—sea surface height (SSH) and water temperatures at 50m and 100m depths. This coincided with an abrupt increase in I. argentinus catch, marking the onset of the first threshold year. In the second threshold year, WSIE and Sea Surface Temperature (SST) simultaneously transitioned to new states, accompanied by anomalous fluctuations in the critical influencing variable SSH. These changes adversely affected I. argentinus, leading to a sustained decline in catch. Research indicates that, even when excluding fishing efforts, climate-driven environmental non-stationarity is a crucial factor influencing the fluctuations in I. argentinus catch. Understanding these non-stationary dynamics is essential for robust sustainable fisheries management under persistent fishing pressure and climate change.