Exploring Nutritional Condition of Merluccius hubbsi During Early Life Stages: Environmental Drivers and Possible Implications on Subsequent Recruitment

The early life stages of fish represent a period of high energy requirements due to profound changes that characterize the passage to adulthood, crucial for fisheries recruitment. This study focuses on the North Patagonian Frontal System (NPFS) that guarantees successful larval development and fulfills the three postulates of Bakun's “fundamental triad” in regards to nutrients, concentration of food, and retention of eggs and larvae inside the favorable area. The objective was to evaluate the nutritional condition of Merluccius hubbsi larvae and juveniles, from the Patagonian stock in January during austral summer (2010–2021). The standardized RNA/DNA index (RDs) was used. Interannual variation in the larval condition was observed in relation to NPFS features. RDs were positively linked to the stratification of the water column in the stratified zone. An opposite trend was observed between larval condition and potential egg production that might indicate the existence of density-dependent mechanisms. On the other hand, the positive relation between larval condition and egg production of older females (≥7 years) supports the idea of a maternal effect on larval survival. There was also a positive relationship between juveniles condition, body size, and recruitment, but no relationship was observed with the stratification of the water column. The high sensitivity of the RDs index links physiological state with survival probability, informing on factors affecting eggs, larvae, and juveniles until their posterior recruitment. This study identified the stratified area of the NPFS as a favorable nursery zone, providing crucial information for managing populations under high fishing pressure.