Whitemouth croaker (Micropogonias furnieri) are you ok? Reduction in nutritional condition of juveniles during winter in the Southwest Atlantic Ocean

Abstract

The whitemouth croaker Micropogonias furnieri is one of the most important coastal fishery resources in Argentina, southern Brazil, and Uruguay. Samborombon Bay (SB) is its main nursery area in Argentina, providing refuge for juveniles up to 2–3 years old. During their first year of life, juvenile growth occurs primarily during the summer period (November to January), with high growth occurring for a short time followed by a period of slow growth during autumn and winter. To understand the factors that influence the recruitment of this species and to characterize areas favorable for growth, knowledge about life traits during the juvenile stage is necessary. For this reason, the nutritional condition of juvenile whitemouth croaker was studied using the RNA/DNA index (RD), from muscle samples obtained during four surveys carried out between 2017 and 2019 in SB during two seasons, warm and cold. Mean RD showed significant differences (p < 0.05, N = 798) across temporal (seasons) and spatial (zone and distance to coast) scales. Our results demonstrated the existence of a reduction in the nutritional condition during winter in this species, since juveniles in the cold season showed lower RD indices than those in the warm season. The observed reduction in metabolic rates during the cold season could serve as a crucial mechanism for survival. This reduction might also facilitate subsequent recruitment to the fishery, i.e., reaching the minimum size limit for fishing. In addition, this study allowed characterizing the species’ nursery area since differences in nutritional condition were observed across the regions of SB and distance to the coast. Understanding the life traits of whitemouth croaker during juvenile developmental stage would allow the reduction of uncertainty in the population state estimation, to predict the recruitment to the fishery as well as establishing appropriate management strategies to guarantee sustainable catches.