Critical thermal minimum and impacts of acute thermal cold stress on year-class strength of juvenile Atlantic Croaker from the Gulf of Mexico

ABSTRACT Objective The Atlantic Croaker Micropogonias undulatus is one of the most abundant mid-trophic predators along the Texas coast. The species spawns offshore and recruits to estuaries primarily during late fall and winter; thus, juveniles are likely to experience impacts due to hard-freeze disturbances. This study combined a laboratory temperature tolerance trial with statistical analysis of fishery-independent catch data to assess the vulnerability of Atlantic Croaker to hard-freeze events. Methods In the laboratory study, we simulated a 155-h hard freeze based on temperature data from a recent event (Winter Storm Uri [2021]) in Texas. Atlantic Croaker were exposed to a coldwater challenge starting at 16°C and ending at −1°C. From this trial exposure, we assessed the critical thermal minimum (CTM) of Texas populations of Atlantic Croaker. In addition to the laboratory trial, we assessed whether there was a significant relationship between historical fishery-independent catch data collected in Texas versus long-term water temperature data collected simultaneously throughout the Atlantic Croaker recruitment period. Results Mortalities in the laboratory study began at a water temperature of 3°C and ended at −0.56°C. Logistic regression analysis indicated that the temperature resulting in 50% mortality (LT50) occurred at 0.31°C. Linear regression also indicated that larger individuals (45–65 mm standard length) had a lower CTM than smaller individuals (30–45 mm), confirming previous studies’ findings of higher cold tolerance in larger individuals. Analysis of Atlantic Croaker CPUE from fishery-independent field data collected between 1986 and 2023 revealed that CPUE correlated weakly with 11°C critical degree-days, but the relationship was unexpectedly positive, suggesting no deleterious effects of severe winters on juvenile abundance. Conclusions This study demonstrated that CTM values for juvenile Atlantic Croaker in Texas may be lower than previously reported in other regions, and Atlantic Croaker recruiting to Gulf of Mexico estuaries may be less vulnerable to cold-weather disturbances than what has been previously observed on the Atlantic coast.