Ecosystem Dynamics of the Summer Flounder

The summer flounder, Paralichthys dentatus, is an important commercial and recreational fish. It is highly sought after for human consumption. Recently, there has been a northward range shift past their historical boundaries. The research analyzed the condition factor (a weight/length relationship) of female summer flounder using structural equation modeling (SEM). The higher the condition factor, the more energy that can potentially go into egg production. Data was collected from stock assessments, as well as internal NOAA reference documents and databases of the Northeast Fisheries Science Center (NEFSC). Using structural equation modeling, framework models were built to evaluate how environmental indicators influence summer flounder condition. They also evaluated the relationship/impact between condition factor and fishing pressure on the spawning stock biomass of this species. The models were fit using the lavaan package in R. Only the most significant variables (p-value < 0.05) were left, while the final selection was based on the Akaike information criterion (AIC) score. Our findings showed that condition factor has a negative relationship with biomass. This led to the formation of a density dependence hypothesis, that higher biomass leads to more intraspecific competition for food and a decline in condition factor. Another potential hypothesis involves the northward range shift of summer flounder due to climate change. Since the flounder are spending more energy moving and searching for food, this might mean less time feeding and a decrease in condition factor. These kinds of analyses have the potential to improve stock assessments and future decisions in fisheries management by providing more information on how environmental indices affect life history traits of managed stocks.