Evaluating the Relationship between the Gulf Stream Index and Recruitment Dynamics for Southern New England Yellowtail Flounder

Southern New England Mid Atlantic (SNEMA) Yellowtail flounder, Limanda ferruginea, belongs to one of the important groundfish fisheries in the Northeast US Continental Shelf. Historically, the stock was overexploited and recruitment has remained low over the last two decades. Although large recruitments have been observed at low stock sizes in the past, the persistent low level of recruitment is not well understood and is a source of uncertainty in the stock assessment. Hence, understanding the underlying mechanism for the continued low recruitment of SNEMA yellowtail flounder is critical to estimating biomass reference points and to evaluate stock status determination. We find that the Gulf Stream Index (GSI), which quantifies the latitudinal position of the Gulf Stream, is correlated with both recruitment (-0.64 with lag of 1 year) and spawning stock biomass (-0.74 with lag of 3 years) among all related climate indices. Further, incorporating the GSI into a stock-recruitment relationship improved the fit of the curve, justifying the potential consideration of the GSI in the SNEMA yellowtail flounder stock assessment model. We hypothesize that the persistent low recruitment since the 1990s is likely related to warmer than climatology shelf water which is the case if the GSI is positive.