Department of Fisheries Oceanography

“Environmental Effects on Population Dynamics of New England Yellowtail Flounder”

By: Jessica Kittel

Advisor: Steven X. Cadrin

Committee Members: Kevin Stokesbury (UMass Dartmouth), Gavin Fay (UMass Dartmouth), Lisa Kerr (U Maine), Alex Hansell (NEFSC)

Monday April 7th, 2025

2:00 PM

SMAST East 101-103

836 S. Rodney French Blvd, New Bedford

and via Zoom

Abstract:

Yellowtail flounder, Limanda ferruginea (a.k.a., Pleuronectes ferruginea, Myzopsetta ferruginea), inhabit the continental shelf of the northwest Atlantic and historically supported target fisheries off New England. However, the Georges Bank and Southern New England/ Mid-Atlantic stocks have declined in recent decades and have not recovered despite severely restricted fisheries, suggesting that productivity may be negatively affected by climate change. Ocean waters off New England are warming four times faster than the global average, and decreased yellowtail flounder productivity has been associated with ocean warming in the region. US stock assessments of yellowtail flounder have exhibited retrospective patterns, in which contemporary estimates of abundance decrease when a new year of data is added, presenting a major source of uncertainty for determining stock status and informing rebuilding plans. Retrospective patterns may result from model assumptions that do not account for environmental effects on population or fishery dynamics. In the face of climate change, there is increasing exploration of climate impacts on stock dynamics in the context of stock assessments. However, incorrectly integrating climate information can contribute to model misspecification. Thus, it is important to identify significant relationships and understand mechanisms before including them in assessments. Process error refers to the variability in population dynamics due to natural fluctuations (such as environmental effects) not captured by the model. State space models explicitly model this uncertainty, potentially improving the accuracy of assessments and supporting more adaptive, sustainable fisheries management. I led a review of the available information on environmental drivers that may be impacting US stocks of yellowtail flounder from literature and harvesters’ ecological knowledge, tested relationships between environmental indices and components of productivity (i.e., recruitment, growth, maturity, survival), and helped developed stock assessment models that account for environmental effects. Chapter One reviews the available information on environmental drivers impacting stocks of yellowtail flounder off New England from literature and harvesters’ ecological knowledge. Results suggest that several aspects of yellowtail flounder population dynamics have been sensitive to the environment, including geographic distribution, recruitment, and potentially other components of production such as natural mortality and growth. Chapter Two tested relationships between environmental indices and components of population dynamics. Generalized Additive Models (GAMs) were applied to explore relationships between the identified environmental variables and stock dynamics to determine what data should be explored in the yellowtail flounder stock assessment models. Several potential climate impacts were identified. Recruitment of yellowtail flounder off southern New England was correlated to the Mid-Atlantic Bight Cold Pool. Recruitment of yellowtail flounder on Georges Bank was correlated with bottom temperature and the Atlantic Multidecadal Oscillation. Chapter Three developed an assessment model for the Georges Bank yellowtail flounder stock that accounts for environmental effects. Results show that incorporating environmental covariates into the stock assessment improves model diagnostics and reduces uncertainty in short-term projections. This research has implications for improving assessment and management of New England yellowtail flounder fisheries and serves as a model for how appropriate ecosystem drivers can be identified for use in integrated state-space stock assessments for other assessments.