Offshore Wind Farm-Induced Spatial Redistribution of Abundance Alters Survey Indices and Stock Assessment Performance

Abstract Fishery-independent surveys provide the primary fish relative abundance information for stock assessments, yet their performance can be compromised when the survey area is restricted and population distributions change spatially. Offshore wind development introduces both challenges by precluding some forms of survey sampling within Wind Energy Areas (WEAs) and by potentially altering fish abundance patterns through attraction- or production-driven processes. However, the combined consequences of these mechanisms for survey indices and stock assessment inference remain poorly quantified. The present study evaluated how spatial abundance redistribution interacts with survey preclusion to influence survey-derived indices and assessment outcomes using a simulation-based approach with historical survey datasets. Three Mid-Atlantic stocks (summer flounder, longfin squid, and Atlantic surfclam) were examined to represent contrasting life histories and assessment frameworks. Two redistribution mechanisms were simulated: attraction-driven redistribution, in which abundance increased inside WEAs through spatial reallocation, and production-driven increases, in which local abundance increased without depletion elsewhere. Redistribution was applied at multiple intensities to recent survey data and propagated through assessments using both complete survey coverage (FULL) and spatially truncated datasets excluding WEAs (Wind Energy Excluded; WEE). This simulation-based exercise represented a full-buildout WEA spatial-exposure scenario over a 10-year operational timeframe. Results showed that increasing redistribution intensity elevated overall and interannual variability in survey indices and increased survey residual dispersion from assessment model results, particularly when abundance change inside WEAs was not accounted for. In contrast, monotonic trends inferred from abundance indices remained largely consistent between FULL and WEE datasets. Estimates of spawning stock biomass showed greater sensitivity to spatial redistribution and survey preclusion than fishing mortality, while retrospective patterns exhibited species- and model-specific responses. Together, these findings demonstrate that survey preclusion and altered spatial abundance patterns can interact to influence stock assessment reliability through reducing the precision and accuracy of survey indices. Differences between findings for different stocks highlight the utility of propagating the effect of survey disruptions through assessment models to inform species-specific mitigation strategies, and the need for this type of quantitative analysis to be standard practice as offshore wind development continues to expand.