Objectives

Successful restoration and continued management of recreational fisheries therefore depends on a good understanding of linkages between broader processes and local dynamics.

Methods

Fisheries independent data describing red drum settlement and recruitment were available for all Gulf States with Florida, Louisiana and Texas providing the greatest spatial and temporal coverage. Data for each state have been collected independently, but all employ systematic, spatially explicit sampling at multiple research sites conducted over monthly, seasonal or annual intervals with multiple gear types tracking multiple sizes of red drum. Samples also contain environmental covariates (e.g. structural habitat, water quality parameters). These data were aggregated and standardized via Generalized Linear Models and random forest models to generate standardized spatially explicit and relatable red drum settlement and recruitment indices.

Settlement and recruitment correlation and causation across space were examined using two different approaches: Correlation analysis and Empirical Dynamic Modeling (EDM). While correlation analysis allows to assess the spatial scale of recruitment correlation, EDM is a more advanced time series analysis method that aims to establish the dynamic ‘legacy’ of one site’s influence onto another’s.

Preliminary results

Red drum settlement (arrival of juveniles in nearshore habitats) and recruitment (survival past the subsequent stage of juvenile density-dependent mortality) were found to be correlated among sampling sites on scales of tens to hundreds of miles. On the whole, settlement was more strongly correlated among sited and over larger spatial scales than recruitment. This indicates that settlement is driven by regional/sub-regional population processes, while recruitment processes at a smaller, estuary/bay scale. There is some regional variation in this pattern, with recruitment among Louisiana sited being more strongly correlated over a larger spatial scale than in Florida or Texas. This is likely to reflect the strong effect of the Mississippi outflow and associated environmental processes on the dynamics of red drum in the region.

Implications

The overarching implication of this result is that, while the red drum stock enjoys a gulf-wide distribution, it shows meta-population dynamics that are driven primarily at smaller spatial scales.

Publications

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Code

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Data sets

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