Environmentally-Driven Fluctuations in Condition Factor of Adult Gulf Menhaden (Brevoortia patronus) in the Northern Gulf of Mexico

We evaluated the effects of environmental predictors on the individual weight-at-length condition of adult Gulf Menhaden Brevoortia patronus sampled from the commercial fishery, from 1964 to 2011. A hierarchical linear model was used to examine the impact of Mississippi River discharge on condition. Generalized Additive Models were constructed to determine the impact of El Niño Southern Oscillation (ENSO) and the spatially-dependent influence of sea surface temperature (SST), chlorophyll-a concentration, and vector winds. Condition was positively related to Mississippi River discharge (β = 1.43, p < 0.001), greatest during El Niño, and increased at locations close to the Mississippi River plume (p < 0.001, deviance explained = 18.2%). Condition exhibited intra-annual variability with a small peak in late April and increasing condition from August until November. SST and temporally-lagged (two months) chlorophyll-a concentration, each without spatial-dependence, provided the best model support and were significant predictors of condition (p < 0.001, deviance explained = 15.6%). Vector winds were significant predictors and spatially-dependent (p < 0.001, deviance explained = 19.1%). We show that bottom-up processes impact the individual dynamics of Gulf Menhaden and these results can be used to predict their impacts on the fisheries and ecology of the northern Gulf of Mexico.