Environmentally driven fluctuations in condition factor of adult Gulf menhaden (Brevoortia patronus) in the northern Gulf of Mexico

Abstract We evaluated the effects of multiple bottom-up processes on the relative condition (an index of length-specific weight) of adult Gulf menhaden Brevoortia patronus sampled from the US commercial fishery, from 1964 to 2011, in the northern Gulf of Mexico (NGOM). A series of Generalized Additive Models (GAMs) were constructed to examine the influence of Mississippi River Discharge (MRD), El Niño Southern Oscillation (ENSO), wind vector components, sea surface temperature (SST), and chlorophyll a concentration. Relative condition was positively correlated with MRD and highest during weak La Nina-like and moderate El Nino-like conditions. The effect of wind vector components was variable across the NGOM. This observation is likely due to geographic differences in wind-related transport of nutrient rich river plume waters. Relative condition was highest at 24°C and declined rapidly when SST was below 23°C or above 29°C. Relative condition exhibited seasonal variability with increasing condition from August until November, likely caused by seasonal provisioning by individuals for winter spawning. We show that multiple bottom-up processes contribute to contrasts in the condition of Gulf menhaden in the NGOM and these results can be used to predict the response of Gulf menhaden to environmental variability.