Effects of recruitment through a coastal hydrodynamic boundary layer on growth and otolith microstructure of larval Gulf menhaden (Brevoortia patronus)


Matthew J. Kupchik and Richard F. Shaw
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Sagittal otoliths (n=208) were removed from larval Gulf menhaden (Brevoortia patronus) collected in a Louisiana tidal pass over a 2-year period, from October 2006 to March 2007 and from September 2007 to March 2008, and analyzed with digital imaging and fast Fourier transformations to estimate age and growth. Length at age was estimated by using a 2-cycle Laird–Gompertz growth model and the growth rates were found to be relatively consistent with rates from previous research in the northern Gulf of Mexico, and the estimated timing of an ontogenetic shift in feeding strategy occurred at approximately 33 days after spawning. Laird–Gompertz growth models fitted separately to age and length groupings revealed that the ontogenetic shift was correlated more with larval age than with length. Measurements taken from digital images were used to conduct fine-scale analyses of otolith microstructure and confirmed that a change in otolith structure coincided with the ontogenetic shift in feeding at approximately 33 days after spawning. Keys of length frequencies at age were used to assess temporal variability in Gulf menhaden spawning and they revealed earlier (i.e., September) recruitment to spawning and estuarine areas and shorter recruitment corridors than those previously reported.