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

The views and opinions expressed or implied in this article are those of the author (or authors) and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA. Abstract—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. The Gulf menhaden (Brevoortia patronus) is both the target of a commercially important fishery in the Gulf of Mexico (GOM; Pritchard, 2005; Vaughan et al.1; McCrea-Strub et al., 2011) and is an ecologically important prey item for commercially and recreationally valuable species (Del Rio et al., 2010; Nelson et al., 2012; Simonsen and Cowan, 2013). Gulf menhaden have an established distributional range from the western central Atlantic to the GOM, and specifically within the GOM from Florida Bay to the Bay of Campeche (Whitehead, 1985). The Gulf menhaden fishery is the second largest United States fishery by both weight and value (Pritchard, 2005), and this reduction fishery harvests an average of 400–600 kilotons annually. In