Using Otolith Chemistry and Markov Chain Monte Carlo Models to Estimate Red Snapper Recruitment Sources When Little to No Information Exists about Juveniles

Little to no information exists about juvenile red snapper occurrences in U.S. Atlantic Ocean waters from southern Florida to North Carolina. Chemical signatures from adult red snapper otolith cores were used to provide an estimate of the number of potential nursery sources contributing to red snapper recruitment for four year classes sampled in 2012. Constituents analyzed were δ¹³C, δ¹⁸O, Ba:Ca, Mg:Ca, Mn:Ca, and Sr:Ca. Multiple linear regression analyses indicated δ¹³C, Ba:Ca, Mg:Ca, and Mn:Ca varied significantly by latitude. Markov Chain Monte Carlo models were then parameterized with these constituents to estimate numbers of potential nursery sources for each age class. Among the four age classes investigated, MCMC model results indicated that between 2 and 7 nursery sources were equally likely to have contributed to recruitment; however, because of apparent mixing between northern and southern signatures, potential nursery sources declined for age-4 and age-5 fish. Evidence from this study suggests that the null hypothesis of a single nursery source contributing recruits among the four age classes investigated can be rejected, but further studies should be conducted across a broader geographic range to improve nursery source estimates.