Characterizing early growth and reproduction of Blueline Tilefish (Caulolatilus microps) to inform stock assessments

Blueline Tilefish is a deepwater species that is found along the United States Atlantic coast and in the Gulf of Mexico. Fisheries for the species have developed in the past five decades, and large increases in landings from the mid-2000s to 2010s have raised management interest. During the most recent stock assessment, age reading difficulties found in the past persisted, and preferred age-structured models were not used. Additionally, maturity was estimated from a meta-analysis of other species with similar life histories. Research recommendations from independent peer reviewers thus included improving age determination as well as collection of small fish. We collaborated with charter fishermen to target small (< 400 mm total length [TL]) blueline tilefish. We also collaborated with scientists at South Carolina Department of Natural Resources (SCNDR) on histological reproductive phase coding and ageing of Blueline Tilefish otoliths. We optimized the information incorporated into sex ratio, reproduction, and growth analyses by merging datasets with SCDNR and Old Dominion University (ODU), and assessed first maturity to the increase immature sample size. Overall sex ratios exhibited a female bias, displaying statistically significant deviations from the expected 1:1 ratio in both the Southeast United States Atlantic (SEUS) and United States Mid-Atlantic (USMA) regions. All immature individuals collected measured below 400 mm. Our findings aligned with previously documented spawning seasons, which extend from April to October in the SEUS and from May to November in the USMA, and may extend to November in the SEUS. The spawning peak identified for the SEUS concurred with previous studies, and suggested October as a spawning peak in the USMA—later than previously described. Sex-specific gonadosomatic index analyses indicated no significant differences between regions. Age determination remained challenging, but the level of agreement in age estimates between the VT consensus and SCDNR readings resembled the highest value from previous studies. Evaluation based on AIC and BIC scores of weight-length relationships indicated potential regional differences and sexual dimorphism within both the SEUS and USMA regions. This sexual dimorphism was further supported by von Bertalanffy growth estimates, revealing L_∞ values of 574.7 and 630.1 mm TL and values of 0.22 and 0.24 for females and males, respectively. Analysis of AIC and BIC indicated sexual dimorphic growth. Length and age at 50% maturity estimates ranged from 283 to 357 mm TL and a few months to 3.7 years, respectively. Length at maturity models also indicated that most fish are mature around 400 to 500 mm, highlighting the importance of targeting smaller individuals to increase the sample size of immature fish. Differences in AIC and BIC scores for length and age at maturity models of three maturity scenarios were low (AIC and BIC < 2). We recommend continued investigation into blueline tilefish age determination, as well as targeted efforts to collect more immature blueline tilefish. Additionally, we propose the use of first maturity and data weighting for maturity estimation of this species.