Reproductive dynamics of Gulf menhaden (Brevoortia patronus) in the northern Gulf of Mexico: effects on stock assessments

Gulf menhaden (Brevoortia patronus) produce one of the largest U.S. fisheries, yet information on reproductive dynamics of the stock is sparse. Males and females reach 50% maturity at 140.8 and 137.2 mm fork length, respectively and recruit into the commercial fishery at this size. Analysis of fishery-dependent data from 1964 through 2014 indicated that somatic condition was lower during the late 1980s and late 2000s and that reproductively active fish from 2014 were significantly larger and had greater gonadosomatic index values than those from 1964 through 1970. Histological analysis performed on fish from 2014 through 2016 revealed spawning-capable and actively spawning fish of both sexes from early October through midMarch. Females have indeterminate fecundity, are batch spawners, and spawn every 2.1-4.3 days, although oocyte recruitment shows some characteristics of determinate fecundity. Mean relative batch fecundity was 107.8 eggs/g ovary-free body weight (standard error 17.1). Estimates from age-structured assessment models based on updated fecundity and maturity measures resulted in a 100-1000x greater production of eggs than previous estimates. Model output, including the number-at-age, age-specific fishing-induced mortality, and spawners-per-recruit are sensitive to alterations in age-specific annual fecundity. Therefore, updated estimates of Gulf menhaden reproductive dynamics can affect assessments of the stock.