Each year, the IPHC fishery-independent setline survey (FISS) collects biological data on the maturity of female Pacific halibut that are used in the stock assessment. In particular, female maturity schedule is used to estimate spawning stock biomass. Currently used estimates of maturity-at-age indicate that the age at which 50% of female Pacific halibut are sexually mature is 11.6 years in average. However, not only maturity is estimated with the use of macroscopic visual criteria, implying a relative level of uncertainty associated with the employed semi-quantitative assessment, but the estimates of maturity-at-age have not been revised in recent years. Furthermore, relatively little is known regarding the actual changes that take place in the gonads during reproductive development leading to spawning in this species. For this reason, the IPHC is conducting studies that aim at characterizing the annual reproductive cycle in male and female Pacific halibut in order to understand temporal changes in reproductive development, to accurately stage the reproductive status, to update current maturity-at-age estimates as well as determine and estimate the incidence of skipped spawning. Through the proposed comprehensive reproductive monitoring of the adult population of Pacific halibut, current estimates of the actual spawning biomass will be updated. This project involves the monthly collection of biological samples and biological information that will allow us to conduct, among other determinations, histological assessment of gonadal development and maturation, endocrine profiling of the reproductive cycle, transcriptome profiling of the hormone axis (gene expression) and gonadosomatic index determinations throughout the reproductive cycle.