Original Article Using the gonadosomatic index to estimate the maturity ogive: application to Chilean hake (Merluccius gayi gayi)

The proportion of mature fish at age or length is one of the most important population attributes in assessing reproductive potential. This pro-portion is usually named the maturity ogive. The most crucial step in estimating this proportion deals with maturity staging assessed by macro-scopic or histology analysis. Macroscopic analysis is relatively inexpensive but usually introduces large amount of error. Histology is the most accuratemethod formaturity staging but is expensive and time consuming.Here,wepropose using the gonadosomatic index (GSI) as an alternative way to estimate thematurityogives. A logisticmultinomialmodelwas implemented to separate immature,mature-active, andmature-inactive fish, based only on their value of GSI. We evaluated the performance of the GSI-based method by comparing the results with ogives estimated from macroscopic andhistological stagingusing the extensivedatabaseavailable forChileanhake (Merluccius gayi gayi).Maturityogives fromGSI analysis were evaluatedat the start and endof the reproductive season. Results showed that, in all cases analysed,maturity ogives fromGSIwere closer to the ogives based on histology than those from macroscopic staging. Comparing across periods, those maturity ogives computed at the start of the reproductive season give estimates very similar to those from histological staging. To have unbiased estimates of maturity ogives fromGSI analysis