Age at maturation predicted from scale measurements in Pacific herring (Clupea pallasii)

Age at maturation is linked to population productivity and directly impacts forecasts of population biomass and resultant harvest limits set by management agencies. Based on the original concept that scale growth can be used as an index of body growth (length) from Johan Hjort and his collaborators, the current study examined a new way of estimating maturity empirically using scales for Pacific herring. We hypothesized that Pacific herring that will spawn in a particular year (spring) will have reached a sufficient size and have reduced growth (length) the summer prior, compared to immature herring, as energy will be allocated to reproduction rather than somatic length. Model results suggested that there was no difference in the measurement of all scale growth prior to the last increment (growth up until the summer prior) nor in the outer ring measurement (growth the summer prior to spawning) of immature and mature female herring; using scales to estimate maturity empirically was not successful in this study. It is possible that the sample size in this study may have been too low to detect differences in growth or differences in growth may be better represented by changes in length-specific mass.