Reproductive, age, and scale measurement observations for Pacific herring in Sitka Sound, Alaska, with new and historic data, 2001-2018

There were three main objectives, along with a sub-study, that were addressed as part of this project. For objective one, we hypothesized that Pacific herring that will spawn in a particular year (spring) have reduced growth the summer prior, compared to immature herring, due to energy being allocated to reproduction rather than body growth. To test this hypothesis, we collected data to compare the histologically-determined maturity stages and outer ring measurements of fish. From thousands of herring caught in three commercial purse seine hauls in 2017 in Sitka Sound, fish were randomly sampled by macroscopically-assessing maturity (Hjort scale) and aging (scales). These samples were then sent to two labs for histologically-determined maturity, to age the fish (scales), and to measure the annuli of scales. As we did not reject the null hypothesis for objective one (i.e., null hypothesis: there was no difference in the outer scale annuli between mature and immature fish), we were not able to successfully complete our second objective (i.e., archived scales from fully-mature age classes of spring-spawning cast net sampled male and female herring in years 2001–2018 would have been examined to determine the age at which they matured based on scale growth increments), but the steps taken in preparation for addressing objective two had independent value: (1) We revisited archived scale collections and measured annuli of each scale for future studies of Pacific herring growth. (2) We conducted a sub-study to determine if scales plucked from different regions on a fish had proportional growth using scales from male and female Pacific herring samples jigged from Saint John Baptist Bay, Alaska, in 2018. The third objective of this study was to evaluate whether previously published macroscopic or gonadosomatic index (GSI)) methods can be effectively used in place of histologic methods to distinguish between immature and maturing Southeast Alaska herring in the fall, so that future maturity studies may be possible at a lower cost. To address this objective, thousands of herring were caught from three commercial purse seine hauls in 2017 in Sitka Sound and randomly sampled. For each female fish, biological attributes of each fish were recorded, gonads were removed, weighed, and macroscopically staged for maturity based on the Hjort scale and GSI. These samples were then sent to two labs for histologically-determined maturity and for aging the fish using scales.