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NOAA’s Alaska Fisheries Science Center’s (AFSC) Ecosystems and Fisheries-Oceanography Coordinated Investigations (EcoFOCI) program has collected spring ichthyoplankton abundance data in the Gulf of Alaska since 1981. Collections were made nearly annually until 2011 when sampling was reduced to only odd years. This dataset is used to better understand population recruitment of major fish species in the GOA and provides early warning of potential year-class strength to inform fisheries management. However, gaps in the time series during even years have made it more difficult to interpret the interannual variability of ichthyoplankton abundance in such a dynamic ecosystem. Recent collaboration with the Northern Gulf of Alaska Long Term Ecological Research (NGA LTER) program has allowed for additional spring sampling of ichthyoplankton in the GOA annually since 2018. Larval fish data collected by the NGA LTER were combined with EcoFOCI data and used to estimate abundance in years when EcoFOCI had no field presence in the GOA. Five taxa were determined to be suitable for this approach based on their percent occurrence in both surveys. A generalized additive model (GAM) was fit to ichthyoplankton data from 1981 to 2022 collected by both EcoFOCI and NGA LTER and used to predict larval abundances in 2018, 2020, and 2022. For each species, models with two different error distributions were compared and shown to produce similar predictions of larval abundance. This report provides a model framework for predicting interannual larval fish abundance while controlling for differences in sampling methodologies, timing, and location, and identifies a subset of taxa for which this framework is currently appropriate. As additional years of concurrent sampling are added in future, this approach has the potential to improve our understanding of interannual variation in ichthyoplankton dynamics and provide more comprehensive indicators for ecosystem-based fisheries management. 

Synopsis In high-latitude environments where seasonal changes include periods of harsh conditions, many arthropods enter diapause, a period of dormancy that is hormonally regulated. Diapause is characterized by very low metabolism, resistance to environmental stress, and developmental arrest. It allows an organism to optimize the timing of reproduction by synchronizing offspring growth and development with periods of high food availability. In species that enter dormancy as pre-adults or adults, termination of diapause is marked by the resumption of physiological processes, an increase in metabolic rates and once transitioned into adulthood for females, the initiation of oogenesis. In many cases, individuals start feeding again and newly acquired resources become available to fuel egg production. However, in the subarctic capital-breeding copepod Neocalanus flemingeri, feeding is decoupled from oogenesis. Thus, optimizing reproduction limited by fixed resources such that all eggs are of high quality and fully-provisioned, requires regulation of the number of oocytes. However, it is unknown if and how this copepod limits oocyte formation. In this study, the phase in oocyte production by post-diapause females that involved DNA replication in the ovary and oviducts was examined using incubation in 5-Ethynyl-2′-deoxyuridine (EdU). Both oogonia and oocytes incorporated EdU, with the number of EdU-labeled cells peaking at 72 hours following diapause termination. Cell labeling with EdU remained high for two weeks, decreasing thereafter with no labeling detected by four weeks post diapause, and three to four weeks before spawning of the first clutch of eggs. The results suggest that oogenesis is sequential in N. flemingeri with formation of new oocytes starting within 24 hours of diapause termination and limited to the first few weeks. Lipid consumption during diapause was minimal and relatively modest initially. This early phase in the reproductive program precedes mid-oogenesis and vitellogenesis 2, when oocytes increase in size and accumulate yolk and lipid reserves. By limiting DNA replication to the initial phase, the females effectively separate oocyte production from oocyte provisioning. A sequential oogenesis is unlike the income-breeder strategy of most copepods in which oocytes at all stages of maturation are found concurrently in the reproductive structures.