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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Organismic and Evolutionary Biology
Year Degree Awarded
Month Degree Awarded
Other Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology
Anadromous river herring (alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)) make annual spring spawning migrations from the ocean to freshwater, where juveniles reside before emigrating to the ocean. Climate change may alter environmental and biological cues that prompt both adult migration and juvenile emigration, with implications for adult spawning success and offspring survival for these imperiled species. Shifts in adult migration have been observed in some rivers, while impacts on reproductive success and juvenile survival remain unknown. Cues for juvenile emigration are poorly understood as they have been explored at limited spatial and temporal scales. Using otolith-estimated spawn dates and genetic pedigrees in Pentucket Pond, we calculated that adult alewife spawned in freshwater for longer (mean = 26 days) and over a larger range (3–64 days) than previously thought. Fish that stayed in freshwater longer had higher reproductive success, potentially reflecting their ability to spawn multiple clutches across a range of nursery conditions. Using a multi-decadal (1979–2020) data set in the Connecticut River, we found that adult blueback herring migrations started 0.20 days/year earlier and became 0.30 days/year shorter over time. Shorter winters and higher winter precipitation were among predictors of earlier migrations. Environmental conditions and climate-related changes in adult phenology influenced juvenile counts in this system; higher juvenile counts were predicted by longer adult migrations, more variation in summer temperatures, and higher winter precipitation. To assess cues for juvenile emigration, we developed a video and computational monitoring method to count emigrating juveniles (9.4% error) over two study years (2017, 2018) at Great Herring Pond. In both study years, juveniles emigrated continuously through the study period (June – December) with high passage pulses in July and October. Juveniles were more likely to emigrate during low-light moon phases (crescent, new moon), but other cues for large passage events differed interannually. These results highlight the value of multi-year and multi-decadal studies to understand life history patterns and traits, especially when there is significant interannual variation. Evaluating climate-related environmental cues for river herring life-history traits across sites and years may facilitate site-specific adaptive management recommendations to support migrating, imperiled populations.
Marjadi, Meghna N., "TIMING IS EVERYTHING: CLIMATE CHANGE IMPLICATIONS FOR PHENOLOGICAL EVENTS AND REPRODUCTIVE SUCCESS IN RIVER HERRING" (2023). Doctoral Dissertations. 2830.
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