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Quality over Quantity: Conservation hatchery intervention diversifies outmigration size and timing of juvenile Coho Salmon (Oncorhynchus kisutch)
- M Johanson, Alexander
- Advisor(s): Lusardi, Robert
Abstract
Climate change is altering environmental conditions and negatively affecting a wide range of species and taxa. In California, endangered Coho Salmon (Oncorhynchus kisutch) have been reduced to critically low abundances, and the total production of hatchery individuals has increased dramatically in response. Evidence shows that production hatcheries are severely diminishing the biocomplexity of wild salmon populations in streams where stocking occurs, but there has been no assessment into whether conservation hatcheries are also homogenizing the life history events of the populations they aim to protect. Maintaining diversity will be critical for populations to persist and adapt to climate change. The Tomales Bay metapopulation of coho includes the putatively-wild Lagunitas Creek and the hatchery-supported Walker Creek. We compare Fork Length (FL), mass (g), and outmigration timing of the Lagunitas Wild (LW), Walker Hatchery (WH), and Walker Natural Origin (WNO) smolts in 2022 and 2023. By comparing the smolt data for the three subpopulations in both years, we attempted to determine if conservation hatcheries that prioritize genetic diversification in breeding pairs can produce offspring with variability at the time of outmigration. Lagunitas Wild (LW) coho were the smallest on average in both years but exhibited the highest abundance of coho smolts and variability in size and outmigration timing. Conversely, Walker Hatchery (WH) coho exhibited the lowest smolt abundance and lowest variation in important life history characteristics. In both years, WH and Walker Natural Origin (WNO) coho outmigrated at significantly different rates when compared to LW, but were not significantly different from each other in 2023. These differences indicate that ongoing conservation interventions to the Tomales Bay metapopulation are improving biocomplexity during outmigration, an important factor to consider under a rapidly changing climate.
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