Disruption of natural disturbance regime decouples habitat and life stage in a keystone species

Anthropogenic disturbance of stream ecosystems, often chronic in nature, has been studied extensively. However, when disturbance is driven by more than one resource policy over many decades, feedback between habitat evolution and biological adaptation can be disrupted and ecological function affected in unforeseen ways. We analyzed over 100 years of Chinook salmon (Oncorhynchus tshawytscha) length frequency trends associated with fisheries management and changes in available spawning substrate (habitat) linked to flow regulation in a highly altered California river. Over time, salmon lengths generally decreased, fluctuating with exploitation (ocean harvest) and hatchery production rates. Female size reduction, coupled with a degrading and coarsening channel, and perching peripheral habitat related to past mining activity, indicates available spawning substrate may be too large to support the current salmon population. Assuming a salmon can move material ~10% of her body length, length f..., Changes in female salmon size (1919–2021)
Length measurements of adult Chinook Salmon returning to the LAR have not been consistently recorded. However, LAR hatchery and natural production are managed as a single population. Therefore, we applied the correlation between Chinook Salmon fecundity and adult FL (Healey and Heard 1984) to 66 years of Nimbus Fish Hatchery fecundity data (Williams 2006; CDFW unpublished data) to estimate mean annual adult female Chinook Salmon body length in the LAR (1955 to 2021). In addition, Clark (1928) provided FL data from 1,423 Chinook Salmon caught by gill-net in the Sacramento River near the LAR mouth (1919–1921). Because sex was not provided for individual fish, we used the female-to-total population FL ratio from recent LAR fish surveys (CDFW unpublished data) and multiplied this by the estimated length frequencies from Clark (1928) to estimate average female size for that period, assuming that this relationship would remain constant over the period..., , # Data from: Disruption of natural disturbance regime decouples habitat and life stage in a keystone species

Below is a brief summary of dataset contents, contextualized in experimental procedures and results.

We linked various state and federal data sets related to salmon escapement, harvest, fish size, and habitat use in an Excel file to perform correlative analyses.

Four files are uploaded including Exploitation and salmon size (FL), salmon spawning use (number of redds observed), and calculations of the theoretical substrate particle size a female could move based on her size.

Chinook Salmon fecundity data were acquired from the Nimbus Fish Hatchery (California Department of Fish and Game. [https://wildlife.ca.gov/Fishing/Hatcheries/Nimbus](https://wildlife.ca.gov/Fishing/Hatcheries/Nimbus)

Salmon exploitation rate estimates were acquired from NOAA Fisheries: National Marine Fisheries Service (NMFS), 7600 Sand Point Way, NE, BIN C15700; Seattle, WA 98115-0700 [www.noaa.gov/fish...