Seventy years of diminishing biocomplexity of California Central Valley hatchery steelhead, Oncorhynchus mykiss

The California Central Valley steelhead (Oncorhynchus mykiss) has declined precipitously since Euro-American colonization and has been listed as threatened under the United States Endangered Species Act since 1998. Hatchery-origin fish now dominate the population and hatchery management is a key listing factor. However, scant release metric information is available. We compiled a time series of O. mykiss hatchery release data for all four Central Valley hatcheries releasing O. mykiss between 1948 and 2017. The biocomplexity of released fish has declined since the early 1980s. Individuals have been released at increasingly similar numbers, biomass, body sizes, times, and locations over time. Moreover, yearling fish have been released at larger sizes, leading to the near-exclusive release of age-1 smolts in February and March since the late 1990s and early 2000s. Pervasive reductions in release portfolios have likely occurred for other hatchery-supported Pacific salmonid stocks throughout..., Release & Return Database Compilation

We compiled release data from 135 annual reports provided by the California Department of Fish and Wildlife (CDFW) for state-operated hatcheries. The state hatchery annual reports spanned one fiscal year from 1 July to 30 June of the following year: NFH (54 reports, 1956–57 to 2009–10), FRFH (40 reports, 1969–70 to 2009–10), and MRFH (41 reports, 1964–65 to 2007–08; no releases were reported for 1976–77, 1988–89, or 2001–02). From 1988 to 2001, release records were obtained for MRFH from the California Hatchery Scientific Review Group (CA HSRG 2012, Appendix VI) instead of annual reports because the former dataset is more detailed and complete. From 2001–2017 for the FRFH and 2003–2017 for the NFH and MRFH, an electronic dataset from CDFW's statewide inventory system was used instead of annual reports or California Hatchery Scientific Review Group data (CA HSRG 2012, Appendix VIII). Hatchery release data were considered “draft” or non-finalized..., All files are uploaded as .csv files and can be opened in Excel, R, and a variety of other programs., # Seventy years of diminishing biocomplexity of California Central Valley hatchery steelhead, *Oncorhynchus mykiss*

## General Information

1. Author Information
A. Corresponding Author Name: Stephanie Carlson Institution: University of California, Berkeley Email: [e-mail]
B. Co-investigator Contact Information
Name: Eric Huber
Institution: University of California, Berkeley
Email: [e-mail]
C. Co-investigator Contact Information
Name: Rachael Ryan
Institution: University of California, Berkeley
Email: rachael\[e-mail]
D. Co-investigator Contact Information
Name: Rachel Johnson
Institutions: NOAA Fisheries, Southwest Fisheries Science Center & University of California, Davis
Email: [e-mail]. Co-investigator Contact Information
E. Name: Anna Sturrock
Institution: University of Essex
Email: [e-mail]
F. Co-investigator Contact Information
Name: ...