Background
Populations of anadromous Pacific salmon within California are declining and many populations are expected to disappear entirely within the next 100 years (Katz et al., 2013). For this project I focus on two of these species, coho salmon and steelhead. Of the two evolutionary significant units of coho in California, one is federally listed as threatened and the other is endangered (Moyle et al., 2017). For steelhead there are seven distinct population segments within the state, five of which are federally listed as threatened and one of which is endangered (Moyle et al., 2017). Numerous factors have contributed to their decline and contribute ongoing threats, including drought and other climate factors, hatchery interactions, and over-fishing (Brown et al., 1994). In some areas, habitat loss is thought to be the predominant mechanism of historical decline, driven by dams, agriculture, and logging (Brown et al., 1994). Urban land use has been linked to the decline of salmon over time and has been shown to impact juvenile survival in the Pacific Northwest (Bilby & Mollot, 2008; Paulsen & Fisher, 2001). In California, many salmon populations spawn within areas that are now considered protected, including lands which have previously been ecologically damaged. For example, Redwood Creek watershed, which now partially resides within Redwood National Park, was previously extensively logged (Brown et al., 1994). I am interested in understanding how protected areas impact salmon populations in California, both in terms of population numbers and rate of change over time. I was unable to find research within California that documented the impact of established protected areas on salmon populations. Understanding this relationship can help managers improve land use practices to protect these species.
Data
To adress my questions, I used data from two different sources. For salmon population data, I pulled data from the California Monitoring Plan for salmon and steelhead (CMP), which is a joint effort between the California Department of Fish and Wildlife (CDFW) and NOAA to monitor and assemble data on anadromous salmon populations across California. For this project, I used estimates for spawning adult coho and steelhead, as this was available for many watershed level populations across a number of years. The data spans from 1981 to 2020 for steelhead and 1995 to 2020 for coho, and was collected yearly within fixed areas for each population. In addition to the count data, I used geospatial data from the CMP which indicated the watershed or sub-watershed extent that was monitored for each population. To determine the amount of protected area within each watershed I used data from the California Protected Areas Database (CPAD), which consisted of polygons of areas protected for open space use throughout California.
Data Wrangling
Geospatial
In order to calculate percent protected by watershed, I used spatial intersection to find the overlap between the protected areas in the CPAD database and each monitored watershed. I removed any protected areas established after 1981, as this was the first year of salmon data available.