METHODS

Overview

We report on the state of salmon in each of the nine regions that represent all major Pacific salmon-bearing watersheds in Canada: Yukon, Northern Transboundary, Haida Gwaii, Nass, Skeena, Central Coast, Fraser, Vancouver Island & Mainland Inlets, and Columbia. These regions are also used to organize data in the Pacific Salmon Explorer. There are a relatively small number of Pacific salmon that spawn in the MacKenzie River basin in Arctic Canada that are currently not considered here. For each of these regions, we compiled and analysed data on six species of Pacific salmon: Chinook (Oncorhynchus tshawytscha), chum (O. keta), coho (O. kisutch), pink (O. gorbushca), sockeye (O. nerka), and steelhead (O. mykiss).

Where possible, we report on both the abundance of spawners and returns for each region and species. Spawners (also called “escapement”) provide information on the number of salmon that “escape” the fishery and make it back to spawn in rivers. These salmon are available to meet ecological needs within watersheds and can reproduce and contribute to future generations. As such, understanding spawner abundance is important to salmon conservation. Where data are available, we also report on returns, which are the sum of spawners and catch. In some years, a substantial proportion of salmon that survive to maturity are caught in commercial fisheries. Tracking returns provides information on the survival and productivity of salmon as well as their ability to support fisheries. Often, the status and trends for spawners are more optimistic than for returns because of widespread declines in commercial catches of Pacific salmon in Canada since the mid 1990s^[5].

Data Sources

We constructed an index of aggregate abundance for spawner and total abundances at the regional scale using the best available data. Details of specific data sources for each region and species are outlined in the Technical Documentation and raw data are publicly available in the associated GitHub repository. We preferentially rely on data vetted by the Pacific Salmon Commission and used to assess international obligations under the Pacific Salmon Treaty. Specifically, these data come from the appendices of reports by the Yukon River Joint Technical Committee, Transboundary Technical Committee, Northern Boundary Technical Committee, Chinook Technical Committee, and Chum Technical Committee. The Fraser River Panel provides data on pink and sockeye abundance directly via their Annual Report Application. Publication of these appendices may take years and more up-to-date versions were provided to Pacific Salmon Foundation staff directly by Fisheries and Oceans Canada (DFO) upon request.

In the Nass region, we worked with LGL Ltd and the Nisga’a Lisims Government - Fisheries & Wildlife Department to construct annual spawners and returns for each species^[24]. Fraser coho, Columbia Chinook, and Columbia sockeye data were provided directly to Pacific Salmon Foundation staff by DFO upon request. The Fraser coho estimates of spawner and total abundances are based on Interior Fraser coho that spawn upstream of Hells Gate, British Columbia, (including five ^{Conservation Units}: Fraser Canyon, Interior/Middle Fraser, Lower Thompson, South Thompson, and North Thompson). Steelhead abundance in the Skeena and Fraser are publicly available from the Province of British Columbia. Steelhead spawner abundance in the Canadian portion of the Columbia is reported by the Okanagan Basin Monitoring and Evaluation Program.

For regions and species that did not have reliable estimates of aggregate abundance at the regional scale, we constructed an index of spawner abundance from spawner surveys reported in DFO’s New Salmon Escapement Database System (NuSEDS). We account for missing data using a proportional infilling approach to impute missing data based on the average decadal contributions of each stream to the aggregate. We then expand the imputed dataset to account for smaller “non-indicator” streams. The details of this expansion approach are outlined in the Technical Documentation.

In total we compiled spawner abundance for 44 unique region-species combinations, with an average time series length of 57 years (range 17 to 130 years). The temporal currency of data varied among sources, with most regions and species having spawner estimates to 2022 or 2023. There were three region-species combinations for which we did not assess the current state of spawners: two that had insufficient time-series length to establish a baseline (<20 years for Columbia Chinook and Columbia steelhead) and one with outdated data (Haida Gwaii Chinook), meaning we only assessed the current state of spawner abundance for 41 region-species combinations. Fewer regions and species had estimates of total abundance because information on which rivers (and regions) salmon are destined for when caught in the ocean is not always available, making it difficult to assign catch to a region. We compiled total abundance for 14 unique region-species combinations, with an average time series length of 45 years (range 23 to 131 years). All total abundance time series were current to 2022 or 2023.

Analysis

We smooth the raw time series of spawners and returns using a right-aligned running geometric mean over the generation length. This smoothing reduces the influence of dominant years for species with cyclic dynamics (e.g. Fraser sockeye) and produces an index of abundance that is less sensitive to stochastic interannual variability that is common in salmon population dynamics^[33]. The generation length is based on the dominant life-history type for each species in a particular region. To facilitate comparison among species that are naturally very different in their absolute abundance, we transform the smoothed time series into a per cent anomaly from the average among all years for that species and region.

We summarised the current state as the per cent anomaly for the most recent year of the smoothed time series (i.e., the per cent difference between the geometric mean spawners over the most recent generation and the geometric mean spawners over all years). For species with long generation lengths (e.g. six years for Yukon Chinook), the current state may not reflect recent, dramatic changes in abundance because the generational average will lag behind. Where there are noteworthy changes in abundance in the most recent year that are not obvious from the current status, we provide that context in the regions section.

We summarised trends as the average annual per cent change in abundance, calculated from the slope of a linear regression model fitted to the log-transformed, smoothed time series. We show both short-term trends based on the slope over the most recent three generations only and long-term trends based on the slope over all available years for each species in a given region.

Data Availability

The outcomes of this State of Salmon report are publicly available through the Salmon Watersheds Program Data Library as two datasets:

Time series of Regional Salmon Abundance by species. This dataset contains both the raw annual abundance and the smoothed time series shown in the trends plots.
State and Trends in Salmon Abundance for each region and species, including the values for the current state, short-term trend, long-term trend, the generation length, and the years of data.

Overview

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Regions

Overview

Regions

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