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COSEWIC assessment and status report on the Chinook Salmon (Okanagan population) in Canada

Population Sizes and Trends

Search Effort

The Washington Department of Fish and Wildlife has been conducting spawning ground surveys in the U.S. portion of the Okanagan basin for the Okanogan summer chinook population since 1956 (Miller 2004). These spawning ground surveys were conducted through aerial redd counts, plus float/walk surveys in some years (yearly since 1991 and sporadically prior to that). It is unknown if the methodology for the aerial surveys has changed throughout the survey years.

The Okanagan Nation Alliance Fisheries Department has enumerated spawning chinook during their Okanagan sockeye programs (when feasible) in the Okanagan River in each year since 2001 (Wright and Long, 2005; Long, 2002), and seined adult anadromous chinook in the river in 2003, 2004 (Wright and Long, 2005), and recently in 2005 (ONAFD unpublished files 2005). However, there are few formal records of Okanagan chinook observations in the river prior to this time. The best records are historic accounts of the major chinook fishery at Okanagan Falls (Ernst, 1999; Ernst and Vedan, 2000), the Gartrell observation of spawning chinook in May (DFO, unpublished SEDS files, 1936), chinook identified as present in correspondence files of DFO region 1920’s to 1999 (DFO, unpublished correspondence files, Kamloops, B.C.), seining of juveniles in Osoyoos Lake in 1971 (Northcote et al., 1972), and annual observations of spawners in the river during sockeye enumeration survey(s) from 1968-1999 (DFO, unpublished SEDS files).


Abundance, Fluctuations and Trends

The historic Okanagan chinook population in the Okanagan River was large enough to support an important food and commercial/economic trade fishery prior to non-native human settlement (Ernst and Vedan, 2000). However, by 1874 it was estimated that over one-half of the salmon run returning to the Upper Columbia (including the Okanagan) was harvested in the downstream commercial fishery. By the 1890s the runs to the Upper Columbia River basin were almost completely decimated (Moore et al., 2004), presumably including the Okanagan River.

Chinook have been sporadically documented as being present in the system since 1965 as a result of incidental observations made during monitoring of sockeye salmon escapement (Figure 6). Estimates of chinook escapement, based on counts of peak numbers of live and dead chinook adjusted by a standard expansion factor used by DFO, are shown for years for which the necessary data are available (Bailey 2004, personal communication). It appears that when studies have occurred in the system, chinook have been documented as present (Northcote et al. 1972, Wright and Long 2005). The only evidence of discontinuity in the presence of Okanagan chinook in the basin has been their absence from gillnetting samples in Osoyoos Lake in 1972 (Allen and Meekin, 1980). By contrast, Okanagan chinook were captured in gillnet sampling of Osoyoos Lake in 1971 by Northcote et al. (1972).

Figure 6: Presence Documentation and Escapement Estimates (where possible) of Chinook to the Canadian Okanagan River

Figure 6: Presence documentation and escapement estimates (where possible) of chinook to the Canadian Okanagan River.

The summer chinook population in the U.S. portion of the Okanagan basin appears to be closely related to the Canadian population. This population is considered to be “of special concern” or “depressed” by state fisheries agencies, with the primary identified threat being loss of habitat through habitat destruction or lack of access (Nehlsen et al., 1991; WDF et al., 1993). The Washington Department of Fish and Wildlife (WDFW) has been conducting aerial redd surveys since 1956, the results of which are summarized in Figure 7 (Miller 2004). In 2002 WDFW used a redd expansion factor of 2.3 to estimate adult escapement (Miller 2004), which is consistent with the expansion factor (2.2) used for interior Fraser populations (Bailey 2004, personal communication). Between 1956 and 1998 redd estimates have been relatively stable. However, since 1999 redd estimates have been increasing. This is thought to be due to years of high run-off during smolt migration and improved ocean survival in recent years (PSC Joint Chinook Technical Committee 2003). Hatchery contributions during this period (1999-2002) may also have contributed to increased population abundance, and have been estimated at 56% with a range of 20-70% (Todd Miller, 2004 personal communication). Murdock and Miller (1999) estimated a spawner escapement of about 1300 summer-run (ocean-type) chinook in 1998, with about 47% being of hatchery origin. Historical accounts of chinook in the U.S. portion of the Okanagan Basin do not include run size estimates, but local newspapers between the 1880s and 1930s regularly mentioned active food fisheries (Smith, 2003a, b).

Figure 7: Summary of Aerial Redd Surveys for Okanagan (U.S. portion below Osoyoos Lake) and Similkameen Rivers from 1956-2002

Figure 7: Summary of aerial redd surveys for Okanagan and Similkameen Rivers from 1956-2002.

Data adapted from Miller, 2004.

Rescue Effect

There is a long history of hatchery activity within the Upper Columbia ESU, starting with hatcheries on the Methow and Wenatchee Rivers in 1899. In the 20th century both local and, occasionally, lower Columbia chinook stocks were used for propagation (Mullan, 1987; Myers et al., 1998). In the past decade, between 300 000 and 1 million yearlings and sub-yearlings have been stocked annually in the U.S. portion of the Okanagan basin (FPC, 2004).

The summer chinook that have been out-planted from hatcheries are the progeny of broodstock collected either in the U.S. Okanogan River or at Wells Dam. The broodstock collected at Wells Dam is a mix of Okanogan and Methow River chinook populations.

There was a decades-long hiatus from stocking spring chinook in the Okanagan Basin until 1991. Between 1991 and 1993, a total of about 480 000 yearling or sub-yearling spring chinook were planted in the U.S. portion of the Okanagan River and its tributaries (FPC, 2004). All of the recent hatchery releases of spring chinook are Carson stock, which have been derived from a composite of Upper Columbia River spring chinook stocks collected during the Grand Coulee Fish Maintenance Program (GCFMP) (Busack and Marshall, 1995).

During the 2003 enumeration surveys in the Okanagan River upstream of Osoyoos Lake, half (four of eight) of the anadromous chinook that were captured on the spawning grounds were of hatchery origin (Wright and Long, 2005), suggesting that in some years a significant portion of the population of anadromous chinook salmon in the Canadian Okanagan River is comprised of strays from U.S. hatchery and, possibly, wild populations. However, none of the anadromous chinook observed in 2004 showed evidence of hatchery origin, and only 1 of 29 anadromous adults in 2005 showed evidence of hatchery origin (adipose clip). The hatchery-origin fish observed in 2003 were likely summer (ocean-type) chinook, as no spring (stream-type) chinook were stocked in the Okanagan basin during the appropriate brood years (C. Fisher, personal communication, 2005). None of the Okanagan chinook caught in Osoyoos Lake have had clips or other hatchery markings (Wright and Long, 2005). As only roughly half of chinook production in the U.S. Okanogan comes from hatcheries, the proportion of fish in the Canadian Okanagan River with hatchery marks represents a lower bound on the number of strays from the U.S. portion of the drainage.

There are plans for a new hatchery to be located at the base of Chief Joseph Dam (C. Fisher, personal communication, 2005). One of its goals is to increase production of Okanagan chinook to levels sufficient to sustain a food and sustenance harvest for the Colville Confederated Tribes (CCT). Additional acclimation ponds are proposed in the U.S. portion of the Okanagan River where currently there is only a long-term acclimation pond on the Similkameen. In their hatchery plan the CCT have expressed an interest in looking at potential hatchery options in Canada. Through their collaborative arrangements with the CCT, the Okanagan Nation Alliance have identified several unknowns that need to be addressed prior to the use of a hatchery in population restoration. Among the issues that must be considered are the genetic relationships between the Canadian and U.S. Columbia Basin chinook populations.