Migratory Timing of Upper Copper River Sockeye Salmon Stocks and Its Implications for the Regulation of the Commercial Fishery

Abstract

Migratory timing of 15 sockeye salmon (Oncorhynchus nerka) stocks in the upper Copper River, Alaska, was determined from a tag and recapture project conducted between 1967 and 1972. Time densities and descriptive statistics were used to estimate mean date of migration upstream, variation about the mean, form, and stability of these measures between years within the geographic reference frame of Wood Canyon. The mean calendar dates of migration through the Copper River commercial fishery district of Prince William Sound also were estimated. River level appeared to have a negative correlation with travel rate and was a source of yearly variation in the mean date of migration. Mean dates of migration varied by stock and were grouped by a Student‐Newman‐Keuls test into six time spans that significantly differed from one another. Variation in mean migration date increased through time, with earlier migrating stocks demonstrating greater consistency of timing between years than the later migrating stocks. The majority of migratory time densities were positively skewed, platykurtic forms which were relatively stable between years. Migratory timing of upper river stocks overlapped and harvest control of individual stocks within the Copper River District of Prince William Sound may not be feasible. However, management of groups of stocks according to clusters of time‐density means is feasible. Identification of the upper Copper River stock composition within a commercial fishery period can assist the manager in assessing stock abundance and the probable impact of the fishery on groups of stocks.

Late-season mortality during migration of radio-tagged adult sockeye salmon (Oncorhynchus nerka) in the Columbia River

“…Rates for the Hanford Reach in this study were higher than those of sockeye salmon in the Karluk (Gard 1973) and Copper rivers (Merritt and Roberson 1986) and of chinook salmon in the Kenai River (Bernard et al 1999) but lower than those of chinook salmon and fall-run steelhead in the Hanford Reach in 1997 (Keefer et al 2004b). Slower passage through the Hanford Reach by sockeye salmon, as compared with Columbia River chinook salmon or steelhead, may be related to smaller body size (Brett 1965;Weihs 1973).…”

“…tributaries (Tagaki and Smith 1973;Merritt and Roberson 1986;Hodgson and Quinn 2002). For example, Columbia River and interior British Columbia stocks of sockeye salmon tend to enter fresh water before peak summer temperatures and hold in spawning tributaries for 1 month or more before fall spawning whereas coastal stocks migrate after peak temperatures just prior to spawning (Gilhousen 1990;Hodgson and Quinn 2002).…”

“…In comparison with reservoirs, the higher velocities in the Hanford Reach were probably the major contributor to slower migration rates than were observed in the impounded reaches, and it is probable that energy expenditure in this reach was greater than that in reservoirs, despite lower ground speeds. For instance, Merritt and Roberson (1986) found that increased river level significantly decreased travel rate of sockeye salmon within a given year and between years. Notably, the observed rates through the Hanford Reach may underestimate the long-term average because of the high discharge conditions of 1997.…”

Hydrologic Regime Changes in a High-Latitude Glacierized Watershed under Future Climate Conditions

“…Anadromous fish travel upstream to spawn at the place of their birth, starting the journey at predictable times of year, and it is uncertain how changes in the magnitude and timing of flow in the Copper River may impact their migration; during the period 1988-2009, most sockeye entered the Copper River in June when monthly runoff was on the order of 160 mm, but at the end of the century, June runoff may be 50% higher at 240 mm. Increased streamflow is known to significantly increase the time required for salmon to reach spawning areas in the Upper Copper River [44]. With peak monthly flow projected to increase and total annual flow projected to double, identification of the critical point at which high flows prevent anadromous fish from reaching their destination, or make winter habitat unsuitable, is beyond the scope of this research, but crossing that tipping point would have significant consequences for the local economy and residents.…”

Population Composition, Migration Timing, and Harvest of Columbia River Chinook Salmon in Late Summer and Fall

“…These types of life history and run reconstruction data have been widely used to manage, exploit, and conserve anadromous salmonids (e.g., Ricker 1972;Allendorf et al 1997;Begg et al 1999). Moreover, the use of population-specific migration timing information is one of the most widely applied techniques for scheduling fisheries to limit harvest of vulnerable populations while targeting robust populations (e.g., Merritt and Roberson 1986;Starr and Hilborn 1988;Beacham et al 2004;Boatright et al 2004;Keefer et al 2008a).…”