Winter Ecology of Kokanee: Implications for Salmon Management

Abstract

Abstract.-We sampled various limnological parameters and measured growth and diet of age-0 kokanee Oncorhynchus nerka (lacustrine sockeye salmon) during two winters in a high-mountain lake of the Sawtooth Valley, Idaho. Although winter has been recognized as an important period for many warmwater fishes and for stream-dwelling salmonids, winter limitations have only recently been studied for coolwater and coldwater species. Ice and snow cover in winter limited light penetration. As a result, chlorophyll-a and zooplankton density were lower in ice-covered periods than during ice-free periods. The weight of stomach contents was often below a maintenance ration, yet the incidence of empty stomachs was extremely low (1 of 63) and the weight of stomach contents increased as energy reserves declined, indicating that kokanee were actively foraging during winter. Kokanee length and weight remained constant during the winter of 1993-1994 but increased from November through May in 1994-1995. Condition factors, however, declined significantly over the winter in both years, and lipid content approached levels associated with mortality. Differences in growth patterns may have been caused by a combination of changes in zooplankton density and kokanee abundance and in kokanee behavior to defend energy reserves or avoid predation. Results demonstrated the ambiguity of some growth measurements and the importance of choosing the correct metric for measuring growth in fishes. Because juvenile kokanee and sockeye salmon are ecologically similar, management efforts to restore the endangered Snake River sockeye salmon to the Sawtooth Valley lakes should recognize that winter conditions might be a bottleneck for this species.

Effects of river ice break‐up on organic‐matter dynamics and feeding ecology of aquatic insects

“…Ice cover and break-up may influence the quantity and quality of organic matter in river ecosystems. For instance, surface ice can decrease light available to primary producers (Steinhart & Wurtsbaugh, 2004), and anchor ice can displace macrophytes (Prowse, 2001b). Additionally, scour from ice break-up may not just temporarily remove primary producers, but stimulate them by providing a clean substrate for growth (Prowse & Culp, 2003).…”

Behavioral attributes of turbine entrainment risk for adult resident fish revealed by acoustic telemetry and state-space modeling

“…In Revelstoke Reservoir (British Columbia, Canada), the density of kokanee near the dam increases particularly during periods of prolonged turbine operation in the winter, possibly due to advection [29]. Furthermore, kokanee usually occur in habitats with high light intensity during the winter [30,31]. Relatively high light intensity may occur near the powerhouse of hydropower reservoirs in the late fall and winter due to the effect of turbineinduced flows in preventing or inhibiting formation of thick ice cover.…”

Kootenay Lake Fertilization Experiment; Years 11 and 12, Technical Report 2002-2003.

“…This would allow juvenile kokanee to enter the winter months at a relatively high maintenance level thus surviving at higher rates than pre-fertilization conditions. In support of this theory, Steinhart and Wurtsbaugh (2003) discuss the importance and critical nature of lipid content when they measured juvenile kokanee mortality during the winter months in Stanley Lake, Utah. Decline in Okanagan Lake kokanee survival rates is suspected to be due to poor quality phytoplankton (blue-greens) with low fatty acid content consumed by cladocerans that are in turn utilized by juvenile kokanee (Andrusak et al 2004b).…”

“…Abundance of Arrow Lakes Reservoir kokanee has increased from about 3 million to nearly 12 million in 2003. Actual mechanisms involved in increased survival of kokanee in both Arrow Reservoir and Kootenay Lake has not been investigated but there is growing evidence that high lipid content in macrozooplanktors (e.g., daphnids) is critically important to juvenile kokanee survival (Rae and Ashley in Andrusak et al 2004b;Steinhart and Wurtsbaugh 2003).…”