Bioenergetic Assessment of Temporal Food Supply and Consumption Demand by Salmonids in the Strawberry Reservoir Food Web

Abstract

This study quantified temporal, spatial, and ontogenetic trophic interactions in Strawberry Reservoir to determine whether salmonid sport fish production was limited by food supply or predation. We combined field data on growth, diet composition, distribution, abundance, survival, and thermal experience with species-specific bioenergetics models for salmonids in Strawberry Reservoir to quantify monthly consumption of all prey fish, Daphnia, and macroinvertebrates. Fish prey represented a minor fraction of the annual diet of large cutthroat Oncorhynchus clarki and rainbow trout O. mykiss, but acute episodic piscivory associated with stocking of juvenile cutthroat trout in autumn could account for the low (1%) initial survival of these hatchery cohorts in recent years. Daphnia and other macroinvertebrates were important to all species and sizeclasses of salmonids. Model simulations suggested that salmonid consumption represented 5-30% of the Daphnia biomass during the June-October growing season in 1996-1997, but planktivorous demand exceeded Daphnia biomass in late winter. The bottleneck in prey supply during late winter and early spring suggests that Daphnia may not be able to support community consumption during this period if planktivore populations increase, either as a result of the expanding cyprinid populations or as a result of increased salmonid stocking or recruitment. Defining the role and impact of piscivorous and planktivorous trophic interactions provided information for management decisions regarding stocking strategies, recruitment, carrying capacity, and other food web processes.

Variability of kokanee and rainbow trout food habits, distribution, and population dynamics, in an ultraoligotrophic lake with no manipulative management

“…When Daphnia are not abundant, other large Crustaceans and Copepods increase in the diet (Richards et al, 1975), as can chironomid larvae and pupae (Northcote & Lorz, 1966;Collins, 1971;Richards et al, 1975). In contrast to our results, different size classes (Beacham & McDonald, 1982;Beauchamp et al, 1995;Baldwin et al, 2000) and age classes (Rieman & Bowler, 1980;Leathe & Grahm, 1981;Thiede et al, 2002) of kokanee, excluding fry, have been found to have similar summer-season feeding habits, while feeding habits during other seasons may vary. Beauchamp et al (1995) found that adult kokanee and sockeye in Lake Ozette, WA, fed on Daphnia, insects, and copepods from late summer to early spring, while juveniles fed on Daphnia year round.…”

Functional response of kokanee salmon (Oncorhynchus nerka) toDaphniaat different light levels

“…Regardless of these limitations, our functional response models should be suitable for application in oligotrophic, mesotrophic, or well-mixed systems where kokanee experience zooplankton densities less than 55 Daphnia·L -1 . Whereas the highest prey densities in the majority of the feeding trials were at or above the maximum average Daphnia densities observed in many regional reservoirs (ranging from approximately 5-18 L -1 ; Schneidervin 1985;Baldwin et al 2000;, wild kokanee may seek patches of prey that can have order of magnitude higher densities than the average concentration measured by sampling gear (PinelAlloul 1995;Folt and Burns 1999). Feeding trials at prey densities much higher than the 55 L -1 we used may be necessary to fully define the asymptotic nature of the functional response and accurately predict kokanee feeding rate at very high prey densities.…”

Hydroacoustic Estimates of Abundance and Spatial Distribution of Pelagic Prey Fishes in Western Lake Superior

“…Thus, lake trout and the commercial fishery represent a demand on the prey fish resource. A commonly used technique to determine if sufficient resources exist to support demand is demand-supply (D-S) analysis (Stewart et al 1983, Ney 1990, Ney 1993, Stewart and Ibarra 1991, Rand and Stewart 1998, Baldwin et al 2000, Johnson and Martinez 2000. D-S analysis combines estimates of prey abundance with predator consumption estimates from bioenergetics models to evaluate carrying capacity limitations (Ney 1990).…”