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

Abstract

Crater Lake is a unique environment to evaluate the ecology of introduced kokanee and rainbow trout because of its otherwise pristine state, low productivity, absence of manipulative management, and lack of lotic systems for fish spawning. Between 1986 and 2004, kokanee displayed a great deal of variation in population demographics with a pattern that reoccurred in about 10 years. We believe that the reoccurring pattern resulted from density dependent growth, and associated changes in reproduction and abundance, driven by prey resource limitation that resulted from low lake productivity exacerbated by prey consumption when kokanee were abundant. Kokanee fed primarily on small-bodied prey from the mid-water column; whereas rainbow trout fed on large-bodied prey from the benthos and lake surface. Cladoceran zooplankton abundance may be regulated by kokanee. And kokanee growth and reproductive success may be influenced by the availability of Daphnia pulicaria, which was absent in zooplankton samples collected annually from 1990 to 1995, and after 1999. Distribution and diel migration of kokanee varied over the duration of the study and appeared to be most closely associated with prey availability, maximization of bioenergetic efficiency, and fish density. Rainbow trout were less abundant than were kokanee and exhibited less variation in population demographics, distribution, and food habits. There is some evidence that the population dynamics of rainbow trout were in-part related to the availability of kokanee as prey.

Characteristics of the Kokanee Spawning Run in Harvey Creek, Washington, and its Potential Use as an Egg Source

“…The observed variation in kokanee escapement in Harvey Creek was consistent with variable abundance in other populations (Rieman and Myers 1992, Grover 2006, Buktenica et al 2007). Predation (Beauchamp et al 1995, Baldwin and Polacek 2002, competition (Spencer et al 1991), food availability (Martinez andWiltzius 1995, Buktenica et al 2007), reservoir operations (Fraley et al 1986, Martinez and Wiltzius 1995, Paragamian and Bowles 1995, entrainment Polacek 2002, Maiolie andStark 2003), and harvest (Rieman and Maiolie 1995) are some of the factors suggested to influence the abundance of kokanee in various locations.…”

“…nerka may have natural cycles in abundance. In the absence of human manipulations, kokanee abundance in Crater Lake, Oregon fluctuated over a 10-year period and was hypothesized to have oscillating periodicity (Buktenica et al 2007). Several Fraser River sockeye stocks exhibit cyclical fluctuations in abundance with a periodicity of four years (Goodlad et al 1974, Ricker 1997, Myers et al 1998).…”

“…Year-to-year variation in abundance is common among kokanee (Oncorhynchus nerka) populations (Rieman and Myers 1992, Grover 2006, Buktenica et al 2007) and when coupled with density dependent effects on growth can result in inconsistent fisheries. Many management agencies in the western United States require stocking of kokanee to meet recreational fishery goals (Wydoski and Bennett 1981, Martinez and Wiltzius 1995, Paragamian and Bowles 1995.…”

Current knowledge on non‐native freshwater fish introductions

“…15 N, 13 C) to characterize food‐web structure now allows their routine use for long‐term monitoring of changes in ecosystem functioning that result from introductions (Vander Zanden et al , 1999). Several studies have integrated this methodology into the study of non‐native ecological impacts and provide useful insights into the role played by various fish introductions to the overall ecosystem (Buktenica et al , 2007). Introductions of fish can alter food‐web structure and ecosystem functioning through top‐down or bottom‐up mechanisms, or through consumer and resource co‐limitation (Eby et al , 2006; Cucherousset et al , 2007).…”

Accuracy and Precision of Age Estimates Obtained from Three Calcified Structures for Known‐Age Kokanee

“…Kokanee populations exhibit strong density‐dependent growth (Rieman and Myers ; Buktenica et al. ), which poses a notable management quandary. At high densities, kokanee are smaller and often less desirable to anglers.…”