Brant C. Allen

Historical Food Web Structure and Restoration of Native Aquatic Communities in the Lake Tahoe (California-Nevada) Basin

Plans for the restoration of aquatic ecosystems are increasingly focusing on the restoration and rehabilitation of self-sustaining native fish communities. Such efforts have not traditionally adopted an ecosystem-based perspective, which considers species as embedded within a broader food web context. In this study, we quantify food web changes in Lake Tahoe (California-Nevada) over the last century based on stable isotope analysis of museum-archived, preserved fish specimens collected during 4 historical periods and under present conditions. We also examine the contemporary food web of nearby Cascade Lake, which is free from most exotic species and contains a species assemblage resembling that of Lake Tahoe prior to historical species introductions. During the last century, the freshwater shrimp Mysis relicta and lake trout (Salvelinus namaycush) have been introduced and established in Lake Tahoe, and the native top predator, Lahontan cutthroat trout (Oncorhynchus clarki henshawi; hereafter LCT), has been extirpated. Isotope analysis indicates that lake trout now occupy a trophic niche similar to that of historical LCT. Fish production has shifted from benthic to pelagic, corresponding with the eutrophication of Lake Tahoe during recent decades. The current Cascade Lake food web resembles that of the historical Lake Tahoe food web. Our isotope-based food web reconstructions reveal long-term food web changes in Lake Tahoe and can serve as the basis for setting historically relevant restoration targets. Unfortunately, the presence of nonnative species, particularly Mysis and lake trout, have dramatically altered the pelagic food web structure; as such, they are barriers to native fish community restoration. Fish community restoration efforts should focus on adjacent ecosystems, such as Cascade Lake, which have a high likelihood of success because they have not been heavily affected by nonnative introductions.

Lake Trout Spawning in Lake Tahoe: Egg Incubation in Deepwater Macrophyte Beds

Abstract –Although most populations of lake trout Salvelinus namaycush spawn over rocky shoals, use of these substrates by lake trout has not yet been found in Lake Tahoe. Large cobble substrate exists at depths less than 20 m, and steep, fractured, rocky substrate can be found in isolated areas from the surface down to at least 100 m, but no evidence of spawning activity in these areas has been found. Instead, at least a portion of the population spawns on deepwater mounds (40–60 m deep) over beds of the macrophyte Chara delicatula. This is the first known report of lake trout spawning over macrophyte beds. We hypothesize that this population originated from a deep-spawning stock and that the macrophyte beds on these mounds may provide some of the best deepwater incubation habitat in the lake, Although egg predation by intermediate sizes of lake trout (375–500 mm fork length) was substantial, the mounds appeared to be a refuge from the potentially more effective invertebrate and small vertebrate egg pred...

VOC Loading from Marine Engines to a Multiple-use Lake

Abstract A detailed boating use survey was conducted at a Northern California multiple-use lake, and the results were used to quantify daily MTBE and BTEX loading from recreational boating. Boat owner interviews and whole-lake activity surveys were conducted on 43 days between June 17 and September 20, 2000, including 38 days during the peak boating months of July and August. The dominant class of marine engines was found to be 4-stroke inboards and inboard/outboards, which constituted 60 percent of the total number of engines and consumed 69 percent of the fuel used at the lake. 2-stroke outboard engines with carburetors represented 26 percent of the engines and 14.3 percent of the fuel consumption, but were found to contribute 68 percent of MTBE and BTEX loading, while 4-stroke inboards were responsible for 4.2 percent. A sampling program was conducted in which MTBE/BTEX samples were collected on 23 days between May 22 and October 23, 2000. Results showed that MTBE appeared in 95 percent of epilimnetic samples up to a maximum concentration of 3.5 μg·l−1 while toluene was detected in 22 percent of epilimnetic samples at a maximum concentration of 0.5 μg·1−1. O-xylene was detected on one day, and benzene, ethlybenzene and m,p-xylene were not detected. The study demonstrated that MTBE is more persistent than BTEX compounds in surface water bodies, and accumulates over time with continuous inputs.

First Documentation of Salmincola californiensis in Lake Tahoe, CA—NV, USA

ABSTRACT. Salmincola californiensis is a parasitic copepod in the Lernaeopodidae family that commonly parasitizes salmonid fishes (Oncorhynchus spp.) by attaching near the fins and on gill filaments. Historically their distribution was limited to streams that emptied into the Pacific Ocean. During the summer of 2006, several rainbow trout (Oncorhynchus mykiss) captured in Lake Tahoe were infested with S. californiensis. This is the first known record of S. californiensis in Lake Tahoe.