Sierra Nevada Aquatic Research Laboratory

28 May, 04 AM - 06 Jul, 04 AM

The purpose of this research is to investigate the effects of nonnative fish introductions as one possible cause of decline in Yosemite toad (Bufo canorus) populations in the Sierra Nevada Mountains of California. It is not known whether introduced trout actively consume aquatic larval stages of B. canorus. Brook trout (Salvelinus fontinalis) overlap multiple portions of the range of B. canorus and are presumed to be a negative influence on their larval communities. It is this reason that S. fontinalis will be used as the stimulus trout predator in this study. This requires an understanding of the predator ? prey relationship that may or may not exist between B. canorus and S. fontinalis in areas of co-occurrence (i.e. within the same water body) in the High Sierra. The Yosemite toad has evolved in the absence of aquatic vertebrate predators (e.g. fish) and it is not known whether toxins present in other tadpoles within the genus Bufo have been maintained in B. canorus due to their high associated costs. This could lead to increased predation risk by the widely introduced S. fontinalis. Furthermore, the ability of B. canorus to respond to predator chemical cues of S. fontinalis may have also been lost due to the absence of such predators. Through a series of laboratory controlled experiments I will test the level of palatability of B. canorus tadpoles by S. fontinalis from areas of co-occurrence, which I will define as ?experienced? trout, and non co-occurrence (not within the same water body) as ?na?ve? trout. Second, I will test the anti-predator response of B. canorus tadpoles to the stimulus of S. fontinalis chemical cues. The importance of this research will allow for a clearer understanding how nonnative fish introductions are effecting local populations of B. canorus and the extent they are contributing toward this species? decline. This information is critical as the Yosemite toad has been petitioned for listing under the Endangered Species Act and found, in part, to be lacking this necessary information to warrant listing. Materials and Methods Brook trout were chosen to be the primary predator in feeding trials because there are well documented areas of co-occurrence with Yosemite toad (D. MARTIN PERS. COMM.; 2003 R. KNAPP PERS. COM.; 2003; PERS. OBS.). Brook trout are also fall breeders as compared to the spring breeding Rainbow trout (Oncorhynchus mykiss) and occasionally Brown trout (Salmo trutta) (MOYLE 1976) so spawning activity that can alter feeding behavior should be negated. Brook trout, Yosemite toad and Pacific treefrogs to be used in this study will be collected from lakes within Inyo National Forest, Sierra National Forest. Specifically the Owens and San Joaquin River drainages located within Inyo, Mono and Fresno County. A total of 50 adult S. fontinalis will be collected by hand, dip net and/or hook and line where there is known co-occurrence with B. canorus (see Table 1.). Captured trout will be temporarily held at original collection location in a 1/4? mesh floating holding box (1m2) for up to 5 hours and allowed to recover from capture before being transported to the Sierra Nevada Aquatic Research Laboratory (SNARL) near Mammoth Lakes, CA (37? 36?51?N/118? 49?47?W). SNARL is a research facility that is part of the University of California Preserve System and is administered by UC, Santa Barbara. At an elevation of 2150m SNARL is an ideal location to conduct these experiments based on the proximity of B. canorus and S. fontinalis populations. This location will alleviate transport time of live animals as well as acclimation effects of altitude that may alter behavior. Fish will be transported in insulated 30L coolers filled with water to an approximate depth of 30cm and surrounded by plastic ice packs. Battery operated aerators will supply fresh oxygen during transport. Prior to experiment fish will be maintained in two 1m x 0.85m deep fiberglass wading pools with continuous water flow from a nearby source stream and kept on a 14L : 10D photoperiod under fluorescent lighting with a water temperature of approximately 18 ?C . Each wading pool will contain 25 Brook trout separated by collection location (i.e. co-occurrence with Yosemite toad or non co-occurrence). At SNARL fish will be weighed in grams using a digital balance. A total of 40 Brook trout will be fasted for up to 10 days prior to experiments to solicit a feeding response. The remaining 10 Brook trout will be used as controls and fed trout pellets once daily based on total percentage of body weight prior to experiments. A total of 500 B. canorus tadpoles will be collected by hand and dip net from locations in Inyo, Mono and Fresno County (see Table 1 & Table 3.) where there is known co-occurrence with S. fontinalis as well as locations where no overlap with S. fontinalis has been confirmed. Tadpole collection is the preferred sampling method because of naturally occurring high mortality rates at this stage (FELLERS & FREEL 1995) and is not thought to have adverse effects on B. canorus populations. Anuran will be placed into pressurized one gallon plastic bags, filled ? and placed into an insulated cooler filled with ice pack provided. Larvae will then be transported back to SNARL inside an air conditioned 4 passenger vehicle. Tadpoles will be separated by developmental stage (GOSNER 1960) and placed in groups of 50 according to location to reduce stress. Tadpoles from co-occurring areas with Brook trout will be maintained separately from tadpoles collected from areas of non co-occurrence. Tadpoles will be fed ground rabbit chow ad libitum. B. B. canorus tadpoles will be maintained on a 14L : 10D photoperiod under fluorescent lighting with well water of approximately 18 ?C. All animals will be held at indoors at the SNARL fish house not to exceed two months. Injured and diseased animals will be placed in a concentrated solution of Tricane methane sulfonate (MS-222) for 30 min. and then frozen in a -20 ?C freezer. Animals to be used in this study will be contained within the fish house observed daily and will be eutnaized at the end of the study to prevent potential impacts to natural systems.

Visit #5191 @Sierra Nevada Aquatic Research Laboratory

Approved

Under Project # 3925 | Research

Effects of Brook trout on Yosemite toad tadpoles

graduate_student - California State University (CSU), Sacramento

Reservation Members(s)

Robert Grasso May 28 - Jul 6, 2004 (40 days)

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