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Spawn Creek fencing and restoration project

REDUCING THE IMPACT AND INCIDENCE OF WHIRLING DISEASE THROUGH CARCASS REMOVAL; A TEST WITH KOKANEE SALMON IN THE INFLOW OF PORCUPINE RESERVOIR, UTAH.

Introduction

Decomposing carcasses of semelparous salmon like kokanee (Oncorhynchus nerka) provide an ideal mechanism for the contribution and spread of millions of Myxobolous cerebralis (Mc) spores. These carcasses can release their spores into stream inflows to reservoirs and lakes, thus sustaining and potentially increasing the concentration of spores and infection in a lentic system. In the Blue Mesa Reservoir system, Colorado, fishery managers successfully reduced the concentration of actinospores in water flowing out of the spawning grounds (settling ponds in this case) by simply removing kokanee salmon carcasses (Nehring and Thompson 2003). Spore densities were reduced by as much as 97% over a one-year time period. Before the carcass removal efforts, spore concentrations in pond effluents were increasing at a rate of nearly 300% per year, on average. These reductions in spore concentrations can be expected to significantly reduce the prevalence and effects of whirling disease (WD) on fishes in this aquatic system. 

Porcupine Reservoir is occupied by a population of kokanee salmon, which spawn in a small tributary, Porcupine Creek and in the East Fork Little Bear River, the principal tributary. This population was discovered to be infected with Mc in 1994, and by 1999, 100% of age-0 kokanee tested positive for Mc based on PCR analyses (Butts and Beauchamp 1999). Reductions in survival of this population in response to the high rate of infection with WD were inconclusive due to reservoir draining but are likely to be substantial. A high proportion of adult kokanee salmon demonstrated severe physical deformity, supporting the PCR results for juveniles and indicating high infection rates. The reservoir also provides a popular sport fishery for brown trout (Salmo trutta), rainbow trout (O. mykiss), cutthroat trout (O. clarki), and mountain sucker (Catostomus platyrhynchus). The salmonids have been infected in past samples to various degrees. Removal of kokanee salmon carcasses from the spawning tributary has great potential for reducing the number of spores reaching the reservoir and thus lowering the prevalence and impact of Mc on kokanee and other salmonids in the reservoir. 

The proposed efforts would involve removal of all kokanee carcasses soon after spawning and subsequent death in parallel with rigorous monitoring of key ecological variables and indices of WD prevalence and impact, pre- and post-manipulation. In addition, we propose to evaluate any ecological changes associated with carcass removal (i.e., altered nutrient budget due to the loss of nitrogen and phosphorous).

This proposed work directly addresses the priority area identified in the RFP as: Watershed/Riparian Management Practices: Documenting the effects of flow or temperature manipulation, channel modification, or changes in riparian-zone management in reducing whirling disease impacts. 

In addition, the proposed project addresses the underlined component of the priority area identified in the RFP as: Evaluation of the importance of possible vectors such as birds, anglers, or the inter-watershed transfer of water or fish, in the spread of the parasite or intensification of existing infections.

Project Objectives 

Objective 1: Kokanee salmon carcass removal from Porcupine Creek to reduce the abundance of spores released into the stream and imported into the reservoir. 
Objective 2a: Evaluation and documentation of changes in the prevalence and impacts of the disease in response to kokanee carcass removal. 
Objective 2b: Consideration of ecological impacts of loss of nutrient input derived from decomposing kokanee carcasses.

Materials and Methods

A. “Pre-manipulation” measurements (Summer 2004):

1. Age-0 kokanee salmon testing with real-time PCR, for presence and level of Mc infection.

a. 100 age-0 kokanee will be captured in August 2004, in the reservoir using tow-nets and gill nets

i. 60 kokanee will be euthanized and tested for Mc using PCR techniques
ii 40 kokanee will be reared in the laboratory and evaluated for visual deformities and behaviors associated with WD

2. Measure of lake productivity and nutrient input taken during the summer of 2004 before kokanee salmon spawning and carcass removal (monthly from May to August):

a. Total nitrogen and phosphorous
b. Chlorophyll a, index of primary productivity
c. Zooplankton density and biomass
d. Hydroacoustic estimates of kokanee salmon abundance

B. Adult kokanee spawners (Fall 2004):

a. All kokanee salmon spawners will be enumerated and abundance will be estimated based on standard Area-Under-Curve techniques
b. All carcasses will be removed and incinerated or buried offsite (minus subsample for “d”. and “f”. below). Mean weights will be calculated for each sex to help develop the nutrient budget (see c).
c. A nutrient budget for kokanee carcasses will be developed based on published nutrient analysis for salmon
d. 12 adult kokanee salmon carcasses will be filleted and the skeletons and heads processed separately by PTD to determine the number of myxospores removed from the system for each portion of the body. 
e. The PTD digest from “d” will also be analyzed by for Mc using PCR techniques.

C. “Post-manipulation” measurements (Summer 2005)

1. Repeat ALL “Pre-manipulation” measurements (Section A, 1-2 above).

Project Outcomes

The outcomes from this project will include a documented evaluation of the potential for reducing WD prevalence and impact through a reduction in spores released into a kokanee and trout reservoir, as a function of carcass removal. We will also provide an estimate of the number of spores that were prevented from entering the reservoir and consideration of ecological impacts that may result from the loss of nutrient input from carcasses that were removed.

Cache Anglers Projects

This page last updated on 11/29/2007