Date of Award:

1983

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

John Neuhold

Abstract

Several aspects of kokanee (Onchorhynchus nerka) ecology were studied in the fluctuating, 80ha Porcupine Reservoir, Utah in order to determine optimum management strategies. In 1981, escapement was enumerated and estimates of egg deposition were made . An estimate of the resulting fry recruitment was also attempted and was successful up to the arrival of spring runoff. In 1982, escapement was enumerated and estimates of egg deposition were made, with subsequent estimates of egg deposition and percent survival to the advanced eyed stage. Age and growth rates were determined and survival rates estimated.

Escapement for 1981 and 1982 was 5,463 and 7,113 kokanee, respectively, depositing an estimated 1,843,955 and 2,393,757 eggs, respectively._ The estimated fry recruitment to the reservoir for the 1981 spawning run was 57,000 fish up to the arrival of spring runoff and appeared to be only a fraction of the total number of fry in the river. From the 1982 spawning run, an estimated 2,265,507 eggs were actually deposited, of these an estimated 64.2% or 1,457,599 eggs were fertilized and survived to the advanced eyed stage. Kokanee growth rates were good. Fish mature and spawn at 34 months of age at an average total length of 364mm. Twelve month old kokanee average 124mm and 24 month old fish 257mm. The kokanee population continues to grow but at a decreasing rate and survival rates are declining. For every kokanee that estimated 8.2 progeny survived to spawn spawned in 1972, an in 1975 and for every spawning kokanee in 1979 an estimated 3.0 progeny survived to spawn in 1982.

The kokanee is presently underharvested and appears to be at or near the carrying capacity of the reservoir. In order to acheive an optimum sustainable yield the spawning population should be reduced and maintained at approximately 2,000 fish ( 1,000 redds).

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