Graduate Thesis Or Dissertation
 

Selected life history aspects of American shad (Alosa sapidissima) and predation on young-of-the-year shad in Lake Umatilla of the Columbia River

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  • Selected life history aspects of American shad, Alosa sapidissima, collected in Lake Umatilla of the Columbia River during 1980 and 1981 were examined and compared to other shad populations. Mean fork lengths of adult shad captured in 1981 were 405-, 415- and 423-mm for age III, IV and V males; 425-, 444- and 457-mm for age III, IV and V females. The mean age at maturity was determined to be 3.2 years for males and 3.5 years for females while the rate of repeat spawning was 36% and 45% for males and females, respectively. Four-year-old shad accounted for 58.5% of the spawning adults in the two years. Absolute fecundity ranged from 97,168 to 284,240 eggs with a mean of 193,074 eggs per female. Young-of-the-year shad were more abundant in 1980 than in 1981. In both years, the tail-race zone was the most important spawning area and the island zone the most important rearing area for young-of-the-year shad in the reservoir. Growth of young shad in Lake Umatilla was similar in all sampled macrohabitats and appears to be dependent on year class strength, water temperature and water flow. Out-migrating young-of-the-yetar shad passing through John Day Dam were significantly largjer than young-of-the-year shad in reservoir habitats indicating size, as well as temperature, influences the timing of downstream migration. Predation on young shad by resident predator fish species was variable and appeared to be dependent on the Abundance of young-of-the-year shad.
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