Early life history and population dynamics of Atlantic tomcod (Microgadus tomcod) in the Hudson River estuary, New York.
Item
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Title
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Early life history and population dynamics of Atlantic tomcod (Microgadus tomcod) in the Hudson River estuary, New York.
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Identifier
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AAI9130309
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identifier
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9130309
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Creator
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Dew, Carter Braxton.
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Contributor
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Adviser: C. Lavett Smith
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Ecology | Biology, Oceanography | Biology, Zoology
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Abstract
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The early life history of winter-spawned Atlantic tomcod (Microgadus tomcod) in the Hudson River estuary, New York, remained poorly understood after large-scale study efforts by the electric utility industry during the 1970's. The present ichthyoplankton study, conducted during winter-spring 1973-1976, describes for tomcod larvae and post-larvae (1) growth, (2) mortality, (3) biomass production, (4) location and timing of hatching, and (5) vertical and longitudinal distribution in relation to salinity and freshwater flow. Peak tomcod densities were observed most frequently at the George Washington Bridge (Milepoint 11), and the magnitude of peak densities was greatest in waters of 8.0-11.0 parts per thousand salinity. The relationship between population location and freshwater flow predicted (R{dollar}\sp2{dollar} = 0.71) that, in any given year, the tomcod population epicenter will be located seaward of the Tappan Zee Bridge (Milepoint 30), under all normal flow regimes from mid-March to early May, and near or downstream from the George Washington Bridge as spring flows approach and exceed 40,000 cfs. Cumulative degree-days explained yearly variation in tomcod growth better than time or temperature alone. In late May 1976, at a length of 53 mm, tomcod growth rate decreased by 53% as water temperatures surpassed 13{dollar}\sp\circ{dollar}C. Analysis of the changes in coefficient of variation and skewness of length-frequency distributions suggested a continuous trailing behind of slower-growing fish after hatching. Size-selective mortality apparently thinned the ranks of these smaller fish during May 1976. Initial standing crop in early March was estimated as 1.8 billion tomcod larvae in 1975 and 3.0 billion in 1976. During May 1976, while growing from 25 to 53 mm, tomcod mortality increased by 27%, and the population died at a rate of 6.3% per day to a level of approximately 34 million fish by late May. To explain these patterns in length-frequency and mortality data, I present the hypothesis that Atlantic tomcod, which are well-suited as prey on the basis of their spatiotemporal availability and their growth characteristics, may serve as primary forage fish for yearling striped bass during spring, prior to the availability of other forage fishes of suitable size.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
