61 research outputs found

    Managed Metapopulations: Do Salmon Hatchery ‘Sources’ Lead to In-River ‘Sinks’ in Conservation?

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    Maintaining viable populations of salmon in the wild is a primary goal for many conservation and recovery programs. The frequency and extent of connectivity among natal sources defines the demographic and genetic boundaries of a population. Yet, the role that immigration of hatchery-produced adults may play in altering population dynamics and fitness of natural populations remains largely unquantified. Quantifying, whether natural populations are self-sustaining, functions as sources (population growth rate in the absence of dispersal, λ>1), or as sinks (λ<1) can be obscured by an inability to identify immigrants. In this study we use a new isotopic approach to demonstrate that a natural spawning population of Chinook salmon, (Oncorhynchus tshawytscha) considered relatively healthy, represents a sink population when the contribution of hatchery immigrants is taken into consideration. We retrieved sulfur isotopes (34S/32S, referred to as δ34S) in adult Chinook salmon otoliths (ear bones) that were deposited during their early life history as juveniles to determine whether individuals were produced in hatcheries or naturally in rivers. Our results show that only 10.3% (CI = 5.5 to 18.1%) of adults spawning in the river had otolith δ34S values less than 8.5‰, which is characteristic of naturally produced salmon. When considering the total return to the watershed (total fish in river and hatchery), we estimate that 90.7 to 99.3% (CI) of returning adults were produced in a hatchery (best estimate = 95.9%). When population growth rate of the natural population was modeled to account for the contribution of previously unidentified hatchery immigrants, we found that hatchery-produced fish caused the false appearance of positive population growth. These findings highlight the potential dangers in ignoring source-sink dynamics in recovering natural populations, and question the extent to which declines in natural salmon populations are undetected by monitoring programs

    Endoscopic View of the Ethmoid Strut

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    THE RELATIONSHIP BETWEEN CARBON, SULFUR, AND PYRITIC IRON IN THE AMJHORE DEPOSIT, BIHAR, INDIA

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    Low C/S ratios have been generally observed in pyritiferous black shales of the lower Paleozoic and late Proterozoic (Berner and Raiswell, 1983). In addition to factors such as high rates of bacterial sulfate reduction which might have existed during these early periods due to the low oxygen content of ocean water, availability and quality of organic matter, or lack of bioturbation and availability of reactive iron, low C/S ratios may also reflect low sedimentation rates. Three distinct situations within a single vertical stratigraphic column in the mid-Proterozoic Amjhore pyrite deposit reflect the effect of anoxic levels and sedimentation rates on pyrite formation. In the first (lower shale with a mean C/S ratio of 2.03), pyrite formation was diagenetic, whereas in the second (massive pyrite ore with a negligible carbon content) and the third (upper shale with a low C/S ratio of 0.27), pyrite formation took place under euxinic conditions. In environments where anoxic levels are high and the sedimentation rate low, low mean C/S ratios may occur. In such environments variations in total sulfate reduction per unit column of sediment deposited (resulting from variation in sedimentation rates or anoxic levels) are reflected in the slope of the carbon-sulfur plot by a greater slope. This may also result in lower intercepts on the sulfur axis. For upper shale samples the carbon-sulfur regression line has a very high slope of 3.73 and a low intercept on the sulfur axis of 0.21. Consistency of anoxic levels during deposition of upper shales is, however, indicated by the low standard deviation (0.051) of C/S data and a dominant control of the sedimentation rate on the sulfur content of the sediments is inferred. Sulfur isotope data on pyrite samples indicate an environment closed to SO4(-2) which was initially open to H2S (or HS-) and later during deposition of upper shale became closed to it due to a limited supply of reactive iron. This confirms that the pyrite bed and upper shales were laid down in a restricted environment and substantiates the interpretation of the carbon-sulfur relationships observed in them
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