Browsing by Author "Greenlee, Robert S."

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    Environmental and anthropogenic influences on spatiotemporal dynamics of Alosa in Chesapeake Bay tributaries
    Bi, Rujia; Jiao, Yan; Weaver, L. Alan; Greenlee, Robert S.; McClair, Genine; Kipp, Jeff; Wilke, Kate; Haas, Carola A.; Smith, Eric P. (2021-06)
    American Shad (Alosa sapidissima), Hickory Shad (A. mediocris), and river herrings (Alewife A. pseudoharengus and Blueback Herring A. aestivalis) are anadromous pelagic fishes, which as adults spend most of the annual cycle at sea, but enter the coastal rivers in spring to spawn. Once as one of the most valuable fisheries along the Atlantic coast, Alosa populations have declined in recent decades and current populations are at historic lows. Various management actions have been conducted to restore the populations, and stocks in different river systems display different demographic trends. Demonstration of synthetic diagnostics on the factors impacting these populations is important to better conserve this species group. We developed a Bayesian hierarchical spatiotemporal model to identify the population trends of these species among rivers in the Chesapeake Bay based on results of surveys conducted by the Virginia Department of Game and Inland Fisheries and Maryland Department of Natural Resources and to identify environmental and anthropogenic factors influencing their distribution and abundance. The hierarchical model structure helped to diagnose river-specific population trends and impacts of surrounding factors, and decrease uncertainties in rivers with less samples available. The results demonstrate river-specific heterogeneity of spatiotemporal dynamics of these species and indicate river-specific impacts of multiple factors, including water temperature, river flow, chlorophyll a concentration, and total phosphorus concentration, on their population dynamics. Atlantic Multidecadal Oscillation and Gulf Stream meanders displayed significant influence on the inter-annual trends of Alosa species in rivers with more data available. The results would help to develop river- and species-specific management strategies to recover these species.
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    Growth Dynamics of Invasive Blue Catfish in Four Subestuaries of the Chesapeake Bay, USA
    Hilling, Corbin D.; Jiao, Yan; Bunch, Aaron J.; Greenlee, Robert S.; Schmitt, Joseph D.; Orth, Donald J. (Wiley, 2021-01-25)
    Biological invasions occur as a multistage process, and life history traits can change during the invasion process. Blue Catfish Ictalurus furcatus were introduced in three Virginia tidal tributaries of the Chesapeake Bay during the 1970s and 1980s but have expanded their range to almost all large tributaries of the bay. An understanding of the species’ growth is important for evaluating impacts on other resident species and population dynamics. Virginia Blue Catfish exhibited wide variability in individual growth, prompting the testing of six alternative hypotheses (similar growth across space and time as well as variable growth by river system, sampling year, cohort, and both river system and time) on its growth dynamics within four Virginia tidal rivers (James, Mattaponi, Pamunkey, and Rappahannock rivers) over the period 2002–2016. Blue Catfish growth in Virginia was best explained by a model considering cohort and river as random effects. The Rappahannock River was the first in Virginia to receive Blue Catfish; growth was slower in this river than in the other systems during the observation period. Growth rates declined for all ages examined in the James, Mattaponi, and Pamunkey rivers but only for ages 7, 10, and 13 in the Rappahannock River. We did not generally observe synchronous growth responses among rivers, supporting that finer-scale factors may be influencing growth rates. This work suggests that the growth rates of nonnative species may decline over time and that comparisons of nonnative growth may be most useful when variability over space and time is considered.