Author : Matthew Joel Scripter
Publisher :
ISBN 13 :
Total Pages : 304 pages
Book Rating : 4.:/5 (954 download)
Book Synopsis Distribution and Assemblage Structure of the Larval Fishes of the Middle St. Johns River, FL by : Matthew Joel Scripter
Download or read book Distribution and Assemblage Structure of the Larval Fishes of the Middle St. Johns River, FL written by Matthew Joel Scripter and published by . This book was released on 2015 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: The St. Johns River is the site of proposed water withdrawal projects to supply water to Florida's growing human population. Larval fish are directly killed by water withdrawal. Knowing where larval fish are concentrated spatially and seasonally allows planners and managers to better locate water withdrawal structures, and put in place water-management strategies to reduce the negative impact to fish populations. While limited sampling for American Shad (Alosa sapidissima) eggs and early larvae has been done in the past, no intensive year-round analysis of ichthyoplankton in the middle St. Johns River has been performed. This study implemented an intense sampling regimen in the middle St. Johns River to determine: i) the temporal and spatial patterns of larval fish abundance and distribution; ii) the effects of environmental variables on the ichthyoplankton assemblage structure and spatial distribution; and iii) the changes in American Shad (A. sapidissima) and Blueback Herring (A. aestivalis) larval abundance and distribution between 1969-1973 and 2008-2009. Six regions in the middle St. Johns River, FL, where water withdrawal structures have been proposed, were sampled using 0.5 m diameter ichthyoplankton nets towed for 10 minutes in a step-oblique manner to sample surface, mid-, and bottom water. Fixed sites, upriver and downriver from the proposed withdrawal structure, were selected for a total of 31 sampling sites. Daytime sampling was done weekly and bi-weekly from February 2008 through September 2009; once a month night sampling took place at the three central locations. A total of 8,071 eggs, 708,050 larvae, and 19,649 juveniles or adults were identified and measured. A total of 44 taxa were captured, but the ichthyoplankton assemblage was dominated by Gizzard Shad (35.4%), Threadfin Shad (34.2%), Clown Goby (7.1%), Naked Goby (7%), Black Crappie (2.9%), Bluegill (2.2%), Tidewater Silverside (2.1%), and American Shad (1.9%). Lake Monroe near Sanford, FL and the river just upriver (i.e., the SR46 location) had the highest larval collections (22% and 38.5% respectively), and were dominated by Gizzard and Threadfin Shad and the two goby species. These two sampling locations are downriver of the hypereutrophic Lake Jesup, and are the recipients of brackish water from relic saltwater deposits. Upriver sites were the most depauperate, with the narrow, muddy, sparsely-vegetated river near the State Road 50 bridge having the fewest larvae overall (5.1%), but containing >92% of all American Shad captured over the course of this project. Almost all spawning activity occurred from late winter through mid summer. Historic collections gauging American Shad reproductive output provided the opportunity to compare data from the modem 2008-2009 study and river herring data from 1953, 1965, and 1969-1973. Blueback Herring were collected over a narrower range of the SJR in 2008-2009 than in the earlier studies. American Shad spawning shifted upriver to the State Road 50 locations. This shift may be a response to annual water levels during the peak spawning season, with downstream spawning when river levels are high and upstream spawning when river levels are low. These results show that water withdrawal structures in either the river section upstream of Lake Monroe or near the State Road 50 bridge would be potentially detrimental to American Shad and Blueback Herring (NOAA Species of Concern) stocks. The remaining fish species have broad reproductive peaks throughout the sampling region, and would not be impacted as severely by water withdrawal. For all sites and species, seasonal water withdrawals in fall and winter for storage in municipal reservoirs, whenever river discharge is highest and spawning is least, may be the best strategy to minimize ichthyoplankton entrainment and negative impacts on fish communities.
