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Methods of Collecting Blue Catfish Otoliths: An Analysis of Growth and Mortality Rates in Tidal River Systems

This study presents the methods used to collect blue catfish otoliths in four tidal river systems from 2001 to 2014. Sampling strategies, growth modeling, and mortality estimates are discussed, revealing declines in growth associated with increases in density. Data from shocking the James tributary show high abundance. The von Bertalanffy growth model and Mann-Whitney rank sum test were employed for analysis.

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Methods of Collecting Blue Catfish Otoliths: An Analysis of Growth and Mortality Rates in Tidal River Systems

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  1. Methods: Collection of Blue Catfish Otoliths Bob Greenlee Department of Game and Inland Fisheries bob.greenlee@dgif.virginia.gov

  2. Stations in Four Tidal River Systems 2001 - 2014

  3. Sampling Strategy • Summer Low Frequency (15 pps) Boat Electrofishing • Fixed station design • EF boat and Pick-up boat • Standard run length • Two netters on each boat • Extra netters to assist in landing of unusually large fish (~> 20 Kg) • Otoliths Collected for Age & Growth beginning in 2002 • 2002 – 2004 otolith subsampling based on N per cm-group • High variability in individual growth => age-length key of limited value • After 2004, stratified random subsampling

  4. Modeling Growth – Mattaponi River Mean Total Length-at-Age w/ 95% C.I. 2006 & 2008 L(Age) = 200.678 + (42.631 * Age) r2 = 0.98 von Bertalanffy (Linf = 1,438 mm; K = 0.048; t0 = -2.305 yrs, r2 = 0.99)

  5. Growth Rates – Differences Among Rivers (mean total length-at-age w/ 95% Confidence Intervals)

  6. Growth – Declines in Three of Four Rivers (mean total length-at-age and 95% Confidence Intervals) Mann-Whitney rank sum test for each age sampled

  7. Declines in Growth Associated With Increases in Density (Mean Total Length Age-10 and CPUE)

  8. Catch Curve-Based Total Annual Mortality Estimates

  9. Variable Recruitment

  10. Sample From Tributary of James Play “Shocking The James” video now

  11. Unbelievably abundant– One of two tanks collected during 10 minutes of electrofishing on the Rappahannock River

  12. Sample From Tributary of James

  13. 2004 ~ 37.6 kg

  14. Sample From Tributary of James

  15. Sample From Tributary of James

  16. Sample From Tributary of James

  17. Sample From Tributary of James

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