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Gareth Davies - Coarse Fish Scale Reading

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Gareth Davies - Coarse Fish Scale Reading

  1. 1. Coarse Fish Scale Reading Gareth D Davies National Fisheries Service Technical Officer 1 March 2015
  2. 2. Why age coarse fish? WFD Age structure of fish populations Core Fisheries Monitoring Programme Pre/ Post-Habitat Rehabilitation Stock Assessments Project Work Climate Change Invasive Non-Native Species
  3. 3. Structures used in age determination Pharyngeal teeth Operculum Fin rays Otolith Scales Vertebrae
  4. 4. Scale Morphs
  5. 5. Scale Proportion Hypothesis
  6. 6. Advantages of Back-Calculation 0 200 400 600 800 1000 1200 1 2 3 4 5 6 7 8 NumberoffishusedtocalculateMLA Age
  7. 7. Advantages of Back-Calculation 0 200 400 600 800 1000 1200 1 2 3 4 5 6 7 8 NumberoffishusedtocalculateMLA Age
  8. 8. 0 50 100 150 200 250 1 2 3 4 5 6 7 8 Length(mm) Age (years) Annuli oMLA Advantages of Back-Calculation
  9. 9. Growth Performance 0 100 200 300 400 500 600 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Length(mm) Age (years) Fast Very fast Average Slow Very slow R.Waverney Percentage standard growth = 110% x
  10. 10. Example 1. Salmonid Scale
  11. 11. Example 2. Coarse Scale
  12. 12. Fishery Management
  13. 13. Fishery Management 3+ ?
  14. 14. Fishery Management 1+ !
  15. 15. Case Study Chub (Leuciscus cephalus) Long lived species – 20+ years Multiple/ protracted spawing Length @ end of 1st growing season ranges from <25 mm to > 70 mm Can lead to errors in scale analysis
  16. 16. Case Study 193 mm 196 mm
  17. 17. Thank you Any questions? Twitter: @GarethDDaviesEA E-mail:Gareth.d.davies@environment-agency.gov.uk
  18. 18. Chub 365 mm 13+
  19. 19. Chub 365 mm 13+
  20. 20. Barbel 565 mm 21+

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