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Training course in fish stock assessment and fisheries management

Training course in fish stock assessment and fisheries management. National Institute of Oceanography and Fisheries Fish Population Dynamics Lab 10-14 November, 2013 ns. Age and Growth of Fish Prof. Dr. Sahar F. Mehanna Head of Fish Population Dynamics Lab.

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Training course in fish stock assessment and fisheries management

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  1. Training course in fish stock assessment and fisheries management National Institute of Oceanography and Fisheries Fish Population Dynamics Lab 10-14 November, 2013ns

  2. Age and Growth of FishProf. Dr. Sahar F. MehannaHead of Fish Population Dynamics Lab

  3. Different metrics of fish growth Length easy, intuitive, history in angling, length rarely shrinks But, lots of change in biomass not related in length Wet Weight used in large calculations (population biomass), metric used in production But, can take more time in field (rocking boat or wind and balance don't mix) Dry Weight accurate description of individual's current state But, time intensive and must kill fish

  4. How to estimate growth? • Length Frequency Analysis • Recaptures of individually marked fish • Back calculation from calcified structures Caught

  5. Length Frequency Analysis (Adv. & Disadv.)

  6. METHODS – LFDA ELEFAN

  7. Recapture of marked and tagged individuals (Adv. & Disadv.) You Come back a year later.... Population is 10000 fish ...at best maybe 60 survived.... You catch and tag 100 fish, good effort, but ...maybe only 10% lost their tags .... so there are 54 tags in 10,000 fish

  8. www.dfg.ca.gov/.../FishTagDescriptions.htm www.daybreakfishing.com/TaggingFish.html www.dfg.ca.gov/.../FishTagDescriptions.htm www.dfg.ca.gov/.../FishTagDescriptions.htm

  9. Back calculations from hard structures 1

  10. Von Bertalanffy Growth Equation Lt = length at time 't' Lt = L∞ (1- e -k (t -to)) L∞= asymptotic length

  11. How to estimate growth parameters? Chapman (1961): Lt+1 – Lt = L∞ (1 - e-K) – (1 - e-K) Lt Ford (1933)-Walford (1946) plot Lt+1 = L (1 - e-K) + e-K Lt Gulland&Holt (1959): Lt+1 – Lt = k * L∞- k [(Lt+1 + Lt)/2] • to= t +1/K Ln (L - Lt / L).

  12. L∞ = 23.03 cm K = 0.58 / year

  13. Exercise on excell

  14. SEASONAL & NON-SEASONAL GROWTH • Many fish do not grow continuously but follow a seasonal pattern of growth • The Von Bertalanffy growth equation can accommodate this by expanding to have 2 new parameters . • These are C=amplitude of growth and Wp = ‘winter point’ where growth is slowest • Seasonal growth equation is therefore: Lt = L∞ {1 – exp – [ K (t – t0) + S(t) – S(t0)]} where S(t) = (CK/2π ) Sin π (t – ts) and S(t0) = (CK/2π ) Sin π (t0 - ts) and ts=WP+0.5

  15. FiSAT Software practical training

  16. LESSONs? • Pay attention to the possibility of seasonal growth • Look at temperature variations throughout the year – if large variations, then seasonal growth might be important • However, in the region, many fish migrate to avoid high summer temperatures – these need to be measured where the fish are! • Most importantly, look at the data – don’t simply trust the program to give the ‘right’ answer!! • Collect additional samples if unsure

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