Turkish Journal of Fisheries and Aquatic Sciences
2013, Vol 13, Num, 2 (Pages: 261-270)
Testing the Sensitivity of the Length-Converted Catch Method Using the Bigeye Tuna Thunnus obesus (Scombridae) Population Parameters
Chia-Lung Shih 1
1 Institute of Oceanography, College of Science, National Taiwan University, Institute of Oceanography, National Taiwan University, 1, Section 4, Roosevelt Road, Daan District, Taipei, Taiwan
DOI :
10.4194/1303-2712-v13_2_08
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The present study investigates how sample size, length interval size, recruitment variation, and mortality over time
influence total mortality, which is estimated by applying the length-converted catch method to the bigeye tuna (Thunnus
obesus) population. Given the assumption of fish dynamics under an equilibrium state, an increasing sample size and
decreasing length interval size can raise the accuracy of total mortality estimates, with a sample size of 3000 individuals and
length class interval of 5 cm generally producing the most accurate estimates. When fish dynamics follow a non-equilibrium
state, randomly varied recruitment does not affect the estimation of total mortality. However, recruitment that varies with
increasing or decreasing trends would affect total mortality remarkably. Therefore, total mortality that varies by time
influences estimated total mortality, and in this situation, fish stocks that undergo stable total mortality for four successive
years could produce an accurate total mortality figure. Finally, we suggest that the non-equilibrium state of fish dynamics
should be considered before applying the length-converted catch method to estimate Z.
Keywords :
Bigeye Tuna, length-converted catch method, total mortality, sample size, length class