Preliminary application of an age-structured assessment model to swordfish (Xiphias gladius) in the Indian Ocean

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Preliminary application of an age-structured
assessment model to swordfish (Xiphias gladius)
in the Indian Ocean

• Sheng-Ping Wang, Ying-Ru Chen, Mark Maunder and
  Tom Nishida

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Data used
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Biological information
Parameter Females Males
Asymptotic size, L8 (cm) 323.4 260.47
Growth parameter, K (year-1) 0.08148 0.1096
Age-at-zero-length, t0 (year) -3.413 -3.3808
Length-weight, A 1.839x10-6 1.839x10-6
Length-weight, B 3.3921 3.3921
Maturity slope, rm 0.0953 -
Length-at-50-maturity, Lm (cm) 170.4 -
Maximum age, ? (year) 15 15
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Assessment model

• The age-structured assessment model conducted by
  Wang et al. (2005) and Wang et al. (2007) for
  swordfish in the Pacific Ocean.
• Owing to the absence of sex-specific information,
  we attempt to modify the model for applying to
  the swordfish in the Indian.

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(No Transcript)
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Assessment model

• Selectivity
• Logistic curve
• Japanese, Australian and fresh tuna longline
  fleets
• Dome-shaped curve
• Other fleets

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Assessment model

• Estimated parameters

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Assessment model

• Pre-specified parameters
• Natural mortality (M) 0.2
• based on the equation of Pauly (1980))
• Steepness (h) 0.9
• based on the information of SWO in the Atlantic
• Variation in recruitment (??) 0.4
• based on the information of SWO in the Atlantic

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Sensitivity analyses

• The CPUEs of Japanese longline fleets were
  separated into two periods for examining the
  influences of changes in catchability on the
  estimations of the model.
• JPLL-NW, JPLL-NE and JPLL-SW
• 1980-1992 and 1993-2007
• JPLL-SE
• 1980-1988 and 1989-2007

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Sensitivity analyses

• The CPUEs of Taiwanese longline fleets in the
  southern subareas were also separated into two
  periods
• TWLL-SW
• 1980-1992 and 1993-2007
• TWLL-SE
• 1980-1997 and 1998-2007

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Sensitivity analyses

• The model estimations were examined based on the
  assumption that selectivities were assumed to be
  logistic curves for all longline fisheries and a
  dome-shaped curve for the gillnet fishery.

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ResultsFits to length frequency data
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ResultsFits to CPUE
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ResultsEstimated selectivity
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ResultsBase-case assessment

• Note
• F is the exploitation rate (defined as the ratio
  of total catch to exploitable biomass)

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Results

• Sensitivity analyses