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<p> Probabilistic biological modeling on structural bio-theory parallel to stock population dynamics provides critical insights that may inform policy development in protecting our wild populations. Here, we investigate the growth and population dynamics, sustainability, and fishing pressure in the Southern Philippines. The analysis of length-frequency distribution, obtained through direct morphometric measurement, showed that the catch was dominated by small, immature fish, with only 7–23% sexually mature. Most individuals measured 22.00–27.00 centimeter forklength (cm FL), indicating that fishing gears primarily capture juveniles before reproduction, providing clear evidence of growth overfishing. The length at first maturity (<i>Lm₅₀</i> = 37.18 cm FL), determined through logistic regression, further highlighted the disparity between size at capture and size at maturity, confirming harvest occurs well before reproductive age and may hamper stock replenishment. The length-weight relationship, derived from linear regression of log-transformed data, indicated positive allometric growth (<i>b &gt;3.00</i>), reflecting improving body condition but also losses in potential biomass yield due to premature capture. Growth parameters estimated using the ELEFAN I method in FiSAT II (<i>L∞</i>&#xa0;= 69.04 cm FL, <i>K</i> = 0.78 yr⁻¹) suggested moderate to rapid growth and potential resilience if properly managed. Mortality estimates from Pauly’s equation and the length-converted catch curve of <i>Euthynnus affinis</i> revealed high total mortality (<i>Z </i>= 1.50 yr⁻¹), with steep declines in cohort abundance pointing to recruitment overfishing. Supporting results from the length-structured Virtual Population Analysis showed disproportionate fishing mortality on smaller length classes, reducing survivorship before reproductive maturity and providing additional evidence of growth overfishing. While the exploitation rate (<i>E</i> = 0.20) implied sustainability, the fishing mortality to natural mortality ratio (<i>F/M</i> = 0.74) indicated that fishing accounted for nearly three-quarters of total mortality. Gear selectivity analysis using the LB-SPR model identified a length at 50% selectivity (<i>SL₅₀ </i>= 23.09 cm FL), 14 cm FL below the maturity size, directly linking gear efficiency to juvenile exploitation and underscoring the need for technical interventions. Finally, the Spawning Potential Ratio (<i>SPR</i> = 30%), estimated with the LB-SPR model, indicated significant reproductive depletion below the 40% maximum sustainable yield benchmark, confirming concurrent risks of recruitment and growth overfishing. Although not collapsed, the stock may insinuate possible depletion, signaling that current fishing practices are unsustainable long-term and emphasizing the urgency of management measures to ensure future viability.</p>

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​​Interplay of Integrative Population Structure in Eastern Little Tuna Suggests Reliance on Smaller, Immature Individuals That May Influence the Stock’s Future Growth Potential

  • 期刊论文

  • 发表日期：

    2025年11月25日

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  • John Christian D. Entia,
  • Niña Mae B. Nabre,
  • Red Arthur Duke A. Amoncio

摘要

Probabilistic biological modeling on structural bio-theory parallel to stock population dynamics provides critical insights that may inform policy development in protecting our wild populations. Here, we investigate the growth and population dynamics, sustainability, and fishing pressure in the Southern Philippines. The analysis of length-frequency distribution, obtained through direct morphometric measurement, showed that the catch was dominated by small, immature fish, with only 7–23% sexually mature. Most individuals measured 22.00–27.00 centimeter forklength (cm FL), indicating that fishing gears primarily capture juveniles before reproduction, providing clear evidence of growth overfishing. The length at first maturity (Lm₅₀ = 37.18 cm FL), determined through logistic regression, further highlighted the disparity between size at capture and size at maturity, confirming harvest occurs well before reproductive age and may hamper stock replenishment. The length-weight relationship, derived from linear regression of log-transformed data, indicated positive allometric growth (b >3.00), reflecting improving body condition but also losses in potential biomass yield due to premature capture. Growth parameters estimated using the ELEFAN I method in FiSAT II (L∞ = 69.04 cm FL, K = 0.78 yr⁻¹) suggested moderate to rapid growth and potential resilience if properly managed. Mortality estimates from Pauly’s equation and the length-converted catch curve of Euthynnus affinis revealed high total mortality (Z = 1.50 yr⁻¹), with steep declines in cohort abundance pointing to recruitment overfishing. Supporting results from the length-structured Virtual Population Analysis showed disproportionate fishing mortality on smaller length classes, reducing survivorship before reproductive maturity and providing additional evidence of growth overfishing. While the exploitation rate (E = 0.20) implied sustainability, the fishing mortality to natural mortality ratio (F/M = 0.74) indicated that fishing accounted for nearly three-quarters of total mortality. Gear selectivity analysis using the LB-SPR model identified a length at 50% selectivity (SL₅₀ = 23.09 cm FL), 14 cm FL below the maturity size, directly linking gear efficiency to juvenile exploitation and underscoring the need for technical interventions. Finally, the Spawning Potential Ratio (SPR = 30%), estimated with the LB-SPR model, indicated significant reproductive depletion below the 40% maximum sustainable yield benchmark, confirming concurrent risks of recruitment and growth overfishing. Although not collapsed, the stock may insinuate possible depletion, signaling that current fishing practices are unsustainable long-term and emphasizing the urgency of management measures to ensure future viability.