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<p>Iranian purse-seine operations in the Oman Sea and the western Indian Ocean have declined due to rising operational costs, reduced fishing efficiency, and a lack of data-driven strategies for optimizing fishing effort. Understanding how environmental variability affects catch rates of dominant tuna species is essential for sustainable management. This study quantified the oceanographic predictors of catch-per-unit-effort (CPUE, tons per set) for longtail tuna (<i>Thunnus tonggol</i>, LOT) and skipjack tuna (<i>Katsuwonus pelamis</i>, SKJ) using zero-adjusted regression models to account for the high frequency of zero-catch sets. Data from five Iranian purse seiners (2015–2019) were combined with satellite-derived predictors, including sea surface temperature (SST), chlorophyll-<i>a</i> (Chl-<i>a</i>), salinity, particulate organic carbon (POC), photosynthetically active radiation (PAR), wind forcing, bathymetry, and fishing location. Four zero-adjusted distributions (ZAGA, ZAIG, ZAWEI, ZALNO) were tested, with ZAGA selected for LOT and ZAIG for SKJ based on AIC/BIC criteria. Results showed that LOT CPUE peaked in warm (~ 28&#xa0;°C), low-salinity (&lt; 34&#xa0;psu), low-chlorophyll waters (&lt; 5&#xa0;mg. m<sup>−3</sup>), particularly in the deeper northern grounds (&gt; ~ 4500&#xa0;m), where PAR levels were high (~ 60 E. m<sup>−2</sup>&#xa0;day<sup>−1</sup>) and wind forcing was moderate. In contrast, SKJ CPUE increased under slightly warmer SSTs (~ 30&#xa0;°C), higher chlorophyll-<i>a</i> concentration (&gt; 10&#xa0;mg. m⁻<sup>3</sup>), stronger wind conditions, and greater bathymetric depth, while consistently declining toward the eastern sector of the fishing area. Zero-inflation components revealed species-specific probabilities of zero-catch events along environmental gradients, highlighting distinct ecological niches. From a fisheries management perspective, these findings provide a quantitative basis for dynamic effort allocation, spatial and seasonal planning, and risk-informed forecasting. Integrating species-specific environmental preferences enables operators to optimize fishing effort, reduce inefficiency, protect sensitive habitats, and support sustainable exploitation of tuna in the western Indian Ocean.</p>

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A zero-adjusted regression approach to modeling catch variability of skipjack and longtail tuna in the Iranian industrial purse-seine fishery

  • 期刊论文

  • 发表日期：

    2026年5月9日

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  • Moslem Daliri,
  • Hossein Zamani,
  • Arezoo Vahabnezhad,
  • Elyas Soleimani,
  • Mohammad Mehdi Saber

摘要

Iranian purse-seine operations in the Oman Sea and the western Indian Ocean have declined due to rising operational costs, reduced fishing efficiency, and a lack of data-driven strategies for optimizing fishing effort. Understanding how environmental variability affects catch rates of dominant tuna species is essential for sustainable management. This study quantified the oceanographic predictors of catch-per-unit-effort (CPUE, tons per set) for longtail tuna (Thunnus tonggol, LOT) and skipjack tuna (Katsuwonus pelamis, SKJ) using zero-adjusted regression models to account for the high frequency of zero-catch sets. Data from five Iranian purse seiners (2015–2019) were combined with satellite-derived predictors, including sea surface temperature (SST), chlorophyll-a (Chl-a), salinity, particulate organic carbon (POC), photosynthetically active radiation (PAR), wind forcing, bathymetry, and fishing location. Four zero-adjusted distributions (ZAGA, ZAIG, ZAWEI, ZALNO) were tested, with ZAGA selected for LOT and ZAIG for SKJ based on AIC/BIC criteria. Results showed that LOT CPUE peaked in warm (~ 28 °C), low-salinity (< 34 psu), low-chlorophyll waters (< 5 mg. m−3), particularly in the deeper northern grounds (> ~ 4500 m), where PAR levels were high (~ 60 E. m−2 day−1) and wind forcing was moderate. In contrast, SKJ CPUE increased under slightly warmer SSTs (~ 30 °C), higher chlorophyll-a concentration (> 10 mg. m⁻3), stronger wind conditions, and greater bathymetric depth, while consistently declining toward the eastern sector of the fishing area. Zero-inflation components revealed species-specific probabilities of zero-catch events along environmental gradients, highlighting distinct ecological niches. From a fisheries management perspective, these findings provide a quantitative basis for dynamic effort allocation, spatial and seasonal planning, and risk-informed forecasting. Integrating species-specific environmental preferences enables operators to optimize fishing effort, reduce inefficiency, protect sensitive habitats, and support sustainable exploitation of tuna in the western Indian Ocean.