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<p>Mosquito net trawling in seagrass meadows is a widespread but illegal fishing practice in southwestern Madagascar, with poorly documented ecological impacts. This study assessed fish assemblages in trawl catches across two warm seasons (2016–2018) using both morphological and molecular-based identification, focusing on species composition, ontogenetic structure, and spatial and temporal variation in fish assemblages. A total of 201 species from 50 families were recorded across 72 hauls, with an average catch density of 2465 ± 2166 individuals ha⁻<sup>1</sup> and a mean size of 4.7 ± 2.8 cm. Juveniles comprised 51.6% of total individuals, with an average of 58 ± 26 juvenile species per sample and a density of 1193 ± 1040 individuals ha⁻<sup>1</sup>. The foremost dominant juvenile species was <i>Siganus sutor</i> (43% of juvenile catch, with a mean body size of 3.3 ± 1.5&#xa0;cm), followed by <i>Stethojulis strigiventer</i>, <i>Lethrinus borbonicus</i>, and <i>Fistularia commersonii</i>. Moreover, trawls captured juveniles of two threatened species—<i>Lethrinus mahsena</i> (endangered, 2% of juvenile catch) and <i>Hippocampus kuda</i> (vulnerable, less than 0.1%). While juvenile assemblages showed no significant interannual variation, spatial differences among substrate types were significant with ANOSIM <i>R</i> = 0.47. These findings confirm that mosquito net trawling contributes to high juvenile mortality, including for long-lived and conservation-priority species. Protecting seagrass meadows as nursery habitats is essential to ensure sustainable recruitment and preserve the fish diversity and production. Effective small-scale fisheries management will require urgent restrictions on destructive gear and expanded community-based conservation initiatives.</p>

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Taxonomic and ontogenetic composition of fishes in mosquito net trawls catches in Madagascar’s seagrass meadows

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • H. Jaonalison,
  • D. Ponton,
  • M. Léopold,
  • R. L. Raharinaivo,
  • A. L. D. Nomenisoa,
  • B. Frédérich,
  • J. D. Durand,
  • J. Mahafina

摘要

Mosquito net trawling in seagrass meadows is a widespread but illegal fishing practice in southwestern Madagascar, with poorly documented ecological impacts. This study assessed fish assemblages in trawl catches across two warm seasons (2016–2018) using both morphological and molecular-based identification, focusing on species composition, ontogenetic structure, and spatial and temporal variation in fish assemblages. A total of 201 species from 50 families were recorded across 72 hauls, with an average catch density of 2465 ± 2166 individuals ha⁻1 and a mean size of 4.7 ± 2.8 cm. Juveniles comprised 51.6% of total individuals, with an average of 58 ± 26 juvenile species per sample and a density of 1193 ± 1040 individuals ha⁻1. The foremost dominant juvenile species was Siganus sutor (43% of juvenile catch, with a mean body size of 3.3 ± 1.5 cm), followed by Stethojulis strigiventer, Lethrinus borbonicus, and Fistularia commersonii. Moreover, trawls captured juveniles of two threatened species—Lethrinus mahsena (endangered, 2% of juvenile catch) and Hippocampus kuda (vulnerable, less than 0.1%). While juvenile assemblages showed no significant interannual variation, spatial differences among substrate types were significant with ANOSIM R = 0.47. These findings confirm that mosquito net trawling contributes to high juvenile mortality, including for long-lived and conservation-priority species. Protecting seagrass meadows as nursery habitats is essential to ensure sustainable recruitment and preserve the fish diversity and production. Effective small-scale fisheries management will require urgent restrictions on destructive gear and expanded community-based conservation initiatives.