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

2026

Article référencé dans le Web of Science WOS:001811925200002

Jaonalison H., Ponton Dominique, Léopold Marc, Raharinaivo R. L., Nomenisoa A. L. D., Frédérich B., Durand Jean-Dominique, Mahafina J.

Environmental Biology of Fishes, 2026, 109 (3), p. 102 [16 p.] ISSN 0378-1909

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.

Limnologie biologique / Océanographie biologique [034] ; Ressources halieutiques [040] ; Etudes, transformation, conservation du milieu naturel [082]

MADAGASCAR

Fonds IRD [F B010097522]

fdi:010097522