The challenges of understanding the biogeography of commercially important crustacean species of the Southwestern Indian Ocean — Separating what we know from what we think we know.

Abstract

Demersal trawl fisheries play an important role in providing income and protein to the people of the Southwestern Indian Ocean (SWIO). These fisheries are very destructive to the habitats in which they operate and have an impact on the associated biodiversity. Three crustacean species, knife prawn (<i>Haliporoides triarthrus</i>), African langoustine (<i>Metanephrops mozambicus</i>) and pink geryon crab (<i>Chaceon macphersoni</i>) are the most important to these fisheries and their management is crucial to securing sustainable fisheries. These species have transboundary distributions so understanding their biogeography is important in formulating effective management strategies. This understanding is hampered through inadequate species identifications despite the occurrence of many research surveys and the retention of these species for trade. Species identities have been allocated based on outdated/inappropriate taxonomic and distribution information. The lack of voucher specimens from research surveys makes it impossible to determine if these species were correctly identified. Despite these three species having important commercial value to the region, little known about their reproduction strategies. This combined with limited information on the availability of suitable habitats thwarts understanding their distribution patterns. Previous researchers have proposed the existence of a limited recruitment area for knife prawns that seed the remaining habitat in the region, but this theory has, to some extent, been refuted through genetic testing that discovered isolated subpopulations in the region. The African langoustine showed a similar distribution of subpopulations, which is not surprising given their short larval phases and subsequent settlement very close to where the eggs hatched. The reproductive biology of pink geryon crabs is also unknown and no genetic research has been conducted on them. In order to maximise the sustainability of the demersal trawl fisheries, it is imperative that comprehensive research be undertaken to determine conclusive distributions of these populations to inform their transboundary management in the region.