Patterns in the occurrence of elasmobranchs in demersal trawl catches in the Western Indian Ocean
Everett, B.I.; Fennessy, S.T.; Okondo, J.; Kishe, M.; Mutombene, R.; Bé, J.J. (2025). Patterns in the occurrence of elasmobranchs in demersal trawl catches in the Western Indian Ocean. Western Indian Ocean J. Mar. Sci. Spec. Issue 1: 67-86. https://dx.doi.org/10.4314/ wiojms.si2025.1.5
In: Western Indian Ocean Journal of Marine Science. Western Indian Ocean Marine Science Association (WIOMSA): Zanzibar. ISSN 0856-860X, meer
In the Western Indian Ocean (WIO) elasmobranchs play important roles in ecosystems as apex and mesopredators and contribute high socio-economic value to coastal communities. Their diversity in the WIO is amongst the highest globally yet few studies have assessed the occur- rence of various species in catches. Demersal trawl catches from Kenya, Tanzania, Mozambique, Madagascar and South Africa (East Coast) were analysed using Generalised Linear Models to esti- mate the probabilities of non-zero catches of sharks and batoids. The data were further subjected to non-metric multidimensional scaling to establish clusters of various communities and to sim- ilarity percentage analyses to determine the dominant taxa. The probability of catching sharks and batoids in trawl nets was high. While communities were not highly separated within factors, it was depth that showed the greatest influence on community structures. The genus Squalus dom- inated the shark catches as depth increased while species dominance of batoids changed from stingrays (Dasyatidae) to guitarfishes (Rhinobatidae) and to skates (Rajidae) as depth increased. This study underlines the need for improved species identification of elasmobranch catches and for marine protected areas on soft sediment habitats to protect these important species.
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