Temporal stability of abundant reef fish assemblages across monsoon seasons at Frégate Island, Seychelles

Abstract

Reef fishes are a cornerstone of Seychelles’ Blue Economy, but their abundance is not static in space and time. To test whether monsoon season and the associated ocean temperature change drive variations in abundant reef fish assemblages, Baited Remote Underwater Video Systems (BRUVS) were used around Frégate Island, Seychelles. Overall, 30 BRUVS were deployed at 10 sites shortly after both the North-West (NW) and South-East (SE) seasonal monsoon periods in 2019 and again after the South-East monsoon in 2020. Twenty four abundant fish species were identified and effects on their abundance modelled (MaxN) by partitioning variation between monsoon season and within sites using zero inflated generalised models. It was found that 18 of the 24 species showed temporal stability in abundance across the two years and monsoon seasons. Only three species; epaulette surgeonfish (Acanthurus nigricauda), doubleband surgeonfish (Acanthurus tennentii) and blue-barred parrotfish (Scarus ghobban) increased in abundance during the NW monsoon sampling period when temperatures are warmer. The results suggest that observed seasonal changes in reef fish in Seychelles are more a result of monsoon associated sea conditions affecting direct access to fishing grounds rather than environmental effects on abundance. Furthermore, it was demonstrated that that BRUVS provide a standardized and repeatable method for quantifying reef fish abundance in Seychelles.