Temporal variation of grouper diversity and distribution on the continental shelf of Sri Lanka: A revisit after four decades

Abstract

Groupers (family Epinephelidae, subfamily Epinephelinae) are reef fishes of high value as food resources that generate export revenue to Sri Lanka. Yet, with less attention and poor resource management, grouper population dynamics remain understudied. This paper investigates the temporal variation of grouper species on the continental shelf of Sri Lanka in relation to seasonal, regional, and seafloor depth variables using data based on quantitative sampling of demersal fish conducted in 1978, 1979, 1980, and 2018 with a bottom trawl on the R/V Dr. Fridtjof Nansen, where the authors joined the 2018 survey. A total of 277 trawl samples were included in the analysis. The analysis of variance of all the grouper species found that the average density significantly declined from 0.89 t/NM2 (tonnes per square nautical mile) in 1979 to 0.28 t/NM2 in 2018. The contribution of groupers to the total catch (by weight) was also higher in 1979 (9.06 %) than in 2018 (1.28 %). The distribution patterns significantly differed among the six regions of the Sri Lankan shelf. In addition, seafloor depth was negatively correlated with grouper density. The results point to an urgent need for better management and conservation of the grouper resources.