Population dynamics of threadfin porgy Evynnis cardinalis,an endangered species on the IUCN red list in the Beibu Gulf,South China Sea

Threadfin porgy Evynnis cardinalis is both a dominant fish species and an important fishing target in bottom trawl fisheries in the Beibu Gulf, South China Sea. It was listed as endangered (EN) in a recent International Union for Conservation of Nature (IUCN) red list. Despite its economic importance and endangered status, limited research on its biological characteristics and spatial–temporal distribution has been undertaken this last decade, creating uncertainty in current conservation and management. We analyse this species' spatial distribution characteristics using data from four seasonal bottom trawl surveys in 2014–2015, and report average catch per unit effort to vary seasonally, from 49.1 to 594.5 ind h⁻¹. Growth, mortality and sexual maturity are reported for four time periods based on data from bottom trawl fishery surveys over 1961–1962, 1998–1999, 2006, and 2014–2015. Length frequency distributions changed from bimodal to unimodal, and the female-to-male ratio increased. Mean body length and length at first maturity decreased, whereas the growth coefficient increased, indicating miniaturization, early sexual maturity and accelerated growth, respectively. We report sparid catch to have first exceeded maximum sustainable yield in 2001, and to have remained overfished from 2010 to 2015. Since the 1980s, low-trophic-level fishes such as E. cardinalis have replaced high-trophic-level fishes such as Crimson snapper Lutjanus erythropterus to become dominant species. As catches have increased substantially, these species have been faced with overfishing, driving the ecosystem into an unstable state.