Spatio-temporal patterns of CPUE of grass carp and silver carp and effect of  temperature on CPUE in Pearl River basin

We investigated the production and economic benefits of grass carp (Ctenopharyngodon idellus) and silver carp (Hypophthalmichthys molitrix) in the Pearl River basin by using the method of isometric random sampling. A total of 90 vessels were daily surveyed from nine locations from 2016 to 2018. The kruskal test, generalized additive model and time series analysis were used to analyze the spatial and temporal patterns of CPUE (Catch per unit effort) of grass carp and silver carp and to explore the effect of  temperature on the CPUE. The results show that the biomass of grass carp and silver carp attributed (6.6±8.1)% and (4.4±5.0)% respectively, to the total catches in the Pearl River basin, and produced (6.0±8.2)% and (2.5±2.6)% economic benefit of the total income. In addition, the CPUE was (5.5±7.3) and (5.6±10.3) kg·(vessel·month)⁻¹, respectively. The CPUE of two species was significantly higher in the middle and upper reaches than that in the estuary area (P<0.05). The temporal variations in CPUE of grass carp and silver carp were mainly effected by closed season. Temperature had a significant positive effect on the CPUE of both species (P<0.01). The CPUE of grass carp and silver carp showed an increasing and decreasing trend with year, respectively. By contrast with the historical data, the biomass of both carps increased obviously in the past decade. The increasing production of grass carp and silver carp observed in this study might be largely benefited from proliferation and release as well as closed season.