Analysis on the composition of by catch in elver nets and the suggestions on the management of elver nets in Yangtze River estuary

Abstract:

To clarify the damage rates of elver nets on some commerical fishes in Yangtze River estuary, fishes were collected from 8 stations (5 in the North Branch of Yangtze river estuary and 3 in the South Branch of Yangtze river estuary) from March to April in 2011. A total of 3 755 by catch fish were collected representing 35 species from 16 families by 96 nets, including 12 marine species, 14 estuarine species, 3 migration species and 6 freshwater species. The developmental stages of fishes were from post flextion to young stage. Coilia nasus was the most dominant species accounting for 31.99% of the total, and followed by Pseudolaubuca engraulis(10.09%), Coilia mystus(9.93%), Lophiogobius ocellicauda (8.92%), Taenioides rubicundus(7.32%), Cynoglossus joyneri(5.32%).There were 20 species of economic fishes which accounting for 61.60% of the total fish. Average were 24.10 ind./net and it showed a higher proportion and quantity. A total of 182 elvers were collected, and each elver collected would damage 12.71 economic fish. Our results indicate that elver nets bycatch fish of species and number are relevant with nets, location, mode of operation and tidal, and early life stages of economic fishes were damaged seriously by elver nets, especially for Coilia nasus. It is one of the important reasons led the Coilia nasus resource declining in the past. In order to protect fish recruitment stock and recover fish resources in Yangtze River estuary, the management should not only limit the quantity and operational periods of elver nets, but also regulate the mesh size.