Catch comparison of electric pulse and beam trawl 

fishing in the East China Sea

LI Huiyu1,2, Zhang Yi1,2, DAI Yang1,2, LIU Zunlei1,2

(1. East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences,Shanghai200090, China; 

2. Key Laboratory of East China Sea Fishery Resources Exploitation and Utilization, Ministry of 

Agriculture and Rural Affairs, Shanghai200090, China)

Abstract:  Shrimp beam trawl has started since the 1980s in the East China Sea, and electric pulse trawl was used in early 1990s because of its increased catch and reduced fuel cost. The principle of electric pulse trawl is to energize by a pulse generator, which generates a pulse electric filed at the net mouth, then the shrimp buried is electrically stimulated and becomes susceptible for capture. At the end of 1990s, the heavy use of pulse trawling caused subsequent overfishing and further biomass depletion of the fisheries resources, and then was banned in 2001. However, its considerable economic returns led to the frequent illegal use of electrofishing. To assess the harmful effects of electrofishing and to quantify its damage on fishery resources, paired samplings of beam trawl and multivariate statistical software PRIMER were applied. Pulse trawl (electrofishing) and beam trawl (control trawl) hauled parallelly at a distance of 0.150.2 n mile with 23 kn towing speed from July 1st to 7th, 2019, off the East China Sea (32°00′32°12′N、122°30′123°18′E) were studied. Then the catch effectiveness and composition between electrofishing and control trawl were compared. Analysis of similarity (ANOSIM) test of the composition dissimilarity between fishing gears and similarity percentage analysis (SIMPER) estimated the contribution of main species to each group. Nonparametric (MannWhitney U test) test determined differences in catch rate between day and night and between fishing gears. Results showed significant differences in composition and catch rate between gears and diel period. Electrofishing produced lower species richness (73 species, including 46 fishes, 16 crustaceans, 11 cephalopod) than control trawl (80 species, including 49 fishes, 21 crustaceans, 10 cephalopod) with 58 sharing species. The catch of electrofishing was mainly composed of fishes (49.7%) and crustaceans (47.3%) while control trawl with fishes (58.9%). The species Chelidonichthys spinosus and Portunus trituberculatus dominated (> 75% by weight) in both of the two fishing gears, while the six shrimps（Trachypenaeus curvirostris and Parapenaeopsis hardwickii etc.）only occupied 2.8%3.2% of the total catch. The result of SIMPER indicated that the dissimilarity of catch composition between electrofishing and control trawl was 43.85% (P= 0.001), and species P. trituberculatus, C. spinosus, Octopus ocellatus, Pleuronichthys cornutus, Paraplagusia japonica, Johnius grypotus and Argyrosomus argentatus showed relatively high dissimilarity contributions (>4%). For diel catch composition comparison, ANOSIM showed that significant differences were obtained by both electrofishing (P=0.001) and control trawl (P=0.001). Electrofishing captured more species at night (60) than at day (57) with 40 sharing species, while control trawl captured the same species (66) at day and night with 51 sharing species. The diel dissimilarity of catch composition was 44.60% by electrofishing and 40.73% by control trawl, and species P. trituberculatus, C. spinosus, J. grypotus, P. cornutus, O. ocellatus and A. argentatus showed high dissimilarity contributions (>4%) with different degrees of contribution to each group. Catch rate was 45 386 g ·h-1 by electrofishing and 24 945 g ·h-1 by control trawl. Electrofishing showed 81.9% catch rate increment, indicating more effective catch than control trawl (MannWhitney U test, P<0.001). Catch rate in fishes, crustacean and cephalopod was 22 547 g ·h-1，21 476 g ·h-1，1 363 g ·h-1, respectively by electrofishing and 14 692 g ·h-1，9 318 g ·h-1，934 g ·h-1, respectively by control fishing, showing significant differences in fishes (53.5% increment) and crustacean (130.5% increment) (MannWhitney U test, P<0.001). The remarkable change of catch rate by electrofishing was observed in species C. spinosus, P. trituberculatus, P. cornutus and T. curvirostris. Catch rate of C. spinosus was 16 899 g ·h-1 and 10 746 g ·h-1，respectively by electrofishing and control trawl, showing 57.3% increment (P<0.001). Catch rate of P. trituberculatus was 19 496 g ·h-1 and 8 026 g ·h-1，respectively by electrofishing and control trawl, showing 142.9% increment (P<0.001). And the species P. cornutus showed significant increment of catch rate (P<0.05), while species T. curvirostris displayed significant decrement of catch rate by electrofishing (P<0.05). Diel comparison of catch rate revealed significant differences for both electrofishing and control trawl. Night time catch rate (55 085 g ·h-1) was more efficient than daytime (35 688 g ·h-1), with 54.4% increment by electrofishing (P<0.001). For control trawl, nighttime catch rate (28 330 g ·h-1) was more efficient that daytime (21 560 g ·h-1) with 31.4% increment (P<0.05). The catch rate of fishes was 14 540 g ·h-1 at day and 30 555 g ·h-1 at night by electrofishing, while it was 11 666 g ·h-1 at day and 17 719 g ·h-1 at night by control trawl. There was a significant diel increment of catch rate by both electrofishing (110.1%) and control trawl (51.9%) (P<0.001). The diel variation of catch rate showed that there were significant differences in species C. spinosus, J. grypotus, T. curvirostris and P. hardwickii. Compared with daytime, nighttime fishing efficiency of the four species increased by 154.1%,494.9%,61.1%,134.2%, respectively for electrofishing (P<0.05), and 60.3%,565.2%,138.5%,39.7%, respectively for control trawl (P<0.05). From the results, it concluded that electrofishing showed more efficientcy in catch, especially at night. Differences in species richness, species composition and catch rate may be determined by the combined effect of differences in electric (electrofishing) and mechanical (control trawl) stimulations. It was also probably due to the differences in diel period, species, behavior and physiological condition of species. Though high efficiency by electrofishing, the percentages of shrimp catches were still very low, which indicated that the catch structure was not improved at all. Electrofishing, in fact, has no significant selectivity for target species (shrimp), but displays more harmful destruction to the demersal fishes and crab in the East China Sea. 

Keywords: East China Sea; electrofishing; beam trawl; catch composition, catch rate