Investigations on juvenile fish excluder cum shrimp sorting device (JFE-SSD)

摘要

Penaeid shrimp is a major resource in India contributing about 7.4% of the total marine fish landings. They are mostly landed by small mechanized trawlers. Shrimp trawling generates large quantities of bycatch mostly consisting of juvenile fishes, due to use of small mesh size in codends of trawl nets. Juvenile Fish Excluder cum Shrimp Sorting Device (JFE-SSD) is a bycatch reduction device with an in situ sorting mechanism, which replaces the conventional codend in a trawl. The device was designed to catch shrimps and commercially important fish species using a specially designed oval sorting grid with appropriate bar spacing and dual codends. Shrimp sorting efficiency and bycatch exclusion characteristics of JFE-SSD attached to a 29.6 m shrimp trawl, was tested by experimental fishing along the coastal waters off Cochin, India. Out of a total of 317.07 kg of catch encountered in the JFE-SSD installed trawl, 58.22% was retained in lower codend, 17.53% in upper codend and 24.25%, mostly consisting of juveniles and sub-adults of finfishes and shellfishes, was excluded from upper codend. The mean CPUE registered for upper and lower codend were 7.23±1.04 SE and 5.84±0.96 SE kg h^-1 respectively. The CPUE of shrimps retained in upper and lower codends were significantly different (Kruskal-Wallis test (1,62), P<0.001), but the mean CPUE for fishes did not vary significantly. The average escapement of shrimps and juvenile fishes from upper codend were 0.06±0.02 SE kg h^-1 and 2.40±0.44 SE kg h^-1 respectively. Significant differences in the length composition between upper and lower codends were noticed for Megalaspis cordyla, Stolephorus waitei, Metapenaeus dobsoni and Parapenaeopsis stylifera. The experiments demonstrated in situ sorting ability of the device and its potential to reduce the bycatch of juveniles and sub-adults in shrimp trawls.