Performance of Separator Trawl off Cochin, Southwest Coast of India

Abstract

Shrimp trawling generates large quantities of
bycatch due to the non-selective nature of the gear.
Behavioural differences and vertical distribution of
the targeted species are among the main factors
considered for designing trawls for selective
trawling. This study attempts vertical separation of
species in a trawl by inserting a horizontal panel,
leading the upper and lower compartments to two
separate codends. A total of 27 hauls were carried
out and the species assemblage in the upper and
lower codends were studied. Multivariate analysis
was carried out to find the differences in the species
assemblage structure between the two codends.
Comparative analysis of the catches in the two
codends has shown that the catch rate was about
25 times higher in the lower codend than in the
upper codend. The catch rate of Parapenaeopsis
stylifera and Metapenaeus dobsoni alone formed
around 77% of the total CPUE in the lower codend.
The contribution of shrimps in the upper codend
was only about 15% of the total CPUE, which
confirmed the importance of vertical height of the
trawl mouth in the selective capture of fishes and
for reducing bycatch, which comprised mostly of
juveniles of commercially important fishes, in
targeted shrimp trawling. Although the diversity
indices did not show any significant difference
between the codends, the difference in the species
were very significant in the ANOSIM test (p<0.01)
and the major species that were responsible for the
difference in the species assemblages were found
to be P. stylifera and Sardinella longiceps. As the catch of jellyfish were significantly lower in the lower codend, their catch in shrimp trawls can be considerably reduced by using nets with low
vertical height.