Influence of Codend Mesh Size on Bycatch Composition of Two Trawls Operated off Veraval, Gujarat, India

Abstract

The deleterious impact of bottom trawling on
benthic ecosystem is widely reported and attempts
are made to reduce bycatch generated by trawling
through technical and operational measures. Systematic
baseline data on the quantity and type of
bycatch will help in comparing the changes that
have occurred to the fish community structure. This
study compares the bycatch generated by two
trawling systems with 15, 20, 30 and 40 mm mesh
size codends off Veraval during 1991-92 and 2005-
06. Analysis of quantity of bycatch generated and
changes in species composition, analysis of diversity
and multivariate analysis were carried out to
elucidate the changes on the community structure
along the Veraval coast. The percentage of total
bycatch generated in trawl systems during 1991-92
were 25.69±4.28 and 31.03±1.58 with 15 and 30 mm
codend meshes respectively while the values were
67.77±3.22 and 22.15±2.44 respectively for 20 and
40 mm codends during 2005-06. Acetes spp and
Otolithes ruber contributed the major share of
bycatch in the 15 and 30 mm codends, whereas
Trichiurus lepturus and Rhopilema spp were the major
species caught during 2005-06 in the 20 and 40 mm
codend mesh respectively. Highest diversity was
observed in the 15 mm codend as indicated by both
the indices of diversity ‘S and d’. ANOSIM test
revealed that the difference in the assemblage
structure during the years were significant with a
global ‘R’ value of 0.176. The results of the SIMPER
analysis showed that the average dissimilarity
between the bycatch assemblages during the years
1991-92 and 2005-06 was noticed to be 87.23%. It was evident from the studies that there are changes in the quantity and assemblage structure of the bycatch generated by different trawling systems over the years. This study also shows the utility of increasing the mesh sizes as a technical measure to reduce impacts of trawling on biodiversity