Destruction of non-edible biota due to bottom trawling: The ecological and conservation issues in a global context

Abstract

Studies on the quantum of non-edible biota (NEB) discarded during the trawl fishing operations hardly exist in literature. The limited availability of baseline data on this specific area of research has resulted in an inadequate assessment of the ecological implications of plant and animal species caught and discarded during trawl operation. In this context, an attempt was made to document the marine faunal diversity and biomass of NEB destroyed and discarded by trawl operations along the Thoothukudi coast, Gulf of Mannar Marine Biosphere Reserve (GoMMBR), India. The results of study revealed that percentage composition of different phyla represented in the NEB bycatch during the sampling period are Echinodermata (47.81%), Cnidaria (16.40%), Mollusca (13.34%), Arthropoda (9.94%), Porifera (5.13%), Chordata (0.12%) and Others (7.27%). In total, 16 taxonomic groups were represented where in group-wise assemblage of the biomass was dominated by sea stars (25.61%) followed by sea urchins (16.64%), jellyfishes (16.40%), gastropods (7.80%), stomatopods (6.65%), sponges (5.13%), while other taxonomic groups contributed less than 5% of the total NEB biomass. In terms of species diversity, echinoderms showed the highest number (21 species) followed by molluscs (20 species), arthropods (11 species), cnidarians (6 species), and others form fewer in numbers (<5 species). The seasonal percentage biomass of NEB shows a maximum in the summer, SuM (36.1%) followed by monsoon, MoN (23%) whereas the Bray-Curtis similarity coefficient revealed high similarity (58.58%) in biomass composition between post-monsoon, PoM & pre-monsoon, PrM. Principal Component Analysis (PCA) showed that the extracted principal component 1 (PC1) explained 65.1% of the total seasonal variability in the NEB biomass. Given the worldwide marine biota destruction due to trawl fishing, this report provides baseline information about the magnitude of the ecologically important marine NEBs dislodged and discarded during the bottom trawl fishery. The study will strengthen the data deficiency for the conservation of marine biota more specifically on the NEBs along Thoothukudi region of GoMMBR.