Does shrimp trawling contribute to the decline in sciaenid stocks?

Trawling is widely used to exploit shrimp resources worldwide and is considered a highly destructive fishing method due to the high by-catch and discard rates. By-catch levels in shrimp trawling are reported to be 5-10 times the target catch, especially in the subtropics and tropics. This study assesses the status of sciaenids landed by mechanized shrimp trawls (single day operated), off Hendala, Sri Lanka. Catch data and samples were collected at the Hendala fish landing site (6 degrees 59'25.5 '' N 79 degrees 52'27.9 '' E) by making biweekly field visits from January to December 2021. On each sampling day, 50-60 % of operating shrimp trawlers were randomly sampled, and by-catch samples (n = 3) of similar to 2 kg each were collected to identify the taxonomic status of sciaenids and their composition. The size at first sexual maturity (L-m) and population parameters of dominant species in the catches were also assessed. Of the estimated total annual by-catch of 19.67 tons, the Sciaenidae family accounted for 31 %. Fourteen sciaenid species belonging to 7 genera including Johnius (Johnieops) dussumieri, a new record for Sri Lanka, were reported in this study. Otolithes ruber (27 %) made the highest contribution followed by Kathala axillaris (21 %), Johnius belangerii (15 %), Johnius macropterus (15 %), and Johnius borneensis (10 %). The L-m (cm) of 3 dominant species, O. ruber, J. belangerii and K. axillaris was estimated as 20.6, 13.8 and 11.0, respectively. Immature individuals of 85.5 %, 73.4 %, and 39.1 % respectively, were caught before reaching their first maturity. Estimates of population parameters suggested that non-target species like O. ruber, J. belangerii and K. axillaris are showing signs of over-exploitation. Management measures such as gear modification and introduction of by-catch-reducing devices as well as awareness programmes will be helpful to sustain the livelihood of fishers while protecting aquatic biodiversity and ecological sustainability.