Background: The present study was undertaken to analyse the monthly and seasonal finfish bycatch diversity of trawler fishery of Nagapattinam coast situated in the state of Tamil Nadu, South India from January 2017 to August 2019.&nbsp; 
 
Methods: Samples of finfish bycatch were collected fortnightly from the commercial shrimp trawlers operating in the coastal waters off Nagapattinam. The collected bycatch of finfish species was identified and month-wise and season-wise trawl finfish bycatch occurrence data collected were subjected to univariate and multivariate analysis using PRIMER Version 6.1.7. software.&nbsp; 
 
Result: In this study, the annual average total landing was estimated at 15,414.41 tonnes with an annual average fishing effort of 9327 boat days. Of this total landing, commercial catch constituted 70.75% (10,905.78 tonnes), whereas finfish bycatch formed 21.12% (3,256.14 tonnes) and rest by other groups. The peak fishing effort was observed in every March during the study period. A total of 210 finfish species belonging to 15 orders, 79 families and 153 genera were recorded, in which the order, Perciformes alone shared 53.81% of the total number of species. The monthly univariate analysis revealed that bycatch diversity was the highest in every September and the lowest in every June during the study period, while&nbsp; the season-wise analysis revealed the highest diversity during monsoon seasons. Likewise, the&nbsp; month-wise multivariate analysis performed through cluster analysis divulged the highest similarity between September&rsquo;17 and September&rsquo;18, while the season-wise analysis revealed the highest similarity between postmonsoon&rsquo;17 and postmonsoon&rsquo;18. Further, the K dominance plot divulged that the highest density of finfish species was in every September and in monsoon seasons during the study period.&nbsp;

Finfish Bycatch Diversity of Trawl Fishery of Nagapattinam Coast, Tamil Nadu, South India