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Fourteen years port sampling data (2005-2018) and three years logbook data (2016 - 2018) in the gillnet fishery of Sri Lanka was used to analyze the catch rates of skipjack tuna. Skipjack tuna is the main target species in the Sri Lankan gillnet fishery. All gillnet catches including the catches made by popular gear combinations operated in the gillnet fishery (gillnet–longline and gillnet-ringnet) were considered under the port sampling. Five vessel types operated in the tuna fishery have caught skipjack tuna. Year, month, boat type, gear type, trip duration (in days) and number of net panels used per fishing operation were incorporated for the analysis. Fishing location (5° square) obtained from fisheries logbooks with regard to gillnet fishing operations made during 2016 – 2018 was also considered for this audit. The logbook data exists at present only for multiday fishing vessels. The skipjack tuna Catch Per Unit Effort (CPUE) was estimated in terms of catch in kg per boat per trip. Gamma based Generalized Linear Models (GLMs) were fitted to determine the relationship between above mentioned explanatory variables and CPUE for two data sets separately. Around 1.3% of the total operated vessels which contained zero catches of skipjack tuna in the port sampling data were excluded for the analysis. The GLM model fitted to port sampling data explain around 48% of the total deviance and vessel type was found to be the most important parameter. Inclusion of 5° square fishing zones for GLM modeling may help only to slightly improve the GLM results.
