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Black marlin (Makaira indica) is commonly caught as frozen by-catch from Indonesian tuna longline fleets.
Its contribution estimated 18% (~2,500 tons) from total catch in Indian Ocean. Relative abundance indices
as calculated based on commercial catches are the input data for several to run stock assessment analyses
that provide models to gather information useful information for decision making and fishery management.
In this paper a Delta-Lognormal Model (GLM) was used to standardize the catch per unit effort (CPUE)
and to calculate estimate relative abundance indices based on the Indonesian longline dataset. Data was
collected from August 2005 to December 2020 through scientific observer program. Most of the vessels
monitored were based in Benoa Port, Bali. The result showed that Year, latitude and longitude were the
only variables remained and statistically significant in the lognormal model, whereas moon and latitude
were excluded from the delta model. The positive catch of black marlin (BLM) was allegedly influenced by
spatial (latitude and longitude) and temporal factor (year), an indication of sporadic catch instead of targeting.
In addition, according to delta model, targeting effect (cluster) and horizontal movement (longitude)
allegedly played significant part on possibility of catching BLM. Whereas, BLM was more likely caught when
incorporated in cluster 1 (mixed targeting ALB, BET and YFT) and cluster 3 (targeting ALB). However,
high uncertainties seemed as lingering issue, which is inevitable due to low coverage of scientific observer data.
