Standardized CPUE of swordfish (Xiphias gladius) from Indonesian tuna longline fleets in the north-eastern Indian Ocean

The main objective of this study was to assess the abundance index of swordfish (Xiphias gladius) in the northeastern Indian
Ocean, using fishery-independent data collected by scientific observers. The study aimed to address the existing information
gap associated with low coverage in this region. A total of 3,302 observer data points were obtained from the Indonesian
scientific observer program, spanning the years 2006 to 2022. These data were spatially disaggregated into one-degree blocks
and were collected alongside commercial longline fleets. To analyze the dataset, Poisson and negative binomial models were
considered, with number of fish serving as the response variable. Six covariates were included in the models, and a backward
procedure based on AIC was employed to identify the best-fitting model. The results revealed that, overall, the trend in
swordfish CPUE remained relatively stable over time, although there were inter-annual fluctuations. These fluctuations were
attributed to natural population variations rather than operational changes or inter-annual environmental factors. Despite the
lower spatial coverage compared to logbook data, the scientific observer data proved to be reliable and generated a robust abundance
index for swordfish in the northeastern Indian Ocean. This highlights the effectiveness of utilizing scientific observer
data to enhance our understanding of the population dynamics of swordfish in the region.