DELTA MODEL APPROACH FOR CPUE STANDARDIZATION OF SWORDFISH (Xiphias gladius Linnaeus, 1978) CAUGHT BY INDONESIAN LONGLINE FLEET IN THE EASTERN INDIAN OCEAN
Abstract: Relative abundance
indices as calculated based on commercial catches are the input data to run
stock assessment models to gather useful information for decision making in
fishery management. A Generalized Linear Model (GLM) was used to calculate
relative abundance indices and effect of longline fishing gear configuration.
Data were collected by a scientific observer program from August 2005 to
November 2013. Most of the boats monitored were based in the Benoa Port, Bali.
Catches are often equal to zero because swordfish is a bycatch for Indonesian
longline fleets. Therefore, a hurdle model and a binomial distribution was used
to model the proportion of positive catch rates, while a gamma distribution
were used to model the positive longline sets. Correlations between the
proportion of positive sets and year () and quarter () were weak. However,
linear correlation between the proportion of positive sets and the length of
branch lines () and number of hooks between floats () were negative and
significant. The probability of success is higher for surface longline with
small number of hooks and short branch lines. Models with year in interactions
as random effects did not converge. Models with year in interactions as fixed
effects did converge, but the estimation of standard errors of year
coefficients were high. Meaningful estimations were obtained only when using
the simplest model, in which year is not in interactions. The low proportional
decrease of deviance indicates that most of the variability of catch rates of
swordfish caught by Indonesian longline boats are not related to year, quarter,
number of hooks between floats and the length of branch lines. Other variables
and information, like the daytime while the longlines deployed in the water
(day or night), type of bait, size and type of hooks, and if the fishermen use
light-sticks to attract the fish, are necessary to better understand the catch
rate, and improve the estimations of the relative abundance indices.
Keywords: Swordfish;
standardized CPUE; GLM; GLMM
Author: Irwan Jatmiko, Humber
Andrade, Budi Nugraha
Journal Code: jpperikanangg170011
