DEVELOPING RECOMMENDATIONS FOR UNDERTAKING CPUE STANDARDISATION USING OBSERVER PROGRAM DATA
Abstract: Abundance indices
based on nominal CPUE do not take into account confounding factors such as
fishing strategy and environmental conditions, that can decouple any underlying
abundance signal in the catch rate. As such, the assumption that CPUE is
proportional to abundance is frequently violated. CPUE standardisation is one
of the common analyses applied. The aims of this paper were to provide a
statistical modelling framework for conducting CPUE standardisations using the
Observer Program data for bigeye tuna, yellowfin tuna, albacore and southern
bluefin tuna, and provide a comparison in the trends between the nominal CPUEs
and their standardised indices obtained. The CPUE standardisations were
conducted on the Observer Program collected between 2005 and 2007, by applying
GLM analysis using the Tweedie distribution. The results suggested that year,
area, HBF and bait factors significantly influenced the nominal CPUEs for the
four tuna species of interest. Some extreme peaks and troughs in the nominal
time series were smoothed in the standardised CPUE time series. The high degree
of temporal variability that is still shown in the standardised CPUE trends
suggests that the data are too sparse to give any meaningful indication of
proxy abundance. Nevertheless, this may also suggest that variables used in the
GLMs do not sufficiently account for all of the confounding factors, or
abundance may indeed be truly variable.
Keywords: CPUE
standardisation; observer program; tweedie distribution; Indian Ocean
Author: Lilis Sadiyah, Natalie
Dowling, Budi Iskandar Prisantoso
Journal Code: jpperikanangg120045
