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An evaluation of Indonesia's Indian Ocean tuna longline fisheries, based on historical and newly established sources of catch and effort information

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Sadiyah, L (2011) An evaluation of Indonesia's Indian Ocean tuna longline fisheries, based on historical and newly established sources of catch and effort information. PhD thesis, University of Tasmania.

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Abstract

Indonesia currently has the largest longline fleet operating in the Eastern Indian
Ocean. This fleet is one of the main suppliers of fresh tuna for the Japanese market
and it fishes the only known spawning ground for southern bluefin tuna (Thunnus
maccoyii). It is thus important to attempt to characterise the fishery and evaluate its
impact. However, there is a shortage of detailed catch and effort information. Three
sources of detailed catch and effort information exist for the fishery: i) a series of
historical data from a single fishing company, ii) data collected by Fisheries High
School students, and iii) data from a trial Observer Program.
This study provides the first comprehensive. exploratory analyses of the three data
sets, with a view to investigate, to the extent possible, the impact of Indonesian
fishing activities on Indian Ocean tuna stocks. The results emphasize the deficiencies
in the three data sets, and highlight the importance of formal data collection
protocols, particularly for stock assessment.
The results of each data set were integrated and compared to evaluate the consistency
of the data sets and the relative merits of each in addressing different issues. The
current data and other sources of information suggest that the fishery is highly
variable and thus difficult to characterise, and there is some evidence that this may be
more due to fleet inefficiency than the fishery operating in opportunistically.
Improved data collection for the Indonesian longline fleet remains a priority and the
ongoing observer program is of paramount importance.
A subsequent focus was to undertake a standardisation of the catch-per-unit-effort
(CPUE) data in order to develop proxy abundance indices for the main tuna species
by using the Observer Program data. As a long time series of Observer Program data
is yet to be established, the aim was to develop protocols for ongoing monitoring and
analysis, and providing a statistical modelling framework into which future data can
be incorporated to provide an updated time series.
A simulation model was developed to evaluate the minimum monitoring
requirements, under different conditions, for delivering data that best reflects the
total catch and effort and the underlying stock abundance. For each scenario trialled,
various levels of coverage were examined, to evaluate the extent of spatial effort and
catch coverage, and the difference between the estimated and true tuna catches. The
results suggest that the fishery can be robustly represented by sampling at least 2% of
the total sets (by assuming that a truly random sample can be obtained across all
vessels).
The three data sets suggest that the Indonesian fishery appears to typically target
yellowfin tuna (Thunnus albacares), bigeye tuna (T. obesus) and albacore (T.
alalunga), but show little consistency and may not be considered fully representative
of the Indonesian lungline fleet. Despite the apparently highly variable nature of the
fishery, the fact remains that Indonesia has the largest longline fleet operating in the
Eastern Indian Ocean. The suggestion of fleet inefficiency is of concern in this
context: if latent effort does indeed exist in the fishery, there is the potential to
impact stocks even more than is indicated by current effort. Given the lack of
conclusive evidence that can be drawn from currently. available information, the
establishment of a robust data collection strategy (as informed by the -simulation developed here), is of utmost priority, both to resolve the issue of the nature of the fishery and its level of efficiency, and to establish a robust CPUE time series.

Item Type: Thesis (PhD)
Copyright Information:

Copyright 2010 the author

Additional Information:

Thesis (PhD)--University of Tasmania, 2011. Includes bibliographical references

Date Deposited: 03 Feb 2015 03:19
Last Modified: 08 Mar 2017 00:47
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