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Studies on sustainable development and comparative ecological evaluation of set-net fishery in Taiwan

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Jenq, Huoo-Yuan (2009) Studies on sustainable development and comparative ecological evaluation of set-net fishery in Taiwan. PhD thesis, University of Tasmania.

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Abstract

The set-net fishery of Taiwan was examined in this study in the context of ecological
sustainable development of a unique fishery. Set-net fishery, unlike many other active
forms of fishing, involves static gear set in near shore coastal environments and targets
migratory pelagic fish. This study is the first comprehensive examination of a set-net
fishery and draws on a comprehensive literature (published mainly in Taiwanese). Data are
presented on annual production in the context of regional fishing cooperators which have
been established to manage the set-net fishery. Information on fishing technology and the
application of set-net gears in coastal waters is presented including net design and
operation through extending questionnaire census responses. Detailed analyses of the catch
from representative set-net fisheries present a comparative evaluation of species
composition including interannual and seasonal variation. Sources of variation in the catch
rates of set-nets are evaluated, particularly meteorological and environmental data (e.g. sea
surface temperature).
The results of the present study reveal that catches of giant trevally, yellowfin tuna,
Hawaiian tenpounder, Japanese barracuda and sword fish are correlated with mean
monthly water temperature. Only Spanish mackerel, which were associated with peak
catches in winter, were negatively correlated with monthly mean temperature. Sea surface
temperature and atmospheric pressure are consistent with the hypothesis that ocean
currents and their variation influence the catch rates of set-nets. Thus, pelagic fish
including tuna, mackerel and trevally follow near-shore coastal currents making those fish
vulnerable to capture by set-nets.
Studies on the bathymetry and underwater topography near set-nets revealed an association
with depth contours and catch rates of fish. Fish are more likely to be caught in set-nets if
the set-nets are located near underwater troughs which in effect influence migration paths.
Knowledge of underwater topography and associated ocean currents is important in
locating set-nets and maximising catch rates of target species. By means of self-developed
fishery detection data processing system (FDPS), an appropriate fishing site for set-net
fishing can be selected.
Acoustic surveys of fish near set-nets were used to examine fish behaviour near set-nets.
The surveys revealed that most fish were active at night and were more likely to be caught
over night than during the day. This is consistent with the daily variation in catches as
set-nets are usually harvested twice a day (i.e., morning catch and afternoon catch).
Whale sharks are occasionally caught in set-nets. Because of their conservation status,
mitigation methods to avoid whale shark capture were evaluated. However, such mitigation
is in tension with the economic benefits of catching and selling whale sharks (in high
demand by premium seafood markets). Studies showed that most fish caught in set-nets
were relatively small (30-40cm total length). Mitigation methods (including wide-spaced
rope grids to exclude large animals such as sharks) may negatively affect catch rates of
target species (e.g. tuna). Thus, there are both economic and practical disincentives to
apply whale shark- reducing devices.
In all other respects, when compared with other fish methods (particularly demersal
trawling), set-net fisheries have a demonstrably benign impact on coastal environments.
Little by-catch is taken with almost all fish caught sold. What little by-catch is taken is
used as food in co-located fish cage farming operations. As set-nets employ static gears,
the quality of the fish caught is very high (compared with active trawl methods). This, and
the regular harvest (twice daily) presents set-net fishery as a source of high value species
with concomitant economic return to regional coastal communities.
Thus, in the context of ecological sustainable development, the results of this study show
demonstrable ecological, economic and social benefits from set-net fisheries in Taiwan.

Item Type: Thesis (PhD)
Copyright Holders: The Author
Copyright Information:

Copyright 2009 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:54
Last Modified: 30 Nov 2016 21:55
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