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The Associative
Dynamics of Tropical Tuna to a Large-Scale Anchored FAD Array
See the
SPC website at http://www.spc.int/tagging.
See also Instrumented Buoys as Autonomous
Observatories of Pelagic Ecosystems.
See also Trophic Ecology and Structure-Associated
Aggregation Behavior in Bigeye and Yellowfin Tuna in Hawaiian Waters
Progress
Reports (PDF): FY
2008, FY 2007
BACKGROUND
Large-scale fishing operations on fish aggregating devices
(FADs) in the Western and Central Pacific Ocean (WCPO) have generated
management concern due to their tendency to aggregate juvenile and commercially
undersize tuna as well as bycatch species, e.g. billfish, oceanic sharks,
and marine turtles (Hampton and Bailey 1993). Of particular management
concern is the unintended catch of juvenile bigeye tuna by WCPO purse
seine fleets as well as elevated landings of juvenile yellowfin tuna
in drifting object sets. The purse seine catch of bigeye is directly
related to the level of setting on drifting objects as bigeye are not
taken in unassociated sets in the WCPO.
In the last few years, yellowfin and bigeye stocks have been pushed
towards or into an over-fished condition. FADs fished by purse seine
are considered a major contributor toward the overfishing situation
as well as large-scale fishery removals by Philippine and Indonesian
fisheries; many of which are also FAD based. The use of drifting FADs
by major Distant Water Fishing Nations (DWFN) purse seine fleets has
decreased since 1999. However, directed purse seine effort on anchored
FADs has increased sharply since about 1996, particularly in the region
of northern Papua New Guinea (Kumoru 2003). Approximately 1000 anchored
FADs have been set or maintained yearly in support of domestic or joint
venture purse seine activity in the Bismarck Sea: roughly between New
Britain and the western limit of the PNG zone. This area is considered
one of the most biologically diverse and "tuna rich" areas of the world
and is an important spawning and nursery area for WCPO tropical tuna
(Itano 2000).
A large proportion of tuna landings by PNG-associated purse seine vessels
are taken from within archipelagic waters of the Bismarck Sea, north
of the main PNG landmass. These catches include high proportions of
juvenile yellowfin tuna and significant catches of juvenile bigeye tuna,
oceanic sharks and billfish. The impact of these large-scale anchored
FAD arrays and associated removals of tropical tuna and other species
is of significant concern to regional management efforts and the Western
and Central Pacific Fisheries Commission (WCPFC) in particular. The
problem is that very little is known on the aggregative dynamics and
behavior of tropical tuna on anchored FADs. In particular, information
is needed on the retention rates, movement patterns and vertical behavior
of FAD aggregated species. This information is considered essential
for evaluating options to improve targeting (reduce bycatch) by purse
seine fisheries. The WCPFC considers this kind of information as critical
to examining methods to mitigate purse seine bycatch of juvenile bigeye
tuna and undersize tuna of all species. The WCPFC has recommended that
a large-scale tagging project be initiated in the WCPO with a priority
on bigeye and yellowfin resources.
OBJECTIVES
In collaboration with researchers from the SPC's Oceanic Fisheries Programme
and the PNG National Fisheries Authority, project investigators will
utilize a combination of conventional, archival and sonic tagging technologies
and biological sampling to support stock assessment and to obtain information
on FAD aggregation dynamics and trophic impacts of FADs on tuna. Project
researchers will investigate the associative dynamics of tuna resources
of the Bismarck Sea in relation to anchored FADs using sonic tags and
automated receivers mounted to selected FADs. The technology has been
well proven in Hawaii and should provide in situ observations of residency,
catchability and between-FAD movements at fine temporal scales (Dagorn
et al. in review).
A combination of individually coded sonic tags and depth sensing sonic
tags will be deployed in bigeye, skipjack and yellowfin tuna to monitor
their behavior on anchored FADs and seamounts. The SPC/OFP will coordinate
tagging cruises and field operations with NFA and the PNG tuna fishing
industry. A subset of the anchored FADs in the Bismarck Sea will be
selected and equipped with a sonic receiver that will be regularly visited
for data retrieval, battery replacement and re-initialization for another
round of data acquisition. Sonic data will be evaluated in conjunction
with concurrently collected data from conventional, archival and satellite
tags as well as information on tropic relationships (gut sampling).
The specific objectives of the project will be, in relation to bigeye,
skipjack and yellowfin tuna, to:
- investigate
residence times and movement rates between adjacent FADs;
- examine
fine-scale temporal patterns of arrival and departure to individual
FADs;
- examine
schooling synchronicity and behavior of FAD associated tuna;
- examine
movements of tuna within a "cluster" of anchored FADs and what this
may infer to between-cluster movements;
- document
fine-scale, species-specific vertical behavior of tuna on anchored
FADs;
- equip
seamounts that are known to aggregate tuna in the region of the anchored
FADs to examine the behavior of seamount associated tuna;
- conduct
this work on as wide a size range of tuna as possible to examine size-specific
FAD related behavior;
- analyze
data, present progress reports at appropriate venues and document
results in peer reviewed publications.
Funding
for this project to be available mid 2006.
References
Dagorn,
L., K. Holland and D. Itano. In review. Behavior of yellowfin (Thunnus
albacares) and bigeye (T. obesus) tuna in a network of Fish Aggregation
Devices (FADs).
Hampton
J, Bailey K. 1993. Fishing for tunas associated with floating objects:
a review of the western Pacific fishery. Noumea, New Caledonia: South
Pacific Commission. 48 p. Tuna and Billfish Assessment Programme technical
report no. 31.
Itano,
D.G. 2000. The reproductive biology of yellowfin tuna (Thunnus albacares)
in Hawaiian waters and the western tropical Pacific Ocean: Project summary.
Pelagic Fisheries Research Program, Joint Institute of Marine and Atmospheric
Research, University of Hawaii. SOEST 00-01, JIMAR Contribution 00-328.
69 pp.
Kumoru,
L. 2003. Notes on the use of FADs in the PNG purse seine fishery. 16th
Meeting of the Standing Committee on Tuna and Billfish. Mooloolaba,
Queensland, Australia, 9-16 July 2003. Working Paper FTWG-4.
WCPFC.
2005. Western and Central Pacific Fisheries Commission - Tuna Fishery
Yearbook 2004. T. A. Lawson [ed]. Western and Central Pacific Fisheries
Commission, Pohnpei, Federated States of Micronesia. 188 pp.
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Dr. Kim
Holland
Hawaii Institute of Marine Biology (HIMB)
University of Hawaii at Manoa
Coconut Island
P.O. Box 1346
Kaneohe, Hawaii 96744 USA
Phone (808) 236-7410/533-4110
FAX (808) 236-7443
email: kholland@hawaii.edu
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Mr.
David Itano
JIMAR, Pelagic Fisheries Research Program (PFRP)
University of Hawaii at Manoa
1000 Pope Road, MSB 312
Honolulu, Hawaii 96822 USA
Phone (808) 956-4108/cell: 387-5430
FAX (808) 956-4104
email: dgi@hawaii.edu
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