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Nursery
Origin of Yellowfin Tuna (Thunnus albacares) in the Hawaiian
Islands
Progress
Reports (PDF): FY
2010, FY 2009,
FY 2008
The aim of the proposed work is to provide information on the origin
of young yellowfin tuna (age-1 and age-2) in the Hawaiian Islands using
natural tracers that are linked to ambient physicochemical conditions
of the water. Our first step will be to develop a reference library
that describes the otolith chemical signatures of age-0 yellowfin from
putative spawning/nursery areas in Hawaii and the broader WCPO (i.e.
are ambient chemical conditions in regional nurseries sufficient to
impart unique signatures in the otoliths of yellowfin?). It has long
been assumed that juveniles from the equatorial region are purported
to be the main source of recruits to the Hawaii-based fisheries and
will therefore be a critical sampling location for the proposed work.
Next, we will target age-1 and age-2 (sub-adult to young adult) yellowfin
from the Hawaiian Island fisheries to determine their source (natal
origin). Three hypotheses will be tested using otolith chemistry: H1:
chemical signatures in the otoliths of yellowfin from regional nurseries
differ, H2: inshore fisheries for yellowfin around the Hawaiian Islands
are supported primarily by local recruitment (i.e. resident populations),
H3: juveniles from the equatorial region are the main source of the
recruits to the Hawaii-based fishery. We will then be able to determine
whether residents (versus transients) constitute the primary source
of yellowfin recruits to the Hawaii-based fisheries.
Research
Objectives
1) Characterize the nursery habitat signatures of age-0 yellowfin from
putative nurseries
in the WCPO using otolith chemistry (stable isotopes and trace elements)
2) Determine the origin of age-1 & age-2 yellowfin in the Hawaii-based
fisheries using
otolith chemistry
3) Evaluate resident and mixing behaviors of yellowfin in the Hawaiian
Islands by
constructing otolith-based life history transects
Methods
Young-of-the year (YOY) or age-0 yellowfin tuna will be collected from
five regional nursery areas: 1) Hawaiian Islands (Inshore FADS), 2)
Cross Seamount, 3) equatorial central Pacific (Line Islands-Palmyra
Atoll), 4) western Pacific (transshipment operations in the Marshall
Islands), 5) western Pacific (transshipment operations in Papua New
Guinea). We will target 30 samples from each region in 2008 and 2009
to investigate inter annual variability (30 individuals x 5 regions
x 2 years = 300 samples), and the chemical signatures in otoliths from
the YOY tuna will be used to construct our library of natural tags for
the different nursery areas in the WCPO. Sub-adult yellowfin used for
assessing stock structure and mixing will come from Cross Seamount and
Hawaii-based fisheries in 2008 and 2009. In addition, samples from the
high-seas fishery will be targeted in both years of the proposed study.
Our target sample size is 100 individuals each year from both Hawaii-based
and far-seas fisheries (ca. 200 sub-adults and adults x 2 years = 400
samples).
Linkages
to other Components of PFRP
This project will make a significant contribution to the PFRP mandate
to provide science-based information useful for the management of WCPO
pelagic resources. YF and BE tuna represent one of the most important
resources to Pacific Island countries and territories, yet the degree
of their movement and residency remains poorly understood. This is particularly
true in higher latitude areas, i.e. Hawaii, where understanding the
degree of exchange with core equatorial populations is critical to effective
management. Tagging data suggests that movement of some tropical tuna
species may be more restricted than previously assumed, while genetic
data have been insufficient to resolve population structure. The use
of the technologies proposed here to examine finer-scale population
components and natal origin will provide improved data inputs to stock
assessment and sub-regional management efforts. The proposed research
is directly related to the top-ranked topic from the Biology and Life
History Session at the PFRP Workshop in Honolulu in November 2005 (“development
of chemical and electronic tagging methods” to investigate long-term
basin scale movements”). Results from the proposed work will provide
strong links to PFRP research priorities related to Ecosystem Integration
(examine movement and influence of mesoscale oceanography to define
functional sizes of ecosystem units) and Biology and Life History (studies
on the early life history of tuna, particularly in relation to the use
of area closures as a management tool). The project will also provide
supportive links to PFRP socio-economic studies by providing information
on the origin and movement patterns of tuna resources. This information
is necessary to support management measures at domestic or sub-regional
scales.
Year 1
funding for this 2-year project to be available late 2007.
References
Sibert,
John, Scott McCreary, and Eric Poncelet, 2005. Pacific
Ocean Connections: Priorities for pelagic fisheries research in the
twenty-first century. Report of PFRP Research Priorities Workshop,
November 16-18, 2005, SOEST Publication 06-01, JIMAR Contribution
06-358, 25 pp. (PDF, 393 KB)
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