|
Biomass, Size, and
Trophic Status of Top Predators in the Pacific Ocean
(John Sibert, John
Hampton, Pierre Kleibert, Mark Maunder). 2006.
pdf 261k
Fisheries have removed at least 50 million tons of tuna
and other top-level predators from the Pacific
Ocean pelagic ecosystem since 1950, leading to concerns about a
catastrophic reduction in population biomass
and the collapse of oceanic food chains. We analyzed all available data
from Pacific tuna fisheries for 1950–2004
to provide comprehensive estimates of fishery impacts on
population biomass and size structure. Current biomass ranges
among species from 36 to 91% of the biomass
predicted in the absence of fishing, a level
consistent with or higher than standard
fisheries management targets. Fish larger than 175 centimeters fork
length have decreased from 5% to approximately
1% of the total population. The trophic level of the catch has decreased
slightly, but there is no detectable
decrease in the trophic level of the population. These results
indicate substantial, though not catastrophic, impacts of
fisheries on these top-level predators and
minor impacts on the ecosystem in the Pacific Ocean.
[...]
Decline of Pacific tuna
populations exaggerated ?
(Hampton J.,
Sibert J., Kleibert P., Maunder M., Harley S.).
2003.
pdf 93k
Tuna
have been the target of large-scale industrial
fisheries in the Pacific Ocean
and elsewhere since the 1950s. In their
analysis of Japanese longline-fishery catch-per-unit-effort
(CPUE) data, Myers and Worm conclude that the
community (species-
aggregated) biomass of large pelagic fish,
mainly tunas, was reduced by 80% during the
first 15 years of exploitation and
is now at 10% of pre-industrial levels. We
show here that an assumption critical
to this conclusion — namely, that Japanese
longline CPUE acts as an accurate index
of community biomass — is invalid. Our
results indicate that biomass decline
and fishing impacts are much less severe than
is claimed by Myers and Worm. [...]
 Predicting skipjack
tuna forage distributions in the equatorial Pacific using a coupled dynamical
bio-geochemical model
(Lehodey P., Andre J-M, Bertignac M., Hampton J., Stoens A.,
Menkes C., Memery L., Grima N)
Skipjack tuna (Katsuwonus
pelamis) contributes ~70% of the total tuna catch in the Pacific
Ocean. This species occurs in the upper mixed-layer throughout the
equatorial region, but the largest catches are taken from the warmpool
in the western equatorial Pacific. The analysis of catch and effort data
for U.S. purse seine fisheries in the western Pacific has demonstrated
that one of the most successful fishing grounds is located in the
vicinity of a convergence zone between the warm (>28-29° C)
low-salinity water of the warmpool and the cold saline water of
equatorial upwelling in the central Pacific.[...]
A spatial population dynamics simulation model of tropical tunas using a
habitat index based on environmental parameters (Bertignac M.,
Lehodey P., Hampton J)
We are developing a
spatial, multi-gear, multi-species population dynamics simulation model
for tropical tunas in the Pacific Ocean. The model is age-structured to
account for growth and gear selectivity. It includes a tuna movement
model based on a diffusion-advection equation in which the advective
term is proportional to the gradient of a habitat index.[...]
El Niño
Southern Oscillation and tuna in the western Pacific (P Lehodey, M Bertignac, J Hampton, A Lewis & J
Picaut)
Assessments
of tuna stocks indicate that recent western Pacific skipjack catches
approaching one million tonnes annually are sustainable. The warm pool,
which is fundamental to the El Niño Southern Oscillation (ENSO) and the
Earths climate in general, must therefore also provide a habitat capable
of supporting this highly productive tuna population. [...]
A
summary of
current information on the biology, fisheries and stock assessement of bigeye tuna (Thunnus
obesus) in the Pacific ocean, with recommendations for data requirements and future
research (John Hampton, Keith Bigelow and Marc Labelle)
Bigeye
tuna (Thunnus obesus) are an important component of tuna
fisheries throughout the Pacific Ocean. They are the principal target
species of the large ‘distant-water’ longliners from Japan and Korea
and of the smaller ‘fresh sashimi’ longliners based in several
Pacific Island countries. Bigeye tuna are fundamental to the economic
survival of the longline fishery in the western and central Pacific
Ocean [...]
The Western
and Central Pacific Tuna Fishery: 2005 overview and status of
tuna
stocks. (Adam Langley, Peter Williams
and
John Hampton)
Regional
Tuna Tagging Project : Data Summary (Barbera Kaltongga)
The large
databases generated by the Regional Tuna Tagging Project (RTTP)
are a regional asset, providing a wealth of information on skipjack tuna
(Katsuwonus pelamis), yellowfin tuna (Thunnus albacares)
and bigeye tuna (Thunnus obesus) for use in biological and stock
assessment. The objective of this technical
report is to provide a convenient summary of these tagging data
collected during the RTTP [...]
Natural
mortality rates in tropical tunas: size really does matter
(John Hampton)
Important
size-related variability in natural mortality rates has been revealed in
populations of skipjack tuna (Katsuwonus pelamis), yellowfin tuna
(Thunnus albacares), and bigeye tuna (Thunnus obesus) in the western
tropical Pacific Ocean using a new, size-structured tagging model [...]
A
spatially disaggregated, length-based, age-structured population
model of yellowfin tuna (Thunnus albacares) in the western
and central Pacific Ocean (John Hampton and David
A.
Fournier)
Catch,
effort, length-frequency and tagging data stratified by quarter (for the
period 1962.... 99), seven model regions and 16 fisheries are used in
the analysis. The model structure includes quarterly recruitment in each
region, 20 quarterly age classes, independent growth patterns for
juveniles and adults, structural time-series variation in catchability
for all non-longline fisheries, age-specific natural mortality, and
age-specific movement among the model regions [...]
Exploitation
and movements of yellowfin tuna (Thunnus albacares) and bigeye tuna (T. obesus)
tagged in the north-western Coral Sea
(John Hampton and John Gunn)
Yellowfin tuna (Thunnus
albacares) and bigeye tuna (T. obesus) were tagged and released in the
north-western Coral Sea in 1991 and 1992. Over the next five years,
recaptures were reported by Australian longline vessels fishing in the
release area, and by industrial tuna fleets fishing in the adjacent
western Pacific region, thus demonstrating clear links between the tuna
stocks in these areas [...]
MULTIFAN-CL
: a length-based, aged-structured model for fisheries stock assessment, with application
to South Pacific albacore, Thunnus Alalunga (David A. Fournier, John Hampton,
and John R. Sibert)
We
introduce a length-based, age-structured model, MULTIFAN-CL, that
provides an integrated method of estimating catch age composition,
growth parameters, mortality rates, recruitment, and other parameters,
from time series of fishery catch, effort, and length frequency data
[...]
Mobility of tropical tunas and the implications for fisheries management
(John Sibert, John Hampton)
We apply an advection-diffusion
reaction model to data from three different tuna tagging experiments in
the western and central Pacific Ocean (WCPO) to reexamine the question of
to what extent the population dynamics and spatial characteristics of
tropical tunas require international cooperation for effective
management. [...]
Seven months in the life of a
Pacific Bigeye tuna
(Bruno Leroy - 2003 - Pdf 1,187kb)
Sept mois dans la vie d'un thon
Obèse
(Bruno Leroy - 2003 - Pdf 1,136kb)
Up to
now, conventional tagging has consisted of attaching numbered tags to
the fish, releasing them into the wild and then waiting for them to
caught again by fishermen. But as vital as the data collected in this
way are, e.g. growth, migration, mortality, they do not give any
indication of the fish’s behaviour between the time it is tagged and
the moment it is recaptured, e.g. the times of day it ate, the depths it
swam at, etc. [...]
Kirby DS, Abraham ER, Uddstrom MJ, Dean H (2003) Tuna
schools/aggregations in surface longline data 1993-1998.
New Zealand Journal of Marine and Freshwater Research 37(3)
The pelagic
ecosystem of the tropical Pacific Ocean:
dynamic spatial modelling and biological consequences of
ENSO (Patrick Lehodey - 2001 - Pdf
1Mb)
|
