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Regime Shifts and Recruitment in Western and Central Pacific Ocean Tuna Fisheries
Reports (PDF): FY 2008,
FY 2007, FY
It is possible to incorporate an environmental variable or index as a covariate of recruitment within the stock assessment software MULTIFAN-CL. The software then has the statistical capability to test the goodness of fit with predicted recruitment and to extend recruitment estimates into periods for which there is no length-frequency data. The identification of ecosystem indicators for the WCPO and their utility for improved recruitment estimation will therefore be explored.
This work will contribute to the GLOBEC Oceanic Fisheries and Climate Change Project (OFCCP), which has the objective of investigating the effects of climate variability and change on the productivity and distribution of tuna stocks and fisheries in the Pacific Ocean. Methodologies developed in this study might also be applied to other oceans in comparative studies under the GLOBEC Climate Impacts on Oceanic Top Predators (CLIOTOP) project.
Stock assessments in the WCPO are routinely carried out for the principal market species of tuna (albacore, bigeye, skipjack, yellowfin) and have also already been attempted for billfish (marlins, swordfish) and sharks (blue shark) using the software MULTIFAN-CL (Hampton & Fournier 2001). MFCL implements a size-based, age- and spatially-structured statistical model based on observed size-frequency, catch, effort and tagging data from the fisheries, providing the best available estimates of recruitment and biomass as well as other population characteristics. Project researchers will obtain catch and effort data for skipjack fisheries pre-1972, which will allow improvement of stock assessments for this species. Researchers also intend to include it in any systems analysis that is carried out for the 1952-1972 period. It is also intended to analyse species composition data from longline fisheries 1952 2002, available at 5°x5° degree resolution.
As well as time series characteristic of the top predators in the WCPO researchers also intend to gather data on the other components of the pelagic ecosystem. For micronekton there are no comprehensive datasets from the WCPO but researchers will be able to analyse data from diet studies carried out ca. 30 years apart (i.e. Roger 1973, Grandperrin 1975 vs. Allain 2002). Although these data are not in the form of continuous time series they are comparable studies that have taken place in the same area. Researchers have simulated forage concentrations generated by the PFRP Mixed Resolution Models (MRM) project (#651438). Researchers hope to use zooplankton and phytoplankton data obtained from Japanese cruises from 1972 to 1992 (Sugimoto & Tadokoro 1998) along with reconstructed time series from the biogeochemical component of the MRM project. The physical component of the MRM project will provide reconstructed data for all relevant physical variables: wind stress, currrents (including divergence & shear), temperature and its gradients (i.e. thermal fronts & thermocline depth). The model assimilates all available data and applies hydrodynamic theory to interpolate across data gaps for the period 1948 to 2002.
are other analytical methods which researchers will also investigate.
For example Beamish et al. (2000) describe the use of Intervention Analysis
and Cumulative Summation. There are also more sophisticated methods
for detecting both periodic variability (e.g. spectral analysis) and
discontinuities (e.g. chronological clustering) in mulitvariate time
Year 1 funding for this 2-year project estimated to be available mid-2005.
Jim Renwick, Climate Dynamics Group, National Institute of Water & Atmospheric Research, Wellington, New Zealand
Miki Ogura, National Research Institute of Far Seas Fisheries, Shimizu, Japan
This page updated August 7, 2008