Regime Shifts and Recruitment in Western and Central Pacific Ocean Tuna Fisheries

Progress Reports (PDF): FY 2008, FY 2007, FY 2006

Project Overview
The main objective to the research proposed is the detection of discontinuities and/or low-frequency periodic variability in multivariate physical and biological time series characteristic of the western and central Pacific Ocean and its tuna fisheries. This analysis will establish whether the regime shifts documented for the North Pacific in 1976 and 1998 (Peterson & Schwing 2003) are seen in the Western and Central Pacific Ocean (WCPO) and whether they are likely to recur; it will identify the variables in which these shifts are most apparent and which variables or indices might serve as early warning signals of regime change in the future.

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.

Proposed Activities
Datasets
Hare & Mantua (2000) analysed a dataset comprising 100 time series (31 climatic and 69 biological) of ca. 20 yr duration, including recruitment estimates and catch for various fish species, to establish the existence of the late-1970s regime shift in the North Pacific. Project researchers will collect and analyse data for similar climate indices, physical and biological oceanographic variables as well as recruitment, catch-per-unit-effort and biomass estimates for species where stock assessments have been carried out.

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.

Analytical Methods
Hare & Mantua (2000) used Principal Component Analysis to isolate the most important patterns of common variability in 100 physical and biological time series. Preliminary work by the project researchers (Kirby et al. 2003) has investigated the Fisher Information (Fath et al. 2003) content of the same data. Although there is no test for statistical significance incorporated into the analysis it is quite apparent that there is an appreciable increase in Fisher Information in the late 1970s, which supports the possible use of this metric as an indicator of an ecosystem regime shift. Researchers intend to develop this metric further within the context of this project.

There 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 series.

Year 1 funding for this 2-year project estimated to be available mid-2005.

Literature cited:
• Allain V (2002) Food web study in the tuna ecosystem of the Western and Central Pacific Ocean. Working Paper BBRG-7. 15th Meeting of the Standing Committee on Tuna and Billfish, Hawaii, 22-27 July 2002.
• Beamish RJ, McFarlane GA, King JR (2000) Fisheries climatology: understanding decadal scale processes that naturally regulate British Columbia fish populations. In: Harrison PJ, Parsons TR (eds) Fisheries Oceanography. Blackwell Science, Oxford.
• Fath BD, Cabezas H, Pawlowski CW (2003) Regime changes in ecological systems: an information theory approach. J Theoretical Biol 517-530.
• Grandperrin, R. 1975. Structure trophiques aboutissant aux thons de longue ligne dans la Pacifique sud-ouest tropical. Thèse de doctorat d'Etat, Aix Marseille II, ORSTOM: 296 pp.
• Hare SR, Mantua NJ (2000) Empirical evidence for North Pacific regime shifts in 1977 and 1989. Prog Oceanogr 47:103-145.
• Kirby DS, Lehodey P, Hampton J (2003) Fisher Information as an indicator of regime change in western & central Pacific Ocean tuna fisheries. Mar Ecol Prog Ser, in press.
• Peterson WT, Schwing FB (2003) A new climate regime in northeast pacific ecosystems. Geophys Res. Lett. 30(17):1896.
• Roger C (1973) Recherches sur la situation trophique d'un groupe d'organismes pélagiques (Euphausiacea). V. Relations avec les thons. Mar Biol 19:61-65.
• Sugimoto T, Tadokoro K (1998) Interdecadal variations of plankton biomass and physical environment in the North Pacific. Fish Oceanogr 7(3/4): 289-299.

Principal Investigators:

Dr. David Kirby
Secretariat of the Pacific Community (SPC)
BP D5
Noumea Cedex
New Caledonia
Phone (687) 26-20-00
FAX (687) 26-38-18
email: davidk@spc.int

Dr. Patrick Lehodey
Secretariat of the Pacific Community (SPC)
BP D5
Noumea Cedex
New Caledonia
Phone (687) 26-20-00
FAX (687) 26-38-18
email: patrickl@spc.int

Dr. Valerie Allain
Secretariat of the Pacific Community (SPC)
BP D5
Noumea Cedex
New Caledonia
Phone (687) 26-20-00
FAX (687) 26-38-18
email: valeriea@spc.int

Mr. Adam Langley
Secretariat of the Pacific Community (SPC)
BP D5
Noumea Cedex
New Caledonia
Phone (687) 26-20-00
FAX (687) 26-38-18
email: adaml@spc.int

This page updated August 7, 2008