PFRP Home > Biology Projects List

Fishery Dynamics in the Samoan Archipelago

Progress reports (PDF): FY 2010, FY 2009, FY 2008, FY 2007, FY 2006, FY 2005

Project Overview
The south Pacific albacore stock supports significant longline fisheries in several Pacific Island Countries (PICs) and territories, particularly American Samoa, neighboring independent Samoa, Fiji, Tonga and French Polynesia. The total catch of south Pacific albacore was 51,000 tonnes (t) in 2002 with 91% of the catch taken by longline fishing. Catches from PIC fleets have increased in recent years and accounted for over 25,000 t (58%) of the total longline catch in 2002. Longline participation has increased dramatically in the American Samoa exclusive economic zone (EEZ), an area within the jurisdiction of the Western Pacific Regional Fishery Management Council (WPRFMC). American Samoa and Samoa-based domestic longline fisheries had albacore catches of ~10,000 t in 2002 or 20% of the entire regional albacore catch.

Increased longline catches in the small spatial areas of the Samoa EEZs have prompted concerns of local resource depletion; the Samoa EEZ is the smallest in the Pacific. Catch competition may be occurring within the individual fisheries or a fishery interaction may be occurring between fisheries in the archipelago, as the concentration of fishery effort in the American Samoa EEZ now exceeds anything previously seen in fisheries managed by the WPRFMC.

Given the value of locally-based longline fishing to the economies of both American Samoa and Samoa, the proposed project will investigate three approaches to improve the understanding of resource availability to Samoa-based domestic fisheries:

1. Analyze the spatial and temporal dynamics and fishery interaction of longline fisheries within and around the American Samoa EEZ.
2. Comparison of albacore fishery dynamics in other Pacific Island countries longline fisheries.
3. Improvements to the regional albacore stock assessment.

The proposed study will concentrate on the dynamics of south Pacific albacore because albacore comprises most of the catch in longline fisheries (~72% in the A. Samoa fishery) and landings are indicative of actual catches due to a low discard rates. Other species (e.g. yellowfin, bigeye, wahoo) will be addressed if time permits. Arrangements have been made with the pertinent Pacific fishery agencies - WPacFIN, Secretariat of the Pacific Community, and Samoa Fisheries Division - to ensure that the data will be made available.

Analyze the spatial and temporal dynamics and fishery interaction of longline fisheries within and around the American Samoa EEZ
• Develop estimates of fishery performance from the mandatory federal logbook system which has been in place in A. Samoa since 1996. Logbook compliance is monitored by the Department of Marine and Wildlife Resources (DMWR) which conducts a longline daily effort census and comparison with cannery unloadings to ensure fishing logbooks are submitted by longline vessels.
• Modeling emphasis will be placed on developing results on appropriate time and space scales for effects of local depletion and fishery interaction. Fishery performance will also be analyzed in collaboration with another PFRP project that is providing oceanographic data for the Samoa archipelago, Oceanographic Characterization of the American Samoa Longline Fishing Grounds for Albacore, Thunnus alalunga (Seki and Polovina). The CPUE time-series for the Samoa longline fisheries are relatively short (~5 years) and are therefore not amenable to most methods of time-series analysis (ARIMA, transfer function models). We envisage two methods for analyzing local depletion and fishery interaction: 1) analyzing CPUE in relation to catch as effort is sometimes poorly defined, especially in the Samoa fishery and 2) depletion estimates of local abundance through Leslie and DeLury methods (Seber 1982).

Comparison of albacore fishery dynamics in other Pacific Island countries longline fisheries
An analysis of the degree of convergence in albacore catch rates with other PIC longline fleets will be conducted with consideration of gear and environmental factors. Current catch rates in several PIC longline fleets are significantly lower than levels attained in the early years of these fisheries. In some cases, high CPUE has been maintained by expanding the area of fishing to the extremes of the EEZs and beyond. There has been a gradual decline in the catch rates in a number of fisheries. This decline has been gradual in some fisheries and stronger in other areas. Other PIC fleets considered for analysis include Fiji, Tonga and French Polynesia.

Improvements to the regional albacore stock assessment
The current south Pacific albacore assessment is conducted with MULTIFAN-CL. Three large-scale zonal regions (0-10°S, 10°-30°S and 30°-50°S) are considered in the assessment and the assessment could be further disaggregated to possibly improve estimates of relative abundance to the Samoan archipelago. One caveat with additional spatial disaggregation is the lack of tagging data which provides little information on movement, but a re-assessment may still be feasible with some restrictive assumptions regarding movement.

The current assessment uses nominal fishing effort for each fishery and assumes independent catchability amongst all the fisheries, with the exception of the Taiwanese longline fishery which has historically targeted albacore in the subtropics and higher latitudes. The quality of the assessment could be improved by incorporating information on vertical habitat utilization by albacore, longline gear configuration and fishing depth information to enable estimation of effective longline fishing effort. The project will use information on habitat and gear information from another PFRP project, Comparisons of Catch Rates for Target and Incidentally Taken Fishes in Widely Separated Areas of the Pacific Ocean (Walsh), to apply habitat-based or statistical habitat-based models (Bigelow et al. 2002, 2003) to estimate effective longline fishing effort as a comparison with nominal fishing effort within the MULTIFAN-CL framework. The inclusion of effective longline effort should reduce the bias due to catchability in the assessment and assist in model stability.

Year 1 funding for this 2-year project to be available mid 2004.

Literature cited:
• Seber, G. 1982. The estimation of animal abundance. MacMillan Publishing Co. Inc., New York, 2nd edition. 654 p.

Mr. Keith Bigelow
National Marine Fisheries Service
PIFSC
2570 Dole Street
Honolulu, Hawaii 96822 USA
Phone (808) 983-5388
FAX (808) 983-2902
email: Keith.Bigelow@noaa.gov

Dr. John Hampton
Secretariat of the Pacific Community (SPC)
Oceanic Fisheries Programme
BP D5
Noumea Cedex 98848
NEW CALEDONIA
email:JohnH@spc.int